[sdiy] Internal clock issue (Roland)

[Tom Wiltshire]

A cracked track still sounds like the most likely culprit to me. I've been over circuits several times and until I'd eliminated everything else, I didn't see the hairline crack that was *clearly* evident after the fact!

On 23 May 2014, at 20:31, Nicholas Keller <niroke at tampabay.rr.com> wrote:

> Dave, 
> 
> Thank you for your response.  
> 
> First, this isn't my synth and it is in another state, so I've only been able to remotely diagnose the problem via phone chats.  But, those are the first things I had him check weeks ago, before he took it to be serviced.  The socket was good, solder pads good, and I tried to have my friend verify the clock signal at different points with his meter, whatever it was, nothing fancy.  
> 
> The LED did in fact respond to the rate slider.  It seemed to me that the LFO clock signal was not getting to the CPU, but was present elsewhere. 
> 
> Someone else has suggested a fried trace may be the culprit.  I'm sure if I had it in front of me, and since I have my own working 101 to compare it to, I could figure out what is wrong.  
> 
> I guess I'm hoping to rule out a known/common failure with the 101 CPU.  At least then I can tell him that it should be a more simple fix.  
> 
> Thanks again
> Nick
> 
> 
> 
>> On May 23, 2014, at 2:04 PM, "Dave Magnuson" <abide at dmdrafting.com> wrote:
>> 
>> 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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