Some K7400/K7500/U2000/U5000 Repair logs...

modessitt

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EDIT - Wish I could change and make THIS the first post. I wanted to add that all of these chassis (except the first one) have had cap kits installed already. If you are working on one of these, it is a good idea to install a FULL cap kit and inspect the chassis and neckboard for cold solder (especially on the drive transistors).

Also, the U2000/U5000 have upgrades recommended for the power and vertical sweep sections. You can find the info on doing those upgrades here:

http://home.comcast.net/~mtpacifico/_kenskorner/files/WG U2000 - U5000 Service Kits.pdf



I'm working on 8 of these for members at the moment (1 U2000, 4 7400's and 3 U5000's), so I figured I'd start a repair log. Might make a good reference for others who mess with these from time to time. Feel free to add your own fixes. (Please keep troubleshooting advice to separate threads. Once it's fixed, then add it here for others' benefit).

I've got three done so far today, and may get another in before bedtime. They've had some interesting issues.

So, without further ado:


27" K7400

Symptom: No picture. Has raster.

Diagnosis: Color goes straight to the neckboard, but swapping neckboards did not bring back the picture. Started looking at the Auto-Beam limiting circuit and the Brightness and Contrast circuits in the 800 section. Noticed that a partial cap kit had been done to the chassis, but none in the 800 circuit. Replaced the caps with new ones and picture was back.

Solution: Install FULL cap kit.



25" K7400

Symptom: Monitor would not sync either vertically or horizontally.

Diagnosis: Found diode D700 on the horizontal sync line to be shorted. Once I replaced it, I had proper sync. While adjusting picture, I got zapped by arcing from pinhole on flyback (ouch!). Replaced flyback and picture is now perfect.

Solution: Replace D700 to fix sync. Replace flyback.



25" K7400

Symptom: Monitor would not sync and what picture I can see looks like it's only showing the blue.

Diagnosis: I could see R600 burned next to the video connector and replaced it. The owner had tried diagnosing it himself and had removed U601, U701, and U702, but had sent them with the chassis. I socketed U701 and U702, but swapping in others did not fix the problem. Noticed the +5 was missing at Pin5 and Pin14 of U702. Tracing back found a bad Z700. Replacing it gave me proper sync, but only the blue part of the image. Swapping on a new neckboard fixed the issue, so the problem was definitely on the neckboard. Found the Red drive transistor (Q505) to be bad, but replacing it did not bring back red. Found Q510 and Q511 to be shorted. Replaced them and all colors were back.

Solution: Replace Z700 and R600 to fix sync issue. Replace Q505, Q510, and Q511 fixed color issues.

Next up are 3 U5000's, so I'll add more as I get them done. if anyone has their own fixes to add, go ahead. Maybe we'll get a sticky...
 
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i vote this be added to and become a sticky someday.


27" U5000 . b+ was misadjusted by previous owner attempting to "make picture perfect". Ran for awhile then blew hot. Replaced hot,recapped, replaced b+ pot, adjust b+ to spec. Runs but monitor has linearity issues. some adjustments do nothing. See picture.
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owner ran it this way for 8-10 hours then hot blew again. did somee more hunting. THis monitor already had most of the service updates on it. Please read these two links for more info about service updates:
http://forums.arcade-museum.com/showthread.php?t=103723
http://forums.arcade-museum.com/showthread.php?t=66080
I ended up finding a shorted mosfet, Q710 or q719( unsure of my typing lol)
"verified that q719 was in fact shorted. THat was "overpowering" my width and pincushion circuits..

replaced q710, also replaced some small "2nxxx" transistors in the deflection circuit and on the pinchshion board, not because they tested bad but just because i had them and went ahead and jammed them in..


Now i have width adjustment on remote board and coil, and i have pincushion adjustment as well..."

Here is a link to the original post. http://forums.arcade-museum.com/showthread.php?t=119758&highlight=u5000


25" K7400: signifigantly out of focus and picture hulas and shakes bad.

