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Old 3rd February 2013, 02:36 AM   #1
diyAudio Member
Join Date: Apr 2005
Location: Simcoe Ont
Default 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.
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Old 3rd February 2013, 12:09 PM   #2
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Join Date: Oct 2011
Location: Somewhere in Germany
Your question is?

Best regards!
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Old 3rd February 2013, 12:46 PM   #3
pilli is offline pilli  France
diyAudio Member
Join Date: Aug 2006
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.

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Old 3rd February 2013, 02:44 PM   #4
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Join Date: Apr 2005
Location: Simcoe Ont
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.
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Old 4th February 2013, 10:37 AM   #5
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Join Date: Jul 2003
Location: Dona paula, Goa
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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