JVC AV28T77SK CRT: Intermittent loss of colour

[tom66]

Don't think this is worth repairing, but it's my dad's TV.

I can pick up a used 28" or 32" CRT for him for about £5 but it would still be interesting to track down the fault.

Basically while watching the TV occasionally loses chroma information and the picture is just greyscale with lots of luma crawl. I have checked the SCART connector and it is fine. It usually only occurs for a few seconds at a time. OSD is -not- affected.

This set was made in the UK and cost about £300 new. I'm expecting good quality for the price! It's lasted 6 years, which is better than most LCD/plasma TVs...

[Toasty]

Re: JVC AV28T77SK CRT: Intermittent loss of colour

Just spit-balling here, but I would be looking at solder joints, board interconnects, and the chroma "jungle IC" if that set has one. I remember some RCA and GE sets that had small cap failures or temperature related drifting that would cause problems like this. Have you tried tapping on or flexing various boards or areas when it goes out?

[selldoor]

Re: JVC AV28T77SK CRT: Intermittent loss of colour

Hi Tom is this set up with a set top box or its own tuner or is he in one of the few remaining areas not gone digital. Or perhaps you are on satellite.

We used to have a 28 inch sony with a built in digital tuner -didnt work originally when switched and Sony said it wouldnt work, as it was too old, when I sent them an irate email. Anyway I was able to tune it by tuning each channel individually.

When it was working it too used to "black out" for a few seconds every now and then but it never got worse and we just put up with it.Our local busses had just adopted some sort of positioning system which supposedly would tell when the next bus would appear. They spent £100k setting it up, never really worked, then they said they couldnt afford the monitoring system so it was scrapped !!.
Anyway it seemed that the tv glitch occurred when a bus went past, not that I could prove it. At the time I seem to recall some people said Taxis caused interference. We were the second area to go on and were on reduced power as it interfered with signals from other transmitters so the change over was not as smooth as it should have been.
Didnt help that in Preston we were midway,in a direct line between Winter Hill and the booster in Lancaster. The aerial was set correctly but as they adjusted the power it would sometimes pick up signal from the booster instead of the main one.
Not much help I know but a few good stories.

[tom66]

Re: JVC AV28T77SK CRT: Intermittent loss of colour

It's connected to a Freeview DVB via SCART. I actually have not checked the DVB box so that could be at fault too but I don't suspect it is, because it looks as if the colour carrier is still there (hence the luma crawl on the image.) I am starting to suspect a problem perhaps with the colour oscillator for the comb filter this TV has.

It may be a Vestel! () 11AK45 chassis!!! Nooooo!!!!!

Either way, I'll still crack it open to see how well it is made.

Funny thing is, my dad's Freeview does the same blacking out occasionally. It's definitely the Freeview because the interface (red button, tv guide etc.) is still there, and sound stays the same. I'll see if it is related to the buses, as he lives near a main road, where there are a lot of buses... hmmm...