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Crest CA6 Power amp- in protection on one channel

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  • Crest CA6 Power amp- in protection on one channel

    Hello Tech world
    I am new hear to this furum.This Crest amp came in with all the syptoms of a short in channel B. Channel A worked fine with PWR harness of B diabled. Now after bringing it up on the variac with channel A PWR diabled, it showed excesive current being drawn on B. So I decided to swap out channel A in place of B with maintaining A PWR harness disabled. It then showed a short with Channel A (the known good channel). thus leading me to think PWR supply problems with that side. Has anybody seen this problem any leads would be helpful. Thanks.

  • #2
    Most power supply problems will be present even without an output module installed, so check for proper rail voltages that way first.

    Could also be a problem on the preamp board, but that usually only happens after a major fault in an output module so comparison-check all the semiconductors between the working and suspect modules with a meter set to diode-check before doing a lot of module swapping.

    Problems on anything other than the output modules are kind of a PITA to run down on the CA series due to physical construction (as I'm sure you have noticed).

    Probably not the immediate problem - but look for any bulging or leaking main filter caps on the power supply board. Most of the CA amps I saw in recent years had caps that were starting to go. The smaller electrolytic caps on that board also tend to "dry-out" and go high-ESR.


    • #3
      Start at the start, check the main rectifier bridge(s) and filter caps.
      Education is what you're left with after you have forgotten what you have learned.


      • #4
        crest ca6, ca9, ca12, ca18 for reference

        I hope they help
        Attached Files


        • #5

          I have some issue with my amplifier. Maybe some one have amplifier schematic? Thanks.


          • #6
            CA6 & CA18 schematics, to help you fix your units
            Attached Files


            • #7
              I can't open these files. I get message that "Invalid File Specified". If it possible could you send it in me email - . Thank you and best wishes.


              • #8
                Originally posted by IGPOVI View Post
                I can't open these files. I get message that "Invalid File Specified".
                Try these ones.
                Attached Files
                "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey


                • #9
                  Yep now its work. Thank you. I hope I fix this animal


                  • #10
                    CREST CA 18

                    It's harder when I think. My amplifier power up and after protection and clip led goes out the protection relays switching (click, click click). Protection and active led blinking. Switching ratio is two time per second. All power supply voltage is correct. Fan working, The problem is that some smart guy power up this amplifier with 380VAC. After that I change SL32-5R020 and amplifier start work. After half hour idle work two output capacitor blow. I change it and now I have situation that amplifier switching between active and protection position.

                    Maybe some one have idea where is problem? Yesterday I check a lot of components I can't finde issue.


                    • #11
                      Hello please some one tell me where should be connected two black pair (T17, T18, T19, T20) GND cables from PSU board. To chassis??


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