Weird input issues with JVC AV-27530

[BenM86]

Hi all! I’ve been getting into CRT TV’s for my retro gaming addiction, hoping I can get some help learning about these beasts as they’re very different from the electronics I’m used to working on. I’m having trouble diagnosing this JVC I just picked up. I’ve never seen as issue quite like this before and Google is failing me. The TV seems to work just fine, but I can’t get a usable picture from any of the inputs. I’ll attach a video of what it looks like, possible sync issue? The coax input works and looks fine, if I use an RF modulator from a console it’s fine. But every other input, Composite, Component, and SVideo all look like this, I tested all of them from multiple sources. Also the OSD works and looks fine, and looks fine on top of the garbled picture on the inputs.

The seller I bought it from said everything was working when I picked it up he tested that day, I supposed he could have been lying but it was a $20 TV I don’t think he was. So it seems likely this happened on the car ride home, possible a broken solder joint or trace somewhere? The only thing I’ve been able to discern is if I put pressure on the main video chip on the board it will slow down the rolling picture the more pressure I put on it, could the jungle chip have gone bad somehow? I did a full inspection of the board and I don’t see any caps or connections that are obviously bad or leaking. Also sound works on all inputs.

Video: https://youtube.com/shorts/QF07it8c-Zo?feature=share

Thanks!

[old_tv_nut]

The on-screen display is triggered internally and will always be OK even if the video sync is wrong.

I don't know enough about this chassis to speculate where you are losing sync. The odd thing to me is that vertical sync seems OK while H sync is off and free running at slightly the wrong frequency. Since it is free running, it's not surprising that touching or pressing things would change the frequency.

[BenM86]

Originally Posted by old_tv_nut

The on-screen display is triggered internally and will always be OK even if the video sync is wrong.

I don't know enough about this chassis to speculate where you are losing sync. The odd thing to me is that vertical sync seems OK while H sync is off and free running at slightly the wrong frequency. Since it is free running, it's not surprising that touching or pressing things would change the frequency.

Thank you, that at least confirms my suspicion that’s it’s some kind of sync issue. If it helps anyone to help my diagnose I did manage to track down the schematic for a JVC that has exactly the same model number of control board. From my best guess on what I’m seeing it seems like the component input bypasses the video selector IC entirely and goes straight to the main IC, so if that input is also causing it it must have something to do with area? But wouldn’t the coax signal also have issues if that chip was bad? Here’s a link to the pdf: https://www.icloud.com/iclouddrive/0...d104_av-27d304

[zeno]

This is in SAMS 5144 I do not have it. If you can find a free one
it will be MUCH easier to follow & find things.
There are only 2 inputs to the micro/jungle so I would expect thats OK.
The switching IC may be the problem but dont make a lot of sense.
Other thing is a corrupted E-prom. But there is nothing I found about the
service menus in the manual.
Biggest head ache is both chips are SMD's so there are a lot of things you
can not do to troubleshoot it.

73 Zeno
LFOD !

[BenM86]

Finally figured it out! It was a service menu issue. There’s a setting in the service menu called AFC. I finally sound a service manual for the D series version of this set that has the same menu. The factory spec for that setting is 0. It was set to the max of 3. Once I lowered it to anything else sync was restored. I put it at 0 and it seems fine now. Fingers crossed it’s all good!

[old_tv_nut]

Originally Posted by BenM86

Finally figured it out! It was a service menu issue. There’s a setting in the service menu called AFC. I finally sound a service manual for the D series version of this set that has the same menu. The factory spec for that setting is 0. It was set to the max of 3. Once I lowered it to anything else sync was restored. I put it at 0 and it seems fine now. Fingers crossed it’s all good!

Setting 3 probably forced the countdown on the external inputs, or something like that. Glad you found it.