modessitt
Volunteer: Encyclopedia Submission Moderator
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...
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...
Last edited:
