Decontaminate Ckt Board

From detritu–(at)–x.netcom.com Wed Jan 6 09:18:39 CST 1999
From: detritu–(at)–x.netcom.com(Lord Valve)
Newsgroups: alt.guitar.amps
Subject: Re: Deluxe Reverb crackle & pop
Date: 6 Jan 1999 06:59:01 GMT
X-NETCOM-Date: Wed Jan 06 12:59:01 AM CST 1999
Xref: geraldo.cc.utexas.edu alt.guitar.amps:150864

In <36924D08.E8DDE2F--(at)--eleport.com> Simply Steve
writes:
>
>I have replaced or substituted almost every part in my Deluxe Reverb
amp
>and it still has a crackle & pop sound. It shows up most with reverb
>turned up and has gotten worse over time. It used to be intermittent,
>now it’s constant. The only parts I have not sub’d out or replaced are
>the power transformer, the output transformer and the choke coil. Of
>these three, which do you think would be the most likely cause?
>
>Oh yeah, I haven’t sub’d or replaced any of the pots but I have
cleaned
>them all and seriously doubt they are the cause since it does it
>regardless of their positions. It puzzles me why it seems to be
>amplified througn the reverb, though and I suppose the reverb pot
could
>be causing it. I’ve sub’d the reverb tranny and tank, too, with no
>effect.
>
>Thanks,
>SS

Lord Valve Speaketh:
Well, plate load resistors are prime candidates for Rice-Krispies
noises, but if you’ve replaced *everything*, that lets those off
the hook. Same with cathode bypass caps and resistors. I assume
you’ve replaced the resistor string in the filter cap section, too.
One thing you may have overlooked is poor soldering…it’s pretty
hard to make a good joint on a Fender eyelet board with a 40-watt
iron, and that’s what most folks wind up with. Even a 60-watter
is borderline; I use a Weller WP-100 and it does a great job.
I think you should go over the entire eyelet board with a higher-
wattage iron. I’d also replace the reverb driver tube socket, since
the 12AT7 in that socket runs really hot, and the phenolic might
be cooked. The only other thing I can think of is that you may have
a contaminated fiberboard; this is a real bitch to deal with. I’ve
had good results with this procedure:
1) Remove all the screws which hold the fiberboard to the chassis,
and pull the board away from the insulating board beneath it.
If the noise stops, or changes in volume or character, you’ll
know for certain you’re on the right track. If it doesn’t,
you could still have a contaminated board, so…
2) You’ll need some good quality electronics cleaner for this next
step…CaiKleen TRP from Caig Labs or (my favorite for this
procedure) some Mr Mac Tuff Stuff, which is distributed by Mojo.
Pull the top board as far up as you can; you may see a wire or
two which can be unsoldered to give you more clearance…make
*sure* to tag the wire or draw yourself a diagram so you can
put it back later. Eyeball the bottom (insulator) board under
strong light, using a magnifying glass if you’ve got one. You’ll
see plenty of crusty-looking places where solder flux dripped
onto the board during manufacture (or resoldering). This is
usually ok, but it can cause problems sometimes. Spray a *lot*
of cleaner onto the underside of the *top* board first; if you
can work a child’s-size toothbrush between the boards, scrub
the hell outta both of ’em. Don’t spare the cleaner; you may
wish to pack the chassis with paper towels to absorb the runoff.
If a toothbrush won’t fit between the boards, try using some
6″ wooden-shaft swabs, which you can get at most drug stores.
(Ask the pharmacist, as they don’t usually put ’em out where
you can see ’em. Medical supply places stock these, too.)
When you’ve scrubbed as much crud off the two boards as you
can, stand the chassis on its end and spray a whole mess
of cleaner down through the boards from the top end, as a
final rinse. Note that on some Fenders, it’s possible to
remove the bottom (insulator) board entirely, by sliding it
out one end; if you can do this on your amp, it will greatly
simplify the job.
3) Leave the screws out, and dry the solvent off the boards with
a heat lamp, or an ordinary 150W home-type floodlamp, which
works fine but takes a little longer. DON’T use a PAR64 or
PAR56 from your band’s lighting system, as those will make
things hot enough to do damage. You can also just let it
dry by evaporation, by letting it sit overnight. Put it
in the garage if you can, ’cause solvent be stinky and
ungood for ya.
4) Do the *same* thing to your power-supply board, underneath
the capacitor-bank cover. Be careful with those cloth-
insulated wires where they go down through the holes in the
chassis.
5) Put everything back together and try it out.

Lord Valve
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