I first asked about my problem on this thread http://www.diyaudio.com/forums/digi...71-readout-panel-doesnt-work.html#post2845400
but as suggested by a member, I start a different thread here.
So my problem: I recently replaced the tray gear on my rcd-975. I must have messed with something, as the display panel does not work anymore, and push buttons do nothing, making my CDP useless.🙁
As suggested by Mooly, I checked continuity of all pins in the connector between the main board and the display/control board. All are fine. I did my tests directly on the PCBs, not the connector, to make sure the problem is not a wire not properly connecting to the PCB.
Then I removed the display board. No capacitor seems to be leaking (haven't tested them though), resistor seem to have proper values and all diodes test ok (I haven't disconnected them, nor any component).
There is an IC chip underneath the display. Haven't tried to test anything regarding it, as I don't really know what to test😕
I attached the schematic of the display board. I have the complete service manual (got it from Rotel), but it's too large to upload. Let me know what else can be helpful and I could upload additional pictures or PM the complete PDF. I also attached a picture of the whole open unit, and one of the display/control PCB.
Any help to isolate and fix (if possible) the problem would be greatly appreciated.
but as suggested by a member, I start a different thread here.
So my problem: I recently replaced the tray gear on my rcd-975. I must have messed with something, as the display panel does not work anymore, and push buttons do nothing, making my CDP useless.🙁
As suggested by Mooly, I checked continuity of all pins in the connector between the main board and the display/control board. All are fine. I did my tests directly on the PCBs, not the connector, to make sure the problem is not a wire not properly connecting to the PCB.
Then I removed the display board. No capacitor seems to be leaking (haven't tested them though), resistor seem to have proper values and all diodes test ok (I haven't disconnected them, nor any component).
There is an IC chip underneath the display. Haven't tried to test anything regarding it, as I don't really know what to test😕
I attached the schematic of the display board. I have the complete service manual (got it from Rotel), but it's too large to upload. Let me know what else can be helpful and I could upload additional pictures or PM the complete PDF. I also attached a picture of the whole open unit, and one of the display/control PCB.
Any help to isolate and fix (if possible) the problem would be greatly appreciated.
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Considering when the fault happened, I'd be looking for a blown fuse device, i.e., fusible resistor, "IC protector"(ICP-Nxx). There is a 2.2ohm fuse resistor right on the display board for the +5V supply feed, which would explain the fault if blown. It would even shut down the remote receiver, preventing all user operations. If your power LED is lit, then it means that the +5V supply for the display pcb is working, but not getting to the display chip.
Checking all the rails has to be a first step as Stephen says.
Have you got 5 volts on BOTH sides of R482 (on the front panel) when measured from ground ?
Depending on the size of the pdf (if it's below around 1mb) you might be able to put it into a zipped folder and post that.
Have you got 5 volts on BOTH sides of R482 (on the front panel) when measured from ground ?
Depending on the size of the pdf (if it's below around 1mb) you might be able to put it into a zipped folder and post that.
Thanks, Stephen and Mooly. I'll investigate those fusible resistors tonight and post results.
*edit* The pdf is 3.5MB - I just put it on dropbox, so you can access it here:
http://dl.dropbox.com/u/55817844/RCD-975-TM.pdf
*edit* The pdf is 3.5MB - I just put it on dropbox, so you can access it here:
http://dl.dropbox.com/u/55817844/RCD-975-TM.pdf
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I had found the SM on elektrotanya, which is why I sounded quite so informed about the fault. That 2.2ohm FR is the only fuse device in the related circuitry, on display or main board. So, if it's not that, and power LED is lit, and remote does not work, you must have a cable problem. If remote works, than you may have a bad display controller chip, which seems unlikely, unless you zapped the hell out of it with static discharge.
Got the manual... see how you get on checking the 2.2 ohm Stephen mentions.
If the 5 volts isn't present then check the -5 and +5 volt rails on voltage regulators U110 and U111 (page 9 pdf)
If the 5 volts isn't present then check the -5 and +5 volt rails on voltage regulators U110 and U111 (page 9 pdf)
First, thanks again for your help. Every input brings some hope, when I thought I was good to part out my sweet CDP.
I just did the tests you recommended.
R402 (looks like R482 on the fuzzy PDF) - fusible resistor on the 5v rail: looks good. It's not open (I measure about 2.5ohm). When power is on, I get 5v on both sides, relative to ground.
There are also two other fusible resistors, which also seem ok:
R404 (looks like R484 on the pdf) on the -vf rail: I measure 1.5ohm and, when power is on, I get -20.5v on both sides, same as the connector's -vf pin.
