Announcement

Collapse
No announcement yet.

Audio dynamics ca-2000e turn on problem

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Audio dynamics ca-2000e turn on problem

    So I have found no schematic at all for this integrated amp. It draws normal current, but rises from .3A to .5A over the course of 7 minutes or so, but has no output. The output transistors measure OK, and I don't hear the relays click on so I assume that is likely the issue.
    Output jacks show little to no DC on them.
    There is also no output from the headphone jack
    Getting at the solder side of the board is not easy, the board has to come out of the chassis. It is hardwired in several places.
    This is a view of the relays which have a strange small circuit board glued to the top of them
    Click image for larger version

Name:	20200308_222726.jpg
Views:	1
Size:	3.37 MB
ID:	876402

    Could someone explain how the protection circuits usually work in most units to help me find out why the relays are not clicking in?
    Thanks!

  • #2
    Well, if there are speaker relays, they are not closing, so if the amp is making DC it wouldn't reach the speaker connectors. See if one of the channels has DC on the emitters of the power stage. Either on the transistors themselves or on the white emitter resistors in front of them. I see a trim pot lower left, is it a bias control? And another for the other channel? That might need adjusting a trifle cooler.
    Education is what you're left with after you have forgotten what you have learned.

    Comment


    • #3
      I found -50VDC on the emitters of one channel.
      -49VDC on base
      56VDC on collector
      Any suggestions as to where to look for the cause is appreciated
      Thanks
      Last edited by Bigdrums; 03-09-2020, 09:02 PM.

      Comment


      • #4
        Update: Comparing the behavior of voltages from the left side to right side amps, I found a curious thing or two. Each of the transistors in the output stage connects to a 3-wire jumper to the main board, so by unplugging them I can disconnect the entire output stage. Measuring the voltages on power up at the base terminal of the 2SC3281's shows -55V until the protection relays kick in. The -55V becomes +55V. The collector is +55V and stays steady while the Emitter is and stays approx. 0V. Same thing happens with the complimentary 2SA1302's except the collector is at -55 instead of +55V. But the base starts at -55v and flips to +55v. I should mention there is a 3rd relay involved here.
        Problem is on the bad right amp the base stays at -55V and doesn't change to +55V like the left side does.
        Can anyone shed some light on what is going on here?

        Comment


        • #5
          Maybe a bad relay? Sounds like they are engaging the supply rails and one of them is not doing it's job?
          Compare the voltages on the relay coils between the bad ch. and the good one.
          If the coil is getting it's voltage and the relay doesn't engage, it's bad.
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


          Comment

          Working...
          X