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

[modessitt]

There are plenty of threads on rejuvenator models and who likes what. A quick search should help you find them...

 

[modessitt]

Adding a couple more fixes I ran into recently:

25" K7400

Symptom: Picture shifts about an inch horizontally in a sporadic manner. See the video for an example. 1:27 is one spot in the video that shows the jumpy behavior:

Diagnosis: This chassis was rebuilt and then troubleshot by various other techs before coming to me: See thread. The problem is obviously in the horizontal circuit, either with the hold or position circuit. Others already tried various solutions such as replacing the flyback, swapping in a new neckboard, reflowing all solder joints, replacing the remote (in case of a bad hold or position pot), and replacing IC701 (which controls the horizontal oscillator). Nothing helped. Once I received it, I concentrated on the horizontal position circuit since it just seemed to move the entire picture about an inch and then back. Tracing from the H-POS pot on the remote to IC701, I noticed there were only two parts on that trace - R713 (2.2k-ohm) and C703 (1500pf). R713 checked out. As I had no way to test a capacitor of that value, I replace C703. The problem is now gone.

Solution: Replace C703.

The cap marked "152":

 

[modessitt]

25" K7400

Symptom: Monitor does not work after full cap kit/flyback replacement.

Diagnosis: A quick inspection showed a couple bad traces which I repaired. The monitor now worked. Later, I turned it on and let it run for a while with a test JAMMA board using a color grid. After about 15 minutes, I turned off the test board to change to a game setting. (I have separate power switches for the board power and the monitor power.) When I turned off the game board power, the monitor went into shutdown. Hmm, very interesting. I cycled the power on the monitor and it came back up. I turned on the game board, then turned it back off and the monitor went into shutdown again. B+ was measuring +118 when working, and +164 when in shutdown. I started checking anything to do with the video input. First I swapped the neckboard, then I tried swapping Q700 (sync processing) and IC702 (video processing). Then I swapped IC701 (horizontal oscillator/blanking/x-ray protection). No change. After about 10 minutes of testing, the monitor no longer waited for me to cycle the board power. It would just randomly shutdown. After a little bit, it wouldn't come back on and I got a "ticking noise".

Now, ticking is normally a sign of a bad HOT, but it didn't test bad. I swapped it out anyway, but it didn't help. My next step was to pull the chassis off the tube/yoke and power it on the bench (anode cup in a plastic jar) using the light bulb test (connect one side of a lamp plug to TP202 and the other side of the plug to ground. if the bulb lights when the chassis is powered up, then the power supply section is good and your issue is in the deflection circuit). This test still gave me a ticking. That was strange. I inspected a lot of stuff in the PS section with no culprits.

Around that time, I decided to swap in another flyback "just to see". I was tired of having the big lamp on the bench taking up space, so I grabbed an extra loose K7400 yoke to use as my load. Interestingly enough, I didn't get ticking this time, so I put the chassis back on my tube/yoke and the picture came up just fine. Cycling power on the game board did not cause it to go into shutdown. I let it run for an hour with no problems. Wondering if the flyback had indeed been the problem, I put the "new" flyback back on. Powered everything up and turned off the game board. The monitor immediately shut down. Swapped back in the "used" flyback I had, and it's back to working properly with no shutdowns.

Solution: Replace the flyback. NOTE: The "new" flyback was a brand new 053X-0671-001 flyback from Bob Roberts. I gave the flyback back to the owner, but I doubt Bob will admit it's the problem despite my findings...

 

[R3LL1K]

K7500 making high pitched sound

I have a K7500 with vertical foldover in the lower half of the screen, after a couple of minutes the image goes away and the chassis starts emitting a high pitched sound. I haven't gotten a chance to dig into it yet but so I would greatly appreciate some suggestions on where to start.

EDIT: Re-capped the chassis, all issues cleared up.

 

[mecha]

25" K7400

Symptom: Monitor does not work after full cap kit/flyback replacement.

Diagnosis: A quick inspection showed a couple bad traces which I repaired. The monitor now worked. Later, I turned it on and let it run for a while with a test JAMMA board using a color grid. After about 15 minutes, I turned off the test board to change to a game setting. (I have separate power switches for the board power and the monitor power.) When I turned off the game board power, the monitor went into shutdown. Hmm, very interesting. I cycled the power on the monitor and it came back up. I turned on the game board, then turned it back off and the monitor went into shutdown again. B+ was measuring +118 when working, and +164 when in shutdown. I started checking anything to do with the video input. First I swapped the neckboard, then I tried swapping Q700 (sync processing) and IC702 (video processing). Then I swapped IC701 (horizontal oscillator/blanking/x-ray protection). No change. After about 10 minutes of testing, the monitor no longer waited for me to cycle the board power. It would just randomly shutdown. After a little bit, it wouldn't come back on and I got a "ticking noise".

Now, ticking is normally a sign of a bad HOT, but it didn't test bad. I swapped it out anyway, but it didn't help. My next step was to pull the chassis off the tube/yoke and power it on the bench (anode cup in a plastic jar) using the light bulb test (connect one side of a lamp plug to TP202 and the other side of the plug to ground. if the bulb lights when the chassis is powered up, then the power supply section is good and your issue is in the deflection circuit). This test still gave me a ticking. That was strange. I inspected a lot of stuff in the PS section with no culprits.

