Expression 2 pedal fault, need schematics please...

[la_panza]

Hello, my expression 2 pedal has stopped working, the unit is 5 year old, I would try to repair it myself since it's not worth sending it to a Service Center from Italy...

I've located a 3-wire strip connector on the KLM-2455B board, this connector carries the EXP.1 and EXP.2 position infotmation as a variable voltage. In my case the voltage ranges from 1.2 to 4 volts for expression 1, but stays at 1.2 volts for expression 2

Both the two optical sensors (RPR237 photo reflectors) that detect the pedal position seem to work, both are emitting infrared light (checked by using a camcorder, IR light is visible to the camcorder). So the problem is restricted to a very precise portion of the circuit, from thw receiving section of the photo reflector to the variable voltage output pin.

The trouble is that this part of the circuit is NOT (or at least i could not find it) IN THE SERVICE MANUAL i DOWNLOADED from

http://www.tonelab.net/files/ToneLabSE_ ... manual.pdf

It may sound ridiculous but this part of the electronics seems the only one that is not reported in the service manual schematics!!

Can someone please help me find the diagram of that section? I will appreciate it a lot!!

thanks in advance

Adolfo

[retrobob]

It appears your expression pedals (1&2) control a BU4052BC multiplexer;
http://pdf1.alldatasheet.com/datasheet-pdf/view/36346/ROHM/BU4052BC.html

See insert below from page #3 of service manual (thank you for the manual, I’ll forward it to Voxman). The pedals send signal to IC1 (4052BC multiplexer) at pins 14 & 15.

Expression 1.jpg (56.09 KiB) Viewed 874 times

[la_panza]

thankyou very much for the schematic, I've seen this circuit in the service manual, but what's missing is the part BEFORE the multiplexer input, I've tested the two 4052 inputs, one changes by movine the pedal, the other one does not, what I'm looking for is the diagram of the electronics starting from the optocoupler's receiver and responsible for the generation of this variable voltage. it should be a very simple electronics... like a transistor or operatinal amplifier between the optocoupler and the 4052 multiplexer, but I can't find it on the diagrams... did you please?

thanks for helping..

[retrobob]

but I can't find it on the diagrams... did you please?

You are correct, that section appears to be missing?

Fortunately, it appears the VC12 pedal uses the same IF sensor (see below), albeit they are controlling a different circuit, but they function the same none the less.

They are using 2 - Photo Reflector RPR 359F (one for each pedal). There should be a calibration potentiometer for each pedal check it.

It appears the IF diodes are wired in series, if one is bad the other won’t work either, ruling that part of the circuit out. Check the input voltage for the photo transistors (pin #3), both pedal photo transistors should read between 3 - 4 DVC (make sure it is not a bad solder connection). Also, there is a possibility that the photo transistor (receiver) is not working or not getting IF reflected back. Check the reflector for dirt or damage, alignment and check the solder connections.

expres2.jpg (21.68 KiB) Viewed 821 times

expres circuit.jpg (68.14 KiB) Viewed 823 times

[la_panza]

Wow!!!!!!!!!!! that's OK!!!! Thanks a LOT !!!!!
We have come to the point. I'll give it a check this evening, back from work, I know the IR emitters are both working, the reflecting strip is clean and correctly positioned, I think I've located the two calibration pots, so there are not so many places left to look for the a trouble... it should be a easy work now... thanks again

Adolfo

[Paragon]

It may be emitting, but it might not be emitting enough to sense it. Check the voltage across the IR LED on both. The below schematic has test points (TP#) not sure if the tonelab has them.
You mentioned that there is a wire connector with the connections from those sensors.. I wonder if you swap connections to make it think the volume pedal is the expression pedal and see if it works as such (not sure if there are any difference except where they connect to the IC chip) just make sure you label the wires so you can put it back to normal or swap the actual part. According to the VC12 schematic below, they should be the same circuits for both pedals.

[tana_satch]

Sorry to post on an this old post but I have the same problem on my Tonelab SE with the expression pedal 2 not working. Not sure what is the problem. Is it too much to ask if you could explain to me what coused yours to malfunction, since I can't take mine anywhere nearby for repairs.