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Channels 5-8 not working


Dave Pursel
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Can anyone tell me what circuitry is in common such that channels 5-8 will not function? Newly assembled and all works with exception of 5-8. All components have been checked for proper insertion. Had a fellow worker who works on the bench all day go over my soldering technique from 20 years ago. Read a lot of forum postings but can't seem to come up with something I should try without understanding how 1-8 versus 9-16 function as it pertains to U4 / U5 and possibly U2. Resistor Pack R16 has entered my mind but it's hard to believe I would have fried the whole thing as it pertains to the 4 channels unless it was bad from the beginning. Tx.

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Only half of the flip flop relates to those channels. The CPU lines to the flip flop for those four are shared with four to the other side... The Resistor pack is the only thing that is in common, but not shared with other channels. I don't think it is likely that all four resistors have failed at the same time, but it is possible that it is the wrong value.. Too high a value, and the LEDs in the opto isolators won't light enough to trigger the trigger triac..

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Thanks to all for replying. cmoore60, I believe you hit the nail on the head. I thought the 5 resistor paks were all the same. I just pulled the manual off the website and see their is a difference between them. I left my unit at work but I'm guessing that I swapped one of the 470's for the 4.7. Thanks.

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