Add this to your G07 repair logs...

modessitt

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Well, I just got done fixing a "Monitor Chassis From Hell" for another KLOV member. I will let him identify himself if he wishes. But I will say that he has been incredibly patient. While I told him I'm not as fast as some of the other places he could send it to (I have a day job), I am cheaper, though. Still, this was a very difficult problem, and took me about two months from start to finish.

A little background on the monitor:

This a G07, and was basically working, although it "had a wave" and was "skewed" horizontally. A cap kit, flyback, HOT, VR, Width Coil, and R908 was installed. After that the monitor was dead. F902 would blow on power up and the B+ was 0v.

Well, I get the chassis, and the first thing I notice is that the neckboard pot was backwards. Apparently, while he checked every damn cap on the chassis a hundred times for correct polarity, he forgot the neckboard one. So, I replace the cap, go over the entire chassis and fix quite a few cold solder joints, and check and find that the HOT and VR are still good and have their insulators, but that F902 is blown. I replace F902 and it powers up. I'm using the test grid from a 48-in-1 on my test bench, and I get this screen:

SDC11095.jpg


Hmmm. Only showing red (and red where the white squares would be). I do a bunch of voltage checks throughout the color input sections, and they are the same in the green and blue sections as the red, but it's not showing anything but red.

Continued in the next post...
 
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Well, I know my test tube is good. I try swapping all the parts in the red circuit (both on the main chassis and the neckboard) with the parts in the green circuit. This should give me all green, I figure. NOPE! Still have the same all red screen. Turning down the red or turning up all the other colors does nothing.

Still, there could be issues with the neckboard, so I decide to swap in a complete good neckboard - and have no change. Hmmm...

Well, I try to think of what critical parts could be the problem. My B+ is running spot on at 120.0v. I try changing IC501, T501, X501, X303, X304 - no change.

During one of my shutdowns, I notice something interesting. Upon power-down, the image shrinks down to nothing in about a second. When it gets to about 2/3 size, all of a sudden all the colors are there. This gets me thinking that perhaps something is overdriving the image causing two of the colors to be cut out for some reason.

Well, I try putting in another new flyback, HOT and VR, just in case - no change. I try replacing ALL the caps again, just in case one failed when the fuse was blowing - no change.

This was boggling my mind. I couldn't figure out why I could have the exact same voltage signals through all three color circuits, all the way to the neck pins, and still only get one color to show.

Continued in next post...
 
Okay, at one power-up, I guess I had the brightness turned way up, because the picture was very bright. However, i could see all my colors now, but very washed out and with retrace lines everywhere. Turning it back down made the green and blue go away.

This made me think that perhaps my problem was with my brightness, but swapping in a different screen control pot didn't help. Still, I thought I was on the right track. Perhaps I needed more voltage in the green and blue circuits to get them to show at the same brightness level as the red.

The problem was - all three color circuits has the exact same voltage readings throughout. Swapping color inputs had no effect (other than what was red). Jumpering voltages over to the other circuit had no effect. Swapping parts had no effect.

This chassis was just pissing me off. I consulted with several other monitor gurus, but none had ever seen this problem. Some offered advice, which didn't pan out although it was a good idea (the +12 was spot on).

Well, I finally had enough with this stupid chassis. I dug through my parts and came up with a known working G07 chassis. I seriously considered just rebuilding that one and sending it back, but I refused to be beaten.

I hooked up this chassis and got a perfect picture. I had my schematics in front of me, and I just went through the entire chassis part by part and measured voltages and wrote them on the schematic. Then I put the problem chassis on and compared voltages. About the only difference i could see was that the voltage to the base of the drive transistors was 4.4v instead of 5.4v. While it's only one volt, it IS 20% low.

So, I traced it back to the main chassis (knowing the problem wasn't on the neckboard). I eventually found that the 4.4v was coming from an area where it was supposed to be 10.3v before hitting the flyback and the screen pot. There were about 4 parts in a parallel circuit with 120v on one side and 4.4v on the other. I started pulling the parts one by one (after in-board measurements were inconclusive), and eventually had R517 break in half during removal. Replaced it and fired it up.

It WORKS! Apparently it was cracked under all that grime and dirt, and wasn't allowing the full voltage pass-thru. I can finally send this damn thing back, and I have another fix to add to the list....

SDC11093.jpg
 
I don't mind admitting I was the one who sent him this problem child. I followed the flow chart and when I went off the chart I yelled for help. Mod offered to look at it, so I sent it to him, not knowing what an ordeal this was going to be.

I have several spare monitors so I didn't need this one back and I really appreciate his taking the time to track this all the way down. This was my first G07 that I tried to recap and I would have always wondered WTF I did wrong.

The cap on the neckboard was a total screwup on my part (always a good idea to get a second pair of eyes on it :eek:). But the rest of the issues were way off the flowchart in uncharted territory (pun intended).

I asked Mod to document this because these sorts of issues are going to start popping up as these chassis get rebuilt for the second or third (or more) time. IIRC, this one had two recap tags on it (1987 and 1992) so this was the third recapping.

