This solder bridge would prevent Q524 and Q526 from properly sharing current. Don't know if this would have caused failure--- my guess would be no.
The added caps at M1 appear intended to block any DC bias at the M1 inputs at from passing into the FET gate. Probably not a bad idea, and shouldn't be a issue.
Are you saying the FETs measured differently in you tester, good channel vs. bad?
Re your questions, your guesses are as good as mine. I will need some active voltage measurements to offer any opinions/advice. You didn't mention the state of your installed parts, so I will suggest two measurement scenarios:
If the daughter board is present but the FETs are out of circuit, would you measure voltage at pin 6 of daughter board, or equivalently sources of the FETs? With any luck, it will be about -60V. If this as hoped, would you then measure current from the same point to ground, i.e. current source output? It should be about 2.2mA. This circuit appeared failed before, but you've worked on it, so now perhaps it's working?
If daughter board and FETs are both present, would you repeat voltage measurements for right channel as you presented in post 8, especially daughter-board pins 2 though 6, and please add gate voltages at both signal input and at feedback. It's conceivable that the FETs have survived because available currents are limited by R513 and R519.
Thanks!
Good morning @BSST
not sure why I am not seeing the quote or reply buttons on my screen for any previous posts, so I will have to just do copy/paste to reply.
"Are you saying the FETs measured differently in you tester, good channel vs. bad?"
-Yes.
on the good Left (good channel) the K240 reads on one half as a Jfet with I= 6.0mA and VGS=65v.
The other half of same reads as a Jfet with I=0.66mA and VGS=0.46v
On the Right (bad channel) the K240 reads as a BJT - NPN on both halves.
One side reads as hFE = 3.17M and Vf = 326mV.
The other side hFE = 3.17M and Vf = 485mV.
I know my little tester is subpar for the job at hand. But this seems really screwy. All other transistors on main amp and daughter boards tested as expect. All tests on transistors were desoldered and removed from circuit. Only really tested resistors and diodes in circuit.
Regarding taking more measurements, the current state of amp is that all components and daughter boards are reinstalled on main amp board (including the fets as placeholders so that I could keep orientation correct). However, the main amp board is completely removed from the chassis and disconnected from the wiring harnesses.
I could hook it back up to the wiring but leave it out and take measurements. But this would entail leaving the output devices out of the equation. I wouldn't want to fire them up without them being heatsinked...right?
Or, I could completely reassemble including the outputs. But then I could only really take measurements from the bottom side of the board, which I find a little intimidating. My copy of the manual only shows the board from the top side so that means mental gymnastics to make sure I'm measuring the correct point. Plus, in my copy the picture of the board is really faded and fuzzy so it's really hard to see the traces. In this scenario I can't really access the daughter board itself, only the pin connections on the bottom side.
I'm willing to give either action a go though.
I need to head over to my GF's today to install her window A/C before I head to work. So it may be a day or two before I can get back on this.
not sure why I am not seeing the quote or reply buttons on my screen for any previous posts, so I will have to just do copy/paste to reply.
"Are you saying the FETs measured differently in you tester, good channel vs. bad?"
-Yes.
on the good Left (good channel) the K240 reads on one half as a Jfet with I= 6.0mA and VGS=65v.
The other half of same reads as a Jfet with I=0.66mA and VGS=0.46v
On the Right (bad channel) the K240 reads as a BJT - NPN on both halves.
One side reads as hFE = 3.17M and Vf = 326mV.
The other side hFE = 3.17M and Vf = 485mV.
I know my little tester is subpar for the job at hand. But this seems really screwy. All other transistors on main amp and daughter boards tested as expect. All tests on transistors were desoldered and removed from circuit. Only really tested resistors and diodes in circuit.
Regarding taking more measurements, the current state of amp is that all components and daughter boards are reinstalled on main amp board (including the fets as placeholders so that I could keep orientation correct). However, the main amp board is completely removed from the chassis and disconnected from the wiring harnesses.
I could hook it back up to the wiring but leave it out and take measurements. But this would entail leaving the output devices out of the equation. I wouldn't want to fire them up without them being heatsinked...right?
