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[vintagesynthrepair]

2010-07-02 by Scott S.

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.

Re: [vintagesynthrepair] MT-32 Audio Problem

2010-07-03 by narfman96

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:

Show quoted textHide quoted text

>
> 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.
>

Re: [vintagesynthrepair] MT-32 Audio Problem

2010-07-04 by Scott S.

Thanks to all for the good tips. Scott Nordland emailed me with a comment that these often want more current, if you don't have the original PSU (which I don't). It wants to see 650ma, I was trying it with a Rat Shack variable PSU because it's often a good quick check, and it has a variety of tips that you can reverse the polarity on. The Rat Shack one was only 300ma, I put it on a bench supply, and it came right up. I haven't seen one of these for years and years, I just wanted to play with some old pre-D50 sounds for a bit.

thx-Scott S.

Show quoted textHide quoted text

On Sat, Jul 3, 2010 at 12:42 AM, narfman96 <narfman96@...> wrote:

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." 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.
>

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Re: [vintagesynthrepair] MT-32 Audio Problem

Re: [vintagesynthrepair] MT-32 Audio Problem

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