Space Invaders sync problems

[lost in cables]

Hi need some help Space Invader sync

Very very very sensitive vertical hold problem with space invaders and 19v1001 monitor.

he smallest of a turn and may get it to stop, It take a thou of a turn to work it out. Gets better when warm but doesn’t fix no matter how long its on. I can get it to stop but have to do it every time It powers up and during play. It

I did a 1001 rebuild kit, still the same, replaced the 2 sync transistors still the same. Cleaned all the pins and switch cleaner on the pot, still the same. Replaced the pot with the horz sync still same.

Any other bits I may try to replace?

Jez

lost in cables2020-04-25 17:00:04

 

[ataridude74]

Probably not the issue, but just in case to eliminate the Space Invaders PCB as the problem can you hook it up to a TV/Monitor with composite input?

(currently having issues myself with a pesky B&W monitor)

ataridude742020-04-25 17:24:07

 

[RaveN]

To rule out the board, there's an electrolytic cap on the video output (can't remember the value, it's something like 10uF). The sync and video are combined and then this cap acts as an AC coupler, removing the DC part of the signal so that the monitor can then DC bias it in the appropriate way.

If this cap is on it's last legs it will cause all sorts of monitor issues. From the description of your issue, i don't think it will be this, but at least you can then narrow the issue down to the monitor alone.

 

[lost in cables]

Thanks for that .
Will look at drawings for the right value.

Will come back and let you know what happens.

Jez

 

[lost in cables]

hi, found the 10uf 25v cap replaced for new and still the same as before, but that's one more thing eliminated.

jez