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Yet Another 2275 Restore

Discussion in 'Marantz Audio' started by jberger, Jun 27, 2018.

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  1. jberger

    jberger AK Subscriber Subscriber

    Messages:
    2,108
    Location:
    Long Beach, CA
    So, I picked this up last weekend, with the owner saying the usual "worked fine that last time I used it", but expecting otherwise.

    So far, I've found:

    Power button has a broken stud; will need to replace switch
    Tape monitor circuits keep playing source when depressed
    Volume control cuts out in weird ways*, and can be jiggled in position. Going to clean and hit all of the solder joints first, then tighten up and test again.
    Even though there are no jumpers in the Pre-Out/Main In jacks, the signal passes thru. Are there internal jumpers that go into place when there are no cables inserted?

    * Left channel has low channel and no bass, but wiggling it into the right position gets full sound back

    Plans:

    Full cleaning of switches, controls, and connectors
    Replace power supply switch
    Review volume control, clean resolder and test or replace
    Relamp and replace vellum
    Check bias and DC offset

    Short of a full recap, what else might I be missing?
     

     

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  2. Steven Tate

    Steven Tate AK Subscriber Subscriber

    Messages:
    2,956
    Location:
    N. Richland Hills, TX
    Yes, the 2275 has internal jumpers. I see it's in your plan, but if you haven't already done a thorough cleaning of pots and switches with Deoxit (or equivalent), I would do that first. several of your symptoms could be related to dirty controls.
     
  3. jberger

    jberger AK Subscriber Subscriber

    Messages:
    2,108
    Location:
    Long Beach, CA
    The volume control concerns me, because it feels like the shaft is loose in the control, and at certain angles it makes contact, and others only partial. I haven't taken the cover off, though; it could just be a loose holding nut.
     
  4. bryans12v

    bryans12v Marantz Junkie Subscriber

    Messages:
    1,376
    Location:
    Hudson Valley, NY
    Make sure the outputs have good thermal compound applied. Just a thin layer of non-conductive thermal compound will do. I apply it to the transistor first, lay the mica pad on top and press out the air pockets with my fingers. Then apply the compound the dry side of the mica and install.

    I would replace the 2sc458s if they're present on the phone board.

    I would clean the tuning capacitor. Especially where the springs touch the brass bar. Only non residue electrical cleaners here. I use Wurth circuit board cleaner.

    Switches and pots always deserve two or more cleanings a day or two apart, especially if it's known they're causing issues. This is only if you flood clean and not disassemble them. Don't forget to clean the headphone jack and rca contacts. Most just clean the outer rings of rca jacks which are only grounds and forget the center pin is the signal!
     
  5. bryans12v

    bryans12v Marantz Junkie Subscriber

    Messages:
    1,376
    Location:
    Hudson Valley, NY

    A little axial play isn't out of the ordinary. But if its excessive (1mm+) I would be concerned. After you clean it up a bit it can be easily tested both in and out of circuit.
     
  6. jberger

    jberger AK Subscriber Subscriber

    Messages:
    2,108
    Location:
    Long Beach, CA
    I got it onto the bench last night, and saw some weirdness. The looseness on the volume control was just a loose panel nut, and I've given it 4 or 5 rounds of DeOxit.

    Here's the weird: I run a signal generator into it, and it passes a nice symetrical waveform all the way up to clipping on top and bottom. However, when I lower the volume pot from this level fairly quickly, the top half of the waveform collapses, for lack of a better term, and sometimes it activates the protection circuit momentarily. I'm going to check DC offset and bias tonight, and another round of cleaning, and see if I have the same problem by lowering the signal generator level (instead of the volume control).

    Other ideas?
     

     

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  7. jberger

    jberger AK Subscriber Subscriber

    Messages:
    2,108
    Location:
    Long Beach, CA
    OK, I got some time last night. The B+ is reading a bit high; it was 44 v when I started, and I could only get it down to approximately 38 v. DC offset was right at 0, but haven't tested bias yet.
     
  8. highvoltage_

    highvoltage_ Addicted Member

    Messages:
    5,144
    Yes, the 2275 service manual lists H405 and H406 as part number 2SC458.
     

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