WG25K71XX undocumented mods

fredster

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After all your help, I fixed a troublesome 25K7191 that stumped me.

So I went back to may stack of part boards hoping to bring another one back from the dead. I have two candidates, but the differences in these boards confuse me. These boards are from an arcade auction buy at a liquidation sale.

They are all about the same, that is, they have the same layout and the same chipsets, same part number boards ; but they have these mods all over them.

One of them has a electrolytic cap on the neck board, and the other does not. One has a cap patch in the mods, and the other has a cap the one I just fixed doesn't have by IC2.
One has cap on IC1.

The one I'm looking to fix first has what looks to be old mods removed, but what looks like brand new caps in it. Another has no mods at all but looks like all the caps are bad. Years ago Ken Layton told me I screwed up royally by removing these mods, as they were factory mods.

Is there any reference for this? My plan was to take the board I wanted, pull all the mods off one of the parts boards I have that has the mod, and go from there. I just don't want to miss one.

Any thoughts?
 

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the third pic looks to be a different model than the a typical K7000.
yes i know it is not the zenith model.

can we get a pic of the top of the chassis of pic 3. more towards the fly back.
it looks like it has a red wire on the H.O.T if it is what i think it is.
it uses a different yoke. than the standard K7000.

Peace
Buffett
 
The one in #3 has the flyback missing. It's a parts board. I want to fix pic #2, but where it's circled, it's obvious that all of those features were at one time installed, but aren't there now. It looks like whomever put the new caps in took them all out.

Every single one of them has the same neckboard, except one has an mica cap where the other two have a 4.7uf electrolytic cap. The one that doesn't is pic 3.

But I'll take a pic of the one I want to fix in my next post.
 
Remember that different versions of the chassis will have things that others won't. A 7191 may be a little different from a 7911, not to mention the 19" & 25" versions. I usually only see the neckboard cap on the 25" (P538) models, but not every one...
 
I took the pictures. The first chassis is the board I want to rebuild. It appears to have the mods removed, either on purpose, or in the cap kit change at some point.

The second chassis is a parts board I used to fix another chassis. It has the mods in it.

The third one is another good candidate, but it's a little different from the other two. (and the last two I worked on). It has this daughter card on it. It has absolutely no mods in it at all. And I'm not even sure it will work on the 25" monitor I have.

Since Chassis 1 and chassis 2 are almost alike, I'm inclined to just put the mods back.

Unless you guys think Chassis 3 will work too. It appears to have a new cap kit in it. It has the same part number board (P538) but it also has this P738 daughter card.

I have tried both of the candidates, and they are all "dead". Fuses blown. I'm guessing replace the hot (and fuse of course) while I'm at it and go with chassis 1.
 

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When you are "fixing" monitor chassis, you should never utter phrases like "I'm guessing replace the hot (and fuse of course) while I'm at it". You should first learn how to TEST the items in question to see if they are in fact bad. I just went out on a service call this morning to a K7000 chassis that was dead, and it was a simple cold solder joint issue. The cap kit and other stuff had been done already - and it was still dead.

I've had two PM's recently from people with different models asking for advice. I told them to "check" certain parts. Their response was "I replaced those parts and it still doesn't work." I didn't tell anyone to "replace" them. I said to "check" them. They just wasted time and money they didn't need to.

These chassis' aren't that difficult to diagnose. you can test the HOT easily, test the VR, test the fuse, inspect the flyback for cracks around the knobs, replace caps, clean up bad solder and burnt traces, and it will usually work. If the fuse is blown, then you have other parts to check, but you take it step by step. If the fuse isn't blown, then you check the B+. The sticky has most of the info you need to get these working. There are only a couple parts on the bottom that have to be there. You just need to look at a working one to see what they should be...
 
chassis 1 is a different model than the other 2 and uses a different yoke. even tho it appears to have the same mods they used different parts.

chassis #3 would be the best to rebuild rite now it uses a standard yoke. and would be the easiest to get working.

i have the correct tube with yoke for chassis #1 if you want i could look at it for you. pm me if you want.

Peace
Buffett
 
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Advice taken! I will follow the flow chart and sticky.

I'll check all that when I decide which one to fix. I have not gotten that far.

But what should I do about these mods? Just get it to run or put these in? Chassis 3 work in a 25"?

I have the proper parts to fix them both.

EDIT: I didn't read Buffet's post.

I'll take a pic of the tube
 
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Here's a pic of the tube I have now and most of the yoke.

The tube P/N is GA63ADG25X. What else do you need off of it?

I can't tell what was originally in it. It's obvious that somebody has been working on this for some time. It's in a conversion cab that has seen better days.
 

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that is the tube#. there were many different tubes used. that wont matter but the yoke will.

there should be a sticker on the yoke its self. look and see what # it is if the tag is still there. if not measure the two pairs on the yoke and post the readings.
use ohm's on your meeter.
the sticker and or the readings from the yoke. will help determine witch chassis you should put on that tube.

also take a pic further away from the tube. have the complete frame in the pic with the yoke. this will also help id witch one you need.

Peace
Buffett
 
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