WG K7197 25" Blows 2A SB fuse & Shorts HOT & VR

[MKFan4Life]

Was recently playing my MK1 cabinet and adjusting the Focus and Screen pots when the entire cabinet went dead. It blew the 2A SB chassis fuse and the main 3A SB cabinet fuse. After replacing those, it blew the chassis fuse again on powering it up, but did not blow the cabinet fuse and was playing blind.

A little history on the chassis:
It is the original K7197 chassis that came in my MK1 and did not look to have been ever worked on until I capped it around 10 years ago. It ran great for a few years, but went out and it took me a long time to focus on repairing it. A while back after it died, I replaced the flyback with a new one from Bob Roberts (to see if it made a difference, and because the original was cracked in at least 2 places near the pots). There was no change. Eventually, a year ago I found the VR to be the problem and replaced it, bringing the monitor back to life for a year of occasional playing.

Fast-Forward to this past week when the cabinet shut down. I pulled the chassis and found the VR I had replaced was shorted, the HOT was shorted, and capacitor C44 was shorted. I had a new HOT and several extra STR30130 VRs, so I installed them and did a full cap kit from Arcade Parts & Repair while waiting on a couple of replacement C44 capacitors. I got lucky, as they arrived super-fast on Saturday. I installed the new C44 after having a day or so to go over the entire chassis, reflowing, cleaning flux, and testing everything I could think of, including diodes, resistors, etc. I felt good about the work. The HOT and VR and the new cap all tested fine back in the board.

Well, while I had been waiting on the cap (& a new tube of heatsink compound), I examined a different K7000 chassis I had stored away about 8-10 years ago, because it really had needed a cap kit, and I preferred the original from my MK1 which has adjustments on a remote board. Everything on it looked ok (except aging caps), so I installed it into the MK1 cab to verify it still worked in case I needed it. It worked just fine. That confirmed everything in the cabinet was working well, and I played it for an hour, adjusting it to the tube.

Then tonight, I put the original chassis I just recapped & did the repair work on back in and fired it up in the dark so I could see flashes of disaster. The main 2A SB chassis fuse immediately bit the dust once again. The cabinet fuse did not blow as it had the first time this chassis went out recently and the game was playing blind again.

I was able to test the HOT, VR, & C44 with the chassis installed, and the HOT & VR tested shorted, but C44 was fine. Now I need to pull it, because I have missed something. I'm thinking it's the flyback. The flyback itself has seen only a year of occasional play from time to time since the chassis was back in operation, but it was a few years back that I bought it from Bob Roberts.

I'm thinking about swapping the known good flyback from that other K7000 in to see if that is the cause of the other shorts reoccurring.

Any advice guys? Thanks!

[Ken Layton]

Bob Roberts has been selling known bad/cheap flybacks that he refuses to stand behind.

Buy your flybacks from Arcade Parts & Repair instead.

[MKFan4Life]

Bob Roberts has been selling known bad/cheap flybacks that he refuses to stand behind.

Buy your flybacks from Arcade Parts & Repair instead.

Seems so difficult to tell on these flybacks since you have to put them through some use to find out if they are junk, but most all of them are made in China aren't they?

[MKFan4Life]

A new flyback solved the issues. Did have to install one more VR, HOT, & fuse, but now it's running well. The new flyback had a clearance issue with a Nichicon cap, so had to swap that cap with a skinnnier off-brand NOS one I had lying around, but I can order a skinnier Nichicon soon.

Thanks for the help!
 

[MKFan4Life]

Well, today I played through the game (about 20 minutes), then left it running while the wife and I watched a 2-hour movie. Found the game playing blind and thought it was blowing fuses, HOTs, & VRs again. But no. The fuse is fine, & apparently so is the HOT & VR.

The first thing I noticed was no high voltage and no neck glow. I flipped the power switch off, and tested the HOT and VR in circuit & they seemed ok. Powered the game back up, and it seems fine. Neck glow is there, screen looks really good, and the B+ is measuring 132-133V on the regulated side of R301, 170V on the back unregulated side.

Again, I played through the game and it's now been running for an hour with no issues.

Has anyone ever had a monitor just shut off and then it fired right back up after cycling the power with these symptoms? Weird.

[snappleman]

Only time I've ever had that happen was when there was a bad solder joint I missed. Maybe reflow the major components in case something is intermittent?

[MKFan4Life]

I have ran it twice since this incident happened. Last night for about 3 hours with no problems, and then today for an hour and a half, no problems. This is really puzzling to me. I mean the monitor was completely off when I discovered it like that, like it went into high-voltage shutdown or blew it's fuse. It hasn't repeated this since. Weird, weird, weird.

[MKFan4Life]

As a side note, the B+ is currently reading 133VDC and the 12V rail is reading about 13.1VDC. Would this higher than normal reading trip the high voltage shut-down circuit?

The game has been running fine for a few days. No monitor issues. No issues at all really.