2220 Bad Channel, Odd Functionality

Discussion in 'Marantz Audio' started by W.T. Holt, Aug 10, 2017.

  1. W.T. Holt

    W.T. Holt Member

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    Hello good people,

    Im working on a 2220 right now. Its in good nick, but the left channel is almost nonexistent. Only when the volume is maxed out to you begin to hear any sound, and when it does come through the signal is quiet and extremely distorted. It sounds like an output transistor issue but I used a DBT, and its not lighting up.

    So far I have done a good clean of the knobs and switches with deoxit, done a quick double check of the output transistors with my MM (Done in circuit, measurements were the same for each) and checked/adjusted the power amp bias (its bang on now).

    So now I'm starting the search for other possible causes of my woes. Please help me out with your thoughts and guidance!
     
  2. Steven Tate

    Steven Tate AK Subscriber Subscriber

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    Just to verify -- it's the same symptoms on all inputs?
     
  3. W.T. Holt

    W.T. Holt Member

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    Yup same problems on all inputs.
     
  4. willyrover

    willyrover Super Member

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    First, get the schematic at hifiengine.com

    Verify that you have signal getting through to J701 on the amp board for right channel and J702 for the left channel. (These pins should be along the top edge of the amplifier board.)

    If you're getting clean signal here, problem must be in the amp board.
     
  5. W.T. Holt

    W.T. Holt Member

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    Thanks, I have the service manual. Could you please advise me on how to go about checking for clean signal at J701 and J702?
     
  6. willyrover

    willyrover Super Member

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    Do you have a scope?

    If not, I would run a mono signal such as a 1kHz sine wave into the AUX input. There are apps that will do this or make a CD with several minutes of various test tones. No speakers need to be connected. Connect your negative meter lead to chassis and probe with positive lead for AC voltage at J701 (good channel) and compare it to AC voltage at J702 (bad channel). Both should have similar voltage and the voltage should increase and decrease as you adjust the volume control.

    If voltage on J702 and J701 are similar, that tells us signal is getting through the preamp on both channels.

    If there is little voltage on J702, signal is getting lost in the preamp.
     
  7. W.T. Holt

    W.T. Holt Member

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    nope no scope, should have mentioned that, sorry. The Multi-meter test you outlined seems to be doing its job though - both test points measure within 5mVAC of each other.

    Looks like I'll be digging into amp board... any thought on what to begin with there? The caps and transistors probably all need attention but if I redo the left side entirely I feel like I should do the right side as well for the sake of balance.
     
  8. willyrover

    willyrover Super Member

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    Since voltages are the same at J701 and J702 (I assume somewhere around 1-5 volts that varies with the volume control?), we can assume the signal is getting that far.

    What I would do next...

    1. Plug in headphones. If both channels work, the problem is in the speaker selector switch. If left channel is still dead on headphones, problem is in likely in the amp board.

    2. Using the same setup as in post #6 measure voltage immediately after R701 and compare to R702. They should be lower voltage but still similar to each other. Then measure voltage immediately after C701 and C702 and compare again.


    Screen Shot 2017-08-12 at 6.33.21 PM.png

    (I edited this next part to reflect petehall347's much simpler suggestion in the next post)


    3.If voltages seem ok I'd want to confirm a fault in the amp board before going any further. Connect a jumper between J701 and J702 and check if you get sound on both channels.
     
    Last edited: Aug 12, 2017
  9. petehall347

    petehall347 the brandy coffee man Subscriber

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    or simply jump j701 to j702 . if no sound then i would be first checking collector voltages at the output transistors .
     
  10. W.T. Holt

    W.T. Holt Member

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    Thanks for helping me out guys!

    With headphones plugged fully into the jack I get no signal on the right and the same deteriorated signal on the left. If I back the headphone plug out a bit and get it in just the right position I can get the same "Stereo Picture" that I get through speakers... poor & distorted sound on the left, fine sound on the right.

    Testing voltage at the resistors and capacitors you mentioned resulted in similar reading on both sides of the amp. Interestingly though, the values were virtually the same at all the test point on one side. Roughly 60mVAC with the volume at noon, boosting to about 1.8VAC with the volume maxed out. Just want to take a sec to double check with you that I should be measuring AC voltage not DC.

