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David Farber David Farber is offline
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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