Announcement

Collapse
No announcement yet.

MXR Dyna Comp repair. Is this the right schematic?

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

  • MXR Dyna Comp repair. Is this the right schematic?

    Im trying to fix my sons MXR Dyna Comp. It has a green PCB but I'm not sure about the year. 05-16-01 printed on PCB, so maybe 2001??
    I found a schematic on electrosmash.com but Im not sure its the correct one for my pcb (see below )

    I only have a bodgers knowledge of electronics, just enough to be dangerous to myself

    The (470k) sensitivity pot was dodgy so i removed it, took it apart, cleaned the wipers, tested resistance and put it back together.

    I've re-soldered the pot but the box doesnt work at all any more. Bypass works fine, guitar feeds into amp, but when I push the button the LED on but no sound output. The problem occurrs with battery and transformer (seperately).

    Cables to amp and guiar are correct input/outputlights.

    I unsoldered the pot again to check the board, when I put an ohmmeter on the top pin where the pot should be (it is marked tp1) I cannot get continuity anywhere else on the board.

    The scheamtic shows the pot connecting to R17 and Q5.

    R17 = continuity good to the middle and lower pin of the pot (which are bridged on the PCB).

    ​Q5 = open circuit on all legs to the upper pin of the pot (tp1) -but I dont see a broken trace.

    Is Q5 the correct transistor for the other side of the pot for all schematic versions of the mxr dyna comp? (or mine?)

    If it is, then I can just run a jumper wire. I recon I might have messed up a trace when I de-soldered the pot originally. If not, if someone can tell me where the pot trace leads to it would be much appreciated.

    any help appreciated:

    many thanks​

    Click image for larger version

Name:	schematicmxr.jpg
Views:	308
Size:	86.9 KB
ID:	977174

  • #2
    The schematic is at least incomplete as it doesn't show the LED or the bypass wiring.

    I assume the bypass is passive like with older versions, so it will always work even if the circuit is defective.

    If your board shows transistor numbers these might deviate from the schematic numbers. E.g. I have an old factory schematic from 1976 where Q5 is labelled Q1.
    So you need to trace the board to see which transistor actually connects to the sensitivity pot.

    Did the effect work before you disconnected the sensitivity pot?
    - Own Opinions Only -

    Comment


    • #3
      Originally posted by Helmholtz View Post
      The schematic is at least incomplete as it doesn't show the LED or the bypass wiring.

      Did the effect work before you disconnected the sensitivity pot?
      yes, it worked before
      the board pn is 04003001523

      I just I tried to upload some photos of my board but the size limit kicked in
      I tied to trace the trace but its difficult because its silkscreened over in places, but it looks like that pot is going to Q3. if so, Ive got the wrong schematic...

      Last edited by paynec; 01-30-2023, 03:57 PM.

      Comment


      • #4
        Ok, its fixed. Broken trace. Soldered jumper wire from RV2 to collector?? of Q3 and it worked.
        Definitely not the correct schematic in the pic above.

        Comment

        Working...
        X