midway space invaders issue

riche100

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hi there i have a midway space invaders machine . it powers on . but i get a massive loud humming noise . and the screen is just white

if i press any of the cp buttons the humming dulls ever so slightly

so i have no game play or image and a massive humming noise ?

what could it be please? please help

many thanks

richard

in the uk
 
Make sure everything is properly plugged in and that the daughterboard is seated properly on the motherboard. Also make sure all the connectors are seated properly, especially the one on the motherboard.
 
Make sure everything is properly plugged in and that the daughterboard is seated properly on the motherboard. Also make sure all the connectors are seated properly, especially the one on the motherboard.

After power supply, I would suspect a connection of some kind. What happens if you flex the board slightly?
 
midway space invaders

thanks for the hints and tips guys , i will try and flex the boards all chips did look nice and tight i can check again

i dont know the history of the machine , so i dont know if anything has been twiddled or turned .

so i will proceed with caution .

however i will say ive just swopped this chassis from my other space invaders which i dont know the history either and on both machines it did the same

with different game boards on one machine there was less of a hum , but still a hum no less and still white screen and no game play, blind or otherwise


hope i now havent confused matters

this is my main concern :

i will try and flex the boards all chips did look nice and tight i can check again

i dont know the history of the machine , so i dont know if anything has been twiddled or turned .
 
As with any repair like this, start by checking your power supply voltages. Hum usually indicates faulty filter caps, which cause unstable (rippling) DC voltage.

-Ian
 
Yeah I'd definitely check the power supply, and/or try to turn down the brightness on the monitor, but humm is bad. I have seen a board go bad where the screen was all white, but its rare.

That said...that board has been repaired before...its hard to tell but it either appears that 2 rams were replaced, or all but 2 rams were replaced (I know the replacements I've gotten are the brown color whereas the originals were black in most cases, but thats not always the case).

These boards, even if 90% dead, will always display garbage if they're not working. If the voltages are correct and the board is outputting all white then it definitely needs repair.

(Check the voltages at the main board connector)
 
new findings

new findings :

powered on machine with pcb unplugged totally i get no humm moniter powers up

checked all voltages on power supply on wall of the cab and its all over the place , ie it wont settle no matter which one i check -5 +5 12v etc etc


then i plugged the big connector on the pcb and i get no humm or squeel .

so i keep it plugged on and plug on the botton connector onto the other board get massive hum

unplug this and then plug other connector onto board at top power on no humm


does it confuse further or can someone see something ?
 
new findings :

powered on machine with pcb unplugged totally i get no humm moniter powers up

checked all voltages on power supply on wall of the cab and its all over the place , ie it wont settle no matter which one i check -5 +5 12v etc etc


then i plugged the big connector on the pcb and i get no humm or squeel .

so i keep it plugged on and plug on the botton connector onto the other board get massive hum

unplug this and then plug other connector onto board at top power on no humm


does it confuse further or can someone see something ?

If there is nothing hook up to the supply voltages will drift somewhat. Try to load up the supply with a light bulb or something to see if it still drifts. A 12v dc light bulb should work and if it still drifts the brightness will vary.
 
where do i attach the bulb too please?

it drifts that much all the things i checked just flucuating up and down up and down

for eg : on the -5 feed .. went from 3.3 to 6.44 and all in between and back down twizzle to set/settle it


nothing ?

thanks for replys so far
 
Here's where to test on the power supply... to test it at the motherboard the edge connector is where to test for voltages...I believe it's pins 1, 3 and 5 (5, 12, -5v). You'll have to look to see which pin is ground there, I think its the 4th or 5th from the end but its pretty obvious if you look at it.

http://www.elektronforge.com/TestMdwPS.htm
 
where do i attach the bulb too please?

it drifts that much all the things i checked just flucuating up and down up and down

for eg : on the -5 feed .. went from 3.3 to 6.44 and all in between and back down twizzle to set/settle it


nothing ?

thanks for replys so far

hook a car light bulb of some kind to the -5 feed and a ground. Observe the light for changes and measure voltages with light on.
 
If there is nothing hook up to the supply voltages will drift somewhat.

Space Invaders uses a linear power supply. The voltages may be a bit off when measured without a load, but they should not fluctuate much, if at all. His power supply needs repair.

-Ian
 
thanks

thanks for your help and advice i have food for thought

i have another midway si cab here im going to test and try them volts if its ok , i will scaff it and put it in this machine this post is about

thanks so much again

rich
 
findings

thanks for all your replys its great .


ive checked power supply and these were the readings with the board not attached :

new findings :

with multi meter set on v-...

+5v was 5.10 i altered it to +5.1

-5v was 5.13 altered it to -5.1

12v was 12.20 altered to 12.02

reset sig was 0.01

didnt check 18v as didnt know what the 1000uf cap was ??


anyways changed multimeter to v squiggle and got :

+5 was 0.00 to 0.01

-5 was 0.00

12v was 0.00


tell you anything

many thanks

richard
 
flicker ? slam game sound ?

Originally posted by Equites

Okay, seems your PSU is fine.

Midway SI PCBs tend to still give some kind of output to the monitor even when they are 90% screwed. So you should really have something.

Try this test;

First remove ALL the game ROMs, then turn the game on. You should see a repeating pattern of a thin and fat lines across the screen. Next close the Slam switch for a moment,
this pattern should change, but still be solid lines (thin or fat doesn't
matter, but they repeat). Now if any lines are flickering, or there are
dots on the screen that are sometimes covered by lines but reappear when
you "Slam" the switch, then you have RAM problems.


i have some line flicker , sometimes even when slam switch isnt shorted

when i do short slam switch i get a explosion noise from the machine , like ive died and been shot is this correct ?

when i first turn on lines are uniform and do indeed more across the screen as described .



ive turned the width right down so i can see the lines now

this is what happens :

lines move across screen

i short switch and :

i get explosion sound and lines flicker from left to right . like the machines being shook

what im describing make sence ?

thanks

richard
 
So you are getting the lines? Can you post a pic? Explosion sound most likely means those boards should be looked at...at a minimum itll have sound issues. If you pulled the roms and got the lines whereas before you had a solid white screen, thats most likely addressing issues on the roms..like a bad socket, dirty rom, bad cpu socket, or a bad rom.
 
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