R405 on the +vf rail: 1.5ohm, -18v on both sides, same as the connector's +vf pin.
When I hit play on the remote control, the laser head moves for a second, so the remote receiver still does something. If I hit the play button on the unit's display board, nothing happens.
As for a static discharge, I don't remember getting any spark, and I always discharge myself before touching anything. But maybe.
Any idea what I should check next?
I just did the tests you recommended.
R402 (looks like R482 on the fuzzy PDF) - fusible resistor on the 5v rail: looks good. It's not open (I measure about 2.5ohm). When power is on, I get 5v on both sides, relative to ground.
There are also two other fusible resistors, which also seem ok:
R404 (looks like R484 on the pdf) on the -vf rail: I measure 1.5ohm and, when power is on, I get -20.5v on both sides, same as the connector's -vf pin.
R405 on the +vf rail: 1.5ohm, -18v on both sides, same as the connector's +vf pin.
When I hit play on the remote control, the laser head moves for a second, so the remote receiver still does something. If I hit the play button on the unit's display board, nothing happens.
As for a static discharge, I don't remember getting any spark, and I always discharge myself before touching anything. But maybe.
Any idea what I should check next?
Next thing I would do is check that the xtal oscillator for both the display & syscon uprocessors are both running. Then check for proper voltage on the reset line, pin 6 of the connector from main to display board. Looks from my low res schematic that it's weirdly a 3.3V reset line, which does not appear to have a pulse cap in the reset drive circuit, that TR1(blob)7 transistor circuit, right above & to the right of the U1(blob)7 syscon uproc ic on the schematic. My schematic download is horribly disorganised, so hard to follow without printing out the whole thing.
Lets go back and start again... without seeing the unit for real it's difficult so if any of these questions sound daft then that is why.
You replaced the tray gear. Did you remove any plugs to the mech ? Asking because I can see two small plugs in pictures. Not mixed up ?
Does the mech appear OK and the tray is free to move ?
If you partly open the tray manually and then switch on does the tray go in automatically as the player powers up ?
Can you manually load a CD. What happens if you press play on the remote.
When the player has been on a while does the display feel "warm". There are horizontal heater wires in these displays which you can see in total darkness as glowing orange.
Check these resistors marked in picture.
You replaced the tray gear. Did you remove any plugs to the mech ? Asking because I can see two small plugs in pictures. Not mixed up ?
Does the mech appear OK and the tray is free to move ?
If you partly open the tray manually and then switch on does the tray go in automatically as the player powers up ?
Can you manually load a CD. What happens if you press play on the remote.
When the player has been on a while does the display feel "warm". There are horizontal heater wires in these displays which you can see in total darkness as glowing orange.
Check these resistors marked in picture.
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Sounds good - a processor can't do much without a clock. With your help, things start looking a little less like a big black box to me.
But my (very basic) multimeter doesn't measure frequencies. So I'll first check that reset line, and then might get a new multimeter.
For the oscillator, the only one on the display board is X201, and the parts list says "ceramic resonator, 4MHz", not "crystal oscillator". Still, this is the one I should check, right?
The cheapest way to go (instead of getting a new DMM), would probably be to try a new oscillator. However, it's located under the display readout, so kind of hard work to replace.
No, I didn't unplug anything (besides the power led) when replacing the tray gear.
If I manually open the tray and turn on the unit, the tray closes poperly.
If I manually load a CD and press play on the remote, the head moves for a second, and than nothing.
I'll check if the display feels warm, and those resistors.
But I don't think I'll have time to test anything this weekend. Will post my results...
Thanks!
The fact the tray closes properly when powered up suggests much of the system control is OK.
Being logical about all this, we know the fault did occur after work was done. So it's not a "normal" component failure. Processor IC's and the like are ultra reliable unless they inadvertently get zapped. If you are sure all power was off when the unit was worked on (sounds obvious I know, but as a technician you would be amazed how many times I've seen it done) then the IC's are the last of the suspects.
For checking clocks and so on you need a scope and divider probe so as not to load the oscillator (which would stop it). The ceramic resonator won't be faulty... these are used in place of quartz crytals where mediocre accuracy is required.
I would say lets try and troubleshoot the display as that might just lead somewhere.
So techs head on, get your meter and just carefully run it down all the legs on the display. The majority should all be in the -18 volt region.
Now get something like a 1k resistor and just short any pin on the display (any but the end group of pins which are the heaters) to ground. A random segment of the display should illuminate extremely brightly for each pin. If any light then the supplies and heaters are OK.
