Midway A082-90400-x000 Power Supply

ikillrinst

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I have a Space Invaders Deluxe that is not fully powering on..

The monitor has some flicker scrolling
the sound is a humm with another sound like the space ships in Asteroids
the back lighting all works

I have checked the power supply and I am not getting +12, +5 and -5 are ok.. but when I check +12 I am only reading 0.28.. Can anyone tell me where I go from here?
 
The 12VDC rail is pretty simple. My initial thought is a bad 12 volt regulator (LM7812).

It's also possible you could have a short on the board set dragging the voltage down. Check the resistance/ohms between 12VDC and ground.

Edward
 
wasn't sure what setting on ohms, so I tried them all.. I got 0.00, is there a way to check the regulator with my multimeter?
 
wasn't sure what setting on ohms, so I tried them all.. I got 0.00, is there a way to check the regulator with my multimeter?

0.00 means a dead short. Unplug the power supply from the board set and try again. You need to isolate where the short is at......the board set or the power supply.

Edward
 
that was the +12 with the board out of the machine.. SO the power supply is ok?

Well, it's difficult to say until you hook a working motherboard to the power supply.....but it's probably fine (it definately doesn't show a short from the meter reading you posted. Now you have to figure out which of the two boards, that make up the motherboard set, has the short. My bet is on the larger of the two boards. Separate them and measure ohms across 12 volts and ground on each board. Find the one with the short......and then the fun begins.

Edward
 
ok, if I checked it correctly which I believe I did, I am getting -0.00 on the +12 terminal on the CPU board

by the way, I checked the power supply without the board set in and i got 12.36
 
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Can anyone tell me the best way to find the short on this board? I am unsure of how to test the individual resistors and caps and such... And is it possible that one of the soldered chips has the short?

Thank You
 
This is the fun part.......start removing everything that is connected to the 12VDC line. Remove a part.....check if the short is gone......repeat......over....and over......and over.......you get the idea.

On a Space Invaders motherboard.....a lot of stuff is connected to the 12 volt line......I'd start with caps (specifically the tantalum caps on the 12V line).

Edward
 
Am I hearing this correctly, I have to pull each cap off the board and then retest for +12, if the short is still there I can replace the cap and move on to another? Is there any tutorial or doc that will show me all the parts on the 12v rail? So i don't waste time removing stuff that has nothing to do with it?
 
I think I found the problem.. there are 2 larger blue tantalum caps at either side of the larger surface mount chips, one is at H8 and one is at H15, when I pulled the one by H15 and retested +12 I get 0.L.. and when I ohm test the cap I get 0.00, I know this is not the proper procedure to test a tantalum cap but I just thought I would throw that out there...

is there anything I can use in place of the tantalum cap? it says 22, 25v

Update: When I check the motherboard +12 line I get 0.L but when I check my SID board for comparison it gives me a reading, not 0.L
 
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last thing I need to find out is why when I test the 12 volt line with my multimeter I am getting 0.L is there something I missed? or something I messed up on? I found the shorted out tantalum, I replaced it and the 4 orange electrolytic caps, they are installed properly, rechecked 100 times..
 
last thing I need to find out is why when I test the 12 volt line with my multimeter I am getting 0.L is there something I missed? or something I messed up on? I found the shorted out tantalum, I replaced it and the 4 orange electrolytic caps, they are installed properly, rechecked 100 times..

Are you testing DC volts or are you checking ohms between 12 volts and ground?

Edward
 
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