Or, I could completely reassemble including the outputs. But then I could only really take measurements from the bottom side of the board, which I find a little intimidating. My copy of the manual only shows the board from the top side so that means mental gymnastics to make sure I'm measuring the correct point. Plus, in my copy the picture of the board is really faded and fuzzy so it's really hard to see the traces. In this scenario I can't really access the daughter board itself, only the pin connections on the bottom side.
I'm willing to give either action a go though.
I need to head over to my GF's today to install her window A/C before I head to work. So it may be a day or two before I can get back on this.
Girl friend and work rightly have priority over hobbies! 😉
I've been been pondering your amp.
I agree that the behavior of the FETs on your tester is baffling, especially with FETs taken from the working channel. Since you have replacements on order, I guess I'd wait till they arrive and see how they behave on your tester. You can also perform some rudimentary FET tests with clip leads, DVM, and a 9V battery; to measure Idss, ground gate and source leads, and connect drain lead via ammeter to +9V. Also, gate should look like a diode to source--- use diode test function on DVM for forward conduction, ohms for reverse leakage test. Reverse resistance should be in the MegOhms.
My initial suspicion was failure of current source Q507b and that hasn't changed. Note that daughter board pins 2 though 6 all have voltage near +60V, in dramatic contrast to voltages on the working channel. The pins do have small voltage drops re the +60V rail that are suggestive of junction drops, but I suspect they they arise from the DVM load; DVM load current would be in the order of 5.5uA (i.e. 60V/11M), enough to show junction drops but not enough to trigger Q512b and Q511b into conduction. Consequently, the outp6ut stages are driven to the negative rail. I imagine that if the daughter voltages had been measured with DVM tied to the +60V rail rather than ground, all those pin voltages would have been even closer to the rail.
I know you've made some repairs to the daughter board but I have the impression that the main board hasn't yet been returned to active testing. I would not be astonished if the amp is back to working. But if a problem remains, I still suggest the measurements from post #21. But predicted current source output would be about 1.6mA rather than 2.2mA. I neglected to account for the current through Q502b.
Let me know how it goes. Good luck.
I've been been pondering your amp.
I agree that the behavior of the FETs on your tester is baffling, especially with FETs taken from the working channel. Since you have replacements on order, I guess I'd wait till they arrive and see how they behave on your tester. You can also perform some rudimentary FET tests with clip leads, DVM, and a 9V battery; to measure Idss, ground gate and source leads, and connect drain lead via ammeter to +9V. Also, gate should look like a diode to source--- use diode test function on DVM for forward conduction, ohms for reverse leakage test. Reverse resistance should be in the MegOhms.
My initial suspicion was failure of current source Q507b and that hasn't changed. Note that daughter board pins 2 though 6 all have voltage near +60V, in dramatic contrast to voltages on the working channel. The pins do have small voltage drops re the +60V rail that are suggestive of junction drops, but I suspect they they arise from the DVM load; DVM load current would be in the order of 5.5uA (i.e. 60V/11M), enough to show junction drops but not enough to trigger Q512b and Q511b into conduction. Consequently, the outp6ut stages are driven to the negative rail. I imagine that if the daughter voltages had been measured with DVM tied to the +60V rail rather than ground, all those pin voltages would have been even closer to the rail.
I know you've made some repairs to the daughter board but I have the impression that the main board hasn't yet been returned to active testing. I would not be astonished if the amp is back to working. But if a problem remains, I still suggest the measurements from post #21. But predicted current source output would be about 1.6mA rather than 2.2mA. I neglected to account for the current through Q502b.
Let me know how it goes. Good luck.
Ok, back at it. Had friend come into town and couch surf with me for the weekend. Didn't have a chance to touch the Luxman until yesterday.
But, it appears I have won a battle while still fighting the war. I can now confirm the AMP section works even though the amp doesn't put out sound (unless hacked).
To summarize:
I've been reading that on some of these Luxman "suckface" components they will not work properly if the suckface mechanism is not working properly. Apparently this is due to the various circuits hooked up to the microswitch that engages when the face panel reaches its innermost position?
I've already ordered a new belt for the suckface mechanism. With the amp section working I feel confident in pushing forward.
I also guess it's time to dig out my old Tektronix 465 scope and finally start learning how to use it to trace a signal through the unit. Today I will go over to FedEx Office (Kinko's) and print out the service manual in full (with large scale schematic pages). I have a hard time tracing circuits across multiple pages on a computer screen scrolling back and forth. I really like being able to use colored markers on paper as I follow the trail.
