Author Topic: CP4500 Threshold doesn't work

March 16, 2023, 11:07:45 AM
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Chiller

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Hello,
today the Threshold Poti of my CP4500 stopped working. I can turn it as usual, but it has no effect on the signal. Yesterday everything was fine, so I have no idea, why it stopped working. Any solutions?
Thank you!:D

March 16, 2023, 12:01:10 PM
Reply #1

JPK

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It could be a pot failure or a connection failure between pot and circuit.
The pot voltage can be checked on TP13 (against 0V)
Check step 1.4 here.
JPK

March 17, 2023, 09:30:21 AM
Reply #2

Chiller

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Thanks, I've checked it, and it's just 0.45 to 0.55 VDC, when I turn the threshold. The solder points are good... is there another way to check out if it is the pot?
Thank you

March 20, 2023, 09:24:12 AM
Reply #3

JPK

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R95-left pin should go from +12V to -12V when turning the threshold pot.
JPK

March 20, 2023, 12:15:10 PM
Reply #4

Chiller

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Yes, that works fine. So the pot is working.

March 21, 2023, 09:00:55 AM
Reply #5

JPK

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So the issue is around U21.
Check solder joints and values of R95...R99, U21.
Try swapping U21 with another OPA2134.
JPK

March 22, 2023, 09:42:17 AM
Reply #6

Chiller

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Hi JPK,

I fixed it! Thank you so much for your help. I renewed all solder joints around that area but I think it was a slightly deformed pin of the U21.
Thanks again and have a good day 8):D

March 22, 2023, 09:50:40 AM
Reply #7

JPK

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