For the SAE amps, I would have to replace all outputs and drivers. I haven't checked further. I can't justify it to the client since they have run all these years.
The Pioneer stuff is simply garbage, not worth consideration. Make them go, out the door.
It blows my mind what some manufacturers have designed and actually sold through the years. The one standout is the "Proximity" amplifier from Quebec. Don't even consider repairing it.
The Pioneer stuff is simply garbage, not worth consideration. Make them go, out the door.
It blows my mind what some manufacturers have designed and actually sold through the years. The one standout is the "Proximity" amplifier from Quebec. Don't even consider repairing it.
R20 and R19 read good at 4.75k ohms.
c5 tests at 7.2uf vloss .9% and esr @ 1.5 ohms (esr @ 1.5 is too high, right?) cap is a nichicon HE 6.8uf 100v
Don't worry about ESR, if you're going to measure something, measure D-A. It's faster to look at ripple waveforms on filter caps than to disconnect and measure them. You can also see what happens when they warm up.
With amp unpowered, adjust P1 so the resistance is 1000 ohms. If it was substantially less Recheck voltage of collectors of Q9 Q10 with power on.
If the voltage eifference Q9 c Q10 c does not increase to 1.6-2.4 v, remove collectors of Q9 Q10 and with power on, check voltage at collector of Q7. If it gets up to 2 v or more, replace Q9 Q10. If not replace Q7.
While you are ordering things, C5 was very tired. As probably are most of the electrolytic caps in this 40 year old product. Don't jump off willy-nilly into replacing e-caps, they are not the cause of your problem. But you could save some freight charges buy buying them on one order. 40 year old ecaps are not reliable, and can unbalance frequency. Also save perhaps a handling charge for making too small an order. I keep a dozen more more MPSA06/56 around, they are useful in many other products. If the pinout instead is ecb, buy $10 of those products instead.
If the voltage eifference Q9 c Q10 c does not increase to 1.6-2.4 v, remove collectors of Q9 Q10 and with power on, check voltage at collector of Q7. If it gets up to 2 v or more, replace Q9 Q10. If not replace Q7.
While you are ordering things, C5 was very tired. As probably are most of the electrolytic caps in this 40 year old product. Don't jump off willy-nilly into replacing e-caps, they are not the cause of your problem. But you could save some freight charges buy buying them on one order. 40 year old ecaps are not reliable, and can unbalance frequency. Also save perhaps a handling charge for making too small an order. I keep a dozen more more MPSA06/56 around, they are useful in many other products. If the pinout instead is ecb, buy $10 of those products instead.
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So, thinking about this amp now all day every day. What could be wrong, etc almost every part on the "bad channel" is new, to the point where I am not sleeping good.
Then I had a thought, what if after I discovered and fixed the backwards diode on the output where the fuse blew, that the amp is ok now, even though the DBT lit up?
Definite amateur at this, but started to think what if the DBT is lighting up because there is no load on either the input, output or both and the current has nowhere to go but back to the bulb?
Searched on Google and did see a few posts about the amp is possibly drawing more than the 100w bulb causing it to light up, but nothing definitive.
Decided this morning to take my untouched 555 and connect to the DBT with no load and voila! The DBT lit up as I got up to full voltage on the variac!
I will wait for opinions on this before proceeding further, but could it be possible that all is well?
The measurements taken in the replies with @indianajo in the past few days were all done with the DBT after the variac...
Then I had a thought, what if after I discovered and fixed the backwards diode on the output where the fuse blew, that the amp is ok now, even though the DBT lit up?
Definite amateur at this, but started to think what if the DBT is lighting up because there is no load on either the input, output or both and the current has nowhere to go but back to the bulb?
Searched on Google and did see a few posts about the amp is possibly drawing more than the 100w bulb causing it to light up, but nothing definitive.
Decided this morning to take my untouched 555 and connect to the DBT with no load and voila! The DBT lit up as I got up to full voltage on the variac!
