Just a note to say that I bought one of these prescaler boards for my CNT-81. One problem is the way the board mounts in the CNT-81 the "in" connector is toward the back instead of toward the front like some of the other counters and I had to make a longer input cable. Pawel does now know this and maybe a different cable can be included for these counters in case you can't make one. Be sure to check on this so there aren't any surprises.
When I put the prescaler board in and connected a signal it didn't divide properly. After getting the service manual and checking the schematic I found the problem was the way the motherboard was set up to detect which prescaler was installed. There are resistors of 10K, 20K, and 40K going from the 3 ID pins (16,14,and 12) to a common 100K to ground. On Pawel's board for the PM6681/ CNT-81 pin 16 is jumpered high to +5 to select the correct divisor ratio with pins 14 and 12 not connected so they should be low. Unfortunately the resistors on the motherboard feed the +5VDC from pin 16 back through the resistors to pins 14 and 12 so all 3 pins are high and this screws up the ratio. If you have the service manual go to the schematic "Logic Circuits, unit 1 sheet 2(6)" and look at grid C 11 to see what I mean. I had to tie pin 14 and pin 12 low to make the prescaler work as it should & it does work great! I hate to think what an OEM board would cost so this is a really good deal and I recommend it. -Arthur _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
