JVC CX 710 VHF/UHF tuner repair.

[ELzekio]

Hello everyone, now that I’ve had some extra time, I thought I’d re visit this JVC CX 710 (the 610s big brother ) that I’ve got, and see if I can get any luck on finding the issue for the vhf-uhf tuner from y’all here at Video-Karma. I believe I posted a thread in boomboxery a while back seeking help for the fm tuner and tv tuner.

I’m not very concerned about the FM tuner, but if I could at least get vhf picture on this unit threw the tuner, I’d be more than happy.

One suggested that the tuners were out of alignment, which could very well be the issue, but I don’t yet have the experience of using an oscilloscope to help with tuner alignment. To me, it also seems a bit unlikely that both the fm, am, and vhf/uhf tuners would all go out of alignment, but I suppose you never know.

What I have done and know:

- This unit has composite video and audio inputs, when using the composite inputs I am able to get a good picture and good audio with NO ISSUES at all. This tells me the CRT is able to process a picture and display it, meaning the issue is somewhere in the VHF/UHF tuning.

- When i inject either a VHF OR UHF signal in to the unit. it is pretty much unable to tune it in.

In the YouTube video I have linked below, I am injecting a vhf channel 4 signal threw into the unit from the VCR and into the TV 75ohm input. as you can see it is pretty much unable to process the input.

If you really work the tuning wheel into a single VERY precise spot, you sometimes can get a barley viewable and blurry picture that of course is not watch able. (As shown 13 and 30 seconds in to the video)

I have AFC on and so IF the unit was working correctly, it should automatically snap in to the perfect picture when you get the tuning dial anywhere around the right area.

https://m.youtube.com/watch?v=lpnzJPUfmkg

Also, as you can see in the video, when I get the tuning dial around where it should be, I am able to get pretty decent audio out of the speakers, but as I said the video doesn't want to come in.


I have repeated this test using a BLONDER TONGE AGILE MODULATOR (am 60 550), and tried injecting different vhf and uhf channels, but no matter what channel I broadcast on, I still get the same result of unwatchable signal even though it SHOULD be perfect.

I am also quite sure that there are NO physical connection problems with the antenna or 75ohm input because when I directly inject the VCRs vhf signal directly into the vhf input on the television’s tuning box as shown in the picture below, I get the SAME result as always (fair audio, but picture not coming in as shown in the link to the video above.)

EFB0811B-D993-4A6F-A6FC-A40480F35D39.jpg

5C6B4237-E6E9-4DB4-A2A5-77833E1847C8.jpg

I checked quite a few voltages around IC 101, but I have yet to find any that differ significantly from spec.


Here is a Link to the Schematic I Scanned. This is for the main tv board. That includes the vhf and uhf tuning. I can scan the other side of the schematic if necessary.

https://drive.google.com/file/d/1s0K...ew?usp=sharing

So what do you all think. Any chance there is anything I can do that does not involve a complete overhaul tuner alignment?

None of the caps have any visible leaking electrolytic. Think there could be one that can cause these problems?

Are there Any pots that I could safely adjust without an oscilloscope? Ive got a fluke multimeter.

I will try and get the full survice manual uploaded as soon as I can.