SOLVED: Toei GM-140TV recapped - picture stretched out

tomservo

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I recapped the GM-140 in my space invaders, and now the picture is all messed up and I can't seem to adjust it. This is the best I can make it look. What did I mess up?

I've gone back over the caps 3x to make sure I didn't mix some up. Any ideas?

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Some pics of the chassis. I just checked the caps again, all look correct. I must be missing something?

Ticks me off, I should have just left it alone, except it still had the original caps from 1978 and I wanted to freshen it up before I sold it. First time I've ever had a problem doing a monitor cap kit.
 

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Thanks. Yep, I found that and checked against that, as well. Kit was from APAR, so I'm confident in the parts. I've gone over my solder joints a few times, I can't find any issues there. All I can think is that another part failed when I powered it up with the new caps. There's so little information out there on these monitors, hard to track down. I did see someone say that Q1 often fails, but I can't find a schematic, and I'm not sure what that does.
 
Agreed - definitely can't go wrong with the parts and instructions from APAR. I too noticed the lack of documentation on this particular monitor, and that does make it really tough to zero in on the issue. It looks to me like primarily the vertical scan rate is unstable - it's wrapping back on itself at the left side (as shown in your picture) - which would be the top in a standard television orientation. Then, as the beam traverses to the right (or down in TV orientation) the distance between scan lines increases and makes the characters appear to break apart. That being said, it looks like there's also some horizontal spreading towards the right side of the screen - but not as severe as the vertical distortion.

I assume you have worked the adjustment pots back and forth (and hopefully applied DeoxIT) - but no amount of fiddling with them will bring the image back to its expected appearance?
 
Correct. Picture is very unstable. No amount of adjusting the pots can make the picture look better than what is in my photo.

I did deoxit the pots, and checking them with a meter they measure out fine. IDK??
 
Where do the yoke wires attach: To the 4-pin connector closest to the flyback, or the 4-pin connector closest to the label with the re-cap date? This looks like a vertical linearity problem - and it would be helpful to identify the AC Return capacitor for the vertical yoke winding. Since there is no schematic, I'm hopeful it can be identified by its proximity to the yoke connector, its value, voltage rating and by following traces.
 
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The yoke connects to the 4 pins closest to the flyback. The other 4 pin is the power/video header. I certainly agree with it being a vertical linearity problem.

I can trace it down tonight. What am I looking for? There is a high voltage cap very close to that header, C30 which is a 1uf 450V cap. There is also a high value low voltage cap close to it too, C41, 1000uf 10V.
 
Good old TOEI monitors. Here was my recent struggle with one, and oh look who's helping you! You will figure it out, it just takes a lot of digging around and cross referencing obscure, unreadable schematics with nonexistent information.

 
OK, so comparing my photos, here are where I think those caps are on the solder side. The yoke header is the orange box. I'll verify tonight, it will be much easier when I have the chassis right in front of me.
 

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Thank you for the additional information and yoke connector location. When zooming in on your topside PCB picture, and it not being 11 PM when I am tired and my eyes are tired, it looks like there are lines on the top side representing the traces – which makes it a little easier to see how things are connected.

I cannot quite make out all the descriptors on the pots, but I can see V. Hold, V. Height, and V. Center. Any capacitors which are in circuit with these three pots should be suspect.

I am in no way calling into question your soldering skills – the joints and workmanship look really good. My only thought pertaining to installation would be the amount of heat applied (duration) to the leads during soldering. I noticed that all the capacitors are sitting flush against the board – with some having one lead which is longer to reach the appropriate through-hole. The shorter leads can transfer more heat into the capacitor seal – and potentially into the bonding joint with the foil where damage might occur.

Also, with the capacitors being flat mounted against the PCB, any mechanical movement (inadvertent bending or side-loading) could put stress on the leads and cause internal damage. Did you do any "straightening" after the fact – to make sure a capacitor was vertical and not leaning? Even a slight bending adjustment, when the can is flush on the PCB, can cause internal damage.