I will wait for opinions on this before proceeding further, but could it be possible that all is well?
The measurements taken in the replies with @indianajo in the past few days were all done with the DBT after the variac...
We must have been typing at the same time, see post #128.
All measurements were taken with DBT after the variac possibly affecting measurements?
Meesurements in post #128 cannot be compared with later measurements done without DBT. If remove DBT, and leave variac retake measurements of post #128 under new conditions. You can leave C5 out for now. Missing it may cause unstable idle bias current under varying temperatures, but you are not going to leave the amp on long enough to warm up.
KSC1008/A708 are near equal to A06/56. They are also available in ECB basing (“C” suffix) or in American standard EBC. Keep both around to have a stash of good general purpose devices. If you have trouble keeping things straight or seeing without a microscope, keep the A06 and 1008C and comps. Easier to tell them apart.
with c5 totally removed and adjusting P1 to .973 (as far as it would go - this is a new P1) AND NO DBT ( variac still at previous setting approx 45V):
q9 - 1.29V
q10 - 1.3V
Also getting about 31mv on both channels now at emitter resistors with common on DVM to red speaker terminal!
I should add that all Q's on this channel are new:
2sa1210's replaced with KSA1381 (Q7, Q6 (Q6 in larger to-126 package with heatsink))
2sa970's replaced with KSA992 (Q8, Q9)
2sa1016 replaced with KSA992 ( Q5)
2sc2240's replaced with KSC1845 (Q3, Q10)
2sc2240's Q1 and Q2 replaced with matched pair KSC1845 (from Hoppesbrain)
2sc2912 replaced with KSC3503 (Q4)
2sa1011 replaced with MJE15033G (Q11)
2sc2344 replaced with MJE153032G (Q12)
I presume on P1 you mean 0.978 kohm.
Check voltage at Q7 c versus Q10 c. If same, great. If not you could have a bad solder joint between source and sink, or a burnt land.
You are not specifying exactly which pin of Q9 and Q10 you are measuring. I am assuming c since that is what I asked about, but many assumptions are the cause of misunderstanding or product malfunction. Perhaps some of your new transistors have a different pinout than you assumed. On and ST change packaging standards many times, requiring the purchaser to read the datasheet issued THAT DAY. On TO92 in particular I check where the base is with the diode scale when installing. TO220 and TO126 are not so variable, but I have had On substitute TO220 for TO247 indicated on my (obsolete) datasheet.
Check voltage at Q7 c versus Q10 c. If same, great. If not you could have a bad solder joint between source and sink, or a burnt land.
You are not specifying exactly which pin of Q9 and Q10 you are measuring. I am assuming c since that is what I asked about, but many assumptions are the cause of misunderstanding or product malfunction. Perhaps some of your new transistors have a different pinout than you assumed. On and ST change packaging standards many times, requiring the purchaser to read the datasheet issued THAT DAY. On TO92 in particular I check where the base is with the diode scale when installing. TO220 and TO126 are not so variable, but I have had On substitute TO220 for TO247 indicated on my (obsolete) datasheet.
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For some reason I cannot edit my post.
Yes, 0.978 kohm on p1.
And yes, c of q9 and q10 is what was measured.
Q7c is at 1.278V
Q10c is at 1.279V
I'll be really happy when you can no longer buy a filament type light bulb. I would oppose discontinuing those lamps except people keep using dim bulb testers. Honestly, do it right! Pretend you can't buy those light bulbs.
You cannot troubleshoot when your voltages are variable, bouncing up and down with load current. They have their specific uses, but you have to know what you are doing and what effect a "DBT" has on the circuit you are working on. We've had light bulbs since before electric radios. They didn't use DBTs in the 30's, not until relatively lately. Want to guess why? Because even the old timers knew you couldn't hope to troubleshoot with them in circuit. What did they do? They bought an expensive variac.
