Space Invaders RAM test

kstillin

Well-known member

Donor 2018
Joined
Aug 24, 2006
Messages
4,698
Reaction score
130
Location
Columbia, South Carolina
OK- I followed some online wisdom for testing out a few boards.

Pull the (E)PROMS, boot up, look for 16 vertical (horizontal for SI) bars across the screen.

Well, I get what looks like 16 repeated 'sections' across the screen. There isn't a single solid line from one side to the other, but all the repeated 'sections' look the same.

I pulled the other trick and momentarily grounded pin 7 on each RAM chip. When I do that, a thin segment of each section goes solid white. I assume this points to bad RAM?

The RAM is a little pricey- over $1 per chip at 16 chips per board. I've got 5 boards (3 good candidates).

Has anyone replaced the RAM with something a little more modern? Single supply stuff versus the old 3-supply chips? The RAM is dead cold, but the voltages are right on. Do you think this means they were zapped at some time?

Is this common? Three boards pretty much do the same thing...

Kerry
 
I forget the exact details of the procedure that you're doing, but bad RAMs are VERY common on SI boards. I fixed one of my boards doing the way you're doing it, but then picked up the SI multi-kit: http://www.arcadeshop.com/si-kit/si-kit.htm , which has a GREAT self-test built in (beep codes tell you which RAMs are bad). If you've got multiple boards, I'd highly recommend that for troubleshooting, and the extra games are actually pretty fun once you get the boards working. IIRC it's also got a sound test, which is great for verifying the sound board is 100%.

I don't think I've ever seen anyone replace it w/ modern chips, but I don't remember the RAMs being that expensive either (though I bought ~20 at one time because I had several bad boards).

DogP
 
At this point...those RAMs are known to be problems.....after all, they're over 30 years old. I tend to find 3-5 per board that are bad.

Edward
 
If you don't want to buy the HSS kit, there is a Bin file you can download and burn a Test rom. It will check all your ram, and sound functions. Quick and easy, and even map out which ones are bad.
 
Back
Top Bottom