Being logical about all this, we know the fault did occur after work was done. So it's not a "normal" component failure. Processor IC's and the like are ultra reliable unless they inadvertently get zapped. If you are sure all power was off when the unit was worked on (sounds obvious I know, but as a technician you would be amazed how many times I've seen it done) then the IC's are the last of the suspects.
For checking clocks and so on you need a scope and divider probe so as not to load the oscillator (which would stop it). The ceramic resonator won't be faulty... these are used in place of quartz crytals where mediocre accuracy is required.
I would say lets try and troubleshoot the display as that might just lead somewhere.
So techs head on, get your meter and just carefully run it down all the legs on the display. The majority should all be in the -18 volt region.
Now get something like a 1k resistor and just short any pin on the display (any but the end group of pins which are the heaters) to ground. A random segment of the display should illuminate extremely brightly for each pin. If any light then the supplies and heaters are OK.
You can get a working oscilloscope on ebay usually for less than $75usd. You can get away with as low as 5mHz scope, and it would be far more useful than a new DMM.
I have yet to ever see a ceramic resonator(which acts as the crystal in that case) go bad, so a "no clock" condition for the display proc would be cause to suspect a bad proc, rather than bad clock source. With a DMM, you can at least check the voltage to the resonator, which should usually be around 2V dc reading if the clock is running, as it would be more or less averaging the 4-5VP-P ac clock signal. If you have 5V or 0V dc on the resonator pins, I'd have to say the processor is dead. The fact that the unit responds to the remote suggests that the clock for the syscon proc on main board is ok, although the failure to actually play the cd may suggest there is a fault in the syscon proc or it's power supply lines. Go back & check the +5V line with your meter set for AC reading. If you have more than 50mV ac reading, then you may simply have a failing electrolytic capacitor in the supply, and excess ac on the line will screw up proc function.
I have yet to ever see a ceramic resonator(which acts as the crystal in that case) go bad, so a "no clock" condition for the display proc would be cause to suspect a bad proc, rather than bad clock source. With a DMM, you can at least check the voltage to the resonator, which should usually be around 2V dc reading if the clock is running, as it would be more or less averaging the 4-5VP-P ac clock signal. If you have 5V or 0V dc on the resonator pins, I'd have to say the processor is dead. The fact that the unit responds to the remote suggests that the clock for the syscon proc on main board is ok, although the failure to actually play the cd may suggest there is a fault in the syscon proc or it's power supply lines. Go back & check the +5V line with your meter set for AC reading. If you have more than 50mV ac reading, then you may simply have a failing electrolytic capacitor in the supply, and excess ac on the line will screw up proc function.
I finally found time to perform a few tests you recommended. But only after doing so, I realised my answer to this question was incorrect (thought I had tested it, but seems like I had not with a CD):
Still, here are the results I got performing some of your recommended tests...
R138 and R139 (each side of U108): ok
R128 and R113 (each side of U102): could not get to them, underneath the CD loader. Removing it looks like a puzzle on its own. But I might come back to it later if it still makes sense...
3: no pin
4 to 9: 18v
10: 0v (not connected)
11: 1v (not connected) strange??
12 to 22: 20v
23: no pin
24 and 25 (heaters): 18v
Don't have a scope, so haven't checked any frequency yet.
All that being said, do you think I should still get something to test the oscillator? Do the display segment test, powering each pin with a 1K resistor?
What else?
Thanks for your great help!
YES, it plays! In fact, I can use all functions on the remote, and at the end of the CD, the player stops spinning nicely. Too bad I don't have an open/close button on the remote (always found it was a stupid function, but it would make my broken CDP much more useful).
Still, here are the results I got performing some of your recommended tests...
I get 5v on pin 6 (reset line). Does it make sense? I couldn't figure out where you saw/determined that 3.3v on the schema.
Yes, heaters are proudly glowing orange.
R151 and R140 (each side of U104): ok (not blown)
R138 and R139 (each side of U108): ok
R128 and R113 (each side of U102): could not get to them, underneath the CD loader. Removing it looks like a puzzle on its own. But I might come back to it later if it still makes sense...
pins 1 and 2 (heaters): 20v
3: no pin
4 to 9: 18v
10: 0v (not connected)
11: 1v (not connected) strange??
12 to 22: 20v
23: no pin
24 and 25 (heaters): 18v
Don't have any resistor on hand😱 Will get some and try...
Yep, getting around 2v dc at resonator pins.
