13K7811 shouts down

[darko]

I have K7000A chassis mounted on OPPER COIN machines. I used Amatic Multy Game 8000.2 and 9000 boards.
Chassis work ok but after 20 minutes or more it shouts down. After restart works ok but for 20 or more minutes then again shouts down. I have schematics from K7000 but not for K7000A.
Is the problem in flyback transformer?

We have more then 50 this types of chasis.

[Ken Layton]

I'm a little confused here. You say you have a Wells-Gardner 13K7811. That translates to a 13 inch K7000 series.

Zenith built the 19 inch version of the K7000 chassis and that version is called the K7000A. I am unaware of Zenith building any 13 inch versions.

There are NO manuals or schematics available for the K7000A chassis

[grantspain]

are you sure its a monitor fault,20 mins is a long time for a chassis to run.
when the machine cuts out have you checked the screen volts adjustment on the flyback to see if you get a white raster
you also mentioned you had 50 of these monitors,are they all doing this?

[darko]

I don't have picture of it at this moment but this is really the zenith chassis, it has its funny flyback tramsformer, number printed on the main board is :204-2205-08A. We have more then 50 machines with this type of chassis.

When it is powered up insolation of cables of the flyback transformer is full with static electricity this is not seen on the standard K7000.

[Ken Layton]

From what I understand, electrically the k7000A is the same as a K7000 except for the flyback and the giant capacitor attached to the high voltage lead wire. So you should be able to trouble shoot it using the k7000 schematics and flow charts.

How is it that you got 50 of these chassis in a row? I've been repairing game monitors for over 30 years and I've only encountered 3 of these 19 inch k7000A chassis.

If you have a high voltage test probe and are aware of proper safety procedures in using it, measure the high voltage going to the tube. It should be around 19,000 volts. If it's above 21,000 volts then that's too high for a 13 inch tube and the safety shutdown circuit is activating.

It's possible capacitor C57 might be bad. Have the electrolytic capacitors been replaced? The B+ power regulator might be bad so it's worth checking that too.

[darko]

This are pictures of 13k7811. I will try to change C56 and voltage regulator. I don't have high voltage measurement instrument .

[darko]

I changed C56, C57 and STR30123. Chassis is now ok. Thank You very much. You save a lot of our chassis.
 

[Ken Layton]

Glad to have helped. 

The parts you replaced are commonly available. If you repair more than one chassis then it would be wise to shop around for the best prices on those components.