I've attached the service manual (also available at hifiengine.com) if anyone wants to take a look and see if their more experienced eyes can figure out why the signal is not making its way through the preamp section.
Oh and also, there is the added hurdle of figuring out if missing the remote is an issue. From what I gather, this is an early implementation of a remote option and there are some screwy things about how they paralleled the remote control board with the analog controls on the front that I don't quite understand. I.e., there is a "remote" button on the front that disengages some of the front controls and turns them over to the digital control sections of the remote board?
Again, all the help so far is greatly appreciated.
But, it appears I have won a battle while still fighting the war. I can now confirm the AMP section works even though the amp doesn't put out sound (unless hacked).
To summarize:
- I sat down to replace the Jfets and when I threw the new ones on my tester I again got a couple reading as BJT's.
- So, after some experimentation I found that if my fingers were touching the insulation of the test leads I got good readings of both the new and the original Jfets. I can only speculate that a little extra capacitance made the difference?
Whatever the reason, I got good and matched readings on the original K240's so I reinstalled them. - I hooked up the amp board back into the amp with intention of taking voltage measurements again.
- At first I kept the outputs removed and got good measurements all around. No neg. rail DC on the Emitter pads nor inappropriate pins at the daughter boards.
- Next I reinstalled the outputs after cleaning old thermal paste and re-applying new. Again, got good measurements. And the the amp comes out of protection (at least according to the flashing light on front panel - note for later)
- I followed the adjustment procedures and set idle current and got absolute 0.00dc on speaker posts (this seemed suspicious - again, note for later)
- Hooked up a pair of sacrificial speakers and used an iPod as a source into AUX..... NO sound.
- All buttons on front seem to work, they change indicators and I can hear all the appropriate relays clicking.
- Tried hooking up a headphone amp to the PRE-OUT section to test the preamp section...NO sound.
- Tried hooking iPod directly to the MAIN-IN section (speakers still hooked up speaker taps)....NO sound.
- Next I removed the main amp output connections from the protection board and hacked speakers connected directly to the amp board output and this time I got... YES sound (with direct input into MAIN-IN).
- Now I was able to actually measure DC offset at amp output and got <5mV on both channels.
- Sounds good and heatsinks got barely luke warm with even heat spread.
I've been reading that on some of these Luxman "suckface" components they will not work properly if the suckface mechanism is not working properly. Apparently this is due to the various circuits hooked up to the microswitch that engages when the face panel reaches its innermost position?
I've already ordered a new belt for the suckface mechanism. With the amp section working I feel confident in pushing forward.
I also guess it's time to dig out my old Tektronix 465 scope and finally start learning how to use it to trace a signal through the unit. Today I will go over to FedEx Office (Kinko's) and print out the service manual in full (with large scale schematic pages). I have a hard time tracing circuits across multiple pages on a computer screen scrolling back and forth. I really like being able to use colored markers on paper as I follow the trail.
I've attached the service manual (also available at hifiengine.com) if anyone wants to take a look and see if their more experienced eyes can figure out why the signal is not making its way through the preamp section.
Oh and also, there is the added hurdle of figuring out if missing the remote is an issue. From what I gather, this is an early implementation of a remote option and there are some screwy things about how they paralleled the remote control board with the analog controls on the front that I don't quite understand. I.e., there is a "remote" button on the front that disengages some of the front controls and turns them over to the digital control sections of the remote board?
Again, all the help so far is greatly appreciated.
Congrats on progress!
A Tek 465 is a wonderful tool to have available and learning to use it will be invaluable.
If I understand correctly, you're able to get to get audio at speaker by tapping into the amp output in front protection relay? If so, try to investigate why the protection is being asserted. Either there's a problem triggering fault or a problem in the monitoring circuit itself.
Keep us informed, please.
A Tek 465 is a wonderful tool to have available and learning to use it will be invaluable.
If I understand correctly, you're able to get to get audio at speaker by tapping into the amp output in front protection relay? If so, try to investigate why the protection is being asserted. Either there's a problem triggering fault or a problem in the monitoring circuit itself.
Keep us informed, please.
