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Moon Cresta (Galaxian hardware) Missing White

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ataridude74 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ataridude74 Quote  Post ReplyReply Direct Link To This Post Topic: Moon Cresta (Galaxian hardware) Missing White
    Posted: 10 Oct 2019 at 8:34pm
I have an original Sega/Gremlin Moon Cresta, which uses modified Galaxian hardware.

Red, Green and Blue are present, but there is no white.  As a result, all other colours are darker.

The game plays fine.

The video RAM appears to be fine, I have swapped the chips around and it makes no difference.

Pressing on a chip made the screen green, although reflowing the solder on the sockets has stopped that.  Although the sockets are really crap ones, maybe still a bad connection?

Or a chip in the video circuit is failing?

The video circuit is pure Galaxian (as far as I know) so same fixes will apply.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lurch666 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 2019 at 5:09am
Puzzling since white is made by mixing all the three colours so if white is wrong then at least one of the other colours must be wrong.

There is a set of resistors coming from the colour prom so if you check the schematic and figure out what the values should be and check the ones on your PCB to see if they are all correct.
If they are it could be a problem with the prom itself.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bones Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 2019 at 7:16am
Maybe put a bit of wood under the PCB where you are pressing down on chips to prevent the board bending. This will eliminate it be something else a distance away from where you may think it is. I'd always change dodgy old sockets, I've had so many that have broken at PCB level and reflowing the joint can temporarily join it again only for it to go again the first time it is moved,also the connection can be read as ok on a dmm but in reality not good enough for signals and current to pass. You can locate a broken socket pin by simply using your soldering iron and gently move the the leg one way and release it, if it springs back it's probably ok.
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