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

25k7401 bright screen

I have a wg 25k7401 chassis. It looks almost new and so does the neck board. I paired it to tube and yoke that I'm sure it is supposed to work on. It was using a wg 7000 series chassis with a decent picture but I dould not get the horizontal to adjust in anymore and decided to put the correct chassis on it. It fires right up but the screen is bright and washed out. I tried all the adjustments and they all work but I cannot get the screen brightness down. The bright and contrast both make adjutments but barely enough to compensate. I also have a second remote board I tried and no difference. Anyone care to take a stab at it?
 
sfbaybeef said:
I have a wg 25k7401 chassis. It looks almost new and so does the neck board. I paired it to tube and yoke that I'm sure it is supposed to work on. It was using a wg 7000 series chassis with a decent picture but I dould not get the horizontal to adjust in anymore and decided to put the correct chassis on it. It fires right up but the screen is bright and washed out. I tried all the adjustments and they all work but I cannot get the screen brightness down. The bright and contrast both make adjutments but barely enough to compensate. I also have a second remote board I tried and no difference. Anyone care to take a stab at it?
Click to expand...

1) What makes you think you paired the tube/yoke with the "correct chassis"?

2) What happens when you turn down the screen control (brightness) pot on the flyback?
 
The tube and frame have matching serial numbers on them and the yoke has never been removed as best I can tell. On the frame it also has a tag that says wgm2574 - u4tr28j. the chassis mounting tray matches perfectly.
I took some test point readings:
ac voltage test points:
103 = .6v
104 = 13v
105 = .5v
106 = no reading(placing probe on and off makes screen flash slightly but no reading)

dc voltage test points:
200 = 4.9v
201 = .2v
202 = 120.6v
203 = 5.6v
204 = 14.4v
205 = 23.8v

what is the value of r811 supposed to be? I will unsolder and test tonight.

turning flyback down will make the brightness go away as well as the entire image that you can see through the haze of the excess brightness. Brightness pot has same effect but less intense.
 
try setting all the controls on the neck board at their mechanical middle position or a little less and fire it up and make final adjustments from there and see if you like the picture.
 
There's a resistor on the neckboard that increases brightness as it lowers in value. It's right next to the focus part of the socket, on the side of the neckboard cable. Might have a jumper underneath it.

Or you could have the wrong neckboard paired with the chassis...
 
resistor 811 checks out fine. swapped in another neck board and it does the identical thing. two of the test point values are very off. the B+ test point only has 5.6 volts and the test point 106 will not give me a reading. I adjusted the screen control on the flyback way down to almost off and adjust the focus and you can see the image but it is behind a white/yellowish haze. I'm not sure how it can even be functioning with the B+ so low unless I'm testing it incorrectly and I have no idea why the tp106 gives no reading and the meter acting as if it is either too high or too low to read. any ideas on what next to check or test?
 
Check D802, as I've heard it can limit cause brightness issues.

Also check R310 and C529, as they can cause retrace lines to stay present if bad.

And just to make sure you have a matching K7400 set, your three boards should be labeled:

Main Chassis: P763
Neckboard: P719
Remote: P790
 
sfbaybeef said:
resistor 811 checks out fine. swapped in another neck board and it does the identical thing. two of the test point values are very off. the B+ test point only has 5.6 volts and the test point 106 will not give me a reading. I adjusted the screen control on the flyback way down to almost off and adjust the focus and you can see the image but it is behind a white/yellowish haze. I'm not sure how it can even be functioning with the B+ so low unless I'm testing it incorrectly and I have no idea why the tp106 gives no reading and the meter acting as if it is either too high or too low to read. any ideas on what next to check or test?
Click to expand...

