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  1. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    Noise stopped suddenly while I was across the room. TR201 (without noise) B: 18.0mV C: -36.8V E: 599mV C: -36.9V B: 21.4mV I think it's time to start thinking outside of the box. I know that things like ceramic caps rarely fail, but I feel like I've already replaced the stuff that commonly...
  2. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    I've never claimed to be a professional with a soldering iron. I just wanted to lift the legs and put them back. The problem with this unit existed long before I even warmed up my iron, though. Right now, I can't get the noise to go away, but here are the readings I was able to get from TR202...
  3. KilgoreCemetery

    Sherwood AM-7040 No Left Channel

    After doing some research, I found that the original transistors are still available, but on ebay. I normally steer clear of websites like that for discrete components, but I've looked at over a dozen different P-Channel MOSFETs on Digikey, and they all have the same pinout. Only the 2SJ162 and...
  4. KilgoreCemetery

    Sherwood AM-7040 No Left Channel

    I suppose, but if at all possible, I'd like to find proper replacements. Here's the info for the P-Channel. N-Channel will be posted soon as well. The original P-Channel is a 2SJ162 Vdss = 160V Drive = 10V Continuous Drain = 7A (Ta) Pinout: G S D Replacement P-Channel is an IRFP9240 Vdss =...
  5. KilgoreCemetery

    Sherwood AM-7040 No Left Channel

    Ack!! Why would they do such a thing? I mean, I assume that the data sheet I was able to find for the originals is accurate, but I guess I didn't realize that manufacturers swapped pins around Thanks, kellys_eye. Good catch. So I guess now my question is where am I going to find the CORRECT...
  6. KilgoreCemetery

    Sherwood AM-7040 No Left Channel

    :eek: Are they really? Checking now
  7. KilgoreCemetery

    Sherwood AM-7040 No Left Channel

    I do have a schematic/Service Manual that I picked up from HiFiEngine, but the file was too big to upload here. I'll try a 40W bulb once I get everything reassembled. My understanding of this particular elastomer was that it is supposed to be highly thermally conductive and fill in tiny gaps...
  8. KilgoreCemetery

    Sherwood AM-7040 No Left Channel

    I've been working on this integrated amplifier with no left channel and it's turning in to a real head-scratcher. I know that when I first got it that the left channel fuse was blown (250V, 7A, ceramic, Slo blow), so I checked the MOSFETs and found one of the P-Channel, 2SJ162's was burnt...
  9. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    After several hours of listening, the static has returned in spurts. *sigh*
  10. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    I'd much rather pinpoint the problem too, but I'm not sure how to make the symptoms reappear. I've messed with all the knobs and switches and used a plastic tool to tap and prod components inside the unit. So far the noise is still absent. I did clean up the board as you requested, Dorke, and...
  11. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    The noise has been very intermittent this morning. An average of 20 seconds on and 20 seconds off probably isn't too far from the truth. Dorke: While the noise is gone, I get near identical voltages when comparing the A798s. When the noise is present, all four collector pins have about...
  12. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    ...aaaand it's back. Edd: I CAN hear the noise at Yellow A. It is much quieter than most of the places I've probed. Jumpering from Yellow A to Red A does allow me to hear the noise from both spots. I can confirm that the balance knob doesn't affect the volume or appearance of the noise. I'll be...
  13. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    Thanks for your patience, guys. I have tested A through X from your picture, Edd, and except for one of the yellow electrolytic caps (the one just above "D2-3" on the circuit board), all of the yellow letters have the noise and none of the red ones have it. Today, I'm not hearing any noise on A...
  14. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    You crack me up Edd. However, while it is quieter, the noise can still be heard on the yellow A. Does this mean I've been barking up the wrong circuit board? As for going through the letters, I've previously checked the yellow B, C, D, and F, and can confirm that the noise is there. I'll try to...
  15. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    I tried cleaning the contacts on the relay just to be sure and I had it under a little better light this time. I've included a picture of one side, but they're both about the same. Also, I uploaded a youtube video of the sound. It's not great, but it's the best my little phone could do and I...
  16. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    I've already cleaned up the contacts on the relay (that's why the cover is off of it), but I will definitely be checking out those transistors. I don't know anything about posting audio on here, but I could certainly post a youtube video of it.
  17. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    Thanks for the info Edd! This unit doesn't have a tuner and I pulled up a picture of a NEC 7000 series and it's definitely the twin brother to the one I'm working on. You could probably switch out the front plate without any modification. Unfortunately, I'm not able to view your attachment, but...
  18. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    Hmm.. So far I've lifted the legs on the left channel MOSFETs, a questionable JBT, and some ceramic caps in the output section, but I still haven't found the problem. Could the relay itself be the issue? It's a 6-pin Daiichi and two of the pins have the noise. I had it out at one point and...
  19. KilgoreCemetery

    MCS 3847 Integrated Amp Noisy Left Channel

    I've been having trouble with this home audio amplifier that a friend gave me. It has constant noise on the left channel from the moment the main relay clicks on until I turn it back off. I recently replaced all of the electrolytic capacitors in the hopes that it would fix both this and a...
  20. KilgoreCemetery

    How do you test a 3-Legged Diode (Rectifier)?

    Thanks, Bluejets!
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