Oberheim Matrix-6 -- No display, no sound but PS seems to be fine

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theotherjen
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Oberheim Matrix-6 -- No display, no sound but PS seems to be fine

Post by theotherjen » Thu May 16, 2019 7:27 pm

Hi There,

I am hoping someone has experience with troubleshooting a Matrix-6.
The display isn't working, none of the LEDs light up and there is no sound on the output. The first thing I checked was the power supply board and all of the voltages that are output seem to be correct. (I was hoping this was a blown fuse or puffy cap situation). Is it possible that the OS chip has gone bad? The voltage on the battery measures 3V so I don't suspect that the memory was lost (but anything is possible, right?). If anyone has had a similar problem, please share your experience. Thanks!

Rasputin
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Re: Oberheim Matrix-6 -- No display, no sound but PS seems to be fine

Post by Rasputin » Thu May 16, 2019 11:47 pm

theotherjen wrote:
Thu May 16, 2019 7:27 pm
The display isn't working, none of the LEDs light up and there is no sound on the output.
Check all the basics such as seeing that the CPU is getting 5V, clock, and reset.

That said... cross your fingers and hold down the STORE button while powering up. If you works again, you're blessed.

theotherjen
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Re: Oberheim Matrix-6 -- No display, no sound but PS seems to be fine

Post by theotherjen » Fri May 17, 2019 1:51 am

Hey Rasputin,

Thanks so much for the reply! So the CPU does have 5v but the clock pin doesn't seem to be doing anything. I tried a reset, and unfortunately it didn't work but I realized that I forgot to check the AC outputs that come out from the transformer straight to the display board and they were wayyyyy of-- 42VAC.

So it seems so unlikely, but I think the issue is with the transformer. When I measured the voltages, they were past the voltage regulators but when I checked the secondaries on the transformer, they were totally lop-sided and weird. I'm going to try to find a replacement for that transformer and see if that does the trick. I hope the erratic voltages didn't damage any other components...

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Re: Oberheim Matrix-6 -- No display, no sound but PS seems to be fine

Post by madtheory » Fri May 17, 2019 11:12 am

Hard to tell from your description what the trafo behaviour is, but it would not be unusual for the trafo outputs to be higher than the voltage regulator output. That's what a voltage regulator is for. As you say, it's less likely that the trafo is at fault than the caps and/ or the silicon in the PSU.

The only way to be sure is to check the service manual.

You should also measure the PSU reservoir caps out of circuit with a capacitance meter. If these haven't been replaced already, they're a major suspect at this age. They're the most taxed capacitor in the system. You might be getting the right voltage on a DMM, but it's very possible it won't show you any ripple (that's what the reservoir caps deal with). That ripple can easily create the symptoms you're describing with the display etc. You'll see ripple on a 'scope. It's kinda hard to say how much ripple is OK, there'll always be a little bit.

The only way to be sure is to check the service manual. It lists the tolerances, very useful.

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Re: Oberheim Matrix-6 -- No display, no sound but PS seems to be fine

Post by crafter57 » Fri May 17, 2019 3:11 pm

Hi, I can't remember as I've sold mine a long time ago but if its a VFD display (vacuum fluorescent display) the voltage requirements are anywhere from 12 - 30V or more, so 42V may not be wrong, if its not a VFD then perhaps its your transformer or maybe drawing more voltage due to some other problem, disconnect the display and the other connectors re-measure the voltage(s).

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