    Moving on... With J701 and J702 jumpered - when the volume is maxed and with the balance knob all the way to the Left, all I hear is clean sound from the right speaker. As I shift the balance toward the right the overall volume rises and the distorted sound starts to come back in the left speakers.

    Results still seem to be pointing toward an issue downstream in the poweramp?
     
  11. petehall347

    petehall347 the brandy coffee man Subscriber

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    to make this less confusing keep those points jumpered . plug in left input rca only . then right rca only .
     
  12. willyrover

    willyrover Super Member

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    Those results tell us that the fault must be on the amp board since feeding the right channel amp with left channel preamp is giving good sound. And yes, so far we have been measuring AC since the audio signal is AC.

    Next steps...

    1. Check/test C004 and C005 output capacitors 2200uF 50V. It looks like they are filtering 23VDC on the output J715/J716.

    2. Verify that output transistors are good.

    3. Verify that H005 and H006 (double diodes attached to heatsink) are good.

    4. Start checking voltages along the bottom edge of the amp board . Most are in pairs. e.g. J711 and J712. Those should be DC voltages and measured with volume control all the way down. Make a list of the voltages, compare them to the values on the schematic. Also note any differences between voltages on the working and non-working channel.
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

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    just to make a note .
    the schematic has at least one error i just noticed ..H001 collector should be connected to same place as H004 collector . the rail supply voltage . which will be about 46v .
     
  14. willyrover

    willyrover Super Member

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    Like this?

    Screen Shot 2017-08-13 at 2.31.57 PM.png
     
  15. petehall347

    petehall347 the brandy coffee man Subscriber

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    yes thats it ... no way it can work without it .
     
  16. W.T. Holt

    W.T. Holt Member

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    You guys rule! I wont be able to get back into this until mid week, but ill make sure to update when I do.
     
  17. W.T. Holt

    W.T. Holt Member

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    Took me a bit longer than expected to get back into this receiver, but I just finished with the tests suggested. The actual measurements are attached in a photo, but here are a few generalizations about my findings along with the methods used to find them:

    1) C004 & C005 measured similarly to each other, but higher than their marked value by roughly 1200uF. For this test I pulled the wire from one of the leads and then tested for capacitance with my DMM with the unit powered off.

    2) H004 & H005 also measured similarly to each other and each exhibited a voltage drop within the range I imagine you should expect to see from a double diode (1.3-1.5 V). For this test I used the diode function on my DMM and tested the diode in both directions with the unit powered off.

    3) One of my first test on this unit was of the output transistors. H001 - H005 all tested "good" to me meaning they all responded similarly when subjected to the same testing. My usual method for finding a bad transistor involves comparing them to one another and singling out the faulty one (or ones) by comparison to healthy ones. In this Marantz both the right (healthy) and left (faulty) side transistors seemed the same. For this type of test I use the process out lined by Echowars here. In this case the test was done in circuit because these transistors are a massive pain to remove. If I should redo this test with a better method I will.

    4) Testing voltages on the pins along the bottom of the board showed that the right side (even numbered) pins were slightly lower than the corresponding left side pins but that both sides were consistently off compared to the expected value found in the schematic. Interestingly, or perhaps frighteningly, the values actually all appear to be virtually the same. For this test I connected the negative lead of my DMM to the amp's chassis and the positive lead to the pin I wished to check with the amp on and the volume all the way down, balance in center, no speakers selected.

    So with all this new info, where to we stand. To me it doesn't seem like any conclusive data but I'm very interested to hear what you all have to say. thanks again for all your continued support!


    IMG_0971.JPG
     
  18. willyrover

    willyrover Super Member

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    Well, someone else will probably have to take over at this point - not sure the best way to proceed without a scope.

    You could test/check the transistors H701-H712 on the bad channel.

    There are also several other voltage test points on the schematic that you could probe.
     
  19. petehall347

    petehall347 the brandy coffee man Subscriber

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    back to post 11 ..still trying determine something.
     

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