Klee calibration problem

[prgdeltablues]

Got my Klee almost working, just stuck on the calibration. It's passed all the bring-up procedure tests. I can adjust R43 to get close to 0V (about 0.1mV) at U9 Pin 1, but can't get U8 pin 1 anywhere near 0V. Adjusting R42 moves it from about -190mV to -150mV. On R42, I've got +11.6V on one end pin, and -11.6V on the other, (running off +/- 12V supply), but the centre pin seems stuck on 8.4V, no matter how I adjust the trimmer. Tried swapping out U8, but no difference. I can still adjust R34 etc to get the correct values at U8 Pin 1 (negative, which I think is correct, although on p.112 of Build 6 documentation they are listed as positive voltages) when the Programming pot 1 is turned fully clockwise, but fully anticlockwise is not 0V, which presumably will upset the tuning.

Any thoughts before I unsolder R42 and try another trimpot, which is my next guess (Actually, trying it without a trimpot might be worth doing?)

thanks

Peter

[Scott Stites]

Hey Peter,

It is strange that you can't get the center pin of the trimpot to alter the voltage - the center pin of that trim pot should swing from positive rail, through 0V to the negative rail through the full adjustment range of the trimpot.

Before you go after it, though, you might try removing any possible voltage source from the input of U8. If you unplug J5 from the Analog Board, this will remove any offset that could possibly be coming from the CMOS switches. This would leave the ground reference from the programming pots intact, but remove any possible erroneous offset from that section of the circuit. If you still can't adjust to zero volts (or close to thereof), give unplugging J7 a whirl. That removes any input from the programming pots themselves.

If the offset is still there, I would look at replacing that trim.

Alternatively, you can lift the end of R44 that's connected to Pin 2 of U8; if adjusting the trimpot from one end to other still doesn't move from + through 0 to - on the center pin of the trimpot, then there can be no explanation other than the trimpot is somehow compromised and needs replaced.

Cheers,
Scott

[prgdeltablues]

Thanks for those suggestions Scott. Off for a couple of days now (late evening here) but will try them on my return and post the results.

Peter

[prgdeltablues]

Problem solved and Klee working wonderfully! Turned out the trim pot was busted. This is one amazing sequencer. Now I need to build more modules.

Peter