Your mention of C30 and C41 make sense to me – as they are near the yoke header. C41 (being 1000uF, 10V) seems the most likely candidate for the AC Return capacitor based on its capacitance value.

I am hoping you have a meter capable of checking Capacitance – in which case I would recommend carefully removing and checking the ones I have circled in blue – starting with C41.

1741100360515.png
 
Much appreciated! Attached is a photo of the chassis before I did anything to it, and you can see the pots better. Several of the original caps had the 1 leg stretched across, and I tried to match it the same. Could I have messed up a cap? Certainly! :)

I do a fair amount of board repairs, but mostly pinball. I'm used to working on Williams sys11 boards, and those traces can lift just by looking at them wrong, so I'm sensitive to how much heat I'm applying. Not to say I didn't damage something.

Thanks again, I'll check them over. My Fluke can measure capacitance, so I'll go through them all.
 

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You are welcome - and thank you for the additional picture - that is most helpful. It looks like C41 is directly in-circuit with the Vertical Linearity pot - so it definitely deserves a second or third look. Also, the "gum drop" film capacitors (circled in the picture below) often take a beating when we are working on these boards. They can get flexed multiple times (sometimes inadvertently) - which cold works the leads and breaks them at the PCB, or at the body of the capacitor. I would check those as well - not necessarily remove and check capacitance - but do a thorough visual check to make sure they don't have any broken leads.

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You are welcome - and thank you for the additional picture - that is most helpful. It looks like C41 is directly in-circuit with the Vertical Linearity pot - so it definitely deserves a second or third look. Also, the "gum drop" film capacitors (circled in the picture below) often take a beating when we are working on these boards. They can get flexed multiple times (sometimes inadvertently) - which cold works the leads and breaks them at the PCB, or at the body of the capacitor. I would check those as well - not necessarily remove and check capacitance - but do a thorough visual check to make sure they don't have any broken leads.

View attachment 803875
Thank you!!!

I removed every cap I put in, tested them, then reinstalled them. All except for C41 since you figured that was potentially a suspect. Every cap tested fine, which didn't make me feel good because that meant I didn't find anything wrong. But since I had C41 out anyway, I replaced it with one I had in my cap organizer. I little bigger than the one that came in the kit because all I had was a 35V in that size, and it barely fits in that spot, but it did. I have no reason to think that there was anything wrong with the C41 that was in the kit, but I was getting tired of taking this chassis in and out of the game, and I figured I'd replace because I had nothing to lose and I had an extra one handy.

I can't say that I found anything wrong, which is a little frustrating because I would have liked to know what what fixed it. I can only assume I had a little short or solder blob somewhere that I fixed by removing and then reinstalling the caps.

Thanks again for the help, excellent advice! Also thanks, Phet, for the read on yours. The lack of documentation on these monitors is quite surprising, actually.
 

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I can only assume I had a little short or solder blob somewhere that I fixed by removing and then reinstalling the caps.

I don't know anything about this chassis but this was going to be my suggested cause.

Maybe it's just the pictures, but the solder pads on this board look insanely close to one another. Looks like it would be very easy to make an accidental bridge somewhere.

The picture looks great btw!
 
You are most welcome - so glad you got it working! As @TheYeti said, it might have been a tiny solder ball or other conductive trace of solder that was the root cause. Glad you stuck with it and got it going. :)
 
Yeah, that's the only thing that makes sense to me because I couldn't find anything wrong. Hopefully this helps someone else in the future because I could only find about a dozen or so posts regarding this chassis on KLOV, and most of the posts I could find were either WTB, FS, or looking for schematics. Not much in the way of troubleshooting. Somehow I missed Phet's in my searching, it didn't come up when searching for GM-140? Oh well, all is good!
 
I'm fixing a Toei GM-140GW which is for the even rarer 12 inch version, although I suspect I'm missing the PSU part.

I have the schematic but I can't find my original downloaded file so I scanned the print out I have to help future searchers. Better than nothing.
 

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