Thanks!
Yes, I got audio in front of protection relay.
I kind of suspect the relay is bad. It's an Omron G2Z-222P-US 12v, which I have been reading were very common speaker relays, have an oddball pinout, are NLA, and are known to be problematic.
Luckily there are modern replacements on adapter boards that are readily available apparently.
Measuring pin 6 of the PC1237h IC upon turn on I get 12v to ground while the "stand by" light flashes for the 1st 10-15 seconds.
When the light stops flashing and the amp is supposed to be out of protection the voltage drops to 0.8v.
There is a constant 12v on pin 1 of connector K-1, pin 3 carries 0.8v to ground
When the voltage drops I don't hear the relay click.
It's going to take some work to get the board unmounted so I can get better access to measure across the coils of the relay, and the actual switched terminals of the relay to see if it's actually closing or opening.
Yes, I got audio in front of protection relay.
I kind of suspect the relay is bad. It's an Omron G2Z-222P-US 12v, which I have been reading were very common speaker relays, have an oddball pinout, are NLA, and are known to be problematic.
Luckily there are modern replacements on adapter boards that are readily available apparently.
Measuring pin 6 of the PC1237h IC upon turn on I get 12v to ground while the "stand by" light flashes for the 1st 10-15 seconds.
When the light stops flashing and the amp is supposed to be out of protection the voltage drops to 0.8v.
There is a constant 12v on pin 1 of connector K-1, pin 3 carries 0.8v to ground
When the voltage drops I don't hear the relay click.
It's going to take some work to get the board unmounted so I can get better access to measure across the coils of the relay, and the actual switched terminals of the relay to see if it's actually closing or opening.
Yup, it's the relay.
Got the board loose enough to check continuity across contacts and nothing even after applying 9v from a weak battery and hearing the coil try to engage the contacts. Pulled the relay and opened it up to find one channel had melted brass (?) leafs to the point that the metal blobs blocked the whole actuator from allowing the other channel to make contact. I guess something big happened?
Got the board loose enough to check continuity across contacts and nothing even after applying 9v from a weak battery and hearing the coil try to engage the contacts. Pulled the relay and opened it up to find one channel had melted brass (?) leafs to the point that the metal blobs blocked the whole actuator from allowing the other channel to make contact. I guess something big happened?
It doesn’t even take that “big” of an event to do that to a speaker relay. Just trying to open up during a fault (or just excessive low frequency) can fry relays that are sized the way they usually do. It takes one of those big ice cube types to do it at all - and even then it’s not 100% safe. What a speaker relay WILL do reliably is prevent an amp from putting out DC to the speaker if it powers up in a broken state - the relay will just not engage. Most of the time that’s what happens.
I've got a new relay ordered (coming from Germany), and also a replacement belt for the Servo-face mechanism (ETA Tues. 30th). The amp is currently splayed open like a cadaver on my kitchen table.
It will probably take a few weeks for the Relay before I can re-assemble and continue testing. So, expect a pause in my posting.
The good news is both the motor and the unobtanium microswitch on the Suckface mechanism appear to be in good working order. The belt was aged and stretched out and had fallen off the pulleys it looks like. The mechanics also need a good clean and lube.
It will probably take a few weeks for the Relay before I can re-assemble and continue testing. So, expect a pause in my posting.
The good news is both the motor and the unobtanium microswitch on the Suckface mechanism appear to be in good working order. The belt was aged and stretched out and had fallen off the pulleys it looks like. The mechanics also need a good clean and lube.
Ok, I'm back.
Last couple weeks have been busy.
The parts to repair Speaker Protection relay and the Servo-face showed up.
Here's a side-by-side of the new and old relays. The new relay works like a champ and is higher amp rating. I get sound out to both speakers when the amp comes out of protection. I still have to use the "amp-in" RCA's. My next post will address the progress I've made in diagnosing why I'm not getting signal through from the inputs to the amp section.
I also received the new belt to repair the "Suck-face" mechanism. What a pain, but I did it. Lubed everything up (with discretion) while I was in there.
The Servo-face now works about 95%. Let me clarify....
It goes through the whole process just fine until you turn the unit off. At that point it's supposed to nudge the cam from it's face recessed position until the lobe moves enough to let the spring loaded carriage return to fully flush position under it's own spring loaded power. Pretty clever really as nothing needs to stay powered up for the return process to happen.
