Sony PVM-6044QM yellow tint on 90% of the screen - Page 1
Forum section: electronics / repair

author: belzrebuth
author_rank: Frequent Contributor
timestamp: June 29, 2023, 04:37:11 pm
content: I've been given this 5" PVM as a test monitor for my bench sometime ago because of this strange problem and I powered up today thinking whether it might be fixable.I have another one identical monitor and I suspect it's the crt that's responsible.It's not the colour board as I swapped it from the other; haven't tried swapping the other board nor anything else; I just tried the color board.So I was wondering what caused this issue in the first place; I know LCDs can develop similar issues due to heat but it seems pretty much impossible for a CRT so it must be something else and it seems pretty uniform for a magnetic issue so I'm out of ideas.Anyone has a clue what might be going on?I hope the picture is clear enough.Apart from a vertical white line the rest of the screen has this dark yellow hue to it, the monitor works great apart from that and I was told it has about 30-40k operating hours so it's not like the tube has reached the end of its life.

author: wasedadoc
author_rank: Super Contributor
timestamp: June 29, 2023, 06:14:10 pm
content: Check the degaussing circuit components.

author: inse
author_rank: Super Contributor
timestamp: June 29, 2023, 07:40:32 pm
content: Degaussing is not so much of an issue for tiny CRTs.If you had access to a video signal generator it would be much easier to track down the problem.What is the colour board, the CRT neck board?Yellow means R+G is working, B not.Try to generate a blue screen and see what it looks like.

author: agent_power
author_rank: Regular Contributor
timestamp: June 29, 2023, 10:02:10 pm
content: Looks too "clean" to be magnetisation issue...I suggest you trace the signal with an oscillscope and check where it goes wrong... or if you have an identical working monitor it's easy to swap parts until something changes in case you don't feel comfortable poking inside CRTs

author: belzrebuth
author_rank: Frequent Contributor
timestamp: June 29, 2023, 11:36:48 pm
content: My thoughs exactly; it looks very clean and the high uniformity somehow tells me it's not magnetisation.It may be a color problem; I don't know but I'm pretty sure I swapped the color board from the good and it didn't make a change.I may do it again just in case I don't remember well.Blue screen is okay no green or red spots so I don't think it's due to degaussing.Blue seems a lot less vibrant that it should.Maybe that's why I'm missing the white alltogether.I attached two images from the good monitor (original image and blue only image) and one pic from the bad monitor (blue only image bad)The "blue only" button on the PVM should display a black and white image but on the bad monitor I have a purpleish tint.

author: james_s
author_rank: Super Contributor
timestamp: June 30, 2023, 12:37:27 am
content: Is it possible that there is screen burn from something blue? What happens if you display solid red, green and blue screens? What if you turn it off and look at the screen closely under a bright light or blacklight?

author: belzrebuth
author_rank: Frequent Contributor
timestamp: June 30, 2023, 01:35:45 am
content: I don't see anything weird when colors are displayed individually.It's on the total white screen that the discoloration is very noticeable.Let me know if there's any photo I can provide to make things clearer.I removed the front acrylic thing and checked with a bright light but I don't see anything out of the ordinary.I've seen screen burns (letters mostly) so I know how it looks like.

author: floobydust
author_rank: Super Contributor
timestamp: June 30, 2023, 03:47:44 am
content: I start by setting the CRT's screens and drive to get white balance right at both low brightness and full brightness.It sounds like the RG guns are staying on and B is lazy. Do you have the service manual?

author: belzrebuth
author_rank: Frequent Contributor
timestamp: June 30, 2023, 07:41:48 pm
content: Here's the service manual.https://archive.org/details/sony_PVM-6041QM_Service_Manual

