AOC 7F CRT intermittent blue & how to discharge a CRT properly?

[Agent24]

My AOC 7F has recently developed a problem with blue failing (going yellow)

This happens intermittently but tapping the side of the case can change it.

Thus, it seems likely there's just a bad connection but I don't really know where to start. I also don't have any experience with discharging CRTs either.

[Th3_uN1Qu3]

Re: AOC 7F CRT intermittent blue & how to discharge a CRT properly?

Discharging the CRT? Well you don't need to do that. Just let it sit for a few minutes for the PSU caps to discharge as you have no business around the CRT anode with a repair like that, and it is well insulated. Just don't touch the area under the flyback, but you don't have business in there either...

Check the connector of the VGA cable, resolder as needed. Resolder the resistors around the video amplifiers (Google the chip model and you'll find out quickly what it is). Resolder the resistors on the board located on the neck of the tube. That should be all.

[Agent24]

Re: AOC 7F CRT intermittent blue & how to discharge a CRT properly?

Well I opened the thing, and really not sure how to access anything.

The damn neck board is covered in a 2-piece shield, which is soldered to itself and to the board. It's also got 5 (maybe more) grounding wires going in every which way.

Not sure what I can pull off or what (if anything) I should leave on.

There's also some big grounding strap\tape stuck to the shield, which goes down to the heatsink for I guess the HOT.

I'll get some pictures up soon.


Oh yeah, and the soldering on the main board looks pretty much perfect. Not sure about neck board of course as I can't see it...

[Th3_uN1Qu3]

Re: AOC 7F CRT intermittent blue & how to discharge a CRT properly?

The damn neck board is covered in a 2-piece shield, which is soldered to itself and to the board. It's also got 5 (maybe more) grounding wires going in every which way.

Pretty standard CRT fare. Take it all off. You'll find a ground on the board itself - that's where you solder all those wires for testing after you remove the shield.

[kaboom]

Re: AOC 7F CRT intermittent blue & how to discharge a CRT properly?

The anode will discharge through the focus/screen divider on the flyback as long as the anode lead is connected to the CRT.

I find it easier to remove completely remove the neck board in these cases. If it's got leads from the main board soldered to it, you'll have to remove both. Just beware of tie-wraps or blobs of silicone between the tube and socket if you do remove the board.

Anyway, once you remove those shields, there will either be three SMT ICs or one SIP/ZIP IC for the video amp. The OSD inserter(s) are probably also on the board. Obviously, resolder everything, and regrease the video amp if you can. Those screws sometimes come loose from thermal cycling. If you have the three SMTs, regrease their thermal pads before covering them up again- usually the back shield on these.

Save work for yourself in the future- replace any craps in the video amp while you've got it out.

-Paul