Unfortunately it only seems to be getting about 1/2 the required nudge at shut off. It could be the little micro-switch, or it could be something else. But, if you turn it on and off again it gets the rest of the nudge it needs.
What's weird is that when using the manual Servo-Face activation button it goes through both retract and extend processes flawlessly. So, I can live with that since it is 40 years old!
Last couple weeks have been busy.
The parts to repair Speaker Protection relay and the Servo-face showed up.
Here's a side-by-side of the new and old relays. The new relay works like a champ and is higher amp rating. I get sound out to both speakers when the amp comes out of protection. I still have to use the "amp-in" RCA's. My next post will address the progress I've made in diagnosing why I'm not getting signal through from the inputs to the amp section.
I also received the new belt to repair the "Suck-face" mechanism. What a pain, but I did it. Lubed everything up (with discretion) while I was in there.
The Servo-face now works about 95%. Let me clarify....
It goes through the whole process just fine until you turn the unit off. At that point it's supposed to nudge the cam from it's face recessed position until the lobe moves enough to let the spring loaded carriage return to fully flush position under it's own spring loaded power. Pretty clever really as nothing needs to stay powered up for the return process to happen.
Unfortunately it only seems to be getting about 1/2 the required nudge at shut off. It could be the little micro-switch, or it could be something else. But, if you turn it on and off again it gets the rest of the nudge it needs.
What's weird is that when using the manual Servo-Face activation button it goes through both retract and extend processes flawlessly. So, I can live with that since it is 40 years old!
As far as tackling the lack of signal through the front end I've spent the last week or so studying the schematic trying to wrap my head around the routing back and forth between the boards. What's apparent to me is the signal takes a circuitous route between several boards. Today I went to FedEx office and printed the schematics in large 11x17 format.
Here's what I've learned so far.
When I plug an ipod into either Tuner or DAD/Aux I do not get any sound.
When I plug into the PHono section (both MM and MC) I do get sound out of only the right channel.
When I plug into the PHono section and use "Phono Direct" I get sound out of both left and right.
Here's the appropriate section of the Schematic showing the EQ (phono section) and the line-level inputs.
RL102 selects between Tuner and DAD/Aux (line-level sources)
RL101 selects between PHono and Line-level sources
RL103 selects between PH. Direct and normal routing
So the signal basically routes out through connector A-3.
It goes through a couple boards and comes back through connector T-4.
And then it goes back out through connector A-2 to the Voltage control amp.
Except in the "PH Direct" scenario the signal is routed out directly through A-2.
What we know from the above testing:
-The phono section is working.
-Everything after A-2 seems to be working correctly.
-Somewhere between A-3 and T-4 (and/or A-2) is where the problem lies.
Note: I did check for continuity between Tuner and DAD RCA's and connector A-3, which was successful.
So, I started suspecting Relays 101 and 103 being compromised as I notices they are different parts than the rest of the amp.
Getting the board out was a pretty surgical adventure. But I did it.
Here's the board freed. As you can see, the blue relays are newer. And when I inspected the back side I could see that all three relays have had some dodgy solder work. I suspect whoever worked on it tried doing the soldering while the board was still installed and they worked kinda blind.
I've already ordered up some replacement relays and will re-install after repairing the pads and properly soldering them in. I'm also cleaning up the old crystallized flux and washing the board. Hopefully this fixes it, but even if it doesn't it still needs to be corrected.
Anyone have any thoughts?
Here's what I've learned so far.
When I plug an ipod into either Tuner or DAD/Aux I do not get any sound.
When I plug into the PHono section (both MM and MC) I do get sound out of only the right channel.
When I plug into the PHono section and use "Phono Direct" I get sound out of both left and right.
Here's the appropriate section of the Schematic showing the EQ (phono section) and the line-level inputs.
RL102 selects between Tuner and DAD/Aux (line-level sources)
RL101 selects between PHono and Line-level sources
RL103 selects between PH. Direct and normal routing
So the signal basically routes out through connector A-3.
It goes through a couple boards and comes back through connector T-4.
And then it goes back out through connector A-2 to the Voltage control amp.
