Hitachi M48JLK22X Red Bleed

[MIPS]

(Not really a TV but the computer forums are starting to ignore CRT repair problems now that LCD's are everywhere)

I have a display here for an early computer graphics workstation and the monitor is a little sick. It's a Hitachi 21" model fixed for for 1280x1024@60hz but the branding has been stripped and replaced with markings from Silicon Graphics.



Internally it indicates the tube is a M48JLK22X.
The main issues I've run across are overall focus issues and the image gradually becomes fuzzy from the center outwards until it's totally unreadable. My assumption there is a recap is in order but I'm a little more concerned about the right side of the screen which has taken on a reddish tint and an amount of horizontal image bleed. The screen uses a manual degauss circuit but while I can verify the circuit works it doesn't seem to be a magnetism issue. Could it be a dislodged shadow mask or should I not be evaluating that until a recap is completed?

[MRX37]

If it's like that iMac I found many years ago, check the caps on the CRT neck board.

[MIPS]

Took the whole monitor through an almost total recap with the exception of some values not even my shop in Vancouver could find and while I'm still waiting on everything to warm up the bleed and red tint is still there.



Edited: Nope. The gradual focus loss is also still there too. God dammit. It's almost feeling like a flyback issue.

[Electronic M]

Wonder if a resistor is heating up and going high/open/flakey. Perhaps it's time for some freeze spray troubleshooting.

[zeno]

Almost looks like 2 problems.
First run the FCC number at fcc.gov that will give you the
origional make & model number. Then see if anyone put
a manual on the web.

The 2nd pix looks like something in the hoz or HV breaking down.
I have seen FBT's do it & other things. Also could be power supply.
On this one IF you can get a manual start with the power supply
voltages & if you got a scope check for garbage on them.
Other than that poke around, try freeze mist, look for overheating
& cold joints. This will be a challenge........

73 Zeno

[rca2000]

Not sure if this is your problem or not....

BUT, iIRC in late 1996...I have I think an NEC monitor, 19" or so...and nit had a BAD sync issue. That turned out to be the video processor. BUT..after it was replaced...the focus just was NOT quite right. There were 2 focus controls on the fly...but NEITHER ONE...would quite 'get it". Almost...but not quite. And I think it WAS worse--was near the sides and edges. For quite awhile....I thought it was a flyback, I think that was tried....and did not help. It seemed there just was something "missing".

that "something" turned out to be DYNAMIC focus. What happened...was they had sent the WRONG processor to us (tandy), where I was working at then). It did NOT have a dynamic focus output....and without it...the tube could NOT focus quite right all over.

The boss, was now able to find out a snafu had occurred and NEC or such sent us the RIGHT chip...but it was USED and being a large pin SMD chip...it was NOT usuable. This set him OFF...and he DEMANDED we be sent a complete BOARD--which contained all of the low-level stuff--since we doubted another chip could be transplanted ont the old one again.

That DID fix the problem !! GREAT focus all over. ANd the dynamic focus line form tha tboard to the H-0out ckty was again correct. There was PLENTY of "reserve" now left on the now new flyback focus controls.

So....see if there is a dynamic focus ckt. this very WELL may be your problem. It "modifies" the focus line--accd. to WHERE the horizontal scan is at any given time, on the screen. ALso...check your video bias supply voltage--if you hav enot already replaced the caps on that line.

[MIPS]

I do know the history of the thing. It was purchased alongside the workstation that now sits in my shed in 1989 and saw weekly use for about six or seven years before it was slowly pushed further into a storage room and I collected everything in 2004 (and it was doing it even then). The tube looks like it's seen a lot of hours. Contrast is poor and the corners have focus and convergence issues. Tried to put the HV probe on it this morning to see if the HV was sagging after a period of time but my portable fluke has decided to stop playing nice it seems.

I did inspect the boards for iffy resistors but they all seemed fine. The monitor actually has a fan in it so the ventilation is a lot better than most 21" monitors I've seen.

[MRX37]

1989? You sure? XGA didn't come out until 1990, and 1280x1024 is SXGA.

[KentTeffeteller]

Silicon Graphics was ahead of the PC world too, consider that.