JVC RX-807V receiver. One channel distorted when SEA is enabled.

I think you should resolder the board. When shit like this happens in one c hannel and then the other independently it is almost not going to be the po wer supply, which is usually the first logical guess. But in this case with both channels intermittent I think it has bad connections.

They may look good, especially with lead free solder, but the reason that y ou experience this the way you described could be due to thermal issues.

I am so disgusted with lead free solder that I quit. Think about that. I al most refuse to work on anything with it. It is too unpredictable and also i t has corrosion issues you cannot see. Resolder it with 63/37 and cook it. I mean COOK IT. But look for the connections that might be possible for the problem, do not do all the connections. In fact if you have a floating iro n you can do it while it is running and find the bad ones more easily. Howe ver, do not expect simple resoldering to fix it. You have to take all that lead free shit off and clean the connections, which means the board as well as the pins or whatever, and use the 63/37 on it.

If you do not want a recall that is.

Isolate the problem first. Does the distortion change with a change in volume? I would guess that there is a transistor in the front end that is starting to fail because of heat. It doesn't take much.

You have an advantage here, one channel works as expected. Take some voltage measurements and compare left to right channels. Use a scope and see where the distortion starts.

IC431 (4580) might be a suspect. Follow the audio signal in both channels.

Let us know how you make out.

Dan

Hmmm, but isn't that receiver from the late 80's, early 90's?

Not sure the "lead free solder" problems would apply.

-bruce snipped-for-privacy@ripco.com

** The JVC RX807V is a thoroughly modern, home theatre, multi channel nightmare. Pb free solder is 100% guaranteed.

But it ain't all that bad.

IME, most Pb free stuff is far from impossible to deal with.

A bit of 60/40 on top of any dodgy looking joint works wonders ..

... Phil

The date on the service manual is 1992 and the solder looks very shiny and easy to work with. I would say that it is not lead-free solder.

Thanks for your reply.

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David Farber 
Los Osos, CA

It looks like an audio switch that connects the L and R channels together in some mode controlled by the Mode 2 signal, for some reason. Is there a mono mode?

I'd disconnect this first to troubleshoot the other problem, it may be related or not.

Once you have the two channels isolated from each other, it may be easier to trace the distortion problem.

Mark

in some mode controlled by the Mode 2 signal, for some reason. Is there a mono mode?

lated or not.

to trace the distortion problem.

also looks like a design error to me re Q551 and Q552. It is hard to foll ow the way they are drawing upside down from how we normally see this circu it, but there should be a pullup resistor on Q552 like 10K from base to emm itter to ensure Q552 is cutoff when Q551 is off. There may be enough leak age when it gets warm that Q552 starts to turn on when it should not. That may be the cause of the distortion?

Mark

There is no mono mode that I can see. I do not have the remote control. Maybe it could be activated in certain surround modes? (This receiver has Pro Logic surround sound.)

Are you saying I should just remove the JFET, Q553, to isolate left from right and see what happens?

Thanks for your reply.

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David Farber 
Los Osos, CA

Hi Dan,

I powered it on again and after about 15 minutes, both channels were distorted. The signal going in and out of IC431 is fine. Adjusting the volume does not affect the distortion. The top half of the wave is clipped. I did notice that both dual op-amps, IC431 and IC503 are inline 4580's. I swapped them to see if that made a difference but the distortion stayed the same after warm up at IC503. Inverting input pins 2 and 6 were distorted while noninverting pins 3 and 5 were not distorted.

Thanks for your reply.

--

David Farber 
Los Osos, CA

Have you tried preheating the assy and see if the distortion appears more quickly or even immediately? A good percentage of timed issues are also thermal ones.

Actually, use freeze spray. spray one IC at a time and give it a few seconds to react. You should be able to isolate the offending IC that way. Works for transistors too.

You know, there was something about that model number that bugged me and finally realized there is a similar one in the junk pile.

It's a model RX-905VTN, I'm sure it's in the same generation but not the same series. I'm pretty sure it was one of those, if you could fix it let me know, if not use it for parts. That was like 20 years ago.

Anyway, in case the problem with yours ends up being some weird obsolete jvc-only IC or something else similar, feel free to ask for the boards out of the thing. It's complete and actually looks brand new but would probably be more to ship whole anywhere than it's worth.

I didn't see a service manual anywhere to see if it's similar but I can take some snaps with the cover off to see if any of the circuit boards are similar.

-bruce snipped-for-privacy@ripco.com

Hi Bruce,

As far as I can tell, the components in question are not custom. IC 503 is a standard dual op-amp whose DC output voltages start creeping up until it reaches Vc or 12 volts and then the positive half of the signal is clipped.

The board in question is ENC-093 version C. It's a plug-in board as many of the circuit boards are.

Thanks for your reply.

--

David Farber 
Los Osos, CA

s a

d.

there are either schematic documentation errors or design errors re IC 503

The + inputs to IC503 don't appear to have ANY DC connection, all connecti ons are via caps. The DC voltage on the + inputs is therefore undefined. This is is either a design error or a documentation error. If DC voltage is being set by the the cap leakage, then that is your problem. Use a 100K connected to a variable DC supply and see if you can't move the DC voltage to the correct value. If you can, then you should be able to figure out t he rest. m

I was wondering the same thing! I will check and report back to you.

Thanks for your reply.

--
David Farber 
Los Osos, CA

Your suggestion of adding some dc voltage to the + inputs led me to this webpage:

There is a section there called: *AC coupling the non-inverting op-amp circuit.Using that guide, I added 100k resistors from the + inputs to ground and now the DC doesn't go above 20mV. I also noticed that whoever worked on that pc board before replaced many of the caps. Most of the replacements

the original values.

Thanks to everyone for their suggestions.

--

David Farber 
Los Osos, CA

_non-inverting.php

und

on

eplace those with

wow a design error then.

glad i could help

:-)

Mark

When I receive the replacement capacitors, which will be the original ones according to the schematic, I will remove the 100k resistors and see if the circuit still works. You have to believe that somehow the system worked for many years until something changed.

Thanks for your reply.

--

David Farber 
Los Osos, CA

I received the new capacitors and installed them. Then I removed the 100k resistors to see what would happen. The voltage started rising again. I reinstalled the resistors and it's been running great for two days now.

Thanks again.

--
David Farber 
Los Osos, CA