JVC CX 710 VHF/UHF tuner repair.

[ELzekio]

For the tests I’ve been doing so far while this thread has been posted, I have been useing a vcr connected to the CX 710s coax 75 ohm input and NOT my blonder tongue.

*when ever I did though try broadcasting over the air with my blonder tongue I would still get the same results I get when having a vcr directly connected to the unit.*

While having the vcr connected again and having the vhf tuner tuned to where it should have the strongest signal, I felt around but i did NOT notice the IC 101 chip getting hot.

I really don’t think anything is wrong with the IC itself. The voltages as posted above are fine, except for the fact that pins 4 and 14 are still showing the N.S voltage for No/Low signal even though I had the vcr signal connected to the unit and tuned to where the signal is supposed to be strong.

I then tried adjusting the noice control according to the service manual, but it did not make a any meaningful difference in the picture at all.

As i mentioned before I am confident the signal is getting to the TU-01 tuner, because I tried injecting it directly into it and got the same results as always. If IC 101 is good, then it is possible that the TU-01 tuner has a problem?

Is it common for those tuner boxes to go bad?

[zeno]

Tuners were pretty good. Most symptoms are snowy, dead, loss
of a band. Yours shows classic IF overload. Washing out, buzz,
tearing etc. RF AGC fail gives snow & or jittery pix usually.
You can test that at the AGC pin for signal/no signal changes OR
if you have a little bias box unhook the AGC & set the voltage.
If it were the olden days I would give an estimate for the IC
& lots of labor. While the IC is out I would check the resisters in
the area ( dont have to lift them usually).

73 Zeno
LFOD !

[ELzekio]

Yea I suppose I will get an IC on order and maybe a few caps in the tuning area for good measure.

Do you have a specific recommendation on the type caps for a tuning circuit on a tv boombox like this that I can get on mouser? I usually use ELNA silmic 2 caps and Nichicon FGs when recapping stereo equipment, but I think those are only rated up to 85 C, and may not be the best for this application.

Not trying to be nit picky, just want some that are a good fit for this environment.


I will also take another look at the resistors when I get the IC out.

[zeno]

Originally Posted by ELzekio

Yea I suppose I will get an IC on order and maybe a few caps in the tuning area for good measure.

Do you have a specific recommendation on the type caps for a tuning circuit on a tv boombox like this that I can get on mouser? I usually use ELNA silmic 2 caps and Nichicon FGs when recapping stereo equipment, but I think those are only rated up to 85 C, and may not be the best for this application.

Not trying to be nit picky, just want some that are a good fit for this environment.


I will also take another look at the resistors when I get the IC out.

I am inactive at this time so not sure who & what to use. 85 deg are fine.
since caps are smaller I would double the voltage unless there is a space problem. Most of it probably uses 25V caps so go to 50V etc. If you want to recap fix the problem FIRST then do a few at a time checking it as you go. Mistakes happen & there is nothing harder than finding a self induced problem.

C U later
Zeno
LFOD !