Wild_Bill wrote in message
...
I have an older Boss TU120 tuner (maybe 1979) that seems to need
adjustment
repaired, but have been unable to locate a schematic or service manual.

The output frequency at the Monitor jack, appears to be incorrect for the
internal Calibrate settings, and when checked with a reliable counter
(SC3100 AutoTracker readout) the freq is about 432Hz, when I think it
should
be adjustable to over 440Hz.

I was about to ask Roland Support when I saw that they require registered
user identity sign-in/account to be established before asking a question.

I have the operating instructions, and it describes the pot adjustment for
the internal Calibrate steps, as something like "adjust the front panel
Cal
(pot) until the drifting stops, and the LEDs appear to be stopped/remain
stationary".

The point of rotation where the front panel Cal pot gets the LEDs to stop
drifting is all the way to the end stop of the rotation, so I can't find
the
mid position between scroll left/scroll right.. and the freq is about
432Hz,
not 440, when I assume that it should be able to adjust from below 440 to
over 440Hz as the Calibrate pot is adjusted.

The Calibrate output freq is independent of the 12-position Note Selector
switch.

I marked the 2 internal PC mount pots before twiddling them, but the freq
doesn't get to 440Hz.
After tweaking, I can see 129Hz For "C", not 130.81..(possibly just a
counter accuracy tolerance issue) but 242Hz for "B", not 246.9Hz.

I believe the tuning reference freq is from a 3-terminal component marked
Iwata 880.0 T (3 '79 Japan) with a tuning fork symbol on it.

I'm operating at a musically impaired level here, as I've only recently
become interested in learning to play guitar, and I don't fully comprehend
a
lot of how actual frequencies relate to notes, other than the harmonics.

I have a functionig Boss TU-12 Chromatic tuner, so I don't really need the
older tuner, but I'd like to know if I can get it to work properly, since
it
does have a strobing display that easier to see at a distance, moreso than
the-needs-to-be-positioned-closely TU-12's meter pointer.

I'd also like to lower the non-adjustable speaker volume too, perhaps
later.

I don't think installing a 0-6 volume knob would be a solution.

--
Cheers,
WB
.............




Assuming the "880.0" is an oscillator is the wiring from the calibration pot
(definitely a resistive pot ?) directly to the 880.0 ? Is there a tuning
capacitor near the 880.0 ?