Vintage Synth Repair

Hi Scott,

I've fixed two of these that had issues with the +/- 5 volt audio power supply section. One had a shorted 330uh inductor and this opened a flameproof resistor that was .24 ohm. The other had an open diode where the power enters probably from the wrong supply. There is a 7805 volt regulator for the +5vdc digital voltage also. I'm not sure about the weak display unless the +5vdc is low. 

I have the schematic as a pdf around here somewhere. I also modify these so they have the Robin Whittle (RWI) battery backup mods with improved CC control and 50 reverb/delay settings. With the mod it will boot on any midi channel and remember the setting or any custom tones and patches loaded.

Good luck, Fran   

--- In vintagesynthrepair@yahoogroups.com, "Scott S." <picoshark@...> wrote:
>
> Hi to all, I've been lurking a bit, but mostly accumulating good info for
> later study. I got a Roland MT-32 recently for (almost) free from a music
> store going out of business. The display is dim, the basic controls seem to
> work, but the audio only puts out a big constant HUMMMMMM from both
> outputs.  I assume sometime in it's life it was plugged in with a regular
> positive tip DC supply, instead of Roland's desired negative-tip.
> 
> I have only had time for a few minutes to hook it up briefly. I haven't had
> a chance to try the reset of "hold master volume, press rhythm part, press
> part 1" yet. I know about the "no channel 1" problem inherent to these.
> 
> I haven't had the lid off yet, are their any obvious PSU caps/regulators to
> look for?
> 
> thx-Scott S.
>