Boss TU-120 Electronic Tuner Schematic Roland LED Strobe Guitar Tuning

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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 ?

If the 880.0 contains a miniature tuning fork, like those watches of the early 70s that hummed to themselves. Corrossion to the forks over decades would lower the frequency

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I would guess you have an 880Hz version of the 360Hz elements in these watches

then corrossion over the decades slowing the frequency of the fork. There is probably some range limiting resistors to the Cal pot. You could probably get away with changing one/both of them a bit to change the capture range,

If you need brushing up on the theory. Closest I have is a TU-15. If it's layout is similar I could give you some freq readings for reference.

--
Live Fast, Die Young and Leave a Pretty Corpse

The TU-120 model (old one with strobing LEDs) has a fairly straightforward user control panel and selectors, and the basic instructions on the bottom label.

If the tuner had had been able to adjust the Calibrate setup to 440Hz at the Monitor output, I would've assumed that it was probably operating normally.

I suspect that the oscillator/tuning reference and/or other components have drifted in value(s), especially since the thing is 30+ years old.

There are a few online manual sellers that list a service manual for the TU-120 model, so I may end up going that route, or contact Roland support.. I just thought I'd check SER since several regulars are familiar with quite a bit of musical gear.

The TU-60 model may be close, containing somewhat similar circuitry, and about the same age, maybe Roland's first model.

The fairly current/more recent *TU-12* model is a completely different unit, not surprisingly.. one SMT quad flat pack and a TV color burst 3.579..? MHz crystal, but of course, numerous other components too (and I was able to find an online schematic for the *TU-12* model). I have this model, and it gets me tuned fairly accurately (using the chromatic mode) according to a friend that's been playing a long time.

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

3.579545 MHz. That number should be burned into the brain of anyone (in the US or Japan, plus some Central and South American countries) who services electronic equipment.

Thanks Nigel.. I believe that you're correct, and that even oxidation of a mechanical tuning fork-type device would likely upset it's characteristics.. detune it.

I didn't think to feel the 880Hz component to see if it was actually vibrating while I had it apart, but maybe it does.

The 3-terminal gizmo is maybe 8x12mm with maybe a 10mm height (metric, how's that? heh). The thing is marked Iwata Japan, and a symbol (((Y))) except the Y looks like a tuning fork.. I just assumed it was a ceramic resonator or something similar. If it hadn't been marked 880, I wouldn't have thought it had any direct relation to the 440Hz that is supposed to be the Cal pitch/note? frequency.

The front panel pot (far right end of front) for the user to set during the Cal setup is about as physically far from the 880 gizmo as it can get.

My days of drawing even partial schematics are essentially over.. I used to do that stuff when I was driven by ambition and inspired by satisfying curiousity.. but anymore, it just eats up countless hours, so I generally avoid it.

I checked the values of a few items near the I/O jacks in case they'd been subjected to a misplaced voltage source or similar mistake/external equipment fault, but that was the extent of actual checking anything other than reading the output freq.

I recall that the 880 gizmo was at one end (by the rotary selector) and the right end appeared to be a combination of I/O jacks, audio circuit for the speaker (faces up thru the top grille) and an area of ICs which seem tied to the circuit that operates the strobing LEDs (which don't actually strobe, but light in sequential groups of 2-3 which will appear to drift left or right, but stop drifting when the note is accurate).

BTW, there is a front panel mic (beside the front pot) for picking up various instrument sounds, or an electronic signal can be input into the unit (electric guitar cable, etc).

I suspect that the 30+ year old components' values have drifted, and a schematic or service manual would be the most practical approach for me.

As I mentioned, I have a tuner that works, but the older TU-120 appears as though it would be handy to use.

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

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Even so-called Standard Kilograms gain something like 1 microgram per year in very carefully controlled environments Holding a guitar tuner to your ear is not normal practise A Mr Iwata was publishing audio technical papers in the 1990s , the same person ?

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I still remember 0.4971 and its significance

Are you referring to the Peter Mitchell paper about the influence of the pocket calculator on teaching math and science? I'd like to read the article, but I'm blocked because I'm not a subscriber.

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Does the questionable unit have an 880 setting? Can you cross- reference the good unit to the questionable unit at any frequency?

There is an 880Hz output, I think, as the chart in the back of the Instructions booklet shows 880 as an A note with the selector switch in the High Octave setting.

It's helpful that you brought this up, and although I'd looked at the chart previously and noted the selections covering frequencies of 130.81 to

996.76, I hadn't made the connection. This appears to be another example of RTFM.

If you've ever heard the radio comedy routine where people call in to ask Mr. Obvious for advice, it's a funny version (although it's all scripted, not real). Mr. Obvious, I think I have a wild animal under my sink.. (questions, replies).. oh, and there's a switch by my sink that doesn't seem to have any purpose, doesn't turn on any lights, (more).

I'd considered connecting the older unit to the newer tuner, but I haven't since I wasn't sure about the output from the Monitor jack of the older unit being an overload for the input of the newer tuner. When I saw the freq readings, I was convinced that the older unit needed repaired.

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

Does the questionable unit have an 880 setting? Can you cross- reference the good unit to the questionable unit at any frequency?