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Long shot-anyone familiar w/ the Poly AT on a CS80?

Posted: Tue Jul 26, 2016 7:31 pm
by rjd2
So I am trying to get the AT on a CS80 working. It is currently pegged at maximum value, in terms of it's functioning via the control panel. I have the schems, but my issue is that I don't understand what voltage I SHOULD be seeing into/out of the TSB/TRG boards. I get no play in voltage on the input/output pins of the opamps on these boards when activating the aftertouch. Can anyone describe the directional flow of the AT function, in terms of what readings i should be seeing when activated? Thanks if so.

Re: Long shot-anyone familiar w/ the Poly AT on a CS80?

Posted: Tue Jul 26, 2016 9:23 pm
by rhino
Never had a CS80, but read this. Sounds like your next move.

http://www.oldcrows.net/~oldcrow/synth/tips.txt

Re: Long shot-anyone familiar w/ the Poly AT on a CS80?

Posted: Tue Jul 26, 2016 9:30 pm
by synthchaser
Perhaps the sensor is dead, test it with a multimeter.

Re: Long shot-anyone familiar w/ the Poly AT on a CS80?

Posted: Tue Jul 26, 2016 11:05 pm
by rhino
Looking at the schematics http://therogoffs.com/cs80/manuals/CS80 ... iagram.jpg
there is no aftertouch strip as in most newer synths. There is a seperate resistive sensor on each key. The board with all the ICs mentioned in the above article is an overly complex 'scanner' that detects afterouch and routes the correct AT signal to the correct voice.

Re: Long shot-anyone familiar w/ the Poly AT on a CS80?

Posted: Wed Jul 27, 2016 12:52 am
by rjd2
yup, all 5 lower boards have been fully rebuilt, as has the PSU, and a number of the upper boards.

yea, as rhino said, it's an individual sensor for each key. at the keyboard pcb, there is no play in voltage, only a slight play in impedance, on pin #3. this is, as best i can tell, normal.

basically, i need to know what type of voltage or impedance behavior i WANT to see, before i can trace it's origin. my read on the schematics doesn't make this clear. thanks.

Re: Long shot-anyone familiar w/ the Poly AT on a CS80?

Posted: Wed Jul 27, 2016 5:27 am
by rhino
Each keys aftertouch resistor is like a pot: a sliding contact on a resistive element. The tops and bottoms of all AT resistors are tied to +15 and -15 volts. I cannot find the values right now but I'd say the AT signal on each key should swing about +5 to -5 volts as the key is pressed (maybe plus to minus, don't know). Chesk for the +/-15 volts on the two busses.

Re: Long shot-anyone familiar w/ the Poly AT on a CS80?

Posted: Wed Jul 27, 2016 5:15 pm
by rjd2
Great-thanks Rhino. That is roughly what i would expect to see; I'll sniff around further at the actual keyboard pcb, and see what i can get readings on.