Check your PM for troubleshooting Tips and Suspects
for your symptoms and missing or wrong voltages.
Heres the correct voltages and tp's
your missing your video B+.tp203.or no crt cathode voltages to the neck board.
Parts like d310 and r310 would be suspects first!

http://www.wellsgardner.com/pdf/voltage/K7400_K7500.pdf

Good Luck!
 
found that r310 was open. b+ pot was cracked. HOT was fried making monitor not fire up and ticking and transistor q710 was fried not allowing horizontal adjustment. I have a spare board for a 27" monitor so I was able to swap good parts onto this board. Now monitor fires up again and screen is better but still not very good. The screen is still very greyish/blueish and the white is slightly yellowish. The image itself is very clear. there are soooooo many components on this chassis I guess it could be anything. The original neckboard fried years ago due to water exposure so I guess it could of taken out any number of components on the main chassis. any ideas on specific components that would affect what I'm describing? I'm going to post a picture of it.

ok so I'm back working on this monitor again. I did the cap kit. lots-o-caps lol. I did not replace two of the caps because they did not match the existing cap values. c127 and c607 are supposed to be 470uf 35v and they sent 1000uf 35v. the color is better for sure. the image adjusts great and is very crisp.....but there is still a blue tint that is always there that will not allow me to get a good white and a good black background. I tried two neck boards and they create identical screen images so I'm back to the chassis. Is there any particular components that could create the constant blue tint?
 

Attachments

  • image.jpg
    image.jpg
    111.7 KB · Views: 84
Last edited:
U5000 repair log

Read through all the U5000 threads and started trouble shooting.

B+ (TP202) is at 148 no ticking.
Lifted W159 to issolate the the power supply section and conected a 60w light bulb between it and ground. Got a solid 116.8 out then.

Connected it again and verified back to 148. TP 203 is at 0V

R760 is good
R728 is good
Q704 HOT(2sc3686) Tests good (diode from middle to outside legs are not shorted)
Q708 tests good (diode from middle to outside are not shorted)

R765 (33k 1/2w) bad, replaced and monitor now starts up.

No vertical deflection
Adjustments make no difference and a single horizontal line across screen.

Remote cable has a pin pushed out on the chasis side, pushed back in and now have deflection.

Little green on test screen
Replaced neck board with known good, now gets all 3 colors.

2SC3782 (for green) tested shorted, replaced and now have green.
 
Last edited:
U5000 Repair log, monitor won't start after cap kit.

Monitor won't start up after cap kit

Monitor was working but was on factory caps. Installed Bob Roberts U5000 cap kit (missing a couple of caps I note).

Turned monitor on and it didn't come up, faint "ticking" sound.

Pulled W159 and used the light bulb test to see if the power supply section was working, no joy. Dead power supply.

Went back to look the caps I had replaced, in particular C117 which is the power supply startup cap. The schematic lists it at 10uf 50v. What was in there from the factory was a 22uf 63v. I put the original cap back in and the monitor started back up.

Solution: C117 is mismarked on the schematic, should be 22uf 63v

NOTE: this was a 25K5191 model monitor, the schematic for this revision does show the 22uf 63v. The 25K5108 schematic shows the 10uf 50v. I have notified Bob Roberts of the delta.
 
Last edited:
as a final update: I had a talk finally with a tech from wells gardner. he said it sounds like a weak tube that could be fixed by a rejuv probably. I did ask why the the k7000 series chassis worked on it also and he said that many of them were interchangeable. I managed to find another tube to test the chassis on and it looked awsome so it's the tube. In the end a cap kit, couple fried resistors, a HOT and voltage reg. not sure if i should buy a rejuv or toss it. I have tossed so many tubes because of weak pictures over the years and have so many chassis layin around because I couldn't fix with just a cap kit. I hate adding to landfill lol
 
are there any particular rejuvenators to look for or ones to avoid. there are several on ebay.
 
You must log in or register to reply here.

Similar threads

jjhudgins
Wells Gardner k7400 k7500 u2000 u5000 Color Issue
Replies
4
Views
543
callanbrown
callanbrown
zenomorp
U2000 - Dead Horizontal Section Repair
Replies
1
Views
211
mecha
mecha
MtWawasee
U5000 flicker
Replies
2
Views
179
MtWawasee
MtWawasee
curtislv426
Horizontal collapse k7400 *solved*
Replies
8
Views
422
curtislv426
curtislv426
K7500 Shutdown - I want to send out for repair
Replies
7
Views
470
chessiv
Back
Top Bottom