CRT (Makvision) image is a large bluish blob. Dead, or repairable?

[Baldbull]

Makvision/Weiya M2929D4G-TS
Tube A68EMN021X121

The monitor powers on and displays an image for a few moments.... the image quickly morphs into the images I've included.  Any ideas?




SOLVED - There was an intermittent short in the picture tube between the blue pin and heater pin(s).

[grantspain]

looks like blue gun is full on, could be drive transistor or tube- desolder blue gun pin on crt socket to prove
the red blob is either down to requiring a degauss or the purity rings are set wrong

[Baldbull]

looks like blue gun is full on, could be drive transistor or tube- desolder blue gun pin on crt socket to prove
the red blob is either down to requiring a degauss or the purity rings are set wrong

Here's another pic... Depending on how long it sits or your viewing angle, can like slightly different.

On this one, you can see the edges come in a bit.

[grantspain]

looks like more than one issue to me, if that discolouration does not go with degaussing then its either the yoke moved or purity ring not set correctly or the shadow mask is damaged in the tube

again like i said before the blue gun looks to be fully firing-desolder blue gun pin

[Baldbull]

looks like more than one issue to me, if that discolouration does not go with degaussing then its either the yoke moved or purity ring not set correctly or the shadow mask is damaged in the tube

again like i said before the blue gun looks to be fully firing-desolder blue gun pin

The monitor had not been moved since installation many years ago.. if that's any help.

It was working fine.. until one day.. it simply wasn't. 

Once powering up.. there is image for a moment.. then it slowly morphs into what you see above.... takes 5-10 seconds.  The image may influence the colors displayed a bit -- the actual image displayed is mostly blue.

Degaussing has zero effect.

[grantspain]

so if it was a chassis i was working on the first thing i would do is desolder the ptc and the blue gun, give you a good idea of whats going on

[Baldbull]

Finally got around to looking at this thing again..

Unsurprisingly, it did not fix itself

It goes without saying I'm a novice when it comes to CRTs.  I'm sure I'm in over my head.  Have to start somewhere right?

I have a basic knowledge of electronics and have found the schematics -- https://na.suzohapp.com/pdf/service_pdfs/M2929D4G-TS.pdf, but am at a loss as to where I should begin.

Am I doomed?

[jennifer]

Without actually running some tests it would only be a guess...But if I was to make a guess...Since you are getting RGB, I would be suspect of the retrace (flyback) circuit on the chassis...Thats a high voltage potentially faulty circuit friend, It may be somewhat unpredictable, be careful and approach with caution ⚠️.

[jennifer]

A good place to start would be (Imo) would be probe the anode with a good quality high voltage Kv probe,  and see what you are actually getting at the tube....Yokes and purity generally don't change over the life of the tube, but if you moved that stuff for some reason, the convergence is most likely off and that would also cause those problems,

[Baldbull]

A good place to start would be (Imo) would be probe the anode with a good quality high voltage Kv probe,  and see what you are actually getting at the tube....Yokes and purity generally don't change over the life of the tube, but if you moved that stuff for some reason, the convergence is most likely off and that would also cause those problems,

Problem just started out of thin air... cabinet was not moved.

[jennifer]

Well I guess Jenn ment to say if someone moved the yoke, or the rings thay would throw off convergence, not if you physically moved the cab
...My guess it is the chassis is where your problem lies, most likely the flyback itself, or something associated with it.

[Zebidee]

First you need to check blue colour drive circuit like grantspain suggested (several times) as a short there can cause an excess of the colour concerned - disconnect and see what happens. For example check/desolder the blue colour drive transistor or CRT pin (on CRT neckboard).

[Baldbull]

I removed the two transistors on the blue gun circuit.... and no change.   

Is it terminal?

[Zebidee]

I removed the two transistors on the blue gun circuit.... and no change.   

Is it terminal?

No - it is normal for a colour to come full-on when there is a problem in that colour's drive circuit. If there is no change after removing the transistors, it further suggests that is where the problem is.

You can test the transistors with a multimeter (there are a bunch of guides out there).

Alternatively, try swapping them with the equivalent transistors on the red circuit. If your problem becomes mostly red instead of blue then you know where the problem is.

