UA726HC

The Roland Jupiter-4 and ProMars Compuphonic Analogue Synthesizer
slo
Posts: 3
Joined: Mon Mar 08, 2010 5:04 am

UA726HC

Postby slo » Thu Sep 09, 2010 1:59 pm

Has anyone bought these transistors from this guy? I have heard there are fake ones one there.

http://cgi.ebay.com/2x-UA726HC-726HC-Roland-Jupiter-4-and-SPV-355-NEW-/390237007302?pt=Keyboards_MIDI&hash=item5adbf02dc6

I've a JP-4 drifting out of tune and doing the research it could well be a bad 726.

Got to get it fixing before I spring for the midi update boards.

George

slo
Posts: 3
Joined: Mon Mar 08, 2010 5:04 am

Postby slo » Sun Sep 19, 2010 6:59 pm

Ok, got a new plan. After looking @ the JP4 service notes and poking around inside the JP4, I notice the negative volts out of the power supply is -16.23v and I can't trim it back to -15v ,this can greatly affect the tuning, so I have to fix this first.
Question: Has anyone run into this before?
I'm planning on replacing the regulator and the electroylic caps.
Any advice would be appreciated.

George

slo
Posts: 3
Joined: Mon Mar 08, 2010 5:04 am

Postby slo » Wed Oct 06, 2010 2:10 pm

Ok at the risk of talking to myself too much, here's the update on the tuning problems. The power supply was re-capped and the neg regulator replaced, I now can trim to -15v. I also think I had a dirty/loose connector @ the key-assigner board, (the out of tune voice would change positons) fixed that. The JP4 now tunes up nicely and seems to be staying in tune so far. Hope this helps anyone with similar problems. Still interested in a source for the UA726HC transistor though.

George

nathanscribe
Posts: 5
Joined: Wed Apr 21, 2010 9:25 pm

Postby nathanscribe » Wed Oct 06, 2010 6:08 pm

Have you tried Vintage Planet? They seem to have a good range of parts, and I've had speedy service from them before.

As for the fix, it's good to hear it was a smooth one. My own JP works fine at switch-on but after a few minutes starts drifting like mad. I suspect the 5V line, but haven't had time to look at it yet.


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