G07 Horizontal Sync Issues

[Michael Roma]

I picked up a non-working Missile Command and have just about everything working except the monitor. It appears that the horizontal sync is off and I am unable to adjust it using the H/Freq pot on the chassis. Adjusting the H/Freq pot develops a high pitched sound and I believe the monitor gets washed out (been a few days).

I recapped the chassis and the problem is still there. I heard that some G07s came from the factory with the wrong value resistors at R314 and R317 and this can cause sync issues but I checked both of those and they are 390 ohms. Also, the B+ is steady at 117V.

A video of my issues can be seen on my pages here...

http://home.comcast.net/~mtpacifico/_arcades/missilecommand/missilecommand.htm

Here are some pictures of the chassis... Any suggestions?

- Mike

 

[mhkohne]

I think in the other thread you said you'd cleaned the connectors, but do you have any way (an oscilliscope) to verify that the hsync output is actually being produced and making it to the monitor?

If you could get a scope onto the hsync test point on the main board, that would probably help prove it's the monitor (or, if there's no signal at hsync, then it's the cpu board).

Failing that, I'd try powering the system down and taking a resistance reading between the point on the monitor chassis where the hsync comes in, and the point on the MC main board where it goes out (I don't know if it's buffered after the test point or not). I'm thinking that a resistance reading would give you some clue if you've got bad wiring in some way that you can't see visually.

 

[Michael Roma]

I do not have an o-scope so I can't troubleshoot it that way. I did however have a spare G07 chassis on hand that I swapped in the cabinet and had the same results. So, it looks like it might actually be PCB issue.

What on the board could be the culprit?

- Mike

 

[modessitt]

1) Check your B+ and make sure it is pretty close to 120.0vdc. If it gets off too much, it will look like the horizontal hold is off.

2) Can you slow it down? You might need a new horizontal hold pot.

3) When you did the caps, did you replace ALL of them? I see one that looks a little chewed on in the pic, but it might be a BP.

4) Did you reflow the solder to the video connector pins? Quite common to get cold solder there, especially on the sync pins...

 

[Todd Tuckey]

that looks likes its missing both the horizontal and vertical sync...we have found a neat way to figure out whether it's a monitor or the logic board...simply back up another of your games to the missle command and then move the video cable from one to the other...you may have to undo some of the harness to stretch it to your other game...at least you can determine if its the MONITOR or the LOGIC BOARD or a connection!!! Todd from TNT Amusements

 

[ELutz]

Does the horizontal frequency pot dial it it any better?

Edward

 

[Michael Roma]

On the original chassis...

The B+ is steady at 117V. I didn't recap every capacitor on the monitor just the ones that come with Bob's cap kit. Also, I did in fact reflow the header pins on the video input. Adjusting the H/Freq pot doesn't make a difference but I get a high-pitched sound when I move it too far counter-clockwise.

I swapped in another G07 chassis and received the same horizontal sync issues so I am thinking that perhaps it is an issue with the game PCB.

- Mike

 

[Todd Tuckey]

ahhhh!! the sync header pins in the edge connector could be bent, or the firstchip on the logic board the sync edge pin goes to!

 

[ManiN]

Was this resolved? I'm having similar issues where mine won't seem to adjust. I may have forgotten to reflow the sync pins, so I'll recheck that.

 

[KenLayton]

I see the two bi-polar electrolytics are still the original ones in your picture. They need to be replaced.

Is Missile Command positive sync or negative sync? According to the pictures of your monitor, it's connected as positive sync.

 

[hindered]

I'm having similar issues too, MC w/g07. Rebuilt A/R II, cap kit on monitor. Monitor works fine on my JAMMA test bench, but that's negative sync. MC is positive sync, as Ken pointed out above. Could be something weird in the positive sync circuit?

 

[Dokert]

Missile Command runs either positive sync or negative sync, depending on how the cab is wired.

Wire it for negative sync and see what happens.

V/W wire to -V sync on monitor end
V/W wire to pin 18 on edge connector P20

remove R/W wire
.

 

[LyonsArcade]

I've had a few G07's where the sync wouldn't work, I reflowed the connectors and still had problems. I had to reflow the pins, remove the old solder, and flow new solder on to get it to work right. So you may try that. Also of course check those resistors Ken is talking about.

Also, and this is going to piss people off, don't do the Sync Mod that all the cap kits tell you to do. I've never seen it HELP, and I've seen it screw up the sync several times. I never do it anymore, a complete waste of time.

 

[Todd Tuckey]

The photo I saw shows the tab for the horizontal frequency control standing at around 12 Noon...in almost every case, it would be around 3pm.....that would make the horizontal sync WAY out....