modessitt
Volunteer: Encyclopedia Submission Moderator
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...
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...
