Just wanted to let everyone know, I fixed the SDE this weekend.
I guessed that the power supply was most likely the source of the problem and determined what I thought the outputs from it should be by studying the part numbers of the regulator chips and tracing their connections to the ribbon cable. Then I worked to get it to output those voltages on the ribbon cable. I ended up replacing all the ICs and capacitors on the power supply board, which may have not been strictly necessary but will hopefully prevent a blowout of one of the other old caps further down the road. The board has extremely delicate traces that broke when I was removing old parts, I had to rebuild 3 of them. The last piece of the puzzle was the 6v regulator putting out 16v (the same as the input voltage) on the output. This was caused by a broken trace on the ground pin of that IC... apparently if there is no ground connection the voltage goes straight through.
I suspect that this same power supply is used in other Simmons rack units of that vintage so I hope this may be useful to some of you.
I was jumping up and down hearing this thing again after more than 10 years. Its just as quirky and weird as I remember it.
Cheers,
Christian
--- In Simmons_Drums@yahoogroups.com, "Ed" <edrose1@...> wrote:
>
> +1 on this. I fired mine up to try and help and voices 1-3 are dead. A schematic and source for the Yamaha voice chip would be great.
> Thanks in advance!
> Ed
>
> --- In Simmons_Drums@yahoogroups.com, "xjnx0x" <concken@> wrote:
> >
> > Hi, I'm new here...
> >
> > I joined to see if anyone has schematics or experience fixing the Simmons SDE. Mine stopped working around 1998 and I'm trying to get it back up and running because I miss it.
> >
> > The power supply went out when the caps blew. I've replaced these and the unit now turns on again, lights up, responds to buttons and knobs, even responds to midi. Everything seems to work from the front panel, but there is no sound, except for a harsh intermittent buzzing for a few minutes after its turned on.
> >
> > I measured the voltage going to the yamaha chips and found it to be lower than their datasheet says is acceptable. Datasheet says minimum 4.8v and its measuring 4.5v. I suspect the power supply still has issues and I think fixing and verifying that is the best place to start.
> >
> > Anybody have schematics? Tips for troubleshooting? Anybody else fixed one of these? If a schematic for this machine isn't available, maybe a schematic from one of its contemporaries would have the same power supply design.
> >
> > Failing that, could I talk somebody into opening their healthy SDE up and measuring the voltages on the power supply ribbon cable so I can at least tell what those voltages are supposed to be?
> >
> > thanks for your help.
> >
>