When I was apprenticed in the 1970's, this was the way it was done (always done), the way I was trained. Not one single good technician ever used one - ever. They knew how to work efficiently and properly. To this day I have yet to meet a good tech that uses a DBT. I think the ideas that sell them is that they are somehow "protection" and a cheap way to power up the unknown. Neither is actually true, although as a byproduct of limiting current they often save you from disaster - but so does a variac.
Not one single service manual I have ever seen recommends this as a practice you should follow. There is a good reason for that, it isn't good practice. When you are troubleshooting, you must not introduce variables. That includes swapping parts from the other channel or other units. WHy? Because now those parts are variables, you can cause the other previously good channel or amp to fail. Congratulations.
Enough ...
You cannot troubleshoot when your voltages are variable, bouncing up and down with load current. They have their specific uses, but you have to know what you are doing and what effect a "DBT" has on the circuit you are working on. We've had light bulbs since before electric radios. They didn't use DBTs in the 30's, not until relatively lately. Want to guess why? Because even the old timers knew you couldn't hope to troubleshoot with them in circuit. What did they do? They bought an expensive variac.
When I was apprenticed in the 1970's, this was the way it was done (always done), the way I was trained. Not one single good technician ever used one - ever. They knew how to work efficiently and properly. To this day I have yet to meet a good tech that uses a DBT. I think the ideas that sell them is that they are somehow "protection" and a cheap way to power up the unknown. Neither is actually true, although as a byproduct of limiting current they often save you from disaster - but so does a variac.
Not one single service manual I have ever seen recommends this as a practice you should follow. There is a good reason for that, it isn't good practice. When you are troubleshooting, you must not introduce variables. That includes swapping parts from the other channel or other units. WHy? Because now those parts are variables, you can cause the other previously good channel or amp to fail. Congratulations.
Enough ...
In view of the number of parts you have changed, with your vast experience as a soldering operator: I propose you buzz the entire circuit. Disconnect the AC power. Make a paper copy of the circuit, acquire a colored pencil. Using the diode scale of the DVM, check every trace from component lead to component lead. I would find a Pamona grabber as at least one probe, instead of two shaft probes. The traces that have continuity, color in the line on the diagram. You may stop when every line is colored.
Then check every TO92 transistor, that the pinout you assumed, corresponds to the product you bought. I am dismayed that ON is selling KSC1845 and KSA992 in two different pinouts. Base must read 550-700 to both emitter and collector.
Then check every TO92 transistor, that the pinout you assumed, corresponds to the product you bought. I am dismayed that ON is selling KSC1845 and KSA992 in two different pinouts. Base must read 550-700 to both emitter and collector.
@anatech I am here to learn and I am learning..... Thanks for the tough love!
@indianajo I did check datasheets from each page of the transistors I purchased from Digikey (no ebay or grey market parts were used) and the pinouts matched. Also double checked pinouts with the 2v toy tester before installing to be absolutely sure.
As far as a paper copy of the circuit, I cannot find one that matches my early version that includes the traces.
I did order some new C5's yesterday and will wait until they arrive, in the meantime buzzing out what I can gather from the later layout.
I am more at ease now feeling that things are looking up! A huge thanks to the both of you!
@indianajo I did check datasheets from each page of the transistors I purchased from Digikey (no ebay or grey market parts were used) and the pinouts matched. Also double checked pinouts with the 2v toy tester before installing to be absolutely sure.
As far as a paper copy of the circuit, I cannot find one that matches my early version that includes the traces.
I did order some new C5's yesterday and will wait until they arrive, in the meantime buzzing out what I can gather from the later layout.
I am more at ease now feeling that things are looking up! A huge thanks to the both of you!
In that case, depower the product, and buzz the working side, to make a drawing that conforms to how that side is arranged.
Then make a copy, and buzz the broken side. Any errors, correct them.
If you post your analysis of the good side here, we may be able to make some sense of it.
