Wells Gardner K7000 almost fixed

dbstallman

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About a year ago, my 25" WG K7000 went black. I had never worked on a monitor before and was rather terrified of the high voltages. But after steeling my courage, I decided I could make it work and talked to some other people at auctions who gave me suggestions as to what the issue could be from my description of the problems before it went out.

I went to Bob Roberts and ordered a replacement cap kit, flyback transformer and horizontal width coil. I took the chassis off and found that the fuse had blown. Since it was apart, I installed all my parts, replaced the fuse and put it back together. The fuse promptly blew again. I then replaced the HOT and the Voltage regulator (2 times each!) but the fuses kept blowing. Many months went by and about 3 weeks ago, I decided to try and tackle it again. I saw a suggestion to someone with a similar problem to check the Crit Safety Cap (C36) for short, which mine was. After replacing that and C38 (also shorted), the monitor fired up.

Now that you know the history, here are my new problems :

Horizontal width will not adjust to fill the screen. I have adjusted the coil all the way, but it gets to a max of about 60%.

The B+ voltage is 150~154 on one side of the 220 ohm resistor and 115 volts on the other.

The tube goes dark after being on about 20 mins., but will turn back on for about 4 mins. after a 1 minute rest and a full 20 mins. again after a 30 minute rest.

I've checked Randy Fromm's flowchart and it says the problem should be my voltage regulator. I swapped it out and there was no change to the voltages. Both VR's check good on my meter.

Anyone have any good ideas where to look next?

Thanks.
 
This will fix your width problem, but I suggest you tackle the B+ voltage issue first, since it is likely causing the width problem.

http://www.therealbobroberts.net/width.html


Test the ceramic resistor hanging off of the side of the chassis, what is it's current resistance? I'll check the manual and be back in a second to point out the other components in the circuit...
 
Test the following reistors as well:

R103, R84, R85, and R86.

Also test the following capacitors:

C55, C56, and C57.


Look for cold solder joints and loose components around each of those components.

Finally, make sure you have the right voltage regulator, it should be either a STR30130 or a STR3130. If you have a 30123 or 3123 you have the wrong voltage regulator installed.
 
I should be able to test the resistors without removing them from the circuit, right?

R84 is testing at 3.3k, R85 is testing at 2.46k, and R86 is reads ~9k when the leads are put on each end of it but the value just keeps rising on my digital meter. I stopped checking after about 20 seconds, but it went up to 15K and was still climbing. R103 reads correct at 2.7 Ohm, and the large cermaic on the side of the heatsink reads 175 Ohm (I think it should be 220).

I don't have a capacitance check on my meter, but C56 and C57 were replaced as part of the Cap kit I installed. None of the capacitors are shorted.

I replaced C38 about 2 hours ago with one from Bob Roberts.

Also, my original voltage regulator was a STR3130 and that is the one that I got from Bob this afternoon.

Thanks.
 
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You can not accurately test the resistors while in circuit unless they have no parallel branches. The rising number you are seeing is a direct result of a capacitor being tested along with your resistor. Pul one leg from each resistor and recheck. I suggest you look for cold solder joints before doing so.

Here is a link to a schematic: http://arcarc.xmission.com/PDF_Monitors/Wells%20Gardner%2025K7191.pdf
 
Before going through a bunch of parts, you probably need to do a bunch or trace and pad repair/jumpers...
 
All four of those resistors are checking with the correct values outside of the circuit. The only one that is measuring wrong is the one hanging off the side. That one is still testing 175 Ohm, not 220 Ohm.

I don't thing that is the cause of the screen problem, though, because the voltage going in is 155v.

Since I don't have the ability to test the caps, I am just going to replace C56 and C57. Randy Fromm's flowchart suggests replacing C57 or the VR when you have these symptoms.

I'll let you know how it goes.

Are there any other suggestions?
 
I'll double check all the traces and pads again, but they all seemed to be good when I looked for cold solder joints. I'll run continuity checks on all the points just to be sure.

Thanks,
 
big resistor hanging off the side is crucial. FWIW, I had a chassis I completely rebuilt and neglected to check that, and installed it and it made this horrible electronic burning smell and did nothing. upon pulling it out, the fuse was blown.

after fucking with it for a long time I realized the hanging resistor was CRACKED IN HALF. you measure B+ there if I recall, so it's a monumentally crucial component to the whole chassis lol.

it's also worth noting after I replaced it with one off another junk chassis I never tested it again, so idk if that actually fixed my problem.

155V sounds extremely high. that's not your AC input voltage is it? or is that your B+? either one's way too high. if that's your B+ you could be putting it into HV shutdown.
 
According to the flowchart, one side of R301 should read 123v (the B+ side, which is connected to pin 4 on the VR) and the other should read about 145v (the side connected to pin 1 on the VR).

Mine reads 115v on the B+ side and 155v on the other.

The flowchart lists and answer for the voltages to be the other way around, but not for what I have.
 
I'll double check all the traces and pads again, but they all seemed to be good when I looked for cold solder joints. I'll run continuity checks on all the points just to be sure.

Thanks,

looking and continuity checks don't always help. Heat can cause a trace that is good go bad. I'd wiggle everything big and look for ANY movement, and maybe add a coupled jumpers in any areas that show heat damage (brown spots)...
 
Ok, Here's what I've done so far :

I wiggled everything on the board and found a few spots on the solder side that were weak. I put jumpers across all of them. There weren't any burned spots.

I replaced C56 and C57.

I also verified that the 175 Ohm reading on the R301 resistor was the value that was labeled on the side of it.

There has been no difference in the horizontal size.

I also noticed while wiggling all the parts that Lin Coil (L2) is not resting on it's base. It looks to have been glued there, but now is floating free (I have placed an arrow in the picture that shows where it is no longer attached at).

The voltages at R301 haven't changed (155v on one side, 115v on the other), but the monitor has now been on for over an hour. It appears that the shutdown has been resolved.

I have also noticed that the display rolls over on it self on the bottom. The scanlines are compressed there and streched farther apart at the top. It isn't really noticeable unless you are adjusting the vertical size.

Should I try to find a replacement for the Lin Coil or just glue it back down? Are there any other ideas on what could be causing the incorrect B+ voltages?

Thanks for the help so far.
 

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Don't worry about the linearity coil.

As for the lines, adjust the 50/60-Hz pot...
 
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