Focus keeps drifting after adjustment.. Found hairline crack in flyback at focus pot.(lucky i didnt get shocked) Relaced flyback and recapped chassis. check b+ ok. Make final adjustments, all happy now.
 
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Thanks Mode it sounds like some are coming along. Cant tell you how nice it is not to have to deal with monitors all the time. I have my hands full with redemption stuff right now. Ross...
 
25" U5000

Symptom: Dead.

Diagnosis: No B+. Fuse is good. A closer inspection found it was making a faint 'ticking' sound. This happens when it is trying to start up, but the Over Current Protection (OCP) circuit is kicking in due to a short somewhere. Usually, this is a bad HOT. Sure enough, the HOT was shorted. Replaced it, and the monitor powered right up, but with a scrambled pic and loud chatter from the neck. Luckily, adjusting the Horizontal Hold fixed the scrambled pic and made the loud chatter fade to minimal levels. Tested fine in both standard (15k) and medium (25k) resolutions.

Solution: Replace HOT.
 
Okay this one was a little tricky. When I first powered it up in medium-resolution mode, I didn't notice anything wrong. Colors and brightness needed to be adjusted up, and horizontal hold tweaked slightly, but looked fine. When I powered it up in standard-resolution mode, I again adjusted horizontal hold. Again it looked okay, but when I tried to increase the vertical height to fill the screen, the image seemed to fold over as it got close to the edge. Backing off on the vert size until it looked good left about 2" of black space on top and bottom. Moving the vertical position upwards also caused it foldover. Unacceptable.

25" U5000

Symptom: Screen cannot be adjusted vertically to fill the entire screen without causing stretching and foldover.

Diagnosis: A normally working U5000 will foldover when the vertical height is made much larger than the screen, but will adjust to full screen height without causing it. Even though the caps looked like they had been replaced within the past few years, I swapped in new ones in the entire vertical section to make sure they were'nt the cause. I also tried swapping in a different remote bd, U701, and U601 just to make sure they weren't the cause. Following my schematic back from the Vert Pos pot on the remote, I tested Q602 and R621 before moving to R620. R620 is on the 30v feed to Q602. I noticed the schematic listed an R620 and an R620A in parallel, but this chassis had only R620. It looked factory, so I checked 3 others U5000's that I had, and all had another resistor (R620A) attached to the top of R620. I added the appropriate resistor in parallel to R620 and the image now adjusts full screen without folding over.

Solution: Install R620A in parallel with R620.



This might help a few people who have issues with screen size and foldover during adjustment...
 
My last U5000 of this batch, and it had the most issues. I'm going to list the symptoms at different tiimes, as it might help someone in the future.

25" U5000

Symptom: Chassis dead.

Diagnosis: B+ was a +145.6, indicating an issue in the horizontal deflection circuit. The monitor was not chirping, which is usually a sign of a bad HOT, and the HOT did indeed test okay. Usually this is caused by a bad solder connection, broken/burned trace or damaged part. A visual search eventually led to finding T701 with a broken wire. Unfortunately, there wasn't any strand found to reattach. Rather than unwind it in search of the broken strand, I replaced it. B+ was now at +118.

Solution: Replace broken T701.


Symptom: Chassis dead.

Diagnosis: I now have a perfect B+, but the chassis is still not working. This is a common issue with these models, and is typically in the start-up circuit. A common fail point of the start-up circuit is R760. Sure enough - it was open. A quick search of the connected parts found that Q708 was shorted. Replaced both parts and the monitor now powers up.

Solution: Replace R760 and Q708.


Symptom: Monitor powers up, but image is very streaky. Horizontal hold will barely lock and the picture is all distorted. Colors do not look right.

Diagnosis: Swapping on a known good neckboard fixed the issue, so my attention focused there. Visual inspection for cold solder or broken traces is my first step, and I quickly found that Q501 had broken off leaving only the legs. Putting in a new 2N3904 transistor gave me a decent picture.

Solution: Replace missing Q501.


Symptom: Image will not lock vertically.

Diagnosis: Swapping in a known good remote board fixed the issue. A quick inspection showed that - while the knob would turn for the Vertical Hold pot, it wasn't actually turning the pot inside because the hex insert had cracked. Replacing the 200k-ohm pot fixed the issue and the image now locks in.

