Space invaders scrambled now no screen

Tantora

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I'm thrilled to now own an SI, Midway ver. However, I will be more thrilled when it's back up and running. It was working last week when I picked up. After 10 minutes of play, it started showing gibberish. Shut it down, and it got worse. Took a break, the next morning it worked fine (back to normal) for about 10 more minutes, then went completely blank. Monitor shows a neckglow and projects a blank screen. Power supply has the appropriate voltage readings. I believe the only other remaining thing to troubleshoot is the motherboard. Cap kit? Pics of the gibberish before it went blank below.

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check rom sockets they degenerate and get loose on these boards. test board by removing roms and see if you get good bars on screen. down load and burn si test rom to check ram which this looks like
 
I would agree if it was constantly displaying gibberish... Not sure if you noticed in the previous post. Screen was scrambled then went blank. I don't think that's a ROM issue, right? This is what displays consistently now:
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the wiring harness that plugs into the edge connector isn't the greatest either. that's what feeds power into the boards. since all the rams and I think roms too are tri-voltage, if one of the voltages isn't clicking, you lose the whole game.

the static garbage is the roms though I think. try reseating them. the sockets they came with as has probably been noted 800,000 times aren't that great. I ran into that with Sea Wolf at work, but I finessed the rom placements just right that it's worked in a free play arcade for over a month without issues.

(disclaimer: the sockets will probably inevitably be replaced one day)
 
Thank you, will give it a try. But what I can't seem to wrap my head around with this theory is... could a wiring harness or IC go from good to bad, back to good... then to bad all within 24 hours? Please educate me on this.
 
with nothing on the screen either your monior is not getting power and lighting up or your connector to the main board is bad. the output on the board is composite i hot terminal and 1 gnd and it reads out the ram info so if garbage in ram you get garbage lights on screen. you probably are not putting out power from power supply or you have a bad connection for power to the main board. if bad power to board don't run it too long missing I can't remember if it is 12 volts or -5 but I think the 12 missing will cause bad things to happen to ram chips.
 
connectors can be corroded and worn out giving intermittent. reset circuit is on power supply and without that working game will always display garbage. I have blown the reset circuit transistor by turning off and on too rapidly and also having the main connector off center
 
your first pictures look like rebooting game with bad rams later on it looks like you lost the reset signal on pin 10 then it looks like you lost all power to board.
 
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I just tested the edge connector, getting 5v, 12vdc and -5vdc as expected. Also traced continuity between orange reset on 11 pin connector to power supply pin 6. I guess it's time to pull the board out and reset the RAMS
 
Heat can cause the ROM's/EPROMs to shift in the sockets slightly, which is why folks are pointing to the sockets.

If you've pulled the ROM's, and powered up the game - did you get correct RAM bars? If you're not sure, upload a pic.

Check the ROM legs - do they look clean (inside and outside)?

If you do a continuity check between the top of the ROMs (each pin) to the bottom of the board, do they all check out? This is how you can verify the ROMs are seating and being recognized.

Heat absolutely could cause the symptoms you're having - works, then doesn't, then works again later.

Some reference sources you may find handy:

http://www.pinrepair.com/video/seawolf.htm

http://www.brentradio.com/images/SpaceInvaders/Midway8080SystemBoards.html

and especially:

http://www.brentradio.com/images/SpaceInvaders/midway_8080_test.pdf

Regarding replacing cap's - if you're still running the original cap's on the power supply board, odds are good they could stand to be replaced, but unlikely they'd be the root cause of the issues you're seeing unless you have a lot of AC ripple on one of the voltages, or a voltage is missing (which appears to be ruled out).

You noted you "reset the RAMs" - is the RAM all socketed on your board, or are you talking about the ROMs?
 
Sprout, thanks for the explanation. In terms of pulling RAMs, I should have said ROMs. I just pulled E,F,G,H, and the long TI Singapore IC, screen is still blank. Should pull the ROMs from the daughter board too?

All ROM legs look clean, but will shine with scotchbrite and report back.
 
Regarding the "long TI Singapore IC" - is this a 40-pin chip? If so, that's your 8080 processor, and you don't want to do that - the board definitely won't boot with it pulled :)

Now - doesn't hurt to pull it, and check/clean it's legs and do the same type of continuity check between the tops of the legs and the bottom of the board as noted. Worth doing for any/all socketed chips. I wouldn't worry about the daughterboard just yet, given the symptoms.
 
pin 10 is reset line on board. 11is vled 18 is the video output with 17 being video gnd can be used as input on regular tv to yellow rca terminal with 18 connected to center terminal. with roms pulled out you should get some signal with the game on
 
Cleaned all ROMs on the mother and daughter board, put all back in except for the alphabet ROMs. Nothing, blank screen.

Multimeter is being a PITA on continuity, not consistently beeping. Going to order a replacement.
 
Not sure if this gives any additional clues. Thanks for all of the pointers
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check with meter for power inputs going to the board with the connector on the board. there should be enough room to access the finger of the board around the connector. are you getting a signall off of pin 18 on the main board?
 
Original linear psu
Pin 1: 4.7 vdc
Pin 3: 11.89 vdc
Pin 5: -5 vdc
pin 18: .001 vdc

Switched to switching psu
Pin 1: 5.1
Pin 3: 12.9
Pin 5: -5.1
Pin 18: .003 then 0


Power on reset
.02 vdc while using linear
.025 on switching
 
we are looking for a signal alternating on pin 18 and pin 10 reset should try to go to 5 volts at beginning then 1/4 second later or less try to get as low as 0 but it usually never does the .02 is as good as 0 but did it spike? if you tie 18 to center terminal of video only into a regular tv and connect 17 to outer ground you should get a picture on a regular tv. video only is usually an rca connector with a yellow connector. only saying this because your monitor might be out or have bad wiring to it. I don't want you chasing down a wrong path of board problem if you are having a bad wiring to monitor. usually the game if it resets plays a sound when it reboots. did you use a switching power supply with the midway adapter that simulates the reboot signal?
 
Video was working just fine before it gave out. Remember, the game slowly gave out. First scrambled imagery, then dead. Also, I still see neck glow, light and what really leaves me to believe that the monitor is okay is that I coin up and I don't hear any sounds after hitting start.

In terms of the switcher, I am using the 8080 kit which has a pcb on top of the switching psu terminals.
 
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