Kortek 26" monitor (screen shifts)

[gusseology]

I just bought a NEO-GEO machine with a 26" Kortek monitor.  The schematics for the monitor were included.

The screen will seem to shift to the left after using it for a bit.  It doesn't however, seem to be time dependent. 

The screen will shift to the left, I can kind of bang on the side of the machine and the screen will jump back to the right an inch or so....and it will last for a little bit, and then will jump back to the left.  (btw, I don't bang it a lot, just trying to debug the problem).

Since hitting it helps, I thought maybe it was a loose connection or something.  But i've jiggled and tugged every harness/wire/etc. I could find with no real tangible result.  Could also be a cold solder joint maybe??

It seems tweaking the horiz. hold seems to have some sort of effect, but nothing consistent enough to give me any real clues.

I talked breifly with someone who fixes televisions and he said it sounded like a horizontal amplifier issue.  Which I guess is equivalent to a horizontal driver which I guess is equivalent to the LA 7823 IC chip??

Everything I've been reading doesn't seem to point to a capicator problem, but I've ordered a cap kit anyway.

Anyone have any clues what it might be??  If it is the "horizontal amplifier" as was elluded to by the tv repairmen, does that mean I should look at changing out the LA 7823 chip?  Of am I misunderstanding what the horiz. amplifier/driver is and what components effect it??

Please help!    I'm excited about this machine, but bummed I can't seem to get the monitor fixed!

thanks in advance

gusseology

[grantspain]

does your chassis have an adjustment board,if so could be a dry joint on that board or the plug on the chassis.also if you adjust your hor shift then your hor hold does that make a difference-could be a cap fault but i dont think so.
dont think its your frame ic unless its just a dry joint.
if you tap the chassis and the fault reacts then you def have dry joint on componant or bad connector.

[Ken Layton]

Bad solder joints are common on Kortek (all models), but there may also nbe a small value capacitor (like a 1 uf or 10 uf) that's drying out and/or becoming heat sensitive.

[gusseology]

ken and Grantspain,

thanks guys for your quick responses.

I'll give a couple more symptoms...

Once it messes up, I can tap on the bottom side of the chassis pretty lightly and I get a reaction (screen jumps back to the right).  But after awhile, even tapping there doesn't seem to do much.

Once it is messed up for awhile, turning the horiz. position pot doesn't do a thing.

Also, tweaking the horiz. hold kinda helps, but then I'll tweak too far and the screen will go nuts.  So I'll tweak the horiz. hold knob back the other way to bring it back, but it won't come back.  I have to power down the machine and power it back up again.

Some pretty inconsistent activity really.

I bought a cap kit and LA 7823.  I'll take the board off (discharge of course), replace those parts, and reflow solder everywhere I can.  Hopefully that will do something.  If it doesn't, I'll be out of ideas. 

It seems like a cold solder joint or connection problem.....but why would restarting it fix it at least temporarily?   hmmm.  again, no rhyme or reason, pretty inconsistent.  The problem being so inconsistent kinda hints at it being a solder joint issue huh??

gusseology

[Ken Layton]

Make sure you have the correct kit for your monitor as Kortek has made dozens of different models.

[gusseology]

I couldn't find a cap kit for my model anywhere.  but since i had the schematics and parts list I just went through the list and ordered (through Zanen) every electorlytic cap on the parts list.  The guy at Zanen was great, he just took all the cap values from me and put together the kit (cheaper than I could have done it through digikey).

i'll keep you all posted when I get the parts in.  Hopefully it's just a solder problem

[Ken Layton]

Oh, I see.      Zanen is pretty good with making kits like that.

As with all Kortek monitors examine the solder very closely at the large resistors and flyback as those are the most trouble-prone areas for bad solder.

[gusseology]

This monitor is driving me nuts!

I replaced all the caps, and one of the IC chips.  Brought everything back up.

Still the same problem.

It goes good for awhile, then all of the sudden the screen will jump to the left.  I can wait for it to happen, or I can make it happen by tapping on the underside of the monitor.  Once it jumps to the left, my horizontol pos. pot seems to go dead.  As in, once it messes up, no matter which direction I turn my horiz. pos. pot, I get no reaction.

Any more ideas out there??

[grantspain]

what you might have is a bit of cracked track,that would explain your fault-its def a bad solder joint or track prob you have,once the screen jumps does the horiz hold pot work?the trouble with them kortecs is they suffered badly from heat and when engineers worked on the chassis they would sometimes damage the track,i am afraid its a case of checking every track and solder joint.

[gusseology]

Yes, I do seem to be able to get reaction from the horizontal hold pot after it messes up.

I'll try reflowing all the solder joints, but how would I repair a trace?

jesse

[grantspain]

see my post to GIjoe on repairing track/trace,but you gotta isolate the problem first