My DMM reads 0v ac on the 5vdc line. But the lowest range is 200v ac, and only precise to 0.1v (yeah, very basic DMM)
Don't have a scope, so haven't checked any frequency yet.
All that being said, do you think I should still get something to test the oscillator? Do the display segment test, powering each pin with a 1K resistor?
What else?
Thanks for your great help!
The fact it plays means 99% of the circuitry is OK
I still think this is a physical problem.
So next step has to be to measure continuity from the main system control IC to the front processor IC.
We know the supply and ground are probably good as the remote receiver works ok.
Fortunately these look to be full size IC's so look at the corcuit carefully and identify the pins I have marked and (with the player off) measure continuity on ohms (use a low ohms range on meter) to check the continuity.
Another double check is then to power the player up and measue DC volts on the main control IC pins (the ones that goe to the front IC) and confirm exactly the same DC voltage is present at the the IC.
The front panel works by having the keys connected in a matrix that is constantly scanned by the the front IC. When it detects a button press it outputs a unique code on the DCK (serial data clock) and DDA (serial data) lines (which you would need a scope to see).
Another thought... if any button was stuck on (do they all feel "clicky" then that could cause weird problems.
I still think this is a physical problem.
So next step has to be to measure continuity from the main system control IC to the front processor IC.
We know the supply and ground are probably good as the remote receiver works ok.
Fortunately these look to be full size IC's so look at the corcuit carefully and identify the pins I have marked and (with the player off) measure continuity on ohms (use a low ohms range on meter) to check the continuity.
Another double check is then to power the player up and measue DC volts on the main control IC pins (the ones that goe to the front IC) and confirm exactly the same DC voltage is present at the the IC.
The front panel works by having the keys connected in a matrix that is constantly scanned by the the front IC. When it detects a button press it outputs a unique code on the DCK (serial data clock) and DDA (serial data) lines (which you would need a scope to see).
Another thought... if any button was stuck on (do they all feel "clicky" then that could cause weird problems.
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The voltages measured on the display... they should be negative volts such as minus 18 and minus 20 ?
As Mooly suggests, voltage correspondence on the connected lines between main & dispay procs is a good avenue. The particular one that seems may be off is the reset line. You should check to see if you also measure 5V on pin 1 of the main proc, whicb is it's reset pin. Looking at the transistor controlling it, I don't think it should be getting 5V, as it is controlled by the zener diode nearby, which is either 3.3V or 3.9V. There is no charge cap in that transistor circuit, nor anything controlling it, so it's just a steady state basically voltage regulator circuit.
Once more, thanks a lot for your help. And Mooly, thanks for marking things in the schemas, it really helps. Here are my results...
The zener (D105) is supposed to be 3.9v, and I measure 3.6v across it. But at T105's collector (the reset line), I have 5v. Is it really supposed to be 3.x volt with that configuration (visible in Mooly's last screen capture)? I'm not familiar with transistors - will have to read.
FWIW, I checked all resistors in that transistor circuit, and they all look good (R189, R190, R191 and R192).
Yep, I get good continuity for all these pins betweem the two ICs. Haven't verified I have the exact same voltages, but if continuity is good, voltages will be the same, right?
That could have been a good catch! But yes, they all feel clicky.
Yes, they are negative (-18v and -20v) - I should have mentioned it
Yes, I'm really getting 5V on pin 1 of the main proc.
The zener (D105) is supposed to be 3.9v, and I measure 3.6v across it. But at T105's collector (the reset line), I have 5v. Is it really supposed to be 3.x volt with that configuration (visible in Mooly's last screen capture)? I'm not familiar with transistors - will have to read.
FWIW, I checked all resistors in that transistor circuit, and they all look good (R189, R190, R191 and R192).
Time for me to find a scope? Any other test you recommend doing with my DMM?
I just tried to test T105, and I think it might be bad... The B-E and B-C junctions look good if I check them as regular diodes - I get an open circuit one way, and measure around 600 in the diode check mode on my DMM.
However, I read I should get an open circuit between the emitter and the collector (silicon transistor, which T105 is). BUT I measure 1.2 kohm. Does that mean T105 is dead? If so, would it explain the incorrect reset line voltage (?) and the problems I have with my CDP?
*edit* I guess what I just said does not make sense, as I took measurements with T105 in the circuit, so the collector and the emitter are somewhat connected, with other components in between, thus the 1.2 kohm??
However, I read I should get an open circuit between the emitter and the collector (silicon transistor, which T105 is). BUT I measure 1.2 kohm. Does that mean T105 is dead? If so, would it explain the incorrect reset line voltage (?) and the problems I have with my CDP?
