[sdiy] Advices for restoring an old Roland SH2

[Florian Anwander]

The first thing is to check the + and - supply voltages with a scope in 
AC-mode, to see whether the 50Hz ripple is on the supply.

If yes, then check whether you have used a suitable transformer. If the 
transformer does not provide enough secondary AC-voltage, the regulator 
won't be able to catch up with the AC ripple. I know this from my SH-1 
which has the same regulator (TA7179P). It was a 110V Version and 
someone had added an internal 220V to 100V Transformer, which resulted 
in a too low secondary AC.

For testing uses you might try the old transformer with an external 
220-110 converter.

Florian


On 28.02.16 23:21 , Jean Bender wrote:
> Hi !
> thanks for the tips.
> For the mains hum, i'm recapping the psu board, and i've changed the
> main transformer from 110V to 220v. We'll see what happens, it's not
> finished, i don't have all the caps. As for all psus, some of them are
> electrolytics, and the others are mylar's one. Could i change these
> mylar caps for MKT's one ? Is there a big deal to do it ?
>
> And then, i haven't found nothing yet for the main out lack of gain
> amplification. The ground trace seems to be ok, not burnt. I'll take
> time to check the schematics and the op amp..
>
> Thanks again,
> J.
>
> 2016-02-27 19:53 GMT+01:00 Chris Juried<cjuried at yahoo.com>:
>> I have seen this issue before as well Richie. The ground trace, to the 1/4"
>> chassis mount connector, is susceptible to excess current and can become an
>> open-circuit rather easily.
>>
>> Sincerely,
>>
>> Chris Juried
>> Audio Engineering Society (AES) Member
>> InfoComm-Recognized AV Technologist
>> http://www.JuriedEngineering.com (Juried Engineering, LLC.)
>>
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>> ________________________________
>> From: "rburnett at richieburnett.co.uk"<rburnett at richieburnett.co.uk>
>> To: Jean Bender<lofideadbeat at gmail.com>
>> Cc: synth-diy DIY<synth-diy at dropmix.xs4all.nl>
>> Sent: Saturday, February 27, 2016 9:12 AM
>> Subject: Re: [sdiy] Advices for restoring an old Roland SH2
>>
>> Maybe someone has plugged it into a faulty "live" valve amplifier or
>> something and it has burned off the ground trace to the line out jack on
>> the back of the synth.  That's what I think had happened to my SH-09
>> when I got it.  The ground trace to the line out jack was completely
>> vaporised off the little board that the jacks are mounted on.  The only
>> thing I can imagine that would cause that kind of damage is having mains
>> power plugged into it somehow.  Fortunately soldering a wire along the
>> route of the previously fused track, brought the line out jack back to
>> life and removed the 50Hz buzz from the output.
>>
>> It's quite a thin trace from what I remember so probably wouldn't take
>> THAT much current to burn it open-circuit.  I'm sure things would have
>> been different if the jack sockets had been electrically connected to
>> the chassis, instead of having little plastic insulating washers around
>> them where they pass through the metal enclosure.
>>
>> -Richie,
>>
>> On 2016-02-27 13:28, Jean Bender wrote:
>>> Hi !
>>>
>>> I've got a Roland SH2 to fix. It's working propoerly, except a "buzz"
>>> that appear around the 50hz  : this buzz is always here once the synth
>>> plugged. I imagine a problem around the power distribution ? I should
>>> chek all the caps and replace some of them ?
>>>
>>> Also, the main output has no gain, and i have to use the headphone
>>> output. Would somebody have an idea about that ?
>>>
>>> Thanks for any advice or answer !
>>> Best.
>>> J.
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>>
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