Sony GDM F520 CRT Monitor

The neons are the backup system. If the main CRT fails, these will display enough basic characters to enable you to sort it out. Conceived in the days of DOS, theyre less well suited to modern graphic displays, but you can reboot into dos and sort your computer from there.

Intermittent blurring is nearly always due to focus voltage variation, which is nearly always due to arcing somewhere in the focus voltage line.

NT

They are spark gaps.

Seems a bit strange they all have darkened glass.

NT

Thanks for your thoughts folks. The service manual is here:

You can see the 'neons' or Spark Gaps at the top right of the diagram on page 30, located around the CRT base.

Before I took the case off, when I had the intermittent blur problem with this monitor, occasionally I'd hear an electrical discharge (crack!) and the focus would recover or at least change. Googling I've found this, which was posted at this newsgroup earlier this year:

This certainly sounds similar to what I'm describing, although another model is involved.

Any further advice gratefully received,

Scrim

Those have darkened glass even when they are new.

I've seen a LOT of flat CRT Sony monitors with bad CRTs that cause arcing and loss, or change of focus. Andy Cuffe

snipped-for-privacy@gmail.com

Hi Andy, Thanks a lot for the info about the 'Neon' spark gaps having a dark coating from new. I wouldn't have considered that possibility. The intermittent blur seems to have stopped for now, but I always got the impression it was worse in cold weather. My hope was that if it turned out to be the tube I might help it with a bit of carefully placed thermal insulation.

Scrim

not a chance. If the tube's arcing you might be able to clear the short

- you might even fix it with just flicking the neck if youre lucky. Just dont break it or all hell will break loose.

NT

To keep the strike voltage up?

NT

Could be. And maybe to avoid scaring the purchasers.

good point. I guess thats why they dont use mercury fill then :)

NT

I used a 21" Sony for quite a while with a CRT that was acting like yours. It was ok most of the time, but would occasionally act up for between a few seconds and a few minutes. Eventually it settled down to the point where it would only act up every few weeks. After about a year I found a broken non-Sony monitor with the same Sony CRT and did a swap. It never acted up again. Andy Cuffe

snipped-for-privacy@gmail.com

My G520 loses focus occasionally too and a power cycle fixes it. I got rid of a similar model last year that would do the same thing, been doing it for years and hasn't gotten any more frequent. Someone told me it was a fault within the CRTs.

It's part of the processing when they make it. Neon lamps are driven hard for a time to cook impurities out of the electrodes, the spark gaps are probably cooked a bit harder to get a uniform striking voltage.

Thanks for the help so far. The intermittent fault has finally shown up again, perhaps because of the colder weather last night.

First it blurred: I started prodding around in the back with a long glass rod. I tried tapping the tube, tube end pcb, focus leads and the focus adjust side of flyback transformer unit, to no avail. The blurred focus cleared itself after a while, but later there were a series of pops from the back accompanied by momentary collapses of the screens image. I have no idea where the pops came from. If I knew this was an insoluble tube problem I'd just give up, but, at best, this is such a good monitor I'm still holding out for the chance it's reparable. Any ideas how I could pin down the problem or eliminate any suspects? Thanks

Scrim

The strike voltage changes if light gets to them?

I wonder if that explains why a neon (integral resistor) fitted in a piece of equipment here flickers intermittently when it's in the dark, but lights reliably when illumination falls on it.

This is not a wind-up!

At first it seemed that it only flickered when the fluorescent light in the room was turned off, which led to thoughts of some bizarre wiring related error ... but then it turned out that it also responded to torchlight ... so light was the common factor.

Never seen it before on any other neons, so it might be just a marginal one!

The only real other possibility is the flyback. Unfortunately, that's a pretty expensive part to replace on a long shot. It's also worth checking for signs of arcing in the CRT socket.

Andy Cuffe

snipped-for-privacy@gmail.com

OK, Thanks Andy and everyone else for the help,

Scrim