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Dead CS80 - finding a short

 

So my beloved CS80 died on me after calibration and tuning.

To resume:

1. After calibrating BA, KAS and M-boards, 4th M Board 1-channel did not play funky3, memory 1,3 and panel presets (last 4).

2. After inspecting BA board for the possible cause of this the PSU died (played a low note for the few seconds first).

3.Rebuild and calibrated PSU - Died again after power on (also low note first).

4. The upper GND and lower 15V rails are shorted!

5. I?ve tried to find a short isolating -6,5 and 8,5V terminals on the KAS, S/H, KBC 1 and 2 boards - no success (desoldered the wires and the ground and checked with my DVM for continuity - there were no shorts).


I am out of ideas. If the rails for GND and 15v are shorted does that mean that I should repeat the point 5 but between +15v and E terminals on every possible board? Seems logical.

I would appreciate any help.
 

Extremely sympathetic regarding the failure! This is just a thought, as more investigation is very likely needed. When you did your PSU rebuild, did you replace this transistor here, and the one in front of it?
 

Was unsuccessful linking a picture, will send to you directly.
Daniel Forró
 

Picture came.

Daniel Forro


On Feb 15, 2017, at 1:31 PM, npselliott@... [yamahacs80] wrote:



Was unsuccessful linking a picture, will send to you directly.?
 

Hello,
No, I did not change them or even think that they can be an issue because the PSU was working after recap and changing two 1ohm white ceramic resistors next to the heatsink (they were both interrupted)
After it failed again in the same way everything seemed intact and the resistors were ok so i changed only the two IC?s and it worked again.
 

So can someone confirm how to find a short of +15v and a ground rail?

1. Disconnect the board from the rails
2. Unsolder E, +15v terminals (should I disconnect -15v too?)
3. Perform a simple continuity test between disconnected +15 and E terminals on the board (is that enough?)

From the information Martin gave me a simple continuity check is not enough. So I should:

4. Hook up the +15V (-15V also?) terminal to the external PSU (can it be something simple or should I get a variable bench psu?)
5. What should be measured now?

PS. I have tried to perform a simple continuity check on some boards and I get some readings - A tiny short beep and something like 1452 reading. Is that within the tolerance or is the board bad?

Lots of questions - sorry guys but it has been a long night.
 

I am really confused now...
Since the upper and lower rails are shorted I?ve figured that if I disconnect the bottom (+15v) rail from the three brown cables and then take the cards out one by one I could identify which one causes the short easily. The short has stopped only when I take all of them (naturally). But if I bring a single one back it causes a small short (0,1ohm or 098 on diode continuity check with a short beep). So it?s supposed to be like that or are all of them bad?

Thanks in advance for any help
 

Change all the tantalum condenser from TSB 1 & 2 and TWS.?

2017-02-18 2:02 GMT+01:00 pyjamagroove@... [yamahacs80] <yamahacs80@...>:



I am really confused now...
Since the upper and lower rails are shorted I?ve figured that if I disconnect the bottom (+15v) rail from the three brown cables and then take the cards out one by one I could identify which one causes the short easily. The short has stopped only when I take all of them (naturally). But if I bring a single one back it causes a small short (0,1ohm or 098 on diode continuity check with a short beep). So it?s supposed to be like that or are all of them bad?

Thanks in advance for any help
 

Capacitors, Sorry!

2017-02-18 14:43 GMT+01:00 Tommy Salsero <tommysalsero@...>:

Change all the tantalum condenser from TSB 1 & 2 and TWS.?

2017-02-18 2:02 GMT+01:00 pyjamagroove@... [yamahacs80] <yamahacs80@...>:


I am really confused now...
Since the upper and lower rails are shorted I?ve figured that if I disconnect the bottom (+15v) rail from the three brown cables and then take the cards out one by one I could identify which one causes the short easily. The short has stopped only when I take all of them (naturally). But if I bring a single one back it causes a small short (0,1ohm or 098 on diode continuity check with a short beep). So it?s supposed to be like that or are all of them bad?

Thanks in advance for any help
 

Thanks Tommy,
Tsb 1 and 2 were partially rebuilt (there are some old tantalums on tsb2 left I think) with all the IC?s changed. I have never touched the TWS.?

Why do you think that might be the problem??

The thing is that no fuse blows. The short simply kills my PSU directly.
 

Because in my old cs80 ?the tantalum in tsb cause the short of the rail. changed the tantalum ?solved my problems,?

2017-02-18 18:18 GMT+01:00 pyjamagroove@... [yamahacs80] <yamahacs80@...>:



Thanks Tommy,
Tsb 1 and 2 were partially rebuilt (there are some old tantalums on tsb2 left I think) with all the IC?s changed. I have never touched the TWS.?

Why do you think that might be the problem??

The thing is that no fuse blows. The short simply kills my PSU directly.
 

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Yep - I had this issue with a CS80 a few years ago and eventually traced it to shorts in caps on the TSBs. Definitely should replace all the tantalums on both. The easy way is the kit offered on eBay if you don't want to figure out what kinds of caps to buy.?

? David


On Feb 18, 2017, at 12:10 PM, Tommy Salsero tommysalsero@... [yamahacs80] <yamahacs80@...> wrote:

Because in my old cs80 ?the tantalum in tsb cause the short of the rail. changed the tantalum ?solved my problems,?

2017-02-18 18:18 GMT+01:00 pyjamagroove@... [yamahacs80] <yamahacs80@...>:


Thanks Tommy,
Tsb 1 and 2 were partially rebuilt (there are some old tantalums on tsb2 left I think) with all the IC?s changed. I have never touched the TWS.?

Why do you think that might be the problem??

The thing is that no fuse blows. The short simply kills my PSU directly.
 

