G07-CB0 vertical problem?

[modessitt]

Hello All.

I've seen this problem addressed with the Wells-Gardner types, but no real in-depth answers to the GO7 version of this same problem.

I am building a universal testing station in order to troubleshoot Arcade CPU boards on the bench instead of walking back and forth from the bench to the game and back every time I think I've got a problem fixed and need to test the board.

I pulled an isolation transformer and power supply board (for the +/-5V's and +12V's) from a Joust and grabbed a used GO7-CB0 monitor with scratches on the tube for my picture.

[Ken Layton]

There's a fusible resistor in the vertical circuit that fails killing the vertical output.

[modessitt]

Sorry, forgot to include that info.

[Ken Layton]

Here's what to check:

Fusible resistor FR401 (68 ohm 2 watt)

Resistor R412 (27k, 1/4 watt)

Capacitor C407 (4.7 uf @ 63 volts)

Do not confuse FR401 with the fuse resistor FR901 in the power supply section.

[modessitt]

Ok, thanks for the input so far, Ken.

FR401 is measuring 68.1 ohms.

R412 is measuring 26.9 ohms

C407 was replaced during the cap kit with a 4.7uf 160V cap that was in the kit and listed in the instructions for that location.  However, I had this problem before doing the cap kit, so I doubt it is causing this problem.

What's next on the list of things to check?  Any possibility it could be a problem with the tube?  I haven't seen this tube work, but I have seen the chassis work.  (Guess I could drive in to the shop tonight and hook my chassis back up to the Zaxxon to see if it is working, then try it on a different tube while I'm there to make sure the combo works together before coming back home.)

[Ken Layton]

Measure those resistors out of the circuit or you'll get incorrect readings. The value you say you got on R412 is way off. It's supposed to be 27 k ohms (27,000).

[modessitt]

sorry ken....one of these days I'll remember to type ALL the info on one of these posts.  i meant 26.9 K ohms.  I will check them out of circuit and see.

[modessitt]

Okay, time for an update....

Took my chassis back to the shop and hooked it up and everything worked great on the Zaxxon.  Guess something's wrong with the yolk.

Grabbed a spare yolk just in case, and went back home.  Looking over the current yolk didn't yield any obvious problems.  All the wires seemed to be hooked up right with good solder joints (although I did reflow them to be sure) but still had the problem.

So......I replaced the yolk with the spare one I had brought and....everything worked!  Guess there's something wrong with the yolk.  So now I have everything monitor-wise working.  Thanks for all the help and ideas, Ken.

Guess this will give everybody something else to look at when they lose vertical deflection.  It's not always the chassis!