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CP500 Signal Path fault

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  • CP500 Signal Path fault

    I have a CP500 that won't come on. I purchased it over a while ago, and it did work then, but it's sat in a cupboard for over a year, and when I came to switch it on today, it gave me the message:

    The following fault cannot be cleared, so the system will remain in Bypass:
    Cat No.675 Card / J12
    The two 675A cards in the left-ish positions (Matrix Decoder and Equaliser) have their fault LEDs lit up.

    I swapped the 675A in the rightmost position (AC3-Decoder) - which does not have the fault LED on - with one of the ones that does, and the previously working card now has the fault LED on, and and the that previously had have the fault LED on doesn't. I tried this a few times with the same results, ie. cards in the two leftmost positions always have their fault LEDs on, and the one in the rightmost position does not.

    I tried reseating all the cards in the machine, and blowing dust out, and once I'd done this I'm presented with a different error message (although the fault LEDs remain the same):

    The following fault cannot be cleared, so the system will remain in Bypass:
    CP500 Signal Path

    I have a box of spare cards (consisting of a 222sr/a, 662a, 661, 670, 671, 673a, 675, 681, 682, 685) that I got when I purchased it (all untested previously by me), and I tried swapping those cards out one by one, but I always get the same error message as before (CP500 Signal Path).

    Anyone have any ideas, or things that I can try? The CP500 has version 1.65EX software installed. Note that I'm just an enthusiast, not in the industry or a repair tech, so I could be making a basic mistake, and may need things explained in basic terms (although I have an understanding of basic electronics).

  • #2
    Check out this service bulletin in the F-T Warehouse:
    Check the serial numbers on your boards to see if they are affected by the issue in this bulletin.

    Another possibility is a power supply issue, something that is Dolby's Achilles Heel in otherwise robust products. For that you will need to have the equipment and skills to measure the various power supply outputs to see if the voltages are within range. IIRC most of the CP-500 power supplies are repairable. Often a replacement of the electrolytic caps will fix the issue.


    • #3
      I wish I'd seen that service bulletin earlier, when it was giving the Cat No.675 Card error, and not the CP500 Signal Path error it's now giving me after I re-seated the cards. Although, the revision numbers of the two 675 cards are 5431 and 7654 respectively, so I don't think they should be affected?

      Is there a way to get more useful error info other than CP500 Signal Path, such as what cards it thinks have faults, etc.? I notice that it's the same error even when the two 675 cards aren't installed, so I fear that when I re-seated the cards and blew the dust out, I might have done some damage.

      I measured the voltages on the test points on cat 670, and they all seem to be correct (5v, 15v, -15v). I'm just using a cheap-o voltmeter though, not a scope, so there could be some fluctuation that I'm not seeing.


      • #4
        I'm pleased to report that I've managed to get it working! Not really sure how tbh, I just took all the cards out and then back in again (which I'd done yesterday, but figured that it was worth another shot), and it came on first time, no issues. I thought it might be a fluke, but after power cycling it multiple times it seems to be okay. Odd, but for the moment, I'm not complaining!

        I would still be curious to know if there's a debug mode, or any way to get more info on what CP500 Signal Path means, so that if it appears again in the future, I have something to try - so if you have advice, please let me know!

        And thanks Tony for the help!


        • #5
          Is it possible any of the cards were in upside down? It is possible to accomplish this feat on some of the boards and you would certainly not be the first or maybe the last if truth be told.
          Last edited by Sam Chavez; 03-24-2020, 01:19 AM.


          • #6
            Aren't there two of those cards in each 500? Try swapping them and see if the error you were getting changes. Those were the most often replaced cards in the 500's that I serviced. Sam most likely has replacements.