Re: Newbie trying to fix a Johnson FT-2 Tremolo Pedal (for guitar)

stairs.
<Kotti75events@xxxxxxxxxxxxxx> wrote in message
news:2e4e0ced-4a24-453e-84d3-16e9e14b3142@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I'm trying to repair this pedal for a friend. There appeared to be
only one burnt out component and I replaced it but it still doesn't
work. It did look like something was spilled inside the pedal and I've
cleaned that out. When in bypass, the signal passing through is
distorted and garbled, like hearing it on a faint radio station. But
when the pedal is engaged, it doesn't pass signal at all. I'm pretty
certain that this is a copy of the Boss TR-2 because the schematic
seems to fit with the exception of the IC chips.
http://www.schematicheaven.com/effects/boss_tr2_tremolo.pdf
Since the "bypass/engage mode" is triggered by a momentary switch, and
the dry signal goes down a very processed chain of components, I
haven't been able to figure it out. What typically goes bad when there
are spills? From looking at this schematic, how would I go about
figuring out where in the "dry signal" chain things are wrong?

Thank you very much!

Olivia


D1 is in the line from the external power adapter. It's only in the circuit if
the external adapter is in use. Since the 1N4004 has a PRV rating of 400V, it's
unlikely that its PRV was exceeded. More likely is that something downline from
D1 is shorted. Look at D4 and C9. If either of those are shorted, then the
external power adapter's output is shorted to ground, through D1, thereby
toasting its innards.
Since the +9V supply powers IC2, IC3 and IC4, it's possible that one or more of
those ICs might have failed, causing the short across the power supply.

Since you mentioned that something was spilled into the box, I'd look closely at
the switches and jacks. Even though you cleaned it out, you might not have
cleaned the gunk off the contacts of the switches and jacks. Go back to those
parts and really inspect the contacts carefully with a magnifier and make sure
they are operating room clean. Make sure that the contact leafs in the jack(s)
and switch(es) are moving freely and aren't sticking when a plug is inserted.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Some people are like Slinkies. Not really good for anything, but they bring a
smile to your face when pushed down the


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