Entertainment Center: TVs, Stereos, VCRs and DVDs - Bad ground? Hum on an old JVC Recv.

I've got an old JVC-507 Pro-logic receiver. A few months ago it developed a nasty hum in the rear channels - to the point of making it useless for surround.

Last night I pulled it apart and began looking for a ground fault. If I went from the neg side of the speaker terminal to anywhere on the chassis I got .3 ohms which seemed fine to me. Just to be certain I ran a wire from ground directly to the speaker terminal. This dropped resistance to 0 ohms and got rid of hum (although I still do not believe volume is where it should be). Should I continue to hunt a ground fault or look at something else?


The unit sits on top of a Pioneer bigscreen. My DVD has two sets of audio outs: 1 set goes to the TV the other goes to the CD in on the receiver. The audio out from the TV connects to VCR1 on the receiver. When I turn my TV on I get a hum in the main speakers when using the DVD. Shutting off the TV eliminates the hum. Any ideas?

Hey Bob, what you have there is probably a bad solder joint on the main PCB. Also since the unit has set for some time it's possible that the large filter caps have dried out. Look closely at the tops of the caps, usually gray around 4300 MFD 64 Volt. See if the tops of the cans are bulged up. If so the caps are bad and actually could explode under duress. First off though I would dig into the board and find the broken/cold solder joints and using a 40 watt soldering iron with 60/40 electronic solder (I actually use silver solder) and resolder anything that even remotely looks bad...

Thanks for the idea. I figured I was in the right direction, but hate hunting down bad connections. When I first received the unit (used) it had the same hum throughout the entire system. I found where a ground plate (to connect a PCB to ground via mounting screw) was missing. So I wrapped a wire around the screw and soldered it to the PCB.

Caps look fine (not bulging anyhow).

Thanks.

Bob

Another thing that JVC was famous for was bad grounds at the mounting screws. I used to take the screws out and touch up the solder pads. I haven't been behind a real bench since I retired from the game of electronics, just my one at home so this stuff comes to me usually after I post. Your idea with the wire is great, I couldn't do that on a customer unit but ur idea in my opinion is perfect.

Big Mike is my hero!

Smokey ;)