Help with 25k7101 repair

[sadstate]

Hello, I'm really new to working with a CRT, so please forgive my ignorance and thanks in advance for any help. I have a WG 25k7101 in a MAME set up. A while ago all green stopped appearing on the screen. At one point I touched the screen and the green suddenly all came back. But that only lasted for a day or so. I'd appreciate any help repairing this problem.

Thanks again

[sadstate]

From the FAQ I gather I should try a cap kit first. I also gather that the K7101 cap kitting follows the caps and schematic from the standard k7100. Is that right or am I going to blow something up? Again, any help would be appreciated.

[ed12]

yes a cap kit would do it wonders
but your under-lying problem
is going to be the neck board
un-plug unit
wiggle neck board off..go very very careful
once off  re-flow all output transistors ie r/g/b
as these things are comman to develop cold solder joints
which will cause that problem

ed

[sadstate]

I finally got around to the cap kit and reflows. It worked great. Things are looking better than ever. So, thanks a lot for the help.
When I got the board out I noticed that I was wrong all along and that its really a k7400 not 7101. 
I've still got one issue with the vertical position being a bit too high up even when adjusted as far down as possible. Do you have any suggestions on how a could lower the screen position a bit more than the pot will let me?

Thanks once again.

[ed12]

if i rember right there is a service kit for that chassic to fix that problem
maybe ken layton could chime in here ?,if not i will look at my kits for them
and get back to u

ed

[sadstate]

Great thanks.

[sadstate]

So a week after the reflow and all of the green has disappeared again. The neckboard looked like it had some burn damage to it when I worked on it last week. Surely, I shouldn't be reflowing each week. Should I be looking for a replacement neckboard or is that an impossible thing to find? Or should I be looking to replace some components on the board? Any thoughts would again be appreciated.

Thanks

[bimm25e]

what resolution do you run from your computer if you don't mind me asking?

[sadstate]

640x480 through a JPAC.

[grantspain]

if you tap and the green comes back then its a broken track-if not then likely its the drive transistor

[lilshawn]

you either still have a bad solder joint there on the big transistor for the green, or the transistor is on it's way out and is going to need to be replaced. quite often they will do as you describe...go out or lock on randomly. (no color or screen turns one solid color) also check the big resistors going to the transistors. sometimes they get corrosion on them and the solder doesn't stick proper. you literally have to remove them and sand the legs with some fine grit sandpaper, re-tin them, and then solder them in again.

be warned these board have a habit of lifting the traces off if they get heated up too much and you risk wrecking the board or ripping off a trace. be super careful.

2SC2068 is the original part you can use to search e-bay for a replacement. I'm not sure what you could cross it to. It's kind of an odd ball part.

[bimm25e]

640x480 through a JPAC.

Thanks, do you happen to know what referesh rate as well?  Sorry to thread-jack but I have a WG7193 that I'm having a heck of a time getting connected to a PC.  Or does the J-PAC handle the refresh rate for you and you have no idea....

[sadstate]

Thanks for all the help guys. Looks like I've got some more soldering to do in the coming weeks.

bimm25e, I haven't messed with that in a while, but I remember that I bought an ATI graphics card with the intention of running soft15khz to output an interlaced 60 Hz. Whatever card was in there before wouldn't interlace so I had to run at a lower resolution. From my understanding, the J-PAC keeps me from messing things up to badly by making somehow making sure the graphics card output and the CRT input are in sync before allowing output to flow from the graphics card to the CRT. But, I'm a novice, so I don't really know. 

[ed12]

crosses to nte 376

ed