Ok I got a weird one.
I ran into a JVC RX-318 that is half dead. when you plug it in, the standby relay comes on, the main speaker relays will also come on 5 seconds after the standby relay comes on, does this under normal conditions also.
But the whole front panel is dead, no VFD, no standby LED, nothing.
i see filiments, thats about it. I checked the incomming standby 5V, it is present.
im at a standstill. any ideas? bad micro?
here is the funny thing.
If i take and wet my finger a little bit, and touch underneith the crystal, sometimes the front pannel will spring back to life, and shortly after it will "lock up" and go dead again. sometimes it dont work at all.
i changed the crystal, didnt resolve it. resoldered the entire area. im at a standstill. any ideas? its like the clockpulse just doesnt want to start.
There could be some contamination in the area, a small cap could be leaky, a reset line being pulled down, 5 volt line being just a "bit" low, who knows? Sounds like a fun one all right. A service manual and some experience with problems like this would be good...
Mark Z.
On Sat, 25 Nov 2006 05:37:36 +0000, Mike Has Frothed:
What other diagnostic instruments do you besides a wet finger?
-- Pierre Salinger Memorial Hook, Line & Sinker, June 2004 COOSN-266-06-25794
Anyway all sarcasm aside, i checked for a clockpulse with a scope, and there is one. I got the service manual and schematic to the reciever, and my voltages are normal, the VFD voltage is normal, the 5v is normal. the reset pin is active low, and it goes low on plugin and back high as it should. none of the keys are stuck electrically. so the only conclusion i can draw is my "wet finger" is causing a momentary clock glitch that starts up the CPU.
these micros are proprietary too which sucks, i could dump the code and program a new one as i cant seem to find a replacement.
I seem to recall that these units had a problem with the CPU locking up. Look on the front panel PCB, I think there is a capacitor in the 5V line for stby to the micro. With the unit unplugged FULLY discharge the capacitor, then give the unit a try. It's been a year since I saw one of these but I do believe that fixed 90% of them, the internal RAM in the micro would get corrupt data and by discharging the cap it would flush the bad data. If this dosen't do it, try replacing the cap, if that's a no-go you'll need to replace the micro.
Jammy
I would check for high esr capacitors in the power supply. I had a Nak receiver with the same symptom and it was caused by a faulty electrolytic. Chuck
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