If that gets you nowhere then desolder the blue pin on neckboard at the CRT socket and see how that looks.

[Baldbull]

Unfortunately I hosed one of the transistors on the removal... So a true swap isn't an option.  It's been a long, long time since I've done this kind of work.  ~20 years.

The one transistor that survived tested fine.  I can attempt to test the other... may be enough of the prongs left, but it's not reusable.

Don't think I can truly desolder that blue pin without getting a good solder sucker... this copper wick isn't cutting it and is likely how I split the transistor in two.

To be continued... maybe.

[Zebidee]

May as well replace them with new then. If you have to order them, then maybe grab a decent solder sucker as well. I don't like the wick either but sometimes there is no other choice. Flux helps.

You may as well prepare to check out all the electrolytic caps while you are in there - they are a common failure point and can deteriorate over time. Caps going bad can be hard to detect, and you have to remove them to test (unless you have an ESR meter). So lots of people will just grab a cap kit and do the whole lot at once every 5-10 years or so.

[Baldbull]

Where do people get components on the cheap?  Is EBay the only real option?

[Zebidee]

People get stuff all over. Digikey, Mouser, RS etc. are some of the better suppliers. There is also ebay Aliexpress and other online markets of course, quality variable as you'd expect. There is a stickied thread here for capkits.

You can also get cap kits from various arcade parts vendors.

[Baldbull]

Desoldered blue pin from socket.... no change.

[Baldbull]

People get stuff all over. Digikey, Mouser, RS etc. are some of the better suppliers. There is also ebay Aliexpress and other online markets of course, quality variable as you'd expect. There is a stickied thread here for capkits.

You can also get cap kits from various arcade parts vendors.

Any thoughts on where the issue could be at this point?  Desoldered the blue gun pin and no change.  Where's all this blue coming from?  Could there be some kind of short in the neck tube?

[grantspain]

if you got the right pin on the crt socket then your tube has a gun short
if you desolder the blue gun pin on the crt socket then there is no way you will get blue unless there is a short in the tube

[Baldbull]

if you got the right pin on the crt socket then your tube has a gun short
if you desolder the blue gun pin on the crt socket then there is no way you will get blue unless there is a short in the tube

Was afraid of that.. Could that explain the strange green/red that show on the sides after a minute or two?

So it is terminal.  Bummer. 

[jennifer]

No, he is saying it needs a rejuvenation.

[Baldbull]

Shouldn't I be able to confirm a short by measuring resistance between the tube pins?

Should I be getting continuity between any two pins? (I am..)  I've got a pin I can't seem to identify.. has continuity with the heater, but isn't used by the board.  No shorts w/ BK pin?  now confused.

Looks like there some quick fixes to try here -> http://www.thegleam.com/ke5fx/crt/sencrt.pdf

[jennifer]

A rejuvinator has a setting to clear shorts, as that is actually a common problem...However be warned it is not a guaranteed fix, the better the machine the better your chances and even then may  shorten the life of the tube....Personally Jenn would use a Beltron but they are hard to find, and as a second choice wouldn't use anything smaller than the BK 467...*(opinion)

[jennifer]

In fact here is one...Notice down on the bottom right there is a setting to remove shorts, as a clean and balance.

[jennifer]

As a comparison the Beltron is a far better machine in my opinion, and will fix things most rejuvenators can't even dream about...But again, hard to find.

[Zebidee]

Someone on another forum recently restored their Sony PVM with an intermittent heater short by putting the CRT face down/neck high, then repeatedly/gently tapping around the neck/gun assembly (not sure what with, maybe a wooden spoon or something like that). The tapping seemed to dislodge whatever crap was causing the short and problem was resolved.

Could be worth a try.

[Baldbull]

Someone on another forum recently restored their Sony PVM with an intermittent heater short by putting the CRT face down/neck high, then repeatedly/gently tapping around the neck/gun assembly (not sure what with, maybe a wooden spoon or something like that). The tapping seemed to dislodge whatever crap was causing the short and problem was resolved.

Could be worth a try.

That's my next attempt... the only short I could prove with the meter were between the two heater pins and this other pin that does not appear to be used by the neckboard...  It's the first pin.. or last, depending on how you look at it.

