[sdiy] "re-cap" when it's SMT?

Pete Hartman pete.hartman at gmail.com
Sun Sep 29 18:13:44 CEST 2013

So what would cause digital crosstalk, in only one channel, for a
synth that presumably didn't have this problem when it was new?

The hint appears to be lost on me ;-)

The only thing that occurs is tracing the path and seeing where it
comes nearest to digital lines that the other channel does not...?

I think I can step away from the idea of "re-capping" the synth; I've
heard other people talk about doing such things, and I did fix an old
Roland S-10 which had NO output by replacing a handful of likely
seeming caps, so that's where I was coming from with that.  Clearly
the weight of experience is that doing so willy nilly is a bad idea
(and my own experience with other hardware at a larger scale would
argue the same), and I'm not married to the idea.

I appreciate everyone's suggestions, and I'll keep the list posted as
to my progress; of course it will be a bit before I can proceed on, as
I have no 10uF SMT caps handy, and I'm very doubtful I'll find them at
Radio Shack.

On Sun, Sep 29, 2013 at 8:21 AM, Magnus Danielson
<magnus at rubidium.dyndns.org> wrote:
> On 09/29/2013 04:36 AM, Pete Hartman wrote:
>> To follow up on this....
>> I did audio probes, and found:
>> Only the left channel has the problem.
>> The D/A chip (IC19, UPD63200GS-E2) left channel out (pin 11) has no
>> sign of hiss.
>> IC175, a 10uF SMT electrolytic--appears to be for blocking DC--has a
>> bit of corrosion on the far side, and there is hiss there.
>> First guess is then replace IC175 (we'll see how well that works for
>> me; I'm not much good with wire trap connectors and there are LOTS of
>> cables all around this section of the board).
>> I'm curious if any of the more experienced members have an opinion on that.
> Are you sure that it's a cap problem?
> I would look at cross-talk from digital lines. Caps can help mitigate
> that, but you need to look at it from a signal integrity way rather than
> just audio by itself.
> That only one channel has the problem is a great hint.
> Cheers,
> Magnus
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