Go8 gap at bottom - folding

Zinfer

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Got about an inch or two gap at the bottom of my G08 picture. When I adjust centering, it curls/folds under. 'Credits 0' gets squished - and it is wavy. Has anyone experienced this?
I recently capped it other than the huge caps. I jiggled a few wires, transistors, paddle boards, wires to the deflection transistors, adjusted the g80 xy board screw terminals on the pcb itself. I tried adjusting the hv, nothing seems to make an impact on this centering problem.
Image is always about 2 inches up from bottom of picture.
Would it help to post a video of it?
 
Put a different know good logic board video into the monitor to see if it is a logic problem.
 
Put a different know good logic board video into the monitor to see if it is a logic problem.

I've seen that before. Check the little input protection board. Swap it out if you have another. Otherwise check the caps, 1N914 diodes, and transistors. Should have 2 pair of 2N3904/6 transistors sets. Sometimes a previous repair will mix them up. Parts are uber cheap...shotgun them if you are in doubt.
 
Well I recapped the protection board with (4) 10uf50v and replaced the (2)2N3906 and (2)2N3904 transistors. Didn't really help anything.
I'll have to check the 1N914 diodes on the protection board.
For some reason now the image is now halfway up the middle of the screen.
IMG_1192.jpg


I've seen that before. Check the little input protection board. Swap it out if you have another. Otherwise check the caps, 1N914 diodes, and transistors. Should have 2 pair of 2N3904/6 transistors sets. Sometimes a previous repair will mix them up. Parts are uber cheap...shotgun them if you are in doubt.
 
Send it back to me and I will figure it out.

Somebody mentioned the 2N6259s. I don't know if the connectors will stretch with the power transistor heat sink assembly bolted up, but if you can swap those two, that would either confirm or deny the power transistors.

If you can switch and the problem jumps to either the left or right side squished, it is the 2N6259s (or replacements).

If you switch and it stays the same, it's either the deflection signal or the Y-deflection side.

Bypass the input protection board to rule that out. The overall image will be bigger, but you should still be able to see the problem or not.

I know that the XY boards from the game checked out good, but to rule them out, you could swap the X and Y signals going into the protection board. Again, the size will be whacked (large Y deflection and small X deflection) and the image will rotate 90 degrees, but that will also rule out the game boards.

I'm guessing that it's one transistor out of the two pairs driving the Y deflection side. It could be one of the output transistors, but I know that you replaced those too.

Kerry
 
Well I recapped the protection board with (4) 10uf50v and replaced the (2)2N3906 and (2)2N3904 transistors. Didn't really help anything.
I'll have to check the 1N914 diodes on the protection board.
For some reason now the image is now halfway up the middle of the screen.
IMG_1192.jpg

I have seen something like that when one of the 2 paddle boards had a loose or bad connection. Give the paddle boards a wiggle. :D
 
Yea that was one of the first things I did. Got nothing when I wiggled the paddles.

I have seen something like that when one of the 2 paddle boards had a loose or bad connection. Give the paddle boards a wiggle. :D
 
Well I'll need to pull the block to turn it and try reversing. I did remove the IPB and yea the screen is huge. Hard to see if anything's the matter then.
You know that practically everythings' been replaced once on this monitor. When I rotate the power transistor block that's only one step from chassis removal.
So I'll try this first and if nothing, I'll probably just pull it all again for shipment. I still have your boy scout cookie box. :D

Send it back to me and I will figure it out.

Somebody mentioned the 2N6259s. I don't know if the connectors will stretch with the power transistor heat sink assembly bolted up, but if you can swap those two, that would either confirm or deny the power transistors.

If you can switch and the problem jumps to either the left or right side squished, it is the 2N6259s (or replacements).

If you switch and it stays the same, it's either the deflection signal or the Y-deflection side.

Bypass the input protection board to rule that out. The overall image will be bigger, but you should still be able to see the problem or not.

I know that the XY boards from the game checked out good, but to rule them out, you could swap the X and Y signals going into the protection board. Again, the size will be whacked (large Y deflection and small X deflection) and the image will rotate 90 degrees, but that will also rule out the game boards.

I'm guessing that it's one transistor out of the two pairs driving the Y deflection side. It could be one of the output transistors, but I know that you replaced those too.

Kerry
 
Ah well I didn't feel like running out to the other room to read the box or read past emails to get my facts straight. Phooey on me. :p
 
It doesn't look like your missing the bottom but rather that it's squished. Real hard to tell from the pic. So all you did was shotgun some of the IP board and you lost more of the picture? I'd still look at the 1N914 diodes.

Without extra working chassis parts I suppose it's repair by elimination. Bottom deflection components are tied to the negative rail of the 600 series components like Q602, Q604 and Q606 (bottom of heat sink nearest the fan). Also the components on the paddle board connected to pins 1,2 and 4 P600. If you have a scope you can walk through the circuit to see where the signal drops out. Otherwise swapping X and Y components is effective (but extremely time consuming)

Something else to check...some G08's have large 1ohm 5w resistors on the heat sink. I had one that was open. Just bypassed it for a fix.

Well I recapped the protection board with (4) 10uf50v and replaced the (2)2N3906 and (2)2N3904 transistors. Didn't really help anything.
I'll have to check the 1N914 diodes on the protection board.
For some reason now the image is now halfway up the middle of the screen.
IMG_1192.jpg
 
I will have to order those 1N914 diodes as I don't have any stock of those. Not sure what those even look like shorted. They're so tiny. I'll post a pic of the IP board.
 
I had a monitor with this problem recently. The problem was one of the 10uf capacitors on the input protection board was reversed. Different screenings had caps sometimes going in different directions than others.
 
Good call Mark. I had one that had the right side folded over. Was a combinations of a bad 3904?6 and a cracked 1N914

I had a monitor with this problem recently. The problem was one of the 10uf capacitors on the input protection board was reversed. Different screenings had caps sometimes going in different directions than others.
 
Well I'm pretty sure I got everything right. The first transistor to the left is a 2n3906, the second 3904, the third 3906 and the last on the right is a 3904.
The caps are all 10uf50v.
I think I can test the diodes by measuring Ohms in one direction and then the opposite. Should get solid in one direction and nothing the other I think.
IMG_1196.jpg
 
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Without seeing the bottom hard to say if that's correct. What happens when you bypass the input board and plug in directly into the deflection board? Might stress your monitor in the short term (picture should be larger than normal), but if the pic looks ok at least you know where the problem lies.
 
If I remove the IP altogether, the picture is much larger. So much so you can't even adjust it to get to the bottom of the picture.
I removed the heat sink and flipped it so that I could reverse the wires and there was no difference in picture.
I'm thinking you meant the bottom of the IP so here's a shot of that.
I just realized something by looking at the underside, shouldn't the negative side of caps 1 and 3 be facing away from the wires?
IMG_1198.jpg
 
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Would either one of these be an adequate replacement?
http://www.mouser.com/Search/ProductDetail.aspx?R=1N914virtualkey51210000virtualkey512-1N914
http://www.mouser.com/Search/ProductDetail.aspx?R=1N914TAPvirtualkey61370000virtualkey78-1N914-TAP
Not sure what the difference in single or switching is.
Anyone know a link to a diagram of the input protection board? I couldn't find any. I tested all the diodes and the 4 that are intermixed with resistors, I was getting around 4 Ohm measurements on either side of them. I'd thought I should only get a measurement in one direction.
Are all the diodes on the IP 1N914's?

Good call Mark. I had one that had the right side folded over. Was a combinations of a bad 3904?6 and a cracked 1N914
 
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