Solution: Replace VR902 on the remote board.


Symptom: Image is bright and stable, but the linearity is messed up. The color bar grid shows normal-sized bars at the top of the screen, but they get narrower as they progress towards the bottom. The bars at the bottom of the screen are half the size of the top of the screen.

Diagnosis: This problem took a majority of my time, mainly because I skipped a step. My normal progression upon receiving a problematic chassis is: Inspection of common fail points (HOT, VR, fuse, traces, etc), replace caps, reflow solder, repair traces, replace known bad parts, test. Since this chassis looked to have had caps replaced within the last couple of years, I skipped that step. I knew the issue was in the vertical section, so I first replaced U601, then Q602, then I did some voltage checks, then I tested some resistors, then I ended up doing a voltage reading on every part in the 600's of a working chassis and comparing it to the non-working chassis - and came up with nothing. Finally, I decided to replace the caps in the vertical section "just to see" - and the damn thing is fixed now. :rolleyes:

Solution: Replace caps in vertical section.


BTW - this chassis also had the issue of foldover on height increase just like the last chassis, and had the same solution...
 

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Why didn't you just link it on WG's site, along with the Service Manual, so that people could view it without downloading?

I have another K7400 to post soon. Easy fix, but wait until you see what it looked like when I got it...
 
??? i dunno. came across that in another post and figured it was worth sharing. will add more links to that as i find them..

i linked this post in the k7000 sticky so lets throw 7400 7500 u5000 info here, if thats cool with you of coruse...
 
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Here's an interesting one:

25" U5000

Symptom: Weird, distorted pic. Everything is way out of focus, colors barely showing, image was folding over when adjusted fully.

Diagnosis: Verified the game was putting out proper video by connecting it to another monitor. Inspecting in the field found two transistors on the neckboard had been replaced but the legs weren't cut. When the cardboard was put back on, the legs got bent over against other pads. I checked them and found they were NOT shorted, so I trimmed the legs and tested again. Same issue, so I pulled the chassis to take back for repair on my bench. When connecting it to my test tube, I got bright colors, but the same foldover issue when increasing the height. I could get a perfect picture if I adjusted it to about 6" tall in the middle of the screen. I checked R620/620A and found them to be proper. I tried swapping remotes with no effect. Swapped neckboards just in case those transistor legs caused a problem, but no effect. I replaced all the caps in the vertical section, U601, and U701 - testing after each change - with no effect. B+ was measuring perfectly at +117.7vdc. I inspected for broken traces or cold solder in that area, but every repair I did of anything that remotely looked suspect did nothing to help. Eventually, I started pushing and wiggling various parts on the chassis. When I pushed on the PTC in the PS section, the image got wider. I shut it off and pulled the chassis, and found some wiggling pads on the PTC. I added jumpers to the next pad in each trace, powered it up - and I now have full picture that adjusts just fine. :confused: Not sure what the PTC has to do with the vertical size, but that's the only thing I did between a bad test and a good test.

Solution: See below in EDIT.


On another note - this customer bought FIVE games from a company online, and of the five that showed up - all of them had issues. :rolleyes: One cocktail had the monitor power connector come loose, two CPS games wouldn't boot (a tech from a different company came and looked and decided the PCBs were bad and the company he bought them from shipped him new ones that I put in), one of the CPS games had no red (a 25" K7000 that I'll be looking at next - I think the tube needs rejuving but we'll see), and third CPS game had this issue. One game - Area 51 - worked, but the sound would cut in and out. I reseated the chip on the sound board and it was fixed.

What concerns me is that this chassis initially looked different on my tube than on his. I hope the shadow mask didn't break loose during the shipping of the game....

EDIT - The problem came back. Apparently it was just coincidence. Finally tracked the problem down to a pinched wire on the remote cable.

And - the shadow mask was NOT broken. Both tubes needed major rejuvenation, but they both look good now...
 
