Space Invaders PSU board issue

Arm123

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I have a Midway Space Invaders that i am trying to fix... Someone has converted this to a switching PSU. They cut the +5v,-5v,+12v,gnd from the original midway PSU board and connected them to the switching PSU. The rest of the power harness is still connected to the midway PSU board.

I have been threw BrentRadios tips / help section and have discovered that the reset line voltage is supposed to .5v However, i am getting 2.3v

Would that cause the game to not start up ? I have heard people with Taito SI's just ground out the reset line and it works fine... Can i also do this ?

Thanks for any suggestions.
 
I have a Midway Space Invaders that i am trying to fix... Someone has converted this to a switching PSU. They cut the +5v,-5v,+12v,gnd from the original midway PSU board and connected them to the switching PSU. The rest of the power harness is still connected to the midway PSU board.

I have been threw BrentRadios tips / help section and have discovered that the reset line voltage is supposed to .5v However, i am getting 2.3v

Would that cause the game to not start up ? I have heard people with Taito SI's just ground out the reset line and it works fine... Can i also do this ?

Thanks for any suggestions.

I would like to know also and what wire is the reset wire
 
I just changed the -5v regulator '79m05uc' and changed a couple caps... The reset line now seems to be reading .18v which i guess is better, but still not .5v

Is that acceptable ?..
 
I dunno. When I did one (switcher in a Midway SI), I didn't cut any wires but the +5 and a ground. Used those from the switcher.

I had some startup issues intermittently, a recurring TILT error message, and even a time when the Player 2 wouldn't fire but the Player 1 would. Eventually figured out I needed to bump the +5 up to about +5.25-5.30. Once I did that, the problems went away....
 
I dunno. When I did one (switcher in a Midway SI), I didn't cut any wires but the +5 and a ground. Used those from the switcher.

I had some startup issues intermittently, a recurring TILT error message, and even a time when the Player 2 wouldn't fire but the Player 1 would. Eventually figured out I needed to bump the +5 up to about +5.25-5.30. Once I did that, the problems went away....

Hey there, thanks for the response.

I have never worked on one of these before and have never seen this machine work before. However, i have been told that it did once work like this.

I still get no boot when the ROMs are installed... I tried the 'line test / RAM test' with no ROMs installed and get nothing. I know the monitor works because i am getting raster and the game doesnt coin up / play blind, but the counter responds.

The only 'life' iv seen is when i left the machine on, with no ROMs installed. After about a minute, i get the space ship sounds and an explosion, then nothing.

I think now that im getting proper voltages, im gonna run everything off the Midway PSU and ge rid of the switching PSU, see what happens.
 
I dont get nothing with mine, just garbage like its not booting at all, all the voltages are good on the ps and on the edge connector and on the main board, and my pots are adjusting very accurate
 
I tried reseating the chips and one of the chips has 3 feet broken off, could this be the result of it not booting at all, no graphics or any sounds just garbage as soon as its turned on
 
I tried reseating the chips and one of the chips has 3 feet broken off, could this be the result of it not booting at all, no graphics or any sounds just garbage as soon as its turned on

Yeah, that's probably a good place to start. If it was one of the 4 chips on the main board, then just get some EPROMs programmed and put them in there... you may or may not have to restrap the board (depending on how it's already set up). You can also put in 1 2764 IIRC and run a couple of wires and have everything on 1 chip while you're at it. I know it's doable, but I've never seen pictures of how it's done, so I just put 4 2732 (with the ROM image doubled) back in mine and called it a day. Normally it'll take 4 2716's, but I didn't have any, so... yeah.
 
Easiest thing to do is to remove all the ROMs and test it... See if you get the 16 lines your supposed to get. Then you know the board is working. If any are missing, then its a RAM issue and you should do the above kit solution.

How about some help with me freaking problem ? ;-p
 
Easiest thing to do is to remove all the ROMs and test it... See if you get the 16 lines your supposed to get. Then you know the board is working. If any are missing, then its a RAM issue and you should do the above kit solution.