Except in the "PH Direct" scenario the signal is routed out directly through A-2.
What we know from the above testing:
-The phono section is working.
-Everything after A-2 seems to be working correctly.
-Somewhere between A-3 and T-4 (and/or A-2) is where the problem lies.
Note: I did check for continuity between Tuner and DAD RCA's and connector A-3, which was successful.
So, I started suspecting Relays 101 and 103 being compromised as I notices they are different parts than the rest of the amp.
Getting the board out was a pretty surgical adventure. But I did it.
Here's the board freed. As you can see, the blue relays are newer. And when I inspected the back side I could see that all three relays have had some dodgy solder work. I suspect whoever worked on it tried doing the soldering while the board was still installed and they worked kinda blind.
I've already ordered up some replacement relays and will re-install after repairing the pads and properly soldering them in. I'm also cleaning up the old crystallized flux and washing the board. Hopefully this fixes it, but even if it doesn't it still needs to be corrected.
Anyone have any thoughts?
Yesterday I replaced all three relays on the input (EQ) board and I was able to get signal from the TUNER and DAD/AUX input. But, it was still dropping left channel except on PHONO Direct.
So I followed the signal path next to the SUBWOOFER board which also houses all the TAPE Mon. and MONO relays. I surmised that since the MONO relay was the last in the chain that if the problem was in this area that engaging mono would output signal to the left channel of the amp board. Nope, didn't make a difference. I also checked for continuity through this section and it was good on both channels.
The next step was the Balance pot. BINGO!
Measuring across the pot revealed the left channel wasn't passing.
I had to go through some disassembly to gain access to spray some DeOxit into it. After reassembly I had audio out of both channels restored.
Still doing some testing to make sure all the functions are working, but so far it's looking good. Gonna hook it up to some good speakers instead of my crappy bench speakers and give it a listen here in a bit.
I know I'm pretty much talking to myself at this point, but thanks everyone for the help.
BTW, paid $20 for the amp.
Have now spent $32 on parts.
So I followed the signal path next to the SUBWOOFER board which also houses all the TAPE Mon. and MONO relays. I surmised that since the MONO relay was the last in the chain that if the problem was in this area that engaging mono would output signal to the left channel of the amp board. Nope, didn't make a difference. I also checked for continuity through this section and it was good on both channels.
The next step was the Balance pot. BINGO!
Measuring across the pot revealed the left channel wasn't passing.
I had to go through some disassembly to gain access to spray some DeOxit into it. After reassembly I had audio out of both channels restored.
Still doing some testing to make sure all the functions are working, but so far it's looking good. Gonna hook it up to some good speakers instead of my crappy bench speakers and give it a listen here in a bit.
I know I'm pretty much talking to myself at this point, but thanks everyone for the help.
BTW, paid $20 for the amp.
Have now spent $32 on parts.
Thanks @dogwan for this write up! I have this same amp and it is also stuck in protection mode, but I’ve not had time to troubleshoot the issue.
Looks like the protection relay might be the culprit on mine, the replacement you used is Finder 41.52.9.012.0000 correct?
Do you have the model of the 3 relays you used to replace the ones on the EQ board?
For the servo face issue, did the phono input work while the this feature was non-functional? Have this issue on my RX-103 and heard it might be an issue on the LX as well. I repaired the servo face on the RX-103 and it worked for a week, but the motor seems to be on its last legs and it stopped functioning. For your issue, the metal tab on the switch might not stick out far enough due to bending in over time, but as I’m sure you know don’t use too much force! They are fragile and NLA (but I did find the model number of a modern day replacement that apparently works, let me know if you want that info).
Thanks again (you may have saved me many hours) and I will update if I get mine working!
Per
Looks like the protection relay might be the culprit on mine, the replacement you used is Finder 41.52.9.012.0000 correct?
Do you have the model of the 3 relays you used to replace the ones on the EQ board?
For the servo face issue, did the phono input work while the this feature was non-functional? Have this issue on my RX-103 and heard it might be an issue on the LX as well. I repaired the servo face on the RX-103 and it worked for a week, but the motor seems to be on its last legs and it stopped functioning. For your issue, the metal tab on the switch might not stick out far enough due to bending in over time, but as I’m sure you know don’t use too much force! They are fragile and NLA (but I did find the model number of a modern day replacement that apparently works, let me know if you want that info).
