Yamaha RX-V595a issues hard to resolve..

Discussion in 'General Electronics Chat' started by Steve Preston, Jun 14, 2015.

  1. Steve Preston

    Thread Starter New Member

    Jun 14, 2015
    Hi. I'm new to the group. I've worked on tons of receivers in my life, but this Yamaha is kicking my *** and making me feel like less of a man, since I need help. :/

    Don't know the history. Maybe surged, maybe simple component failure, but I've had it sitting around for seven or eight years as I got it from a friend who has a repair shop, and the customer left it. I like it due to the phono input.

    Here are my symptoms:

    1) Dead tuner, and almost no audio from any input.
    2) Removing tuner restores audio, and inputs switch normally, but unit goes into protect mode with every input switch. Have to turn unit on and make input selections before protection relay engages, or it will kick off. Other buttons will kick it off also. Could not go through diagnostic service options because of it.
    3) Right channel has very distorted audio, unless I press down on a filter capacitor on the main amplifier board. If I don't press down, I have zero volts of bias on one output base and three volts on it's counterpart's base. Pressing down restores .6 volts +/- on each base and my audio is normal. I removed the board (no access through steel cabinet underneath - HATE THAT), and found not even the slightest poor solder connection. Resoldered a lot anyway, but didn't help. I suspect a cracked low wattage resistor, but can't find it. If I was smart enough, I might know right off the bat what part nearby being open would cause the bias to shift like that, but I'm not that good. :(

    Actually, troubleshooting any problem with this unit is very difficult with the lack of solder-side access to the main boards. My guess with the kicking off on input switching is that perhaps the micro is not muting as it should. My thought on that is to monitor the switching I.C.'s L and R lines and look for DC offset when switching. I cut myself a nice big access hole underneath the related circuitry with a pair of snips so I can work on it. :(

    Anyway, any light that could be shed, I'd greatly appreciate. Don't know why I'm putting this time into the unit, but it has great sound, and I like it.

    Thanks. Steve