My hat is off to Mod for his persistance.

ken
 
i love it when you guys post this kind of stuff. helps me learn how to troubleshoot. i hate it when i get stuck and cant figure something out and it gets put on the shelf to collect more dust.
weird how some of the squares are elongated as well as being stuck on red.
 
A good read. While I don't have a G07 in anything yet, it was a good lesson on how important it is to check all parts when rebuilding a monitor. Repair logs are great, especially ones with lots of pictures, because it teaches us newcomers what does what, what goes where, and what certain things look like. If it wasn't for the internet I wouldn't own an arcade machine right now. Anyway thanks for sharing.
 
... swap in a complete good neckboard - and have no change.

....try changing IC501, T501, X501, X303, X304 - no change.

... try putting in another new flyback, HOT and VR, just in case - no change.

... try replacing ALL the caps again, just in case - no change.

..

I'm curious. After you found the bad resistor, did you swap all these parts back out?

I see the same thing in the programming world. I (or someone else) will make some changes to fix something... no effect. Make more changes.. no effect. etc etc
Finally make the change that was needed all along to get things working. Do the unnecessary changes come out or not?


From time to time in source code, you see these artifact changes left behind.
 
I'm curious. After you found the bad resistor, did you swap all these parts back out?

Yes. After all, I charge $50 + parts. As Ken had already bought the new "normal parts" and put them in, I changed them to make sure they were in fact good, and put them back once I verified they weren't the cause. This way Ken doesn't pay more for parts he didn't need...
 
Good work and thanks for the details here... I would have been at my limit about half way through...
 
damn mod. You have the patience of buddah. I woulds gave up man... ill admit it :D

i gotta definately add that one to my faves....
 
Mod, Would you be willing to share the schematic with the voltages written on it? I love the Atari schematics since they have the voltages and would love having this for the G07.

If your worried about your handwriting or something, I could redo the schematic with a nice font and make it available.

-VJ
 
I may do this myself at a later date. I may have exaggerated a bit when I said "every damn part", but I did do every transistor, diode and chip. Unfortunately, I scribbled these into various sections, so I'd probably have to interpret it for someone else...
 
I may do this myself at a later date. I may have exaggerated a bit when I said "every damn part", but I did do every transistor, diode and chip. Unfortunately, I scribbled these into various sections, so I'd probably have to interpret it for someone else...

No problem. I have to rebuild the G07 in my Joust and may just go ahead and capture the values while I have it on my bench "if" the image is top notch. I finally got another tube for it since the one it had included some wicked Crystal Castles burn.
 
FYI - I had another of these pop up today, with slightly different symptoms.

This time I had blue and red, but no green. Well, actually I should say I had no DARK green. The entire picture was dark, but I could see red and blue, and I had yellow, and I could get some bright green but no dark green. This means that on the 48-in-1, I could see the yellow centers on the bugs in Galaga, but I couldn't see the dark green of the "teleporters".

I rejuved the tube, then tried swapping the tube, then reflowed the entire color sections, then swapped some transistors - and it actually made it a bit worse, as my green seemed to go away completely.

It was during a time I had my brightness way up that i noticed I could start to see the green again. This made it click in my mind as to what started this thread. I immediately went to R517. I was getting some funky readings in circuit (the part looked okay), so I pulled it and checked it again. Still had funky readings, so I replaced it. BOOM! All my colors are back and my picture is nice and bright again.


People should keep it in mind now when helping with (or fixing) G07's that a dark picture or missing color (starts with green first it seems, then blue, then red, depending on how bad the part is), and all cold solder joints, tube rejuvs, and color circuits have been examined with no fix, that R517 should be the very next step.

Perhaps some of you have problem G07 chassis' on the shelf that just need this simple fix. Hope it helps someone. This is now my 2nd occurrence, so it may pop up more often as these get older....
 
What is the value of R517, I don't see it in the parts list of the manual?

Think I found it in the scat 220K 1/2W?
 
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What is the value of R517,

Think I found it in the scat 220K 1/2W?

Yeah, that's it....

Although, now that I think about it, I don't remember the colors being red, red, anything. I need to check it again tomorrow....
 
What is the value of R517, I don't see it in the parts list of the manual?

Think I found it in the scat 220K 1/2W?

Yeah, that's it....

Although, now that I think about it, I don't remember the colors being red, red, anything. I need to check it again tomorrow....

Okay, checked the actual part (and compared it to a couple other nearby chassis and found them to be the same.

The resistor colors are brown-gray-yellow-gold, which would be 180k-ohms +/-5%. It is a half-watt resistor...
 
Okay, checked the actual part (and compared it to a couple other nearby chassis and found them to be the same.

The resistor colors are brown-gray-yellow-gold, which would be 180k-ohms +/-5%. It is a half-watt resistor...

The scat shows R516 to be a 180K 1/2W.
 
Well, the two parts are parallel, i believe, so I'm willing to bet they weren't worried about which went in which spot. if you have a chassis handy, take a look...
 
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