CRT monitor issues again - Dell Trinitron D1626HT 21"

[momaka]

Well, not sure if this is an issue or not, but that's why I would like to ask you guys.

I've been using this Dell D1626HT monitor for the last 2 months on a daily basis. Before that, it only saw occasional use (1-2 times a week). Anyways, the "issue" it has is that every once in a while when using the monitor, it will make a static discharge "snap" noise and the picture on the screen would shrink for a split second and then come back to normal. When that "snap" happens, a small instantaneous arc will form between what appears to be area underneath the flyback (or at least nearby) and the shield / metal tray that is holding the deflection board with the flyback.

Now, I've actually noticed this "issue" way back (like 2 years ago), but it happened very very rarely and I never noticed the instantaneous arcing mentioned above. Yesterday, the monitor did it several times. Moreover, I've noticed something new that didn't happen before:
- Before, when the monitor was turned off, it would make the "usual" static discharge sound that CRTs make when you turn them off.
- After yesterday, when the CRT monitor is turned off, the "usual" static discharge sounds are interrupted every now and then by a short moment of silence and then some louder static discharge "snapping" noises, just like when the picture is "snapping". When that happens, I can actually see the same static discharge arcing between the flyback area and the shield. And as far as I recall, I never saw it do this before.

So any ideas what this could be? I opened this monitor about a year and a half ago for clean-up in hopes that it was dust causing this issue. It didn't seem very dusty, though. Is there like a discharge circuit that is not doing it's job? Or something else is bad?

I hope there's still some CRT guru's around. Your answers/comments/suggestions are always welcome and appreciated. Would really like to know what's causing this issue as I don't want this monitor to go down. Currently, I'm using it with my desktop PC for school work. Also really like the color on it. The tube is still in very good condition and focus is excellent.

I included two pictures of the monitor. The construction is very similar to my GDM-FW900 (actually, the GDM-FW900 and other big Sony CRT's were likely based off of this monitor since it's from 1998 ). That said, taking out the D-board for a clean-up won't be very easy. But if you need more pictures, I will do.

[momaka]

Re: CRT monitor issues again - Dell Trinitron D1626HT 21"

Found the source of the arcing: spark gap SG901 near the flyback. I attached a partial service manual of the D1626HT. Page 4 has a schematic of the D-board on which SG901 is located. SG901 is connected to pin 13 on the flyback. Any ideas?

[kaboom]

Re: CRT monitor issues again - Dell Trinitron D1626HT 21"

Found the source of the arcing: spark gap SG901 near the flyback. I attached a partial service manual of the D1626HT. Page 4 has a schematic of the D-board on which SG901 is located. SG901 is connected to pin 13 on the flyback. Any ideas?

There's a cap in the FBT that's starting to break down. Every time it "leaks," the gap fires.

The raster shinks when it snaps? Does it get brighter or darker?

I think it's time for a flyback...

I'd still keep the monitor. It actually has proper dynamic focus! Also, the HV out is seperate from the horiz sweep. It's got a "module" for the HV (IC901.)

It's from back when this

meant something- a winner for sure!

[momaka]

Re: CRT monitor issues again - Dell Trinitron D1626HT 21"

There's a cap in the FBT that's starting to break down. Every time it "leaks," the gap fires.

Thanks for the reply kaboom.
That make sense now. Prior to that, I was just beginning to wonder what else it could be, because I already checked the caps and resistors in that circuit, and they were pretty close to spot-on with their values.

I'm guessing this must be some high-voltage cap inside the flyback so I can't really put a large cap in series with the output of that pin to lower the voltage across it and possibly limit the leakage, correct?

The raster shinks when it snaps? Does it get brighter or darker?

Yeah, the raster shrinks a bit. Not sure if it gets brighter or darker, though - it's too quick for me to tell. Going from my memory, I think the raster first starts to become slightly brighter as it shrinks, but then after it has shrunk a few mm on each side, the picture cuts out for a split-second and then everything comes back to normal.

I think it's time for a flyback...

Not good . I don't think it would be very easy to find a new one. I already had a very tough time finding one for my Sony GDM-FW900.
Would it be okay to run the monitor like this until the flyback totally craps out? IIRC, these monitors have good protections, so if the flyback goes bad, it won't damage any other parts (at least all of the newer Sony CRTs did - and looking at their schematics, it seems Sony didn't really change that much in the core areas).

Also, the possibly good thing is; I looked at the schematics of the D board of the GDM-FW900, and aside from the HV_det circuit, everything else (most importantly: the HV drive circuit and HV control/feedback circuit) seem to be identical, down to component values. The tube voltage is the same too, IIRC: 28.5 KV. So do you think there may be a chance that my spare GDM-FW900 flyback may work in place of this one (provided I match the pin outs)?

I'd still keep the monitor. It actually has proper dynamic focus! Also, the HV out is seperate from the horiz sweep. It's got a "module" for the HV (IC901.)

It's from back when this

meant something- a winner for sure!

Yeah, I'm keeping it for sure, even if it stops working. Unlike the GDM-FW900 and other newer tubes, I think these older non-flat tubes are a little tougher. Luckily, I played some games on it this last fall before it started doing this. It's such a great gaming monitor! The contrast and the colors make the game feel so much more real. Also, since it's a CRT, it has built-in anti-aliasing too .

I saw a bunch of videos on how they make CRTs - it really is a form of art IMO . Wish I caught the analog era a little earlier.