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Vintage Synth Repair

Index last updated: 2026-04-28 23:41 UTC

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Re: Yamaha DX21 will not power up

2010-08-06 by Paul

Hi Guys,
A snip from Bob at sounddoctorin.com
quote
Anyway it's a switcher...has ac through a choke to a rectifier that charges up the 200V electro. Make sure it has something like 160V on it first.
Then check inputs of IC1 and IC2, the voltage regulators (pin 1 on ic1 and pin 3 on ic2)

If nothing there then it's a problem with either the switching transistors, the transformer (test continuity from pin 1 to 2... then 3 to 4, then 5 to 6, then 7 to 8 to 9 (8 is Center tap). Coil 5/6 should be putting out 5V across the caps it's connected to while the regulators are supplying plus and minus 15V. So their ins will be around 20V or so.
End quote.
There may be a circuit on the way, I'll let you know.
Cheers
Paul

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