[sdiy] Internal clock issue (Roland)

[Nicholas Keller]

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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