Thanks again (you may have saved me many hours) and I will update if I get mine working!
Per
Hey @perphunk ,
This is the protection relay I ordered....
https://www.ebay.com/itm/115682432662
as you can see from the pics I posted above that the unit I recieved was a little different than the pic in the ad. It works great though. I'm sure I could have sourced the relay far cheaper on my own. But, what I really needed was the adapter PCB board as the original has an oddball layout and is NLA.
These are the smaller relays I ordered for the EQ board.
https://www.amazon.com/dp/B09P1D1K64?psc=1&ref=ppx_yo2ov_dt_b_product_details
Didn't have much faith being cheap asian knock-offs, but so far they are working great. I still need to go in and replace the rest on the Subwoofer board (where the tape monitor relays reside). I'm getting some channel imbalance I suspect may dirty relays. I had some drop-outs when I tested the tape monitor and mono switch functionality that went away with exercise.
I'm sorry I can't answer the phono question because I was never able to test that section until after I repaired the servo-face. I do notice that all signal cuts out if I hit the servo-face switch as the face moves in an out while music is playing. So, I suspect that if the micro switch is not at exact endpoint position it might be your problem?
I did drag a piece of paper soaked in Deoxit through the contact points of the micro-switch (ever so gently....!)
Also, the issue with the servo-face stalling at shut down has resolved itself. I found out there is a cap that stores the energy to give the motor the small bump it needs to move the cam to extend position. I think the cap on mine has re-formed itself with use. Just one day (a week or two after I started using it almost daily) it started working as designed at shutdown.
My next task after replacing the rest of the small relays is to source a replacement for the volume and balance pots. Both on mine are problematic.
This is the protection relay I ordered....
https://www.ebay.com/itm/115682432662
as you can see from the pics I posted above that the unit I recieved was a little different than the pic in the ad. It works great though. I'm sure I could have sourced the relay far cheaper on my own. But, what I really needed was the adapter PCB board as the original has an oddball layout and is NLA.
These are the smaller relays I ordered for the EQ board.
https://www.amazon.com/dp/B09P1D1K64?psc=1&ref=ppx_yo2ov_dt_b_product_details
Didn't have much faith being cheap asian knock-offs, but so far they are working great. I still need to go in and replace the rest on the Subwoofer board (where the tape monitor relays reside). I'm getting some channel imbalance I suspect may dirty relays. I had some drop-outs when I tested the tape monitor and mono switch functionality that went away with exercise.
I'm sorry I can't answer the phono question because I was never able to test that section until after I repaired the servo-face. I do notice that all signal cuts out if I hit the servo-face switch as the face moves in an out while music is playing. So, I suspect that if the micro switch is not at exact endpoint position it might be your problem?
I did drag a piece of paper soaked in Deoxit through the contact points of the micro-switch (ever so gently....!)
Also, the issue with the servo-face stalling at shut down has resolved itself. I found out there is a cap that stores the energy to give the motor the small bump it needs to move the cam to extend position. I think the cap on mine has re-formed itself with use. Just one day (a week or two after I started using it almost daily) it started working as designed at shutdown.
My next task after replacing the rest of the small relays is to source a replacement for the volume and balance pots. Both on mine are problematic.
Thanks @dogwan for the link, that is very helpful. I’ve come across that listing before but will probably order it regardless of whether mine is functional.
Did you ever figure out what was sending it into protection? Sounds like you disassembled then reassembled and it worked? Was it the bad protection relay?
I’ll look to replace the small relays as well, sounds like they are a weak point on these receivers. Thanks for the link in that.
I’ll look to fix the servo face after the amp is out of protection, thanks for suggesting some fixes there.
Thanks again, this is all very helpful for me!
Did you ever figure out what was sending it into protection? Sounds like you disassembled then reassembled and it worked? Was it the bad protection relay?
I’ll look to replace the small relays as well, sounds like they are a weak point on these receivers. Thanks for the link in that.
I’ll look to fix the servo face after the amp is out of protection, thanks for suggesting some fixes there.
Thanks again, this is all very helpful for me!
