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

Pete Hartman pete.hartman at gmail.com
Thu Nov 7 05:13:56 CET 2013


Bringing the original topic of the XP-50 repair back up because I have
some appropriately sized SMT electrolytic caps now....


Now that I have the PCB removed (I was able to figure out all the
connectors without damaging any, thankfully), I can see that there are
a couple of vias that show signs of corrosion as well as what was
apparent on the ceramic caps (which I neglected to get replacements
for, but there you go).

Is there a preferred method of cleaning this kind of corrosion out of
those vias?  Or off the ceramic caps, for that matter?  I can replace
them as well if need be but if there's a sufficient solution without
waiting another few weeks to get another order together, it'd be a
good thing.




On Sun, Sep 29, 2013 at 1:07 PM, charlie wallace
<charlie at finitemonkeys.com> wrote:
> frys carries some SMY stuff if you have one. though usually 1206
>
> On Sun, Sep 29, 2013 at 9:13 AM, Pete Hartman <pete.hartman at gmail.com> wrote:
>> 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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