Boss TU-2 tuner voltage...

[slideman82]

Can anyone tell me IC2's pin 8 voltage? Mine's 0.51V... and the tuner it's not working.

Thanks for helping!

[Ice-9]

Can you post a picture of the PCB and or the chip id number.

[slideman82]

The schematic is here http://www.synfo.nl/servicemanuals/Boss/TU-2_SERVICE_NOTES.pdf and IC2 is a dual op amp M5218L. Pin 8 is main voltage. 

[slacker]

On mine, Pin 8 measures 0.52 volts when the pedal is in bypass and 4.99 volts when it's on. Looks like Q4 is a switch that cuts the power in bypass. When it's on all the other pins of IC2 are about 3 volts except pin 4 which is ground. Could be as simple as a bad footswitch.

[slideman82]

Great data, thanks! But mine doesn't even turn on! I'll check for bypass circuitry...

[Ice-9]

Having just looked at the schematic I would start by checking if you have the correct voltage on the collector and the emitter of Q1 which should be 8.4v and 7.7v. Then check the voltage on 1C1 pin 2 and pin 3 which is a 5v regulator so should have 8.4v in an and 5v out.

[slideman82]

I think I've measured those voltages... I'll tell you later what do I have!

[slideman82]

Having just looked at the schematic I would start by checking if you have the correct voltage on the collector and the emitter of Q1 which should be 8.4v and 7.7v. Then check the voltage on 1C1 pin 2 and pin 3 which is a 5v regulator so should have 8.4v in an and 5v out.

With a 9.43V supply I measured 8.76V at Q1's collector and 8.1V at its emitter. 5V regulator is working ok, and there's no change at IC2's pin 8 when footswitch is enganged... and footswitch is morking right.

[slideman82]

morking = working! 0.3V at Q3's collector... and 0.61V at its base... it's supposed to be like that? I don't like it...

If there's a problem with IC3 (that huge bug... looks like a DSP) I'm scr*wed!

[Ice-9]

morking = working! 0.3V at Q3's collector... and 0.61V at its base... it's supposed to be like that? I don't like it...

If there's a problem with IC3 (that huge bug... looks like a DSP) I'm scr*wed!

Measure the voltage at Q3 collector then press the bypass switch see if the voltage changes. also do the same at pin 34 of IC3 , datasheet is available for that chip.
Also does the effect/bypass led come on when you press the footswitch ?

http://www.datasheetcatalog.org/datasheet/MitsubishiElectricCorporation/mXvrzxy.pdf

[slideman82]

No, led isn't doing anything... I'll check that!

[PRR]

> it's not working.

Not enough info. LED? Bypass? Tuner?

If ALL that stuff ain't working, the only practical repairs are SW3 and its connector, R49 C27 switch filter, and the connectors between the several boards.

> If there's a problem with IC3 ...I'm scr*wed!

True, but that's very unlikely.

> looks like a DSP

It isn't anywhere near as smart or fast as a DSP. It's more like a microwave oven controller. It can check pins, count backward from 9:99, trigger lights/relays. Smarter than a 4040 but not as smart as an 8080 (the way-way-way distant ancestor of the PC).

It seems to take overdriven signal at a Counter input. Code checks this counter at known intervals of time and converts to pitch. For extra smarts, if you hold some buttons, it reads-out its ROM-Version number. With different code it could run a robot to insert rivets, unless a safety-switch were hit. Pretty dumb and slow.

[slideman82]

Audio signal is ok, but tuner is not working... no led at all, even bypass led.