Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old March 17th 17, 09:19 PM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

On 17/03/2017 10:20 PM, Phil Allison wrote:
Bruce Esquibel wrote:


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

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


** The JVC RX807V is a thoroughly modern, home theatre, multi channel nightmare.


**Nah, it's ancient history in the world of home cinema. A nightmare?
Certainly. Horrible thing. Only good for use as a door-stop. Hell, I
doubt you can find a TV, Blu Ray or DVD to connect it to anymore.
Composite only. Absolute POS. If I recall correctly, it has no removable
base-plate, making service a very lengthy and certainly non-viable
option. Why anyone would contemplate repairing one of these things is
beyond me. It was not even a high end model with decent audio output
stages.


Pb free solder is 100% guaranteed.


**Nah. I doubt it. Too old.


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 ..


**Sure does. Luckily, proper solder is still easy enough to buy.


--
Trevor Wilson
www.rageaudio.com.au

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Old March 17th 17, 10:47 PM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

On Friday, March 17, 2017 at 3:54:14 PM UTC-4, David Farber wrote:
wrote:
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


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.
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Old March 18th 17, 12:20 AM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

On Friday, March 17, 2017 at 5:47:07 PM UTC-4, wrote:
On Friday, March 17, 2017 at 3:54:14 PM UTC-4, David Farber wrote:
wrote:
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


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.
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Old March 19th 17, 05:40 PM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

David Farber wrote:

I'm servicing a JVC RX-807V receiver.


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

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Old March 19th 17, 07:00 PM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

Bruce Esquibel wrote:
David Farber wrote:

I'm servicing a JVC RX-807V receiver.


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


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




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Old March 20th 17, 06:58 PM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.



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.


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 connections 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 the rest.
m
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Old March 22nd 17, 02:33 AM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

David Farber wrote:
wrote:
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.


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
connections 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 the
rest.
m


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

Thanks for your reply.


Your suggestion of adding some dc voltage to the + inputs led me to this
webpage:
http://www.radio-electronics.com/inf...-inverting.php

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
involved changing the 4.7f values to 10f values. I will replace those with
the original values.

Thanks to everyone for their suggestions.
--

David Farber
Los Osos, CA




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Old March 23rd 17, 06:12 PM posted to sci.electronics.repair
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Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

On Tuesday, March 21, 2017 at 9:34:11 PM UTC-4, David Farber wrote:
David Farber wrote:
wrote:
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.


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
connections 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 the
rest.
m


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

Thanks for your reply.


Your suggestion of adding some dc voltage to the + inputs led me to this
webpage:
http://www.radio-electronics.com/inf...-inverting.php

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
involved changing the 4.7番 values to 10番 values. I will replace those with
the original values.

Thanks to everyone for their suggestions.
--

David Farber
Los Osos, CA


wow a design error then.

glad i could help

:-)

Mark
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Old March 24th 17, 09:41 PM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Jul 2006
Posts: 524
Default JVC RX-807V receiver. One channel distorted when SEA is enabled.

wrote:
On Tuesday, March 21, 2017 at 9:34:11 PM UTC-4, David Farber wrote:
David Farber wrote:
wrote:
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.


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
connections 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
the rest.
m

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

Thanks for your reply.


Your suggestion of adding some dc voltage to the + inputs led me to
this webpage:
http://www.radio-electronics.com/inf...-inverting.php

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 involved changing the 4.7? values
to 10? values. I will replace those with the original values.

Thanks to everyone for their suggestions.
--

David Farber
Los Osos, CA


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




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