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Nice work Mod. I hate those monitors as you spend a fortune on caps and usually someone has dorked up the neckboard transistors pretty bad. I bought a bunch of neck boards from Chad a while back and only have a few left. Going to be posting my remaining U5000/U2000/K7500 chassis in the for sale forums soon for those of you that feel up to a challenge. Most have NOT been worked on by me and were only acquired as part of a bulk buy. Wish I had this post a year ago when I was working on these. Now I can't find my notes for my repairs. Again, thanks for keeping a log and sharing.
 
27" K7400

Symptom: Monitor was capped by client and it worked for 15 minutes before shutting off and no longer starting.

Diagnosis: This one was an interesting puzzle, as the obvious solutions did not work. the main problem was that it was in HV shutdown - B+ was running +166vdc. Tested the PS section using the light-bulb trick and it was good, so that means a problem in the horizontal deflection or startup circuit - usually a bad solder joint or broken trace. Well, I found a couple that I fixed, did a whole bunch of testing with no problems found - and it still didn't work. :mad: Trying to narrow it down, I swapped in another flyback (even though the new one seemed ok), then a new HOT (even though it tested okay), and another U701 (with a socket) - but it still didn't work. While doing some voltage checks on the bench, I accidentally pushed down on one end of U701 and the chassis came on! Did some inspections of the chip and socket with nothing popping out, until I found a short between pins 11 and 13. But there was no short on the chip itself. I eventually found that the little chicklet cap at C711 had one leg on the solder side that was bent over a nearby trace, and apparently had rubbed through the green coating and was shorting to the trace. (This is not a part that would have been changed during a cap kit.) Apparently, my flexing of the board when pushing on the chip caused it break contact with the trace. I unsoldered it, bent the leg upright, resoldered and trimmed - and now the monitor works! I put the original flyback, HOT, and U701 (with a socket now) back in - and it still works!

Solution: Repair short between C711 cap leg and adjacent trace.


I always get the fun ones.... :rolleyes:
 
I deleted my lengthy questions as Modessitt quotes me as he answers them. I wanted to keep this thread his as much as possible as it is an excellent resource for troubleshooting.
 
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Been sick for the last few days, but I'll try to answer...

I wanted to ask about some of your testing methods (maybe some newb in this, but I am learning and fixing).
- When you say that a transistor is shorted, how do you test?

For the U5000, you put the black lead on the center leg of the HOT, and the red lead on each of the outer legs. if you get a short reading, then it is bad. Do not measure between the two outer legs.

- How do you test the HOT? are they all done basically by the same method?

The method above is how to test the HOT on a U5000, and the related chassis this repair log pertains to. Other models may have different testing procedures.

3 quick questions specific to the U5000:
- What do you use to replace the L103 inductor with? Seems like all of mine are burnt (Mouser #?). Any other common inductors to have a spare for?

I have seen some models with a different part there instead of the wire-wrapped circular inductor you refer to. I'll see if I can find an example to see what is there instead.

- I had a monitor that worked fine, recently shut down with a burnt smell, found R760 is open. Why is R760 such a common failure?

Not sure. Perhaps the resistor needs an increase in wattage. Perhaps the stress of turning on and off so many times over and over causes it to fail.

- Lastly, I have 5 chassis that have various levels of the service update kits installed. For the most part, the IC's look to be the update kit numbers, but many of the resistors/diodes do not appear to have been changed. Am I safe to assume that if the HOT is a 3686, it is OK? (meaning updated, not necessarily functional) I have one chassis that I assume isn't updated as it has a 3687 and the Q703/Q703 are not 2482's. None of my chassis's have there heat sink on the Q703 which are 2482's.

No, having a C3686 at the HOT (Q704) location does not mean the upgrade kits have been done. C3686 was the original HOT part. If you have one with a C3687, I'd replace it. I think it is included in the upgrade kit only for those who are upgrading already-failed chassis. In fact, many of the upgrade parts you may find to be the same as the ones already there. The missing heat sink is more of an indicator, but I've seen them come off, too. If you're worried, just put in a fresh kit and ease your worries. Personally, it's not something I worry about, maybe because most chassis I see have already had it done...
 
