WG K7500 Help

DJMOJO

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I have a WG K7500 that came out of my Gauntlet Dark Legacy cab. it had a wierd vertical colapse issue where i could only stretch it out to 3/4 of the screen and was displaying red really weak. I was trying to adjust a pot on the neck board and fixed the red issue. then i went to try and adjust the rest of the screen but could not get it to strech all the way. next thing you know it just died on me. it doesnt even come on now...

i ordered a cap kit from bob and a new flyback too but... im not sure if this thing is toast now...

what could be the problem and how can i test it if its not even coming on?
 
Definitely hard to say for sure. But sounds to me like U701 was failing (which caused the reduced vertical scan), and when you ran it with a component that was starting to fail, it finished it off. Then once U701 was dead (and the horizontal circuit was dead), the monitor goes into shutdown.

Also hard to say why it happened. Sometimes ICs fail on their own, other times it's because capacitors go bad causing improper voltage, could also be that a resistor went open, or a variety of other things. Before you test again, you'll want to check the components in the horizontal circuit.

If it's not U701, then it could be a combination of multiple failures, a resistor (R627?) out of value, or a bad U601, a broken Vert pot or even caps could cause the vertical shrinkage and bad caps, or a failing component in the power supply, a bad or misadjusted B+ pot or another failure that blew the HOT could send you into shutdown.

It's definitely repairable, but I think you'll need to do some further testing or cap it and shotgun chips (start with U701).
 
You probably didn't need the flyback.

Cap it first. There are a couple resistors that can cause it not to stretch vertically, but you need to cap it first, then see if it's still messed up.

As far as it shutting down, that can be cap related, too, especially if you're messing with settings and you get it to a point where it stresses the oscillator.

Considering that you stated in another thread that you can get this fixed for $55, why are you messing with it yourself?
 
U701 looks fine it doesnt look burned or anything, how could i even replace that?
U701
IMG_3604.jpg


IMG_3605.jpg


U702
IMG_3602.jpg


IMG_3603.jpg


If i could save the 55 id rather do that.
 
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At this point you need to cap it and worry about other parts later.

You'll probably spend more than $55 of your time screwing around with it - and possibly making it worse - if you're not experienced at monitor repair. The K7500 isn't the easiest chassis to repair. If you don't know how to remove and replace a chip, you'd be best off paying someone else to fix it...
 
well i have plenty of experience soldering so i think ill give it a shot, now when you say the K7500 isnt the easiest chassis to repair are you referring to the amount of soldering that needs to be done? or is there something else.

i might not know much about crt repair but im pretty familiar around a soldering iron.

also, where can i find the ICs i need to replace?
 
You said you ordered a cap kit from Bob Roberts. Start with that. You wouldn't want to replace parts just to have them get toasted by out-of-range caps.

Since it's so cheap, may as well do it as preventative maintenance. And even if it is an IC that went bad, it may have gone bad because of bad caps, and you'll just be wasting money swapping in a component to have it fail again.

Bob Roberts also carries the common ICs.

Service manual:
http://www.wellsgardner.com/pdf/Service/K7500.pdf
 
Don't order and replace parts just to replace parts. Replace the common fail parts first (caps). If that doesn't work, measure the B+ and diagnose from there...
 
Ok I got my cap kit today, started working on it at 10 pm and I just now finished (3 AM)... i have a few questions...

I noticed there where a few caps missing and a few spare caps...

These are the caps missing from the kit

C105
IMG_3610.jpg


C734
IMG_3611.jpg


C119
IMG_3615.jpg


These are the caps i am confused about

C616 Its just so much bigger than the cap that came off of it but according to bob this cap in the one that belongs here.
IMG_3612.jpg


C729 its just so much smaller than the allotted space. Makes me think that this cap is wrong... oh and on a side note, there was nothing on C729, It was empty when i started.
IMG_3614.jpg


C725 Says its a jumper... i know what a jumper is but i dont know what/if im supposed to replace it... i actually couldnt even find the damn thing!

C512 (neck board) Doesnt even look like a cap(looks like a small blue resistor looking thing) not sure what the polarity would be even...

Any help to clear these things up for me would be greatly appreciated!

Thanks in advance.
-José
 
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Ok so i have now double checked and triple checked everything and I found 2 errors I made (luckily I didnt hook anything up or power anything on)

I have 7 spare caps in my U2000 K7400 K7500 combo kit. Of those 7, 5 of them are for the other chassis and the other 2 are spares. all the correct caps are accounted for.

