G07 Questions

[M_May41]

I have a Galaga with a G07-CBO When I first bought the game the picture would start to scroll uncontrollably to the left after the game warmed up and couldn't be adjusted out. So I capped It and also replaced the HOT transistor and XO4 transistor. I also replaced the width coil as someone had sealed it with what appeared to be epoxy. (figured that was probably the main problem but It wasn't) When I Re-Installed the chassis and powered the game back on. Same problem. The pic has a minor but noticiable horizontal wave and scrolls to the left uncontrollably to when warmed up. Even when cold the V-hold must be adjusted all the way to the left to hold the pic stable. So what next?? I figured I'd change the vertical output transistors and see If that cures the problem. Is this what I should be looking for?? Or do I possibly have some other problem? If so what might that be?? Also the new transistors came with mica Insulators. The old ones had only heat sink compound between the transistors and the heat sinks. Should the Insulators be Installed or left out??

 

[KenLayton]

On some G07's the factory has mistakenly inserted the wrong value resistors at locations R314 and R317. They both are supposed to be 390 ohms, but the factory stuffed in 4.7 k resistors instead. Both these resistors are in the sync circuit. Check for this factory error first before you change any transistors.

Most G07's also need to have the negative vert sync and neg horiz sync jumpered together for proper operation.

 

[M_May41]

Well Ken I think your on the right track. I do believe It's a sync problem after researching and reading a bit more. But I think It depends on what sync the game board puts out as to whether you would jumper the sync wires or not. So being Its a Galaga board putting out negative composite sync I checked the wiring and the sync wires are connected together at the game board plug. But they seperate and one plugs to J1 and the other to J2 on the chassis. Is this correct or do they need to be jumpered at J1 and J2 ?? And If they should not be jumpered what should I look for next? x302 x 306?

 

[KenLayton]

On the monitor there are two connectors for your game signals. The 3 pin connector that is labeled "J1, J2, J3" is the negative sync input connector. The terminals J3 (leftmost pin) and J2 (center pin) must be connected together by a jumper wire in the female harness connector to work with an Electrohome monitor.

The other connector on the monitor chassis is the 6 pin R-G-B color input. Don't touch that.

This link to Bob Roberts may explain it better:

www.dameon.net/BBBB/sync.html

 

[M_May41]

Ok Ken. I was mistaken before. The composite negative sync from the game board splits and one goes to J2 and the other to J3. Nothing at J1 as Its ground. So both -sync pins are receiving negative composite sync. I would think that would be right but I'm no expert. So I will jumper them at the monitor chasssis and see If that fixes the problem. I already read all the stuff at Bob roberts site and have most of It printed out but still hard for a newbie to totally understand all that. But I'm getting there. Thanks for your help. I'll let you know If jumpering the wires at the female plug fixes the problem. Oh yeah. I did check those resistors and they were the correct 390ohm ones.

 

[M_May41]

Nope same problem :-( I think I'm looking In the wrong place. When I can get vertical lock and the graphics look decent the picture Is way to the left like I can only see the ME OVER of GAME OVER. And when the ship or bees move from left to right you can see they shrink going to the left and get bigger when moved to the right. Anymore Ideas. I'm stumped at this point.

 

[Mongo]

The trouble you are having may be related to the yoke/convergance/purity rings. Look at the brown magnetic rings on the neck of the monitor. They should be glued in place or have a line marked across them indicating the proper position. These are easily knocked out of alignment during board removal/installation...

I am making this observation in part based on your statment that your characters are changing sizes in different parts of the screen.....

 

[M_May41]

Not to say someone didnt knock them outta wack before I got my hands on this game but I had this same problem before I ever removed the chassis and capped It. I did notice there was what looked like hot glue across the rings. I will take a better look this evening to make sure they don't look like theyve been moved. Maybe I need to explain better what's going on. When the game was cold I could get It synced and a full pic. But still had the shrink to the left expand to the right. Could even play some games but eventually the thing would get squirrely. At that point I would try to regain vertical lock. And could. But then I get the ME OVER screen. Cool down and do It again. Now even cold I cant get It stabilized. So far I have capped the monitor changed the HOT and the voltage regulator the B+ Filter Cap by the way B+ reads 120.1vdc The other end of R01 reads 150vdc. Changed x401 x402 x302 x306 same problem??

 

[M_May41]

I looked at the rings and there is glue accross all of them. I dont see any other marks and they dont rotate with light pressure. So I assume they haven't been moved. How are they adjusted or any Ideas what else may be wrong??

 

[KenLayton]

When you did the capkit, did you replace the caps that were under the soldered in metal shield? Have you replaced IC501?

Transistors X305 and X306 are for negative sync. Transistors X301 and X302 are for positive sync.

Don't forget that cap C302 polarity is marked incorrectly on the foil side of the board.

 

[Warlord]

If the ship gets bigger on one side off the screen and smaller on the other then it sounds like to me you need to adjust the vertical linearity pot.

 

[M_May41]

In response to the last two posts. first adjusting the V. lin pot from one to the other extreme helps this problem none. I did change the caps under the metal shield. But I havent changed IC501 yet. And I was aware of the silkscreen problem on the foil side of the pcb for c302. But the orientation mark Is correct on the top side and It's In right. I have checked orientation from Bob Roberts Cap Map Repeatedly to make sure. I'm confident that's not the problem. Remember I had this same thing before I ever capped this thing. Randy Fromm's GO7 Flow chart Indicated a check of x302 and x306 for a vertical sync problem so that's what I changed. So what to do? I guess next I should change IC501 and those other transistors. Sound like a reasonable plan of attack?? Or any other suggestions??? By the way what are the chancesRadio Shack would have that IC? The store I usually get my stuff at Is closed on the weekend :-(

 

[KenLayton]

I can say that Radio Shaft will NOT have that IC. You can get it from Bob Roberts or MCM Electronics (www.mcmelectronics.com)

 

[M_May41]

OK I replaced IC501. Same problem. Also have replaced x301 through x306 and tested all 400 resistors. All looked good except possibly r419 and r420 If I'm correct r419 should be 2200ohms and measures 2615ohms. r420 should be 5.6ohms and measures 6.16ohms. Both are over the 10% tolerance but not much. D401 and D402 also check good. But still same problem. Any other Ideas on what to do next??