Help please with circuit analysis

Discussion in 'The Projects Forum' started by superduper, Mar 23, 2011.

  1. superduper

    Thread Starter Active Member

    Dec 5, 2010
    Hi folks. I have a radio tuner that I'm working on.... AM is dead, FM is working but weaker than normal. I injected a 455khz signal at Q104 and a tone can be heard at the speakers so presume the downstream circuitry is OK.

    I checked voltage at Q104 and they come in close to spec as per schematic. But Q103 voltages are out of line with specs. The collector is reading about 7volts and both the base and emitter are reading around 2-volts, both deviating from specs enough to that suggests that there is definitely a problem in that area?

    I wonder if someone can offer any suggestions as to possible causes of the voltage discrepencies and which components might have failed to cause that. This is like the 5th tuner that I've encountered with similar symptoms (same manufacturer -- sanyo). I am wondering if there is a common cause. All shows no AM symptoms.

    2nd question: Below Q103 off the base, is a component that the diagram shows as D107 with part number MV-11T. The symbol looks like a diode with an extra triangle -- I would guess it almost looks like dual diodes in series? I tested it with diode test function of my DMM and it test about .65v in forward direction, open in the other. Can anyone tell me what the device is, and any recommendations for that item? I can't find a datasheet on that part number and NTE cross search shows no results.

    HELP! I would really like to get this radio working again.