HP D8911 CRT losing red from VGA

[Boohyaka]

Hello there!

First post, as I was recommended this board I didn't know and it looks like the perfect place let me say first that my knowledge of CRT's is pretty limited but I'm aware of their potential danger.

So the issue is I have a great hp D8911 19" CRT with an integrated VGA cable. Suddenly yesterday it started not displaying red color component on VGA (white became cyan, yellow became green, etc...). I of course tested it on another computer and problem was the same.

By wiggling the VGA cable at the back right out of the cover the picture would quickly come back, but always go back to losing red.

Today I've opened it, discharged the anode, paid attention not to touch anything, and only checked the VGA cable. Noticed it was a continuous cable that went through the chassis, the cable shield grounded to it, and continuing to a connector inside a metal shell at the bottom of the gun. As the cable was continuous it didn't make much sense for me that wiggling the cable outside the chassis would fix the issue, yet it did... as I saw no particular visible problem or damage, I did put the cover back on, tried again to see if it was miraculously gone but (as expected) the issue was the same.

I re-opened it, and this time unscrewed the cable chassis grounding, and took the whole cable out. Put the cover back on, tried again, and this time the picture was perfect, even when wiggling the cable...that's good enough right now but still a bit puzzling, so I'm turning to you guys to see if there is some sense to make out of this and if I could do anything to make sure it's fixed for good.

That's basically it..here are a few pictures to illustrate it:

https://imgur.com/a/qXPAEm1

This album contains a few pictures and a video of the issue. In the video, I'm wiggling the VGA cable right where my fingers are in the 3rd picture. When strongly pulling the cable to the right side the picture was fine, when I let it go back to its natural position the problem occurs.



This is what it looks like now, not showing any problem.

Thanks a lot in advance!

[petehall347]

Re: HP D8911 CRT losing red from VGA

break in the cable .cut it open and splice or fit another cable .

[Boohyaka]

Re: HP D8911 CRT losing red from VGA

Thank you! It seems an obvious answer now, but the fact the cable has no visible damage or pressure point and started showing the symptoms after months of not being moved around, it didn't feel intuitive to me. As it's working right now I'll probably keep it like this, if problem happens again or gets worse I'll follow your advice.

Quick additional question: how safe is it to reach inside the metal shell at the bottom of the gun where the VGA cable plugs, with all the grounding solders? Isn't that where the PSU and potentially dangerous capacitors are? I'm just thinking that if I were to replace the VGA cable and as I don't know where the potential break exactly is, I'd rather change the whole thing for good.

[stj]

Re: HP D8911 CRT losing red from VGA

your fine, the only high voltage when it's off is between the tube and the HV transformer.
that runs at about 18Kv and the focus on the neck is probably about 1Kv and the colour guns are powered by between 140 and 200v.
but only the 18Kv charge stays with the power off.

bit of advice, try to mount a 15way connector where the cable exits the chassis - so you dont have to do this again - it's a very common fault.
the cable usually breaks at the pc end.

[Boohyaka]

Re: HP D8911 CRT losing red from VGA

Thank you! That's exactly what I had in mind - mounting a 15pin female connector out of the chassis and use a regular VGA cable to connect the PC. My only concern would be if the cable break is actually inside the chassis, but that seems less likely.

[momaka]

Re: HP D8911 CRT losing red from VGA

Since the issues seems to have gone away when you unplugged and plugged back in the cable inside the monitor, I'd suggest to check all solder joints on the internal monitor connector and nearby components on the neck board. At this age, and given the heat generated on the neck board, solder joint failures can and usually do occur over time.

As for the high voltage inside - I wouldn't worry too much about them after the monitor has sat off for a minute or 5. Most "modern" CRTs from the late 90's and later will typically discharge even the HV anode to fairly safe voltages. Of course, never assume that is always the case... and generally speaking, if you don't mind discharging the anode every time, then feel free to do so.

Also, the danger from the HV anode is not that you will get hurt from the electric shock, but rather that if you have your hand stuck somewhere in the monitor or if you are holding a sharp tool, then getting shocked in that situation can cause muscle reflexes to trigger, and you may end hurting yourself from the sharp tool(s) you're holding or from pulling away your hand and scraping it on something in the monitor.

[Boohyaka]

Re: HP D8911 CRT losing red from VGA

Well...bummer :/

At first I had the impression the problem was somewhat random when I posted here.
Then after that I kinda noticed a pattern: after a long rest the screen would almost never power up with the issue but it would always eventually happen, as like a component was failing after warm up.

The last few days the issue got worse. I was not only losing red, but sometimes going full black&white, or even losing another color channel.

Yet, as wiggling the cable outside the case definitely had an effect when the cable goes through the case then to the neck board, the defect cable explanation still had merits.

So today I decided I'd try to change it to exclude this potential cause. I removed the whole cable and honestly it looked perfectly fine. Kept the original internal connector and a small section of the cable and soldered a female vga connector at the end as suggested earlier. Before plugging it back I tested all continuities with my multimeter and everything was ok and steady even when moving the cable around.

