G07 troubleshooting

Scott C

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I recently picked-up a virgin G07 from an operator. In testing, it worked except the picture took a while to brighten fully and there was partial deflection collapse. I capped it and found two caps that had leaked (typically two purple caps), so I expected the cap kit to make it pretty again. I also did the curl mod.

However, what I find now is I get no display. When I first turned it on after the rebuild I got a lot of static on the front of the tube, but that lessened as I continued testing it. In following Randy's G07 flowchart, I get:

- 2.4Khz under the anode with my HV probe
- DO have heater glow
- F901 and F902 are testing good
- The HOT and Regulator show good (using OHM on my DMM their reading goes to infinity)
http://forums.arcade-museum.com/showthread.php?t=126760 - Thanks Dokert.
- Turning-up & down the "screen" on the flyback does NOT produce ANY picture at all.
- Tested with/without video from the game plugged in.
- Tested with/without the width coil being plugged in.
- The video input pins were reflowed (looked good)
- The color input pins that go to the neck board were reflowed (looked good)
- One leg of the flyback was reflowed (looked ?, so I did for good measure)
- Game plays blind and can be seen if I use another monitor (K7901).

I am still going through the chart and have next to test R1, but assuming it's good, then the chart doesn't suggest were to go after I do have heater glow. Anyone have any additional thoughts? I also plan to recheck my cap kit to ensure something didn't get put in incorrectly (location) or backwards. No popping was heard.

Scott C.
 
You don't just test R1, you test the B+. It's like the third step in the flowchart after - F902 good/bad? - and - F901 good/bad?

Then:

Look for cold solder on R901, R902 - pretty much all of the big R900's. Check R908 for proper value (pull it to test). Cold solder on R523. If the flyback was changed, check for cracks in the chassis and across traces around the flyback, as this happens quite a bit when people have trouble getting the flyback out or forget about the screws holding it in.

And you can pull X701 to see if you get a picture. If so, then the problem is most likely in your 900's (power section)...
 
You don't just test R1, you test the B+. It's like the third step in the flowchart after - F902 good/bad? - and - F901 good/bad?

Then:

Look for cold solder on R901, R902 - pretty much all of the big R900's. Check R908 for proper value (pull it to test). Cold solder on R523. If the flyback was changed, check for cracks in the chassis and across traces around the flyback, as this happens quite a bit when people have trouble getting the flyback out or forget about the screws holding it in.

And you can pull X701 to see if you get a picture. If so, then the problem is most likely in your 900's (power section)...
Yes, that is what I meant about R1, Modessitt, but thanks for the clarification. The flyback is original, but I plan to check those areas for cold solder. My thinking is it's doing enough (HV and heater glow) that it has to be something simple. Just irritates me it partially worked before I did the cap kit and curl mod. :(

Scott C.
 
It's always a good idea to replace the original flyback when you do a cap kit on a G07, as the flyback can die (explosively) from the stress of the new caps...
 
Double check your caps as well... remember that, I think it's, C302 is printed backwards on the bottom of the chassis.
 
Ah, I fat fingered that! My logic probable goes from 0 to 3.5 Kvolts, so my HV, under the anode, was reading 2.4. The B+, measuring across R1, is reading 119.5v when powered up, then settles to 119.1v. I may try adjusting the B+ pot ever so to make it an even 120v.

I'll also doublecheck C302 to make sure I didn't put that in backwards (pretty sure I remembered that).

Thanks for the suggestions everyone.

Scott C.
 
Your B+ is close enough for it to work. In fact you should have neck glow and a pic with the brightness turned up now. Do you? It's possible that you may have a problem with the heater voltage going to the neckboard. If you have no neck glow, check the wire connections on the back of the focus and screen pots....
 
I had heater glow all along, but no picture and that is the weird part. I did some testing later that same day, disconnecting, reconnecting and still no go. However, I started playing around with the neckboard about the same time I tried to test it again and it suddently came to life. At the same time I started hearing crackling from the neck board. Each time I would hear a crackle the image would respond negatively. I left it on for a while, the crackles lessened, the picture stablized and came into focus. My suspicion is either moisture in the neckboard socket or a bad solder joint. I left the monitor for a day and the little testing I did last night produced a picture and no crackle.
Hopefully, that is it and time will tell (I'll run for several hours). I will still review the neckboard for any cold solder, since I am still not convinced.

Scott C.
 
I would touch every solder joint on the neckboard up, including the focus wire inside the socket. It'll take about five minutes.

It could also be a bad connection on the tube pins.
 
Those GO7 neck sockets should get reflowed any time you're working on the monitor. Years ago I never thought to do that, but after struggling through a similar afternoon as the one you've had with that monitor, I never skip it now.
 
Just to close this thread, the G07 is working. I am suspecting there was moisture or something in the neckboard, since after letting it set for a few days, detached from the neck, it fired right-up and hasn't had an issue since.

Scott C.
 
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