[sdiy] problematic sh101

[Dave Magnuson]

At 10:42 AM 11/6/04, Senso wrote:

>>hi everyone,
>>
>>i'm trying to troubleshoot an sh101 for a friend (yes senso, that one again!
>>;-) first i thought it was the sequencer board, since when you push on the
>>case there, all the lights for the sequencer, arpeggiator etc go on and off
>>at random. however, i disconnected this board and now i find that also when
>>the synth is powered up and the case is stretched or pressure is on it in
>>any way, it completely loses its power. bend or push around a little and it
>>comes on again.. when working, the synth is fully functional.
>>inside, i noticed the bottom board being a bit warped. i cleaned it up, and
>>resoldered some connections that were a bit shady.
>>
>>my big question is: is all this more likely to be caused by the
>>wiring/connectors, or by bad solder joints? before i start on resoldering
>>all connections, i'd like to ask some advice on that.. the wiring looks
>>solid, and i've taken most of the connectors off and cleaned the contacts.
>
>Seems you will have to finish what you started. :-(
>If you don't put pressure on the board itself and pulling and bending the 
>wiring doesn't cause a problem, then the boards itself needs to be scrutinized.
>Could be a solder joint of course, but once you've done all of those, you 
>might have to look at the traces and check for hair fractions. Not a fun 
>job when the problem comes and goes.
>Since the machine also loses power at times, maybe you should concentrate 
>first on that part of the circuit. Could very well be the reason for all 
>the other problems.
>
>Senso

I had an idea.  Your problem seems to be power related, so you should start 
by tracing out the power supply structure first.  Since the problem is 
intermittant this will be hard to do with a DVM.  Maybe an LED/current 
limit resistor with alligator clips on each end.  Find a good ground near 
the power supply connection for one ned of the LED, and clip the other lead 
to the supply voltages elsewhere on the board...    The LED will be fast 
enough to catch short drop-uouts that you may not see on a slower digital 
meter.  It would also keep your hands free for bending and flexing the board.

You'd need to check all of the various voltage rails on multiple spots of 
the board, as well as checking the ground traces.  But the first place I'd 
look is right near the powersupply jack... there's no mechanical support 
for that jack on the SH-101... all of the strain is on that little circuit 
board it's soldered to.   I've fixed quite a few solder connections here on 
my both mine and several friend's SH-101s   It's unfortunate that roland 
didn't put some support on the jack boards.  They seem to develop cracked 
joints on the power supply, headphone and line out jacks all the time.

Dave

Resonant Frequency:
resfreq at hoohahrecords.com
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