[jennifer]

Don't know what kind of sites you guys are hanging out on, but banging on it with a spoon or whatever kinda sounds like a bad idea, even if it works you still got the potential short floating around, and never did address the clean and balance...It's your tube man, Good luck.

[Zebidee]

Don't know what kind of sites you guys are hanging out on, but banging on it with a spoon or whatever kinda sounds like a bad idea, even if it works you still got the potential short floating around, and never did address the clean and balance...It's your tube man, Good luck.

Might sound scary but unless he goes at it gangbusters he doesn't have much to lose. Only other practical alternative is to find someone generous and local that can help out with a rejuvenator - which would try to burn the short off, which honestly sounds even dodgier.

[jennifer]

Ya what was I thinking, A rejuvinator that is just a stupid idea...Bang on it with your stick I guess.

[Baldbull]

Grabbed my other meter as a sanity check... There is definitely a short between blue pin and heater.

Tapped on the tube 5-10 times.... short doesn't show up anymore???

Definitely something floating around in there it seems...

[Zebidee]

Ya what was I thinking, A rejuvinator that is just a stupid idea...Bang on it with your stick I guess.

Be nice, I said gentle tapping not banging. If it works then it works, it has for others, not everybody has a rejuvenator in their workshop.

Anyway I don't want to "bang on" about it.

[Baldbull]

IT WORKED!!!!!!!

Now I just have to find this damn transistor I broke... 2SA1371-E

if only I'd have started with the tube.

[Zebidee]

IT WORKED!!!!!!!

Now I just have to find this damn transistor I broke... 2SA1371-E

if only I'd have started with the tube.

Well, grantspain did say that up front (desolder blue gun pin) 

I'm just happy it seems to have fixed the problem, you can never be sure. But for today, percussive repair techniques rule! 

[jennifer]

Glad it works...problem solved.

[jennifer]

After some thought...I have to be of the opinion that smacking that tube with a brommhandle is not fixing it, and now that it is working the problem has been made more difficult to track down as a done out the door fix, and to isolate the short now you are looking at a mutiburst pattern generator as to have some control over the color and refind the original problem not to mention the other guns haven't been cleaned or balanced...Not everyone has a rejuvenator this is true, but if you can't find one cheap, you just ain't trying very hard, or flat out don't even want one...If I was to guess, that tube will be worse next time, and will most likely even burn the screen.

[Zebidee]

Seeing as it must be silly season, how about we try hitting a CRT "home run" with a baseball bat then? Maybe that will improve things? Of course I am being ridiculous, but just continuing the hyperbole.

For giggles I decided to look up rejuvenators for sale (again, I do it occasionally). As usual, almost all listings are in the USA, and they are all ancient tech so I worry I'd spend more time fixing it than using it. Best option I could find that was close to me was in Singapore, US$297 + $134 shipping, fairly typical (LCT-910A). Chump change for some but serious money for me. Still...:

https://www.ebay.com/itm/CRT-tester-Leader-LCT-910A-Cathode-Ray-tube-tester-rejuvenator/323878499016?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160727114228%26meid%3D87a407f9f94c43479b1f77dd3443b8cd%26pid%3D100290%26rk%3D1%26rkt%3D3%26sd%3D323878499016%26itm%3D323878499016%26pmt%3D0%26noa%3D1%26pg%3D2060778&_trksid=p2060778.c100290.m3507

Of course in the USA, land of milk-and-honey for arcade enthusiasts, I could maybe grab a B&K 46X for around $150 or even less. Drive around the corner to pick it up.

I've never owned a rejuvenator, but have done some research and watched some YT vids on them. Something that stands out is that while they can maybe (or maybe not) breathe new life into a tube for a few months or years they can actually damage the guns and filaments and that rejuvenation is really a "close to end-of-life" option. Still, nice to have and good for other things like diagnosis or CRT health etc.

[dmckean]

Considering arcade cabinets and TVs tend to sit in one place for years at a time, moving the problem down the road a decade is basically the same thing as fixing it. For most of us at least. By the time this becomes an issue again, the tube may be ready for rejuvenation.