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Thread

A-143-2 problem

2019-07-05 by karelvanbezooijen@yahoo.com

While using one of the EG of this module all of a sudden it did not function well anymore. None of the pots has any influence on the envelope. The attack stays at max. I already replaced both TL084 and CMOS555 but that didn't solve anything. The other three still work fine. Any suggestions are more than welcome.

Best regards,

Karel.

AW: [Doepfer_a100] A-143-2 problem

2019-07-05 by yahoo@doepfer.de

I'm sorry about the problems with the module. Maybe one or more of the diodes and/or transistors are defective.

If you cannot fix the the problem please follow the repair notes on the FAQ page of our website:

www.doepfer.com > English > FAQ > General > Repair procedure

Best wishes
Dieter Doepfer

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> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Freitag, 5. Juli 2019 07:14
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] A-143-2 problem
> 
> While using one of the EG of this module all of a sudden it did not function
> well anymore. None of the pots has any influence on the envelope. The attack
> stays at max. I already replaced both TL084 and CMOS555 but that didn't solve
> anything. The other three still work fine. Any suggestions are more than
> welcome.
> 
> Best regards,
> Karel

Re: A-143-2 problem

2019-07-06 by karelvanbezooijen@yahoo.com

Thank you for your fast reply. I'll check and see if I can replace the diodes and transistors. I assume they are general ones. Otherwise I'll send it for repair.

Best regards,

Karel.

Re: A-143-2 problem

2019-07-06 by man.of.mystery@ntlworld.com

Karel,

Electrolytic capacitors are probably the shortest lived of all components in common use, so I'd always suspect those first.

I've never seen an A-143-2, but I've found a good image of one on schneidersladen.de, via a google image search. I see what looks like four identical boards, with at least two electrolytic capacitors each.

You might be able to spot the difference between the capacitors on the faulty board and the others, but not necessarily. Sometimes you can see damage, but not always.

You could desolder them and measure their capacitance, but a lot of meters give false readings on faulty ones - they tend to show a higher value, when the ESR increases. They are mostly quite cheap to replace, so it may be better to just try that first.

If there are any tantalum bead capacitors, those can be damaged by reverse voltage, but otherwise are more robust.

- Andy

RE: [Doepfer_a100] Re: A-143-2 problem

2019-07-06 by swalker@fraserwalkerltd.co.uk

Hi Karel

 

I can certainly endorse the electrolytics as the first component to check.

 

I had a faulty dx7II.  Wouldn’t switch on.  I replaced all the electrolytic capacitors on the power board.  Cost me less than 5 Euros.

 

Works like new now.

 

Stu

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From: Doepfer_a100@yahoogroups.com <Doepfer_a100@yahoogroups.com> 
Sent: 06 July 2019 13:24
To: Doepfer_a100@yahoogroups.com
Subject: [Doepfer_a100] Re: A-143-2 problem

Karel,

Electrolytic capacitors are probably the shortest lived of all components in common use, so I'd always suspect those first.

I've never seen an A-143-2, but I've found a good image of one on schneidersladen.de, via a google image search.  I see what looks like four identical boards, with at least two electrolytic capacitors each.  

You might be able to spot the difference between the capacitors on the faulty board and the others, but not necessarily.  Sometimes you can see damage, but not always.

You could desolder them and measure their capacitance, but a lot of meters give false readings on faulty ones - they tend to show a higher value, when the ESR increases.  They are mostly quite cheap to replace, so it may be better to just try that first.

If there are any tantalum bead capacitors, those can be damaged by reverse voltage, but otherwise are more robust.

- Andy

Re: A-143-2 problem

2019-07-07 by karelvanbezooijen@yahoo.com

Thank you all for the replies. Checking the capacitors seems the easiest option. As switching between M-L-H position doesn't have any effect on the envelope maybe one of them is defect. The one that is in all signal paths.

Karel.

Re: A-143-2 problem

2019-07-07 by karelvanbezooijen@yahoo.com

I checked the board.

M - position uses 100n Film + 2u2u electrolytic

L - position uses 100n Film

H - position uses 100n Film + 100u electrolytic

As the envelope attack stayed long in every position it couldn't be the electrolytic caps I guess.

I tried to measure the diodes but the boards are too close to each other to measure every one of them. Disassembling is not easy.

Anyway I put the module back in the case.

Surprised I was to notice that it works again! Am I happy? Yes. Am I satisfied? No, because I don't know what was wrong.

Karel.

Re: [Doepfer_a100] Re: A-143-2 problem

2019-07-07 by Steven Jenkins

Dodgy cable ?   I’ve had more than the odd patch cable fail/have a poor connection/loose joint.   Just a thought. 

Steve

Out of office - sent from mobile device

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> On 7 Jul 2019, at 20:31, karelvanbezooijen@yahoo.com [Doepfer_a100] <Doepfer_a100@yahoogroups.com> wrote:
> 
> I checked the board.
> M - position uses 100n Film + 2u2u electrolytic
> L - position uses 100n Film
> H - position uses 100n Film + 100u electrolytic
> 
> As the envelope attack stayed long in every position it couldn't be the electrolytic caps I guess.
> 
> I tried to measure the diodes but the boards are too close to each other to measure every one of them. Disassembling is not easy.  
> 
> Anyway I put the module back in the case.
> 
> Surprised I was to notice that it works again! Am I happy? Yes. Am I satisfied? No, because I don't know what was wrong. 
> 
> Karel.
>

Re: A-143-2 problem

2019-07-07 by man.of.mystery@ntlworld.com

Since it's an intermittent fault (i.e. sometimes works), it could be a dry or cracked solder joint, maybe on something that can get subjected to mechanical stress, like a socket or header pin.

I have an A-106-6 filter, which I bought used. When it arrived, one of the outputs didn't work at all - which happened to be the first one I tried. I resoldered the pins for that socket, which cured it, and it's been fine since.

Dry solder joints are often visibly different to other joints on the board - they might look duller, or more uneven. In my case, the problem one didn't have much solder on it at all, so someone at the factory had an off day.

- Andy

Re: [Doepfer_a100] Re: A-143-2 problem

2019-07-08 by karelvanbezooijen@yahoo.com

No dodgy cable for sure. The cable is plugged in the upper EG. The other are normalled to this one.

Karel.

Re: A-143-2 problem

2019-07-08 by karelvanbezooijen@yahoo.com

That could be an explanation. As long as it works I'll leave it alone. Pity it isn't the lower one. Thanks for pointing out.

Karel.

AW: [Doepfer_a100] Re: A-143-2 problem

2019-07-08 by yahoo@doepfer.de

I don't think that it's a problem of the electrolytic capacitors because in the center position of the range switch no electrolytic capacitors are involved. Only in the upper and lower position of the range switch electrolytic capacitors are used as timing capacitors. In the center position a foil capacitor is used and I don't think that it's damaged.

Best wishes
Dieter Doepfer

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> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Sonntag, 7. Juli 2019 05:38
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] Re: A-143-2 problem
> 
> Thank you all for the replies. Checking the capacitors seems the easiest
> option. As switching between M-L-H position doesn't have any effect on the
> envelope maybe one of them is defect. The one that is in all signal paths.
> 
> Karel.

Re: AW: [Doepfer_a100] Re: A-143-2 problem

2019-07-11 by karelvanbezooijen@yahoo.com

Thank you Dieter. I figured out this myself too. As andy2no suggested a bad solder joint could be the reason. After taking out the module once again and tinkering a bit it works fine now. I haven't used the gate input of EG 3 yet though. One never knows. Maybe that's the one. Disassembling the module looks like a hell of a job.