[sdiy] OB8 power transformer

[g m montalbano]

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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