Around that time, I decided to swap in another flyback "just to see". I was tired of having the big lamp on the bench taking up space, so I grabbed an extra loose K7400 yoke to use as my load. Interestingly enough, I didn't get ticking this time, so I put the chassis back on my tube/yoke and the picture came up just fine. Cycling power on the game board did not cause it to go into shutdown. I let it run for an hour with no problems. Wondering if the flyback had indeed been the problem, I put the "new" flyback back on. Powered everything up and turned off the game board. The monitor immediately shut down. Swapped back in the "used" flyback I had, and it's back to working properly with no shutdowns.

Solution: Replace the flyback. NOTE: The "new" flyback was a brand new 053X-0671-001 flyback from Bob Roberts. I gave the flyback back to the owner, but I doubt Bob will admit it's the problem despite my findings...

this is exactly what I was telling you about with a K7400 in that Ms. Pac/Galaga I probably asked you about several times. where the B+ goes from 118 to 164V. for what it's worth, I capped that chassis and replaced the flyback and it still persisted in randomly shutting off. I never bothered messing with cutting power to the game board though, cause it was one of those whack power supplies to maybe reproduce what you got.

I don't work there anymore, and I guess they sold all the games anyway, so not my deal anymore heh.

 

[modessitt]

I have a K7500 with vertical foldover in the lower half of the screen, after a couple of minutes the image goes away and the chassis starts emitting a high pitched sound. I haven't gotten a chance to dig into it yet but so I would greatly appreciate some suggestions on where to start.

Full recap - then check again...

 

[cadillacman]

Not sure if you have a u2000, u5000, 7400, or 7500 chassis? Read this:
http://forums.arcade-museum.com/showthread.php?p=2371552#post2371552

 

[modessitt]

27" K7502

Symptom: After recap, the monitor works fine for a while, then shuts down. It starts back up immediately when power is cycled, but then shuts down again after a while. Repeat.

Diagnosis: The flyback might have been replaced also. It looked new, but the zip tie around the core wire looked original, so who knows. Any way, what I found interesting after spending a bunch of time fixing cold solder and repairing some lifted traces was that after it warmed up, I could make it go into shutdown just by checking the B+ or STOP checking the B+. I had an alligator jumper on TP202. If I had my meter attached and let it run for a while, the act of removing my lead from the jumper would make it go into shutdown. If I didn't have it attached, simply touching the jumper to my lead would make it go into shutdown. It didn't do this when first turned on, or even several minutes later. But let it run for 20 minutes and it would do this repeatedly. After a lot of testing and stuff, I finally decided to replace the flyback with a new one I had. Problem gone. Has run for 6 hours straight without shutdown and nothing I do with my meter and TP202 will cause it to shutdown.

Solution: Replace the flyback (again?).

 

[Tighe]

That is really interesting symptoms!

 

[marcux]

Adding a couple more fixes I ran into recently:

25" K7400

Symptom: Picture shifts about an inch horizontally in a sporadic manner. See the video for an example. 1:27 is one spot in the video that shows the jumpy behavior:

Diagnosis: This chassis was rebuilt and then troubleshot by various other techs before coming to me: See thread. The problem is obviously in the horizontal circuit, either with the hold or position circuit. Others already tried various solutions such as replacing the flyback, swapping in a new neckboard, reflowing all solder joints, replacing the remote (in case of a bad hold or position pot), and replacing IC701 (which controls the horizontal oscillator). Nothing helped. Once I received it, I concentrated on the horizontal position circuit since it just seemed to move the entire picture about an inch and then back. Tracing from the H-POS pot on the remote to IC701, I noticed there were only two parts on that trace - R713 (2.2k-ohm) and C703 (1500pf). R713 checked out. As I had no way to test a capacitor of that value, I replace C703. The problem is now gone.

Solution: Replace C703.

The cap marked "152":

Thank you, this fixed my issue, that 1 cap which didn't look bad, was..

 

[modessitt]

Good to hear. I corrected the Photobucket link in case anyone else needs it.

 

[Charles Kline]

Thanks for documenting these repairs Modessitt.

I'm trying to figure out what is causing a no power issue on this k7400. (pretty sure its a 7400 based on the P763 sticker)



From looking at different threads I've found that R728 going open is a common problem.

I checked R728 and it for sure was open. Weird thing is it's a 10 ohm resistor and not the 1k shown in the manual. it does looks original.

This monitor ran before it started doing this no power issue so I know it ran with that 10 ohm resistor.

I had a 10 ohm 2w resistor on hand so I replaced it and it's still dead.



Unless that 3rd stripe turned black when it went open that sure looks like Brown, Black, Black..

Is the burned up R728 the cause or the symptom? Doesn't anything else usually get fried when that resistor opens? the HOT was replaced and I confirmed it is still good.

Thanks,
-Charles


*Edit; interesting thing is the resistor next to R728 is a 1k, Finding a full part list on the 7400 is proving to be a pita, everything I've found only shows the 'replacement parts' not the full list.
I'm wondering if those 2 resistors were put in wrong at the factory and it just now died...

 

[curtislv426]

Subscribed so I don't lose this thread.
Thanks