Space Invaders - Fuse Problem

Onion920

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I've got an "L-Shape" Taito upright Space Invaders machine that's got me stumped, and I was wondering if anyone could help me out...

Whenever I go to power up the machine, if everything is connected, I blow the 3A fuse on the transformer. If I disconnect the edge connector running to the daughterboard (Connector G), everything else seems to power up just fine.

Checking voltages, the +18v line seems to be running at about +19.3v, and the +5 and +12 v lines are at +5.17 and +11.92, respectively. Pots on the power supply don't seem to adjust the 18v line.

I've also spot-checked the diodes on the daughterboard, but they all seem to be working just fine.

I'm kinda out of ideas... any thoughts?
 
Well I've never worked on one. But I'm assuming it powers up similar other designs. Which means that it does the dc rectification on the board. On say the Midway Omega Race the 18Vac will go through diodes to rectify the 18Vac to DC voltage for the 3 different voltage regulators.

Assuming that the Taito is basically the same. I would check for shorted Voltage regulators, shorted Diodes, and possibly bad caps on the board. As a quick check you can measure the resistance across the 18Vac points on the edge connector of the board. I've also seen transistor leads shorted to ground traces, or caps shorted to traces as well.

Are there schematics for it? I'm looking and not quickly finding anything with my google fu.
 
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Well, I followed the 18V input and started testing capacitors. Sure enough, the first cap on the 18V line was bad. Swapped it out, and now everything powers up just fine...

Except now, instead of the game, I get a series of about 8 horizontal lines, with one thicker (scrambled) band. By reading the forum, it looks like bad RAM chips, yes?
 
try cleaning the edge connector on the daughter board, and also, you may want to try dialing down the +5 and +12 a bit closer to +5 and +12. reseating and cleaning all the legs on socketed chips probably wouldn't hurt either.
 
Sadly, none of those things seemed to have worked.

I guess the next question is, does anyone sell the ROMs for the L-Shaped Taito board?
 
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If the Taito version is anything like the Midway version, those bars basically mean the board is working good enough that something should boot, and chances are you do need roms or at least new sockets for the ones you have.

Steph @ Hobbyroms should be able to hook you up with the roms but I think he's on vaca for a few days (he posted in the main forum a few days ago).
 
Got the ROMs from HobbyRoms, and switched my jumpers (S1, S2, S3, S5) to take the new 2176s... and I've gone from 8 horizontal lines to 14.

More lines - that's gotta be good, right?
 
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