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argonrepublic 3rd February 2013 02:36 AM

Synthesizer power supply
This PCB is from my Kawai K3 synthesizer. 5 transformer leads come in. 8VAC across 2 orange leads, 20-0-20 across red, black, red or 40VAC red to red.
I picked the synth up dead. I immediately found a dead rectifier. I changed the rectifier and the two fuses let go.

Kay Pirinha 3rd February 2013 12:09 PM

Your question is?

Best regards!

pilli 3rd February 2013 12:46 PM

There must be something downstream that pulls too much current, a short of some type.
Coincidence: I had something like that on a Yamaha something, and it was a bad tantalum cap that would systematically kill the 5V rail. Not easy to detect, if I remember correctly, I traced the rail out of the regulator, looking for causes.

You're not saying anything about regulators: check those first next thing.


argonrepublic 3rd February 2013 02:44 PM

When I first glanced at it. It had a peculiar appearance to it but as it turns out it is fairly straight forward in design. I ran out of fuses while testing it but I swapped in new 7815 and 7915 and all new caps for the 15 Volt section. Still losing fuses in the 15 V section so I think the 5V is shorting it. Think I will spend some time today.

gmphadte 4th February 2013 10:37 AM

Check for ohms across the dc supply. A tantalum will show dead short. Also make visual inspection, for burnt component.

Gajanan Phadte

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