*edit* I guess what I just said does not make sense, as I took measurements with T105 in the circuit, so the collector and the emitter are somewhat connected, with other components in between, thus the 1.2 kohm??
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T105... it must be OK or the player wouldn't work at all.
When you test a transistor (diode) on a DVM on the "diode" check range the meter is actually displaying the forward volt drop across the junction. So 600 is 600mv.
The 5 volts on the reset line is OK. It works like this. T105 is normally OFF because of the resistor/s conecting B and E (can't make the number out). So until the supply reaches the zener voltage the reset line is held low via R192. As the supply passes the zener voltage the zener begins to conduct "pulling" base current through TR105 causing it to conduct too. That applies the full 5 volts to the reset line.
You won't measure the reset time on a DVM as it all happens so quickly.
Not sure where else you can check on this.
The "big IC's" are always always always the last to suspect, however...
The facts are that the player responds OK to the remote and plays. So we seem to be looking at a "front panel" problem.
Again as a tech, a favourite test of mine when all else seemed to be failing was to just go around EVERY pin on the suspect IC/panel and see if the readings made sense.
So that means measuring from the main PCB ground to every pin on the front processor IC. And same again (which I think we have done) to see that they all go to their intended destinations on the main PCB. Is ground pin on IC really at ground for example... don't assume anything.
The 4Mhz crystal on the front. None of the legs fractured ? They are thin and fragile.
Back to the switches again. With solder braid this takes seconds to do.
You see pins 26,27,28 and 29 on the IC. These are four of eight data lines that scan the keyboard. I would now unsolder (isolate) these four and also isolate (lift one leg of) the four diodes D102,3,4 and 5. Those above the keys... markings not clear. Power up again and see if display lights normally. Thats just in case a switch were leaky.
After all that and if we are sure everything else is good then we have to consider the possiblity that the IC has got zapped somehow.
When you test a transistor (diode) on a DVM on the "diode" check range the meter is actually displaying the forward volt drop across the junction. So 600 is 600mv.
The 5 volts on the reset line is OK. It works like this. T105 is normally OFF because of the resistor/s conecting B and E (can't make the number out). So until the supply reaches the zener voltage the reset line is held low via R192. As the supply passes the zener voltage the zener begins to conduct "pulling" base current through TR105 causing it to conduct too. That applies the full 5 volts to the reset line.
You won't measure the reset time on a DVM as it all happens so quickly.
Not sure where else you can check on this.
The "big IC's" are always always always the last to suspect, however...
The facts are that the player responds OK to the remote and plays. So we seem to be looking at a "front panel" problem.
Again as a tech, a favourite test of mine when all else seemed to be failing was to just go around EVERY pin on the suspect IC/panel and see if the readings made sense.
So that means measuring from the main PCB ground to every pin on the front processor IC. And same again (which I think we have done) to see that they all go to their intended destinations on the main PCB. Is ground pin on IC really at ground for example... don't assume anything.
The 4Mhz crystal on the front. None of the legs fractured ? They are thin and fragile.
Back to the switches again. With solder braid this takes seconds to do.
You see pins 26,27,28 and 29 on the IC. These are four of eight data lines that scan the keyboard. I would now unsolder (isolate) these four and also isolate (lift one leg of) the four diodes D102,3,4 and 5. Those above the keys... markings not clear. Power up again and see if display lights normally. Thats just in case a switch were leaky.
After all that and if we are sure everything else is good then we have to consider the possiblity that the IC has got zapped somehow.
Thanks again! And sorry for not posting results for a while, it's been hard to find time for this lately. So here's what I have...
Would an oscilloscope really help finding the faulty component?
I finally did that test and segments do illuminate.
The ground (pins 21 (VSS) and 30 (TEST)) is at 0v. Below is a screen capture that shows, side by side, the IC pins config and the voltage I get on each pin. Does something look wrong?
Looks good. Not easy to examinate closely as it's located under the display. But I could reach, for each leg, a part very close to the crystal itself, and I get continuity with the solder point under the PCB.
With power off, I tested each switch's continuity both in normal position and when I press the button. As expected, it's closed when pressed and open (no continuity) in normal position. Is this enough to state no switch is leaky, or should I unsolder those pins and diodes? If I need to unsolder, wouldn't isolating the 5 diodes (including the D201) be enough? Seems easier than isolating an IC pin (making sure it does not touch the PCB contact point).
Would an oscilloscope really help finding the faulty component?
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