How about some help with me freaking problem ? ;-p

Sorry about that... got distracted.

From what I saw on mine, it looks like they used some crappy sockets on these boards as well... I guess I'd start with replacing all the sockets that I could and going from there... atleast rule them out.
 
According to this...

http://www.elektronforge.com/TestMdwPS.htm

It says .5v or LESS, so I'd say .18v is good to go!

Icidentally, I've seen the b&w monitors go bad where they show a raster, but no actual picture! You can test using a pair of clip leads and a test monitor or tv with AV input. Just connect to the 2 video wires on the monitor plug, which I believe are pins 1+2 (they're next to each other and fairly thin).
 
Checked all the fuses... all are testing as good.

I noticed something strange with the power board... all voltages test fine when the 18 pin motherboard connector is not connected. Then when i test it with the 18 pin edge connector connected, the +5v falls to +0.7v Does this mean my board is messed up / bad due to a bad component ?

Because of the above, I used the switcher to power the +5v / gnd to the board.

I then tried eliminating the monitor by splicing a rca cable and hooking the ground and hot wires to a TV. The same thing (blank screen) with and without ROMs.

Starting to get frustrated. :-(

Any ideas ?
 
Checked all the fuses... all are testing as good.

I noticed something strange with the power board... all voltages test fine when the 18 pin motherboard connector is not connected. Then when i test it with the 18 pin edge connector connected, the +5v falls to +0.7v Does this mean my board is messed up / bad due to a bad component ?

Because of the above, I used the switcher to power the +5v / gnd to the board.

I then tried eliminating the monitor by splicing a rca cable and hooking the ground and hot wires to a TV. The same thing (blank screen) with and without ROMs.

Starting to get frustrated. :-(

Any ideas ?

I too failed at hooking SI output up to something other than the internal monitor. I tried composite in on a old commodore monitor and also on a vcr.
 
Its just strange because the Midway PSU that i recapped and changed the -5v reg. IC on, works fine when there is not load (not connected to the pcb). I checked at the PSU harness header and the pcb edge connector. It seems to drop out to 0.7v, dont know what that means or where to go from there.
 
Its just strange because the Midway PSU that i recapped and changed the -5v reg. IC on, works fine when there is not load (not connected to the pcb). I checked at the PSU harness header and the pcb edge connector. It seems to drop out to 0.7v, dont know what that means or where to go from there.

I'd start by checking the 2N3055.....less likely, the LM305.

Edward
 
Just got a spare 'untested' powerboard and tested it... +5v was not able to get past +4.4v even with the pot turned all the way.

I replaced the 470uf 16v cap and +5v was restored.

Tried this new board and the machine fired up !..

SI Sweetness... im so happy :)
 
I noticed something strange with the power board... all voltages test fine when the 18 pin motherboard connector is not connected. Then when i test it with the 18 pin edge connector connected, the +5v falls to +0.7v

I have exactly this issue with our Midway Space Invaders Deluxe - when the PSU is not connected to the board set I get a strong +5V and then as soon as it is connected via the 18 pin motherboard connector, +5V drops to < +1V.

Any recommendations on what you changed on the PSU to fix this?
 
Just got a spare 'untested' powerboard and tested it... +5v was not able to get past +4.4v even with the pot turned all the way.

I replaced the 470uf 16v cap and +5v was restored.

Tried this new board and the machine fired up !..

SI Sweetness... im so happy :)

This was the fix....

I replaced the 470uf 16v cap and +5v was restored.

Great job and thanks for posting the repair.
 
This was the fix....

I replaced the 470uf 16v cap and +5v was restored.

Great job and thanks for posting the repair.

Thanks for the reply

I think the post above implied that was the fix for the Power board where the +5V wouldn't go higher than +4.4V

The one I have is where the +5V drops to <+1V when trying to power the SI Motherboard - wonder if anyone posted how that one was fixed?
 
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