Ok guys, I will rebuild the TWS, TSB and I will report how it went.
Seems scary however that one capacitor or ic can cause so much trouble.
 

I have replaced all the remaining tantalums on the TWS and TSB boards. I have checked them all for short - there appears to be none.
My synth still shows the following values between the +15 and G:

- Diode (continuity): 0,70 ,Short beep
- On the 20k Ohm setting: 0,07

I might be wrong but there still seems to be a short somewhere.?
I have checked several boards with my bench PSU - I have only one output. The TSB boards for example draw 0,060A on 15V setting with no signs of overheating any IC.

My PSU is working and calibrated but I am afraid to do another test of the synth because - i repeat - there are no fuses that were blown only PSU fried while the synth was making a brief low tone.

I am out of ideas but I have a feeling that it can be something simple.
One more thing: With no molex connected to the psu the ground from all the cards show continuity with the ground on the PSU ( the green cable) is that normal?
 

No short after all??
I have just read that the short beep on the dvm can be capacitors charging!
And the overall resistance should be 0,00 Ohm for a short.

I have changed the two biggest caps and the two big transistors on the psu. One of the caps had a bump on the top.
So it could have been a psu problem after all.
It is now fully rebuilt and calibrated. All the voltages are present.

Still I am afraid to connect my synth to it and test.?
Is there a way to test the psu itself under load without a specialist equipment?

Please advice.
 

I am happy to announce that my CS80 is fine and working great again.
I would like to post a resumé for anybody who will have that problem in the future.

1. My CS80's power supply died after i made adjustments on BA, KAS, S&H and M boards for tuning. First it was the problem that 4 presets were not working on the M board 4 channel 1. Note: KAS, S&H, TKC and both TSB boards had all their CMOS changed and. TSB1 was fully recapped and TSB2 partially. No fuses were blown.
2. I don't really know what caused the problem. I was paying attention not to do any shorts. It could have been altering the voltages on the KAS board, the PSU has never been rebuild, and i had few tantalum capacitors left on TWS and TSB2 boards.
3. After replacing all the tantalums and rebuilding the PSU the CS80 was working with no issues.
4. I was thinking, that I have a short between the GND ans +15 rails (I had 1s beep on my DWM). Apparently that was not the issue (the short beep could be the caps charging).

Thank you all for your help.
I would like especially thank Martin who has been a wonderful help and while he's not an synth technician himself he shared all his knowledge and experience with me walking me through several procedures to test my CS80 responding patiently on my emails.
 

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Great news!

FYI, when I had similar problems with TSB cap shorts, it was confusing because it didn’t show up as a short to ground. ?Instead, the short was between +15 and and -15. ?Something about the load on the +15 causing too much current - and blowing the fuse - on the -15. I don’t remember the details - I think I posted about it. ?Took some time to figure out.

?David


On Feb 27, 2017, at 1:41 AM, pyjamagroove@... [yamahacs80] <yamahacs80@...> wrote:



I am happy to announce that my CS80 is fine and working great again.
I would like to post a resumé for anybody who will have that problem in the future.

1. My CS80's power supply died after i made adjustments on BA, KAS, S&H and M boards for tuning. First it was the problem that 4 presets were not working on the M board 4 channel 1. Note: KAS, S&H, TKC and both TSB boards had all their CMOS changed and. TSB1 was fully recapped and TSB2 partially. No fuses were blown.
2. I don't really know what caused the problem. I was paying attention not to do any shorts. It could have been altering the voltages on the KAS board, the PSU has never been rebuild, and i had few tantalum capacitors left on TWS and TSB2 boards.
3. After replacing all the tantalums and rebuilding the PSU the CS80 was working with no issues.
4. I was thinking, that I have a short between the GND ans +15 rails (I had 1s beep on my DWM). Apparently that was not the issue (the short beep could be the caps charging).

Thank you all for your help.
I would like especially thank Martin who has been a wonderful help and while he's not an synth technician himself he shared all his knowledge and experience with me walking me through several procedures to test my CS80 responding patiently on my emails.
 

Happy End!?

2017-02-27 19:23 GMT+01:00 David Rogoff david@... [yamahacs80] <yamahacs80@...>:



Great news!

FYI, when I had similar problems with TSB cap shorts, it was confusing because it didn’t show up as a short to ground.? Instead, the short was between +15 and and -15.? Something about the load on the +15 causing too much current - and blowing the fuse - on the -15. I don’t remember the details - I think I posted about it.? Took some time to figure out.

?David


On Feb 27, 2017, at 1:41 AM, pyjamagroove@... [yamahacs80] <yamahacs80@...> wrote:



I am happy to announce that my CS80 is fine and working great again.
I would like to post a resumé for anybody who will have that problem in the future.

1. My CS80's power supply died after i made adjustments on BA, KAS, S&H and M boards for tuning. First it was the problem that 4 presets were not working on the M board 4 channel 1. Note: KAS, S&H, TKC and both TSB boards had all their CMOS changed and. TSB1 was fully recapped and TSB2 partially. No fuses were blown.
2. I don't really know what caused the problem. I was paying attention not to do any shorts. It could have been altering the voltages on the KAS board, the PSU has never been rebuild, and i had few tantalum capacitors left on TWS and TSB2 boards.
3. After replacing all the tantalums and rebuilding the PSU the CS80 was working with no issues.
4. I was thinking, that I have a short between the GND ans +15 rails (I had 1s beep on my DWM). Apparently that was not the issue (the short beep could be the caps charging).

Thank you all for your help.
I would like especially thank Martin who has been a wonderful help and while he's not an synth technician himself he shared all his knowledge and experience with me walking me through several procedures to test my CS80 responding patiently on my emails.

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