Bought a Marantz PM7200 - dead channel

Discussion in 'Marantz Audio' started by Homer4beer, Oct 8, 2017.

  1. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia

    Done! You are an absolute legend :rockon::banana:
     
  2. mbz

    mbz Well-Known Member

    Messages:
    972
    Location:
    Melbourne, Victoria
    Suggest the following,
    Replace 3276 47k R
    Replace 7258 and 7260 2SA970 (ecb) with KSA992(ecb) hfe matched pair
    Replace 3262 220 R
    Check 3298 10 R, replace if out of spec

    The following is more for the inconsistent measurements around 7256
    Replace 6252 and 6254 with 1N4148
    Replace 7256 (2Sc2240) with KSC1845

    Power up with DBT
     
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  3. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Now found another blown transistor

    7282. :(

    Checking other side....
     
    Last edited: Oct 12, 2017
  4. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    I'm not sure but I think the heat has damaged the board where the transistors on the heat sink are. While taking off the 7282 transistor (type 2SC5242) the trace came off with it :(

    Looking more closely at the other transistors it looks like they are not in great shape?

    [​IMG]
     
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  5. mbz

    mbz Well-Known Member

    Messages:
    972
    Location:
    Melbourne, Victoria
    Yep, it's a mess but probably good news. You've probably found the short. The white thermal compond looks a bit messy, maybe someone has been
    there before. In any case, you need to check virtually all components, tr's, diodes etc... Make up a full parts inventory. Mouse ships free for orders
    greater than AUD60-. UPS delivery to Qld is maybe 3 days. Order monday night, delivered thursday afternoon.
     
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  6. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Yep I'm working my way through the board and ticking off good parts as I go. I'm taking some of the transistors off and checking them properly when I get odd readings.

    Can that trace be fixed? Is it an issue?

    None of the other main transistors are an issue on either side. Just that one so hopefully that was why the right channel wasn't working in the first place.

    The other resistors connected to the bad transistor are ok.
     
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  7. mbz

    mbz Well-Known Member

    Messages:
    972
    Location:
    Melbourne, Victoria
    7282 2SC5198?/2SC5242?.
    Mouser part number 512-2SC5242OTU, $3.50
    RS part number 184-874, $4.90 + GST, 5 day delivery

    7268 ok? 2SC3419(ecb), maybe KSC2690(ecb)? or 2SC4793(bce)
    Mouser 512-KSC2690AYS, $0.63
    RS part number 802-2991 $0.60 + GST in pack of 30 ($17.82+) next day

    You've done well, some people would have stopped after finding the first
    blown transistors. Also, everybody that's picked up a multimeter has
    shorted something out, your not the first. I had a look at the amps specs,
    class A etc,,, looks very respectable, worth saving.
     
  8. mbz

    mbz Well-Known Member

    Messages:
    972
    Location:
    Melbourne, Victoria
    Ypu will probably need a jumper, an off-cut wire from a capacitor or resistor leg. One end soldered to the TR leg, the other
    to a solder blob on the same track, ideally in a straight line. Strip some insulation off some wire and use that as an
    insulation barrier for the jumper.
     
  9. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Yep it's fine. I pulled both channels to make sure. They test as they should. Handy diagram you posted for me :)

    Thanks. I could not have gotten this far without your help! Again, I am very grateful for it. I thought it worth saving also. I do hope we fire this up one day with success :)

    I'm off for a drive to the mountains for a nice brekky with a mate so I'll resume around lunch time.
     
  10. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    I have obtained the 2SC5242 transistor from a local audio group who do repairs for the princely sum of $11.20. Reassembly soon.
     
  11. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    All new components fitted. Methodically checking EVERY component now prior to powering up. About 1/3 of the way through so far.

    Any suspect reading found in any component results in the component being pulled off the board, tested, and reinstalled.

    [​IMG]
     
    Last edited: Oct 13, 2017 at 9:24 AM
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  12. mbz

    mbz Well-Known Member

    Messages:
    972
    Location:
    Melbourne, Victoria
    Great, methodical, systematic work!
     
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  13. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Guys I pulled both of these ceramic capacitors off the board as I couldn't get a reading off them. The ESR meter can't either. How do you test these?

    4.7pF 100V

    [​IMG]
     
  14. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Transistors 7252 and 7254 found fried
     
    Last edited: Oct 14, 2017 at 3:49 AM
  15. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Well after 2 days of testing components I've put it all together using a dim bulb tester. When I powered it on for the first time again it clicked on and off about 3 times with the bulb going dim/bright before it clicking on and the bulb pretty dim.

    I haven't heard the second click of the relay as the amp would send power through to the speakers.

    No sound as tested. All fuctions such as source etc work. Would the amp simply not be getting enough power for the second relay to activate and power the main amp?

    I only have a 50W bulb (stupid power saving means very hard to find anything higher) and I'm sure the main amp uses over 50W.
     
  16. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,509
    Location:
    uk.. the middle bit
    try 2x 50w bulbs in parallel
     
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  17. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Do you think the wattage of the bulb is the problem?
     
  18. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,509
    Location:
    uk.. the middle bit
    yes
     
  19. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Thanks Pete. I'm jumping in the car now to try and find something a bit more substantial, say 75W. Everything on the right channel has now been tested and faulty components replaced. Some things circled that were tested in circuit that were not quite right however from testing similar elsewhere when a leg is pulled and tested the component is correct.

    I'm making a (hopefully safe) assumption that these parts should be good.

    [​IMG]
     
    Last edited: Oct 14, 2017 at 6:14 AM
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  20. Homer4beer

    Homer4beer Active Member

    Messages:
    490
    Location:
    Brisbane - Australia
    Sigh.....I'm pretty gutted right now :( I put in a 72W globe with the same results. If I power up with the "class A" on it powers up with a big click but no secondary click as the power amp comes on and music is played. If I then turn the amp off, turn off the "class A" switch and then power the amp back up I get 3 clicks on/off with the bulb going bright/off bright/off bright/off before it turns back on, stays on, with a dim bulb. If I turn the amp off and back on again WITHOUT using the "Class A" function the amp powers on/off normally with out the secondary click for main amp operation. If I then turn amp off and press class A on, it repeats as before. :wtf:

    So so gutted right now......I honestly do not know what to do now. I haven't checked the left channel however I was in the right channel circuit when I shorted it with the left channel working perfectly well prior to the short. Honestly didn't think I'd have stuffed up the left channel :(

    Could I have? :dunno:
     

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