Vintage Synth Repair

You checked the main (mains) fuse - either on the machine or in the plug...!?



--- In vintagesynthrepair@yahoogroups.com, "Mark" <casiotone1331@...> wrote:
>
> OK, I just plugged in the supply on my workbench and tested the pins. I also checked and tested all of the traces and found no cold joints or cracks in the PCB. Just to be safe I reflowed all of the joints and cleaned up the board to no avail. Anyway, these are the voltages I should be getting, and what I AM getting. There is literally NO power leaving the PSU.
> 
> Pin 1+2 should be 5V, I get 0V
> Pin 2+3 are ground
> Pin 5 is 0V
> Pin 6 should be +15V, I get 0V
> 
> What should I do next? I'm not too used to working on power supplies, so any direction is a good direction.
> 
> Thanks!
> Mark
> 
> --- In vintagesynthrepair@yahoogroups.com, Alan Probandt <alan_probandt@> wrote:
> >
> > 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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