Dell P1110 Spark Gaps firing

[Toasty]

Dell P1110 21" circa 2001.

Unit came in with momentary all green video on power up with heavy retrace. Then winks out to second picture of the blob that occasionally flashes the video but mostly stays in that state. Spark gap tubes at HO flash/pop and flashing/popping inside neck of tube at guns can be seen. Unit shuts down in about 30 seconds and power cycle restores it.

HV seems good at 27kV.

Tube shot?

[kc8adu]

Re: Dell P1110 Spark Gaps firing

focus/screen divider or bad crt.
pull socket and measure focus.around 6 kv iirc.
watch out for the base of the crt to be live.if its bad that 27kv could jump out and get you.

[Topcat]

Re: Dell P1110 Spark Gaps firing

I have a parts one here, it works, but has an intermittent PSU issue (sometimes it takes a few times of powering it on and off to get it to come on). Pay the shipping, you can have it. CRT is good.

[Toasty]

Re: Dell P1110 Spark Gaps firing

Yup, thank you. Expected your response going on that bad yoke set from 2 months ago. I had the connector off and said to myself, hang on until I check that procedure.

HV was a bitch to measure. Cap kept rolling up and arc would jump to the shield frame. Wheee!! Run away!!

[Wizard]

Re: Dell P1110 Spark Gaps firing

Hahaha.

I have occasionally see a CRT fail like that. Total loss and if warranty job, new CRT or do a exchange with the maker (some do).

Any of these.

Sparking in the gun assembly.
Tap on the CRT neck and get a weird picture like you had.
CRT snapped in two (where tube flare begins to flare out from the tube) with no sign of impact. (Ever had like this even the HV is not going high?)
Cracked CRT face (always found on the projector either if coolant ran out or flaw in the CRT itself).
I had a intact CRT (works!) with a HV pinhole leak at the epoxy seam where CRT had face glued to the bell. It was making hssing shhing noise. Ear and HV probe all over finally localized that.
And HV leaking to the gun assembly making the spark gaps light up.

Cheers, Wizard

[Toasty]

Re: Dell P1110 Spark Gaps firing

CRT socket off. Built a plastic "cap" over CRT pins, from 2 spray can caps, in case it tried to bite. Worked a charm!

Set on for under 10secs each measurement.
Red FC = 3.5kV
Black FV = 3.7kV

See attached schematic.

[Wizard]

Re: Dell P1110 Spark Gaps firing

When CRT board is off the tube did the spark gap kept snapping?

That wiring where does this circuit the spark gap that arcing leads to what part of circuit of CRT board?

Did you use your HV probe to the CRT pins to see if you find any HV leak? That's also diagnostic process.

Cheers, Wizard

[Toasty]

Re: Dell P1110 Spark Gaps firing

I did not leave the set on long enough to see of gap would snap. I am VERY fearful of the tube being bad and arcing. Not to me, but to the circuit board that surrounds the tube end. Dozens of SMD chips and several 40 pin IC's, etc.

>>Did you use your HV probe to the CRT pins to see if you find any HV leak?<<
See above answer...

I'll give it a go. Burn a little incense for me will ya?

Arcing SG is right next to FBT. Line off that (R924/935 junction) leads to HV Control IC , BA9758FS, Pin 11.

I'll get more of the circuit up in a bit. Damn schematic is in .djvu format and I have to convert it to .jpg format to post here.

Toast

[Toasty]

Re: Dell P1110 Spark Gaps firing

More of schematic:

[Toasty]

Re: Dell P1110 Spark Gaps firing

Tested unit on until it "timed out" and shut off.

Spark gap is not firing with socket off.

Incense must have worked. The circuit board, Toast, nor the cat got zapped.

About 1kV present on tube pins. HV shhh hssss sound when you get near with probe. Had to use VOM to get reading as HV meter scale is not fine enough.

Toast

[Toasty]

Re: Dell P1110 Spark Gaps firing

I reconnected the socket to the tube and remounted the surrounding board ("A" Board - video inputs and drivers).

Now, the spark gap is not firing nearly as much and can go a minute or more before it fires. Set runs for 45 seconds with no video until it shuts down. With video it stays running.

When first powered on, the input video (comp boot screen) is sharp and distinct, although green w/retrace. It quickly goes fuzzy and then changes to the blob.

I flipped the A/B video switch on the front and got a horizontally shrunken bright green screen with heavy retrace lines for about 1 second, then it goes full screen, then it goes back to the blob. There is no video being input on B.

Flipped the switch to A, and got the bright green w/retrace, only the input video is not displayed as it is when cold started.

Then I started pressing the buttons on the front panel. One is "Factory Reset" which caused it to flash green and then back to blob. Playing around with brightness and contrast buttons and then pressing reset, I could get the monitor's menu to pop up briefly in the bright green screen, then back to the blob. When the menu was displayed, it was clear and sharp.

Something very odd is going on here...

I've check PSU outputs and all are correct. I'll do some checking on the video board and see if anything stands out.

The hunt continues.

Toast