25" U5000

Repair was attempted by someone else who said it was blowing HOTs, that it looked like someone had worked on it and may have put the wrong parts on it, and wasn't worth the expense of continuing to try to fix it. I received it with a partial cap kit and no HOT (or insulator).

Symptom: Blowing HOT's.

Diagnosis: Before putting in a new HOT, I checked around the chassis for shorts. During my inspection, I found that the B+ adjustment pot had been replaced, but it was cranked all the way up. I did a measurement check on an original glued pot on a working chassis, then set the new pot to the same value. Put in the new HOT (with insulator) and it fired right up - if blurry and dim.

Solution: Set B+ to proper setting and replace HOT/insulator.


Symptom: Picture was dim and bit blurry.

Diagnosis: Went to adjust the focus and got zapped by lightning (again). You'd think I'd learn, although a plastic screwdriver or glove wouldn't have revealed the problem, as it was working and not arcing to anything nearby. Put in a new flyback and the picture came up but still dim.

Solution: Replace flyback.


Symptom: Picture too dim. Turning up brightness on flyback or remote just made the picture get all washed out. Colors stayed dim.

Diagnosis: Since all the color goes directly to the neckboard, I swapped neckboards and had a nice bright picture. While tracing through the brightness circuit, I came across R500. Now, this is supposed to be a 3.3-ohm 1-watt resistor. I found the resistor to be a 6.8-ohm 1-watt resistor. This doesn't seem like much, but I replaced it with a 3.3-ohm and the picture got noticeably brighter, but was still a bit dim in the upper register (reds mostly). Inspecting the good neckboard, I saw a factory jumper bridging R500 directly under the resistor. So - I put a jumper across where the resistor was, and the picture came up nice and bright on all colors.

Solution: Replace/Jumper R500.


Symptom: Picture will not adjust vertically.

Diagnosis: Now I had a nice picture, but with about 2-3 inches of black along the top. I could change the Height to make the image reach the top, but the bottom went off the screen too much. Adjusting the Vert Pos pot only made the picture wiggle a tiny bit. I swapped on another remote with no change, then another remote cable with no change. I started tracing through the schematic from the Vert Pos pot back to the Vert Output IC (U601). Everything seemed to measure okay, but then I noticed Q602. This is supposed to be a 2N3904, but what was there was an MPSW05. It looked factory, so I didn't have good hopes on swapping it out, but a new 2N3904 gave me Vert Pos control once again.

Solution: Replace Q602 with proper part.



Enjoy...
 
25" k7400 (25k7401) Intermittently, especially when cold, width will shrink inward then snap back out. Sometimes the screen goes kind of white at the same time. In some cases it will eventually shutdown when this is going on. Reflowed some bad solder joints on the remote adjustment board but it did not help this issue.

Found a cold solder joint on the flyback that is on the same trace that goes to the width connector for the yoke. Reflowed all the pins of the flyback, and reflowed the video connector pins, adjustment board connector pins, and color transistors on the neckboard just because i already had the chassis out.

So far so good but there is a crack in the flyback so i will need to replace that soon.
*UPDATE 7/6/12: I epoxied up this fly(which im sure i will regret later hehe) and this thing just ran an accidental 24 hour burn test :D SO i think its fixed.. till the fly goes anyways.

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^^^^^ Of course, in proper fashion as soon as im 95% done with this area 51 trio project my monitor starts acting goofy again. Just a smack of the cab wil cause these same issues. TIme to repull it and see what cold solder joint i missed.

Found it. I had a few sketchy joints at the b+ or shutdown pot and ac connector but whaqt i missed was r111 was ready to fall out the solder joints were so bad. Reflowed all that, now its happy again. I will repost if it gives me anymore fits but i think i nailed it finally.

edit 11/2012: THIS HAS BEEN ROCK SOLID EVER SINCE THIS POSTING.
EDIT 5/2013: still going strong!
 
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BTW - if you still have edit capability on your K7000 sticky, can you change the link to this thread to go to the 1st post rather than the one you have it pointing to?
 
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