As I see the early schematic posted earlier, Q6, Q7 & Q3 make s sort of constant current source for input amplifier Q1 and feedback amplifier Q2. Q4 is a VAS that drives the bias spreader stack Q9 Q10. The collectors of those drive the drivers Q11 Q12. The output transistors increase the current of those.
Best of luck.
@anatech I never disputed the repair worthiness of older amps. They're clearly worth repairing IF you can do it the right way with the proper parts.
Working on previously butchered amps is usually where I draw the line, mainly because the guys who worked on them would often make the original problem worse and use poor quality or inappropriate parts.
Once things like matched input and output transistors are toast and so called "equivalent" parta are substituted in, the amp will no longer sound the way it used to. Back when I made my money as a repair tech in mom and pop repair shops, alot of guys would use ECG or NTE substitute transistors (often mixed together with the old parts which still measured good). That caused two problems, one which was the old stressed parts failing soon after the first repair, not being replaced in matched sets. The second problem was the generic replacements failing due to being inferior quality, one size fits all parts that didn't meet OEM level specs.
These bigger amps with multiple pairs of output devices immediately become expensive to repair when just one output device fails. If you're lucky, its just a diode or rectifier bridge that failed, but you still have to go through the entire amp to make sure its going to be reliable with no other looming impending doom. It just takes a flaky little 10 cent bias pot to wipe out a whole channel worth of $25 transistors and its supporting parts. Now you have to find the correct matching parts in sufficient quantities and hope they're not counterfeit. Most adcom GFA555 aren't worth that kind of investment and (hopefully at a minimum) become parts donors.
Working on previously butchered amps is usually where I draw the line, mainly because the guys who worked on them would often make the original problem worse and use poor quality or inappropriate parts.
Once things like matched input and output transistors are toast and so called "equivalent" parta are substituted in, the amp will no longer sound the way it used to. Back when I made my money as a repair tech in mom and pop repair shops, alot of guys would use ECG or NTE substitute transistors (often mixed together with the old parts which still measured good). That caused two problems, one which was the old stressed parts failing soon after the first repair, not being replaced in matched sets. The second problem was the generic replacements failing due to being inferior quality, one size fits all parts that didn't meet OEM level specs.
These bigger amps with multiple pairs of output devices immediately become expensive to repair when just one output device fails. If you're lucky, its just a diode or rectifier bridge that failed, but you still have to go through the entire amp to make sure its going to be reliable with no other looming impending doom. It just takes a flaky little 10 cent bias pot to wipe out a whole channel worth of $25 transistors and its supporting parts. Now you have to find the correct matching parts in sufficient quantities and hope they're not counterfeit. Most adcom GFA555 aren't worth that kind of investment and (hopefully at a minimum) become parts donors.
Hi wiz1,
I trained technicians for years. I would never tell you to do something without extremely good reasons. If I am emphatic about something, well, it's because whatever it is, it is important and has been proved time and time again. You can get away with something at times. Sometimes not, and sometimes it will get you years later.
Hi profiguy,
Yes, butchered nuits can be straight forward, or next to impossible to find all the problems in. That's because they also get hit with "panicking technician syndrome". That's when they do stupid things, or do silly things in areas unconnected to the fault. The worst ones are units that are "improved" by self-styled experts that only copy what they think is right after reading the internet. I wish those folks were financially accountable for the destruction they cause. Only occasionally they are.
I trained technicians for years. I would never tell you to do something without extremely good reasons. If I am emphatic about something, well, it's because whatever it is, it is important and has been proved time and time again. You can get away with something at times. Sometimes not, and sometimes it will get you years later.
Hi profiguy,
Yes, butchered nuits can be straight forward, or next to impossible to find all the problems in. That's because they also get hit with "panicking technician syndrome". That's when they do stupid things, or do silly things in areas unconnected to the fault. The worst ones are units that are "improved" by self-styled experts that only copy what they think is right after reading the internet. I wish those folks were financially accountable for the destruction they cause. Only occasionally they are.