[sdiy] saw core VCO tuning/scaling (Roland SH-2)

[Magnus Danielson]

Dear Adam,

On 23/08/11 07:53, Adam Inglis wrote:
> Thanks Magnus and Juergen for the tips:
>
> Thermally challenging a MF resistor in the range CV input reproduced the
> problem, however 2 hours after replacing it, the problem was back!
> I then got out the hair dryer. Heating the circuit brought the problem
> on again from a cold start, but it was hard to localise - it seemed to
> be around the integrator though. Refreshing all the joints made no
> difference, so I finally replaced the integrator/comparator op amp (IC
> 18), and now after 4 hours she's rock-steady, and sounding sweet.
>
> I'd still be looking for the problem come next year, without this help!
> And thanks for reminding this dummy about Ohm's Law... ;-)

Good news.

Thanks for the progress report.

Some of these problems can be a bit tricky and challenging to find, but 
oh so rewarding when downing it. The trouble is to keep options open 
while ruleing out things. Hot air for thermal stress can be good at 
times. Just need to be careful not to cause more problem than one 
solves. A friend of mine killed more EPROMs using freezer spray than the 
fault analysis called for, but he learned.

Cheers,
Magnus