author: floobydust
author_rank: Super Contributor
timestamp: July 01, 2023, 04:08:29 am
content: What I have seen is one gun goes weak and somebody just cranks up the screen voltage which causes the weak gun to do better- but the other two stay on, they don't go into cutoff.Try to set up the CRT for white balance and see where that takes you.It's difficult because there are ~8 controls that interact a bit and you will have to play with them to understand them. This set seems to have fixed Red (not adjustable) so blue and green are adjusted.3-4. White BalanceScreen G2 voltage adjustment is on the flyback under the focus adjust.RV118 - Sub-brightness on the B boardFixed - R cutoffRV121 - B cutoffRV119 - G cutoffFixed - R gainRV120 - G gainRV122 - B gainSince you can't dial down red, there are no adjustments, I would guess the screen voltage is overall too high making things yellow.I lower the screen voltage as much as possible for the dim white line, just to see how the CRT is doing. Have fun but use a good insulated screwdriver and be careful going in.Wild guess the blue gun is weak, so I would next start getting it up, then go on to the green.After the CRT is sort of leveled/evened out as best as possible, I would do these per the service manual:RV124 - R gain/black levelRV125 - G gain/black level

author: wasedadoc
author_rank: Super Contributor
timestamp: July 01, 2023, 07:44:52 am
content: But why is that vertical strip at the left edge OK? That is just after the H blanking comes off. Put a scope on the blue drive to the CRT. Any discontinuity at the corresponding time?

author: floobydust
author_rank: Super Contributor
timestamp: July 01, 2023, 10:25:58 pm
content: In pic "blue_only_bad" I notice a brown vertical band on the left, only for the coloured (not the white) portion of the screen.The white text (and his white face) is also badly smeared brown in the background. Usually text, fine detail smearing is a slow (cable capacitance) or video amp/CRT driver.It looks like blue appears white yet white appears white, gray appears as purple?

author: inse
author_rank: Super Contributor
timestamp: July 02, 2023, 06:11:40 pm
content: May I repeat my question: was it the CRT neck board that you swapped?I suspect the video amplifier, which could be proven that way.Otherwise unfortunately the tube is done.There once was the now lost art of CRT testing and rejuvenating, but that’s long gone…

author: james_s
author_rank: Super Contributor
timestamp: July 02, 2023, 07:24:42 pm
content: Quote from: inse on July 02, 2023, 06:11:40 pmIt's not gone, CRT monitors are still in widespread use in vintage arcade games and quite a few of us in the arcade collecting community own CRT analyzers. The Sencore Beam Builder models are some of the more popular ones. They still show up on ebay fairly regularly.

author: belzrebuth
author_rank: Frequent Contributor
timestamp: July 03, 2023, 10:26:22 am
content: @floobydustRaising G2 voltage does not make any difference on the yellowing.The screen goes more yellow with more voltage and dims to the point I get retrace lines when I lower it.I tried messing with the pots before but I couldn't get it to even out.I can affect the problem but the image is still wrong no matter what I do.I just set them back to factory position for now,@inseThere is no video amplifier on the neck board, this is not like a typical TV arrangement where you have a color amp on the neck. With that said there are 3 transistors that are responsible for each colour right before it hits the neck board. I could swap the blue with either the red or green on to see if it makes any difference.@UunoctiumI will check R705 when I get home..

author: inse
author_rank: Super Contributor
timestamp: July 03, 2023, 11:32:27 am
content: I did not look into the details, but swapping the drive lines is a good idea 👍

author: belzrebuth
author_rank: Frequent Contributor
timestamp: July 04, 2023, 11:35:26 pm
content: R705 is good..so no issue there..I thought about replacing those driver transistors but these are on the color board that I replaced with the known working one so these are not at fault.Next thing would be to just put the good tube inside the "bad" monitor.This will definitely indicate whether it's the tube that's faulty.Would this pose any risk to the good tube?

author: wasedadoc
author_rank: Super Contributor
timestamp: July 05, 2023, 03:32:35 pm
content: Quote from: belzrebuth on July 04, 2023, 11:35:26 pmI would try the simple swap of drive lines long before even thinking of swapping the CRTs. But they are your monitors to mess up and your time to waste so no-one is stopping you!

author: floobydust
author_rank: Super Contributor
timestamp: July 06, 2023, 03:28:16 am
content: Quote from: belzrebuth on July 04, 2023, 11:35:26 pmI would say stop blaming the CRT and troubleshoot the electronics. If the colour is dynamic with H sweep then it's not the CRT.Still can't figure out what it's doing - it looks like red and green guns are slow to turn off, but then blue appears as white.Can you try some test patterns to get a better idea what is wrong. Most of the battle is just figuring out what is not working right.