Mounted it back, and you guessed it by now, first the picture was perfect and after a moment it was bad again. Yet, the cable wiggling is even easier now that the cable hangs out of the case with a connector and I still manage to restore a perfect picture this way , at least temporarily.

momaka, I had read your message before attempting this so I did carefully look on the neck board but didn't notice anything fishy...but I'm starting to think it may be a contact issue with the cable socket on the neck board and you were onto something, that would probably explain the "outside wiggling" fixing it?

I guess the next step would be to fully dismantle the neck board to carefully check and measure it, but there's lots of glued up connectors (removing the glue on the monitor connector was painful enough already) so I'm feeling a bit down about it now :/

[R_J]

Re: HP D8911 CRT losing red from VGA

How does the on screen display (menu) look? is it also missing red etc. ?

[Boohyaka]

Re: HP D8911 CRT losing red from VGA

the OSD looks fine and is absolutely not affected by the issue!

[R_J]

Re: HP D8911 CRT losing red from VGA

Then the problem is likely between the plug P801 and the ic801, If it was just the red, it could be C801 going open, or bad connections on the board

[petehall347]

Re: HP D8911 CRT losing red from VGA

" Kept the original internal connector and a small section of the cable "
fault could be here or maybe the socket on the board or its solder .

[momaka]

Re: HP D8911 CRT losing red from VGA

Then the problem is likely between the plug P801 and the ic801, If it was just the red, it could be C801 going open, or bad connections on the board

+1

Sounds like a bad connection between neck board and cable somewhere. But whether that's on the cable, the connector, or the PCB, you'll have to check carefully. Multimeter in continuity mode may not tell you the full picture.

but I'm starting to think it may be a contact issue with the cable socket on the neck board and you were onto something, that would probably explain the "outside wiggling" fixing it?

I guess the next step would be to fully dismantle the neck board to carefully check and measure it, but there's lots of glued up connectors (removing the glue on the monitor connector was painful enough already) so I'm feeling a bit down about it now :/

No worries. Take your time and work on it when you can.

Also, when you do, could you also please upload pictures of the neck PCB here (preferably from both sides, if that is possible.) Maybe we may be able to see something you're not.

And bad comes to worse, I recommend you get some flux and retouch some of the solder joints on the neck PCB, even if they look OK. No need to add fresh solder. Just put rosin flux on the bigger joints that are more likely to have cracked (typically on bigger through-hole components and connector leads) and re-solder with your iron. This being an old CRT monitor, it probably uses leaded solder, so the joints should come out nice and shiny.

[Boohyaka]

Re: HP D8911 CRT losing red from VGA

OK, thanks guys. I'll probably get to it at some point, not sure when right now but I'll make sure to update you when I do and I'll probably need your help anyway many thanks for all your comments and help so far. Cheers

[Boohyaka]

Re: HP D8911 CRT losing red from VGA

I must say that since changing the cable, and pulling the "new" cable straight out of the case and holding it this way, the problem hasn't happened in 4-5 consecutive hours (when testing the screen right after changing the cable it happened in less than 5 minutes).

My assumption at this stage is by pulling on the cable I'm actually holding the cable socket in a proper position that makes proper contact on a solder that is failing. That's my noobish assumption at least, based on your experts comments. I'll hold to it as it is right now but at some point I'll get down to business, remove that whole neck board and check it carefully

[Boohyaka]

Re: HP D8911 CRT losing red from VGA

Hey guys! It only took 3 years lol
Thought you guys deserved some closuse haha

+1
And bad comes to worse, I recommend you get some flux and retouch some of the solder joints on the neck PCB, even if they look OK. No need to add fresh solder. Just put rosin flux on the bigger joints that are more likely to have cracked (typically on bigger through-hole components and connector leads) and re-solder with your iron. This being an old CRT monitor, it probably uses leaded solder, so the joints should come out nice and shiny.

That's exactly what I did. Removed the neckboard and the whole shielding...annoying, they did use a shitload of solder, blobs were massive, but with the right tools and my improving yet still noobish skills I was able to do it with some patience.

Checked the whole neckboard visually, couldn't see anything wrong with it really. Still went ahead and reflowed every single connector with a bit of liquid flux, and for those that looked like they could do with a bit more, I still added a tiny bit of solder. Everything came out beautiful and shiny. Put everything back together (shielding included, easier to do than undo lol) and lo and behold...perfect picture, and I haven't been able to reproduce the red problem at all! So it looks very much like a win

All hyped up I decided to tackle another CRT (a Compaq 17") that works fine picturewise, but had front controls issues. Left and right button would sometimes trigger the wrong side, menu/ok would only work half of the time. So opened it up, and this was a bit more work in terms of reaching the small PCB that controls it. Managed to make my way through everything to reach it, took it out, started with some DeOxit on all switches for a few minutes, then cleaned it all with IPA, then reflowed every single connector as well. Mounted everything back, and buttons now behave as good as new. So good.

That's nothing too amazing for many people here I'm sure, but this was SO satisfying! I'm feeling the addiction to try and repair retro stuff growing and really feel like learning more electronics, so I'll probably be more active around here

Thanks again for the help 3 years ago it was worth it!

Cheers!