Greetings Olivia & others..
First of all, what kind of test equipment do you have use of? Do you
know how to use it? If not, you're going to need to find someone that
IS familiar with anything from a DVM (Digital Volt Meter) to,
ultimately, an oscilloscope and has use of them.
Regarding:
"There appeared to be only one burnt out component and I replaced it
but it still doesn't work."
What specific component was that? Further, does it relate to the
schematic of the .pdf file referenced?
"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."
"It did look like something was spilled inside the pedal and I've
cleaned that out."
Any idea what was spilled in it? Was it sticky? If it was something
like a soft drink that has sat for some time without being cleaned
out, there's a good chance that the potentiometers may also need to be
replaced in spite of a electronic component failure. I've had such
experience fixing a fellow radio amateur's HF radio where his daughter
spilled Coke all over the front of the radio. It was a mess and a good
deal of labor to resurrect the front panel alone, not to mention the
rest of the radio!
=== === === ===
It would probably be a good idea to actually get the schematic to the
piece of electronics that you've got. Writing Johnson may provide
this, request a service manual -
http://www.johnsongtr.com/Fifties_Tremolo.888.0.html. At the very
least, explain that a schematic would be immensely helpful. Expressing
the interest to order parts for your unit may show the need they need
to hear about. IF they won't provide the schematic, ask them how they
propose that you order new components that you suspect you'll need?
Don't be surprised that the units are produced over in China and
aren't serviced, per se', but entire boards removed and replaced.
China has revealed a 'throw away' society of electronics like none
we've ever seen before. Meanwhile, in your local area wherever that
may be, a substantial hourly rate to merely swapping one board with
another.
Keeping in mind that this REALLY isn't the correct schematic for the
unit you have, in order to resolve this, you're going to first need to
verify that you've got B+ to the electronics. The power supply circuit
is at the bottom of the schematic above AC ADAPTOR. Namely +9V, +5.5V
& +4.5V DC should be verified to exist. NOTE: Depending on what was
burnt out will also dictate where one should also be looking. If any
of these biases are missing, they will have to be fixed before you can
do any further diagnosis!
Next, with the above voltages present, turn OFF any and all special
effects and apply a signal into the input and follow it through with
either a DVM or, ultimately, an oscilloscope towards the output.
Incidentally, that signal path initially passes through R15, C8 to the
source of FET transistor Q4. Continue to follow that signal towards
the output through either the IC1B, IC2A, Q1 or the Q3 path all
leading to the positive lead of C1 (1uF/50V). Finally through Q2's
base to the emitter and through C2 & R1 to the output.
If you lose the input signal anywhere along this path, back up to the
component or region where that signal will not pass and verify that
the signal exists on one side but not the other. Attempt to isolate to
your suspect component. Verify correct DC bias to the component, if
it's still not passing a signal, that will be the component to
replace.
As you get the direct (non-effect) path for the pedal to work, then
you can look into the individual circuits for the Rate, Wave and Depth
effects according to the picture at the above URL. By using the same
method of tracing a signal from the input of the effect electronics
through towards the output of that circuit, one by one, you'll verify
each subsection of the circuit.
Trying to learn all of what you need in a Use-group reply or two is
usually not adequate. Again, having someone that is versed in
electronics theory, diagnosis and repair that either has use of or
owns their own test equipment will substantially reduce the amount of
effort and time you'll end up dedicating for, essentially, a $60/USD
piece of electronics.
Good luck!
Cheers,
Mr. Mentor
| 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