I think I oversimplified the steps taken to get the amp out of protection, I'm still learning myself 🙂 I'm curious if you have a sense of what the issue(s) were that caused it to go into protect mode (solder bridge? pin issue on daughter board?). I was thinking of starting with the output transistors (desolder, isolate from pcb, test, resolder) to see if the issue lies there first, then start to check some of the other places you did. I also have a Hakko 301 desolder gun and it is amazing!
Mine appears to be stock on the inside and is in amazing overall condition physically. I found the LX-104, GX-101 and TX-101 in mint condition with OEM boxes on Craigslist. So hoping to get all 3 up and running together someday soon. The GX makes a terrible noise when turned on but the TX sounds great as is. Currently using a RX-103, but my speakers (ADS 910) love power so would be nice to switch to the LX. The 910s are 4 ohm, so 120w into 8 ohms will be provide a good bump at 4 ohms.
Thanks again @dogwan
Mine appears to be stock on the inside and is in amazing overall condition physically. I found the LX-104, GX-101 and TX-101 in mint condition with OEM boxes on Craigslist. So hoping to get all 3 up and running together someday soon. The GX makes a terrible noise when turned on but the TX sounds great as is. Currently using a RX-103, but my speakers (ADS 910) love power so would be nice to switch to the LX. The 910s are 4 ohm, so 120w into 8 ohms will be provide a good bump at 4 ohms.
Thanks again @dogwan
No, I never did figure out what the cause was. Let me clarify. I quickly found I had full negative rail voltage on one of the speaker outputs. So, the protect circuit was working. But, I never did figure out where the rail voltage was jumping over.
I did the same thing you suggest and pulled all the output transistors and tested out of circuit (thinking one or more were blown), but they tested fine. Somehow, once I poured over the amp board and re-installed the issue went away.
My suspicion is that one of the small TO-92 transistors that are clamped to the heatsink with a metal clip had a short between a lead and that clamp. And, when I re-installed I was more careful than whoever previously worked on it.
I did the same thing you suggest and pulled all the output transistors and tested out of circuit (thinking one or more were blown), but they tested fine. Somehow, once I poured over the amp board and re-installed the issue went away.
My suspicion is that one of the small TO-92 transistors that are clamped to the heatsink with a metal clip had a short between a lead and that clamp. And, when I re-installed I was more careful than whoever previously worked on it.
Thanks for the clarification, good to have your thoughts on what the issue might have been. I will check for shorts on the heatsinked transistors and also check the outputs while I’m in there.
Will update if I have anymore questions and thanks for taking the time to reply, helpful to have feedback from someone who has worked on this receiver.
Will update if I have anymore questions and thanks for taking the time to reply, helpful to have feedback from someone who has worked on this receiver.
Reminded me of a old Maplin amp I bought in faulty.
It worked but with heavy distortion.
As it powered up without blowing fuses it was ok to measure voltages.
Kept coming back to Q4 as the voltages around it didnt seem right.
However, Q4 buzzed out ok.
In the end I came back to Q4 and measured it again, then it hit me while it buzzed out ok it was wrong way around.
Someone had previously attempted repair and put in NPN instead of PNP !
Amps can be a pain to fix due to being in a feedback loop so faulty goes around the loop.
In your case there are a lot of transistors test which is a pain but there are few short cuts.
Removing outputs and feeding back output into LTP gives soemthing that powers up without blowing fuses.
Then check voltages around the circuit until a problem is found.
Another problem with amps is sometimes an output blowing can take out drivers too.
So simply replacing bad outputs results in them blowing again.
It worked but with heavy distortion.
As it powered up without blowing fuses it was ok to measure voltages.
Kept coming back to Q4 as the voltages around it didnt seem right.
However, Q4 buzzed out ok.
In the end I came back to Q4 and measured it again, then it hit me while it buzzed out ok it was wrong way around.
Someone had previously attempted repair and put in NPN instead of PNP !
Amps can be a pain to fix due to being in a feedback loop so faulty goes around the loop.
In your case there are a lot of transistors test which is a pain but there are few short cuts.
Removing outputs and feeding back output into LTP gives soemthing that powers up without blowing fuses.
Then check voltages around the circuit until a problem is found.
Another problem with amps is sometimes an output blowing can take out drivers too.
So simply replacing bad outputs results in them blowing again.