The two errors I found where...
1. I had a the wrong cap on C115, I had a 220UF 100V when it should have been a 100UF 200V, so I fixed that.
2. I had a cap on backwards so I desoldered it and put it back on the correct way.

C512 Before
IMG_3616.jpg


C512 after, I hope I got the polarity correct
IMG_3617.jpg


IMG_3618.jpg


What do you guys think? does it look ok?
 
1) As mentioned, the kit you get from Bob is made for all variations of this chassis, so some caps won't be used.

2) The 470uf cap is the filter cap and is almost never included in the kit. That 330uf cap and any other polarized caps should have been included, though, in my opinion.

3) The neckboard cap is in correctly.

4) The big 2200uf cap Bob sent you replaced a 1500uf cap that was there originally. The 200uf will work, although I always order 1500uf's for when I cap these.

5) The cap size difference for that one cap is fine...
 
ok i got the monitor put back together and plugged it into my gauntlet dark legacy cab and all i get is a ticking, sounds like a clock, coming from the flyback i think... not sure what this means...
 
also i would remove the cap you installed that was never there. if it always worked this way, i would not be adding components to it.

the K7500 and K7400 will have ONE cap in either spot. meaning, the K7500 has a cap in one spot, and the other is empty, and vice versa for the K7400.

I can't remember specifically which one is which, so I hope you remember which one needs to get pulled out.

the "extra caps" are for a pincushion board if you have a 27" or larger tube. I can't remember if those Gauntlets had 25s or 27s... they're like the other Midway cabs but a little different.

now I'm not sure if having that extra cap would cause your ticking issue, but if you happened to pop the HOT having that cap in there, that will cause your ticking. without horizontal deflection, you can't have high voltage. the only other thing I can think of is that you made an error in your solder work elsewhere, perhaps a solder bridge between two joints.

I'm no scholar on the subject, but I suspect that the primary difference between the standard resolution K7400 and medium resolution K7500 is the jumper wire arrangement in the middle of the chassis and that either-or cap placement. there's probably some other shit that's different, but I'm also going to assume you blew the HOT having that other cap in the circuit, if it's even attached to horizontal deflection. I don't memorize anything with these at all, soo....

I'm not even sure which of the 3 transistors on the black heatsink is the HOT. I don't think it's the 3rd one, probably the middle one, and the first one is maybe the vertical IC?
 
its a 27 and it does have the extra pin board and I did replace the caps on the pin board aswell, I should have clarified that.

This is the extra cap C729
IMG_3614.jpg

I'll take that extra cap out and try again.

I'll also look for solder bridges too! Thanks for the advice!
 
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Good luck on your repair.

Nice to see some high res close up pics for a change -- usually here you see cell phone pics that are so blurry or so far away that they're of little use...
 
ok, I think I remember now, I think it's C729 and C731 that's the either-or. lol

I'd have to compare a 7400 and 7500, just for fun. they're loosely based on the previous U5000 model where you had 2 headers in the middle of the board for either 15k or 24k operation (that's standard or medium res) and I happened to notice when I was working on a Ms. Pac/Galaga monitor that where those headers used to be, there's still wiring arrangements, and they're different between the 7400 and 7500, and those 2 cap locations.

before I ever did my first monitor cap job, I did a LOT of reading up on it, and there's a few rules: 1) voltage rating can vary, microfarad rating cannot (unless it's one of these whackjob monitors... they changed that shit) 2) if there was no cap there to begin with, leave it empty. 3) always verify your work! I've capped monitors in loud game rooms, and I've observed I made the most mistakes under said conditions vs. doing it after we were closed.

way I started capping monitors the last like 3 or 4, I did the biggest caps first, and I always X off what I changed. sometimes I forget to, juggling an iron and a desoldering iron. when you get to the really small ones, that's when you start sorting them all together. other instances, you'll get kits that have caps with variations, and that's when it becomes a pain in the ass.

throw another monkey wrench in when you're dealing with these Wells monitors and the solder pads get toasted.

I learned the hard way that you can do like a 2 hour monitor capping (in loud settings, mind you, with workers asking questions every 2 minutes) leaving the irons plugged in the whole time. they reach a point where they become ungodly hot, and that's how you can start doing damage. so take a break every 30-45 mins.

there, that's all the advice I have left to offer lol
 
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