Sometimes you just need a break - a G07 repair story

modessitt

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Sometimes you just need a break - a G07 repair story

So - a KLOV buddy brings me over a dead G07 and some cash for me to fix it for him. I install a cap kit, flyback, HOT, and new small fuse, touch up some solder, inspect for issues, fire it up - and it doesn't work. B+ is running at +150. Pulling X701 doesn't help, so I know it's something in the horizontal deflection.

So - the width coil is kind of falling apart, so I replace it - nothing. Check X501 and swap it just because - nothing. Check R908 and it's okay, but I change it anyway - nothing. Swap out the IC501 with a known good one - nothing. Replace the VR anyway - nothing.

So - I tell him to leave it with me to mess with over the week. It's hotter than hell in the garage, and I'm busting my ass at work, so I leave it alone for a few days.

Today I pull it back out on the kitchen table (AC in the house) and start tracing the horizontal circuit. I'm getting almost no voltage out of the IC501. Comparing readings between a good chassis and the bad chassis, I determine the problem to be related to pin 12 of IC501. This makes sense, because it leads to the Horiz Freq pot. I do some readings of various parts, and notice R503 is reading about 6.5k-ohms in circuit, when the good chassis has it reading 11.8k-ohms (it's proper reading) in circuit. I pull it and check it and it's 11.8k-ohms, so I figure the problem is elsewhere in that circuit. I use the schematic and start pulling one leg of various parts to isolate that R503. I figure that once I remove a section of the circuit, it should cause R503 to measure properly, and I can narrow down the area to look at.

Well, after removing many parts, i find the only parts that cause it to read properly in circuit are removing the Horiz Freq pot or the jumper wire that leads to the IC pin 12. Either one will cause R503 to read properly. I swap out the Freq pot, but that's doesn't help. I know the IC is good. So - what to do? Maybe R503 is measuring fine out of circuit, but is failing under load? I pull R503 (which still measures good out of the board) and replace it with another - and the monitor now works just fine. B+ steady at 120.

So - sometimes it pays to just take a break from a problem and come back to it.

BTW - for those who say that G07's won't work with 60-in-1's, I'll post some pics later in another thread disproving that theory...
 
Cool repair log, it's always helpful to read about troubleshooting various parts of a monitor and how to rule out good parts. The steps apply to all electronics troubleshooting. From the sound of it, you replaced most of the board, that monitor should last another 30 years! Time and patience really helps, so does a soak box...or as i call it, a pissed off box. My PO'd box has grown to about 3 boxes but sometimes I get lucky and fix things later. It's always a thrill when a PCB with issues gets fixed.
 
I am glad you found what was wrong.
Sometime even when a part seems ok. It doesn't function under load. I seen transister resister and cap that do this from time to time these typically are not common failure points.

great job.
 
Gotta bump this thread and agree. I recapped a G07-Cao and the B+ was stuck at 110 no matter what I did with the pot. Took a break and came back to it. Removed the pot and cleaned it with W40, metered it and it seemed to modulate now. Took R908 off and metered it. Tested the transistors. Put it back together and now I can turn the B+ up. I really think it was a dirty pot but who knows. Sometimes you just need to walk away for a bit and think up a battle plan.
 
I couldn't agree more...
I've got a butt load of projects going right now. Setting something down for a few days ~couple of weeks does wonders for me. Lately it's been figure something else on another game that helps fix the stubborn one.

Probably me best 'walk away' story... I had a row of lights out in my Jackbot (green row at the visor) since the day I got it. I saw videos before it hit the pallet so I know they were working. I assume a cold solder joint somewhere after the ship. I tore it apart..measure this..that, touched up some solder points. Spent quite a few hours off and on across a week.

I put it back together as I was having a party with the green row still out. One day about 6 months later I turn the game on and poof...the green row is back...and has been for about 4 years now.

I really wish my games would learn from Jackbot..and take the initiative to fix themselves. It sure would make life a lot easier!
 
BTW - for those who say that G07's won't work with 60-in-1's, I'll post some pics later in another thread disproving that theory...

It depends on which revision of chassis you have. The later versions with the exposed jumpers (in clear insulation) on the solder side will work, the early versions without the mod won't sync properly.
 
It depends on which revision of chassis you have. The later versions with the exposed jumpers (in clear insulation) on the solder side will work, the early versions without the mod won't sync properly.

well damn...gotta check my chassis now. ordered a 60-1 for my pac cab which of course has a G07.
 
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