Vintage Synth Repair

I would assume that it is a problem in the power supply.  I suggest getting a cheap used PC power supply and bypassing the DX21 supply just for testing.   I got a recent Dell supply from one of their mini DeskTops for $5.  It's only 15"x5"x2" in size.  It puts out +5, + and - 12V, +3.3v regulated.  For a PC supply it's unusual in that it works without any minimum load.  Usually PC power supplies need about 0.5 amp load on their +5V line in order to operate correctly.

  There is a DX100/DX27 schematic floating around and possibly here in the files section.  It shouldn't be that much different from the DX21.

--- On Sat, 7/31/10, Doug <dougslocum@...> wrote:

> From: Doug <dougslocum@...>
> Subject: [vintagesynthrepair] Re: Yamaha DX21 will not power up
> To: vintagesynthrepair@yahoogroups.com
> Date: Saturday, July 31, 2010, 6:42 AM
> Mark,
> 
> Rhetoric: Troubleshooting anything without seeing it is
> always difficult, at best.  :-)
> 
> That said, I'm not familiar with the DX21 specifically, but
> I would be looking for voltage measurements and values from
> a oScope to determine if it is acually the power supply that
> is at fault here.
> 
> I wouldn't be too quick to judge the power supply, just
> because it's the easier thing to troubleshoot.
> 
> Doug
> 
> --- In vintagesynthrepair@yahoogroups.com,
> "Mark" <casiotone1331@...> wrote:
> >
> > I recently scored a non-working DX21 on the cheap, and
> it will not power up. No lights, response, or life
> whatsoever is in this machine. I don't even hear the audible
> "click" when I turn the machine on. I tested the power cord,
> the switch, the fuse, and replaced most of the capacitors on
> the main PSU board, and it still is doing the same thing.
> > 
> > What worries me is that a previous owner replaced the
> big black cap in C5 with a 100uf 50V capacitor, and I know
> that it is MUCH too low of a voltage to be there. I'm not
> even sure if the capacitor is even the right value... I'm
> used to seeing things like 2200uf and such in power supplies
> like this one. If anyone could point me to the proper
> replacement, that would be great.
> > 
> > Anyway, before I start to go nuts tearing this thing
> apart, I was wondering if anyone here could possibly help me
> out, I had great success bringing a dead TX81Z back to life
> thanks to the collective minds on this group. Where should I
> start? Many thanks!
> >
> 
> 
> 
> 
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