Vintage Synth Repair

I could be way off my understanding if its like the tr-909 that using
capacitors and zeners to a dual transistor set, to hold the voltage back
until it builds up to 5 volts.  Then the transistors unleash a ping
(discharging the cap) down the pipe to the cpu reset to wake up and boot.
The idea is to prevent scrambling memory and circuits with incorrect
voltages, so it's a protective gate that wont let it boot until a stable and
correct voltage is available for its operation.  

Bad cap? Bad zener? Bad transistor?  Replace all?  

 

Brian Castro showed me that there are also issues with thin traces that run
under the big caps in the 909 PS that idiots like me sometimes over
heat/overcooking solder for a "big' mechanical support for big caps, melting
delicate traces and then it needs bridging to fix.  Because the trace is
hidden under the big caps most people miss the damage, but a continuity
trace reveals it.  But it doesn't sound like you have that (symptom no reset
5v ever).

 

Lorne "caveat: barely knows what he is doing" in Canada

 

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of jammie
Sent: Tuesday, April 03, 2012 3:34 AM
To: vintagesynthrepair@yahoogroups.com
Subject: Re: [vintagesynthrepair] Jupiter 6 common no sound problem

 

  

reset should be a momentary pulse usually 5v if it is constant held high
then it will be in constant reset plus being 10v for a cpu chip is to high a
voltage so cpu could be damaged

----- Original Message ----- 

From: adhmzaiusz <mailto:adhmzaiusz@...>  

To: vintagesynthrepair@yahoogroups.com 

Sent: Tuesday, April 03, 2012 5:47 AM

Subject: [vintagesynthrepair] Jupiter 6 common no sound problem

 

  

Hi again, so I found a messed up JP6 recently that I bought to try and get
it up and running. It turns on with all the LEDs Lfo lights blink etc, but
seems to be frozen with no sound. If I wait about 10 minutes it seems to
unfreeze so I can push buttons and lights come on but still no sound. I've
been reading that this seems to be a common problem, and the suspect is the
voltages that drive the digital side of the machine.

I measured the power supply and all voltages are within spec except one that
I am a little curious about, the reset out of the power supply seems to be
at a constant voltage (i think it was 5v maybe could've been 10v off the top
of my head). Being called a reset output makes me think that maybe this
voltage isn't supposed to be a held voltage and should maybe be a triggered
momentary pulse to reset the cpu or something like that? Can anyone confirm
how the reset out is supposed to behave, let me know if i'm on the right
track and possibly give a little insight of how to remedy this common
problem. Thanks again!

Greg