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Sansui 4000 help needed

Discussion in 'Exclusively Sansui' started by bzb882, Jun 30, 2017.

  1. bzb882

    bzb882 AK Subscriber Subscriber

    Messages:
    443
    I consider myself an amateur, with that in mind here goes. I picked this unit up while back. Almost no sound out of the right channel and no dial lights for am/fm/meters. While deoxing I noticed smoke (turned out to be vaporized deoxit) arising from under one of the grommets on the selector switch. I marked one of the wires (white) at that location for future reference. I went on to recap the entire unit also replacing the 2sc871 transistors with 2cs2240s and the 2sc458s with ksc1845s. I then adjusted the two VR803s to 15 mA and replaced the thermal past on the output transistors. It now sound great BUT the light issue didn't resolve. After deoxiting the hell out of the selector switch (I still get the smoke from that grommet) the dial lights and meter lights(s) will light dimly and eventually go out. Any ideas as to how I can fix this? The white wire I marked goes to the dial lights. Barring any other solution, is there a way to bypass the selector switch so that the dial light and meter light(s) are always lit?
     
  2. Robisme

    Robisme Sansui Enthusiast Subscriber

    Messages:
    11,366
    Location:
    Martinez California
    Find the lamp power feed to the selector switch, them move the wire that goes to the dial and meter lamps from its place on the selector switch to that terminal.
    That should do it.

    Rob
     
  3. bzb882

    bzb882 AK Subscriber Subscriber

    Messages:
    443
    Thanks! I did some more research, so this afternoon I tried to locate the lamp power feed to the selector switch. When I make the switch stop part way between AUX and FM the dial lights come on and stay on. At that moment I have 6.3 VAC to the white wire that goes to the dial lights as well as the the brown wire on the selector switch (both wires on same wafer). Thought I had found where to install the jumper. No go, when the selector switch is in either fm position or am, there's no voltage to either wire. Jumper wire from white to brown does nothing. Occasionally I'll get weak lighting in am and fm, so I doubt its a fuse issue. I haven't popped the top yet to test the wires that I can't access with the bottom off, any ideas?
     
  4. Jon D

    Jon D Member

    Messages:
    50
    Location:
    Livonia, MI
    Try moving the white wire instead of using a jumper.
     
  5. bzb882

    bzb882 AK Subscriber Subscriber

    Messages:
    443
    I'm thinking I have more wrong than just the selector switch. Tonight I checked the voltages again on the white and brown wires. In AUX I had 0.17 VAC on the brown. Half way between AUX and FM (dial lights lit) I had 0.17 VAC on both brown and white wires. All other positions of the selector switch, no VAC. I then installed a jumper wire between the white and brown wires. Dial lights come on in AUX only. No 6.3 VAC tonight, for no apparent reason. Any ideas?
     
  6. bzb882

    bzb882 AK Subscriber Subscriber

    Messages:
    443
    Problem resolved! Measurements in post 5 above are incorrect (my DMM meter wasn't set to measure VAC). I ran a jumper wire from the the selector switch tab with the white wire (the one that runs directly to the dial lamps) to a green wire of the top-side of the selector switch. The green wire has a 15 ohm (brown-green-black silver, I measured to verify the resistance) from its tab to an adjacent tab that has no wire. Dial lights now stay lit now no matter where the selector switch has been dialed to. The only issue I have left is that the FM Stereo indicator light is dimly lit all the time. I read somewhere there's a pot that can be adjusted, but I can't find that thread. Does anyone know how to do that?
     
  7. bzb882

    bzb882 AK Subscriber Subscriber

    Messages:
    443
    Any thoughts on the FM Stereo indicator light dimly lit all the time? I deoxited VR401 and now it lights faintly and does appear to go dark. From one extreme to the other VR401doesn't make much difference in the intensity of the FM Stereo indicator light. Strength meter only goes to just past 3 on strong stations (I use a small rectangular Terx antenna hooked to 300 ohms connectors), but the reception sounds great. I did notice that stations on the area of the dial where I listen are off by almost 0.2 (89.9 FM will be strongest at 90.1). I am getting stereo reception, I can hear the difference when I switch to mono...
     
  8. Robisme

    Robisme Sansui Enthusiast Subscriber

    Messages:
    11,366
    Location:
    Martinez California
    I would start at TR407. This is the transistor that switches power to the lamp. It could be bad.
    In stereo there should be 5.5vdc on the collector. Close to 0vdc when not in stereo.
    The voltage for the lamp comes from the emitter. You can check the base voltage to see if it changes when it goes in and out of stereo.
    This voltage is fed from TR406.

    Rob
     
  9. bzb882

    bzb882 AK Subscriber Subscriber

    Messages:
    443
    I took 6 readings on the pins from TR407 (2SB324). Difficult to tell the pin-out, all three legs go to a strip of pins. From there a red wire goes to the lamp, a green (Green1) wire goes to pin 3 on the MPX board slot and another green (Green2) wire goes to board F1187 (ripple filter block), the spot is marked "OC". I took readings with and without a station tuned and with VR401 in its as-found position as well as full clockwise and full counter-clockwise. Here are the readings, hopefully they'll display correctly:


    no station; no station; no station; station; station; station

    VR401 clock-wise; VR401 counter CW; as found; VR401 clock-wise; VR401 counter CW; as found
    Red 2.05; 2.03; 2.0; 1.4; 0.6; 1.23
    Green1 6.78; 6.79; 6.8; 6.99; 7.25; 7.0
    Green2 6.97; 6.98; 6.98; 7.17; 7.42; 7.2
     

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