[sdiy] OB8 power transformer

Benjamín Velasco guatis at gmail.com
Wed Jun 5 13:19:18 CEST 2024


Hi Greg. Which PS did you use? I'm tempted to do this on mine.

Ben

El mar, 4 de jun de 2024, 23:05, g m montalbano via Synth-diy <
synth-diy at synth-diy.org> escribió:

> This is indeed the most likely explanation. I've ditched the suspect
> transformer and decided to try the switching PS replacement (as has been
> done with the Prophet VS, Rhodes Chroma and others).
> Made a few modifications to the CPU board (cut some traces, removed some
> original power supply components) and wired up a Meanwell multi-output
> switching supply.
> So  far, all is good -- runs quiet, cool, and no bootup or memory
> problems.  If any do show up, will inform the list;  otherwise, considering
> this one done.
> Thanks to all who replied to the original post.
> ~GMM
>
> On Mon, May 27, 2024 at 1:24 AM Tony Allgood via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
>>  > An intermittent shorted turn ?
>>
>> That would be my conclusion too. I had a five year old Peavey guitar amp
>> in for repair. It was initially fine for about half an hour and then
>> would take out the mains inlet fuse. Changing the fuse, it would work
>> only for five minutes or so before blowing again.
>>
>> I concluded that as the transformer naturally warmed up the physical
>> size would change and maybe some loose windings would slightly shift
>> causing the wires to rub against each other. The wire's insulation
>> coating may have been weak at some point and eventually, kaboom.
>>
>> I also had a transformer in an old Logan String Melody that would not
>> fail but, after three or four hours of being powered up, would get
>> stupidly hot (with accompanying 'warm electronics' smell). Testing it in
>> isolation on the bench all seemed fine but I found it was very slowly
>> heating up. If one wasn't specifically looking for excessive heat rise
>> you wouldn't notice anything untoward until the unit had been powered
>> for at least two hours - even with no load applied to the secondaries.
>> In this case I assumed it was due to losses within the laminated core
>> rather than any shorted turns.
>>
>> Tony
>>
>> New album out: https://takla-makan.bandcamp.com/album/solway-firth
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