Bringing an old synth back to life

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geoff04
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Bringing an old synth back to life

Post by geoff04 » Thu Dec 10, 2020 10:06 am

First post here - thanks in advance for the response.

I'm getting an 80s polysynth from a friend. He says it hasn't been turned on in about 15 years, so I'm definitely nervous about booting it up.
I should also add that I consider myself a qualified tech, though I've never worked on synths. I mostly tech and build tube-based audio equipment.

Should I rebuild the power supply before turning it on? The capacitors are old as it is. Not being on for 15 years doesn't help.
Is it okay with synths to bring them up with a Variac?
Is there anything else I should be careful about that?

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KSS
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Re: Bringing an old synth back to life

Post by KSS » Thu Dec 10, 2020 10:15 am

Which synth?

geoff04
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Re: Bringing an old synth back to life

Post by geoff04 » Thu Dec 10, 2020 10:19 am

It's a Voyetra

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KSS
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Re: Bringing an old synth back to life

Post by KSS » Fri Dec 11, 2020 3:12 am

Nice friend!

If you haven't already done so. Start here. There's a lot to this synth. And you'll want to become really familiar with its expected states and operation.
http://www.retrosynth.com/docs/v8/
http://www.synthfool.com/docs/OctavePla ... Manual.pdf

No, i would *not* suggest you rebuild the PSU before anything. Check? Yes. Rebuild? No. Resistance checks of rails before turn on is always a good idea. In this case include checks of continuity to the.. case.

Then it's much the same as any other synth. Intense visual inspection. Both internal and external. Look for clues to component issues. Disconnect anything that might be hurt by an improper power supply and then turn it on. <--Pull the voice cards and do more inspection of them before putting them back in. Be sure to make pre-re-insertion resistance checks of their rails too.

Don't jump on the it needs re-capping-rebuild bandwagon. Unless it does. But let the synth tell you that, not some internet thread.

Take your time, learn what the synth has to tell you before doing anything to it. It's worth it.

geoff04
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Re: Bringing an old synth back to life

Post by geoff04 » Fri Dec 11, 2020 10:56 am

Nice friend indeed.
Thank you for the advice and resources!

geoff04
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Re: Bringing an old synth back to life

Post by geoff04 » Sun Jan 10, 2021 2:36 pm

Quick update on the Voyetra:

I picked it up just a little before Christmas. I did power it up but it didn't seem too happy. It hadn't been turned on since at least 2006. Also I didn't have the midi to XLR cable. I didn't get a keyboard with it (more on that in a minute) so I needed the cable to test it. I could tell from headphone output that something wasn't happening, plus it didn't really respond to key inputs. It did light up, but wasn't right.

Over the last couple weeks I got into it. Measured the voltages and found that the +15 supply wasn't working. I rebuilt most of the power power supply and recapped most of the boards, then powered it up and it works.

The buttons all seem to work, though I haven't tested it too much yet. Many LEDs seem to be stuck on and the numeric readouts have sections that are stuck on. Is there a logic IC that maybe controls the LED indicators? Or should I look for broken solder joints?

I happened to find an actual Voyetra keyboard (VPK5) on reverb, but it had been totally disassembled. However, the price was right. At this point it's not together, but nearly all the parts seem to be there. It is missing some springs for the key returns, but I think I found a source for them. It's also missing all the screws, but that's an easy thing to source. In the meantime I've put some work into my Siel DK600 to make it a little more stable for use as a controller. I've got a couple synths but never use midi.

I'll have a better idea about how it's working once I have some time to play with it - hopefully this week.

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KSS
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Re: Bringing an old synth back to life

Post by KSS » Mon Jan 11, 2021 4:58 am

That is some nice progress!
Yes, always check solder joints and connectors first when dealng with old synths. While it's possible for a logic chip -or readout element- to be at fault, and even more likely with an older synth, it's still far less likely than other 'mechanical' issues.

Since it was turned on with the negative rail active, and no positive rail, chips relying on both -or chips expecting inputs to fall within a certain range- may have been made wonky by the partial power-up. Keep a mind to that possibility without letting it overpower other simpler issues you can check too.

jorg
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Re: Bringing an old synth back to life

Post by jorg » Mon Jan 11, 2021 11:42 am

I had an old synth (Korg Poly-800 II) that went all nuts. I changed the battery, un-seated, cleaned, and re-seated all the connectors. That fixed it right up.

bookends
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Re: Bringing an old synth back to life

Post by bookends » Sat Jan 16, 2021 5:26 pm

Get in touch with Jeff at The Analog Lab about it. He helped design the synth and offers (pay) online consultation and a tech mentoring course on repair work:

https://www.theanaloglab.com/tech-online


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