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nucelar 28th May 2020 11:09 PM

Drawmer 1962 burned smell
 
2 Attachment(s)
Hi, Ive been using this preamp lately quiet often and during long sessions. The unit gets hot, but I consider it normal , from experience with similar gear.

But today we had 4-5 very short brownouts (less than a second long) and coincidentally the preamp started to smell like that awful burned electronics we all know.

I immediately plugged it off, and opened it. the Power supply section was very hot. The toroidal was very hot and the heatsink for the regulator (?) was too hot to touch.
I also found a loose black plastic disc that surely popped off of a capacitor.

One of the capacitors seems to have "grown taller" rather than just bulging and the plastic cover fell off. this plasic has deformed from the heat i believe like a contact lens.

Do you think that just replacing this capacitor will make the preamp work normally again? Shoud I seize the opportunity to change other caps in the PSU?

Or could the overheating be caused by some other malfunction in the preamp?

Thanks!

enginefire 28th May 2020 11:26 PM

What is all that dust all over the pcb and components? Most gear when you open it is pristine. Have any caps full out exploded? That leaves residue.

Recapping the power supply would be a good place to start I think. Be thorough, check the sxhematic, double check for any damaged parts. See if it still gets really hot.

nucelar 28th May 2020 11:38 PM

Yes it's regular dust, the unit is about 15 years old and has never been opened before. And it has ventilation slits on the top cover, just over the PSU. The rest of the PCB is cleaner :)
But it definitely needs a blow or two of compressed air :)

mrfantastic 29th May 2020 06:55 AM

I'd replace the cap that has grown taller. Definitely doesn't look right.

Thomas W. Bethe 29th May 2020 01:09 PM

Quote:

Originally Posted by nucelar (Post 14768281)
Yes it's regular dust, the unit is about 15 years old and has never been opened before. And it has ventilation slits on the top cover, just over the PSU. The rest of the PCB is cleaner :)
But it definitely needs a blow or two of compressed air :)

IMHO that "dust" does not look "normal". I would replace ALL the capacitors in the power supply to start with. When one cap goes the others may not be far behind. Best of luck!

jensenmann 30th May 2020 01:22 PM

If a brownout made the unit die then it´s quite likely that a HV peak in the mains killed something. Brownouts can feed upto 3kV spikes into the mains. That can destry various parts, but semiconductors being the most sensitive ones. Definitely check the rectifiers and voltage regulators. The dead cap can just be a symptom, not the cause of the problem. It should be replaced, anyway.