[sdiy] Internal clock issue (Roland)

[Dave Magnuson]

Hi Nick,

First thing I would check is the 1/4" jack.   Maybe it's dirty or has a
cracked solder joint on the normally closed connection?   Sorry if this is
obvious, but it's the first place I'd start.  

 Then start following components backwards until you hit the LFO.   Since
it's a square wave, a simple logic probe would probably be sufficient to
diagnose it.

Does the LFO light flash and respond to the rate knob?   Does it work for
modulating VCF, etc?

Dave

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Nicholas Keller
Sent: Friday, May 23, 2014 1:39 PM
To: AH; synth-diy
Subject: [sdiy] Internal clock issue (Roland)

Apologies for the cloak and dagger, but I was afraid to mention SH-101 in
the subject line...

My friend has an SH-101 which stopped responding to the internal clock.
Arp, seq, random generator ... None work from internal clock.  All work from
external clock.   

He has taken it to a tech but reports that they seem stumped about the
clock.   

Has anyone here fixed a similar issue?  After looking at the schematics, and
while I admit I am no expert, I think that if it works via external clock,
the CPU must be working.  I question transistor TR8, but again, I'm just
following the signal path and don't fully understand the circuit.  Seems to
me that the LFO generates the clock and TR8 is one of the only parts between
the Clock source and the CPU. 

Any help or suggestions are appreciated, and your patience too as I don't
have the synth here.  

Nick

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