Ever had a Gorf RAM board so bad the game wouldn't boot?

RetroHacker

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Ever had a Gorf RAM board so bad the game wouldn't boot?

I'm going through and fixing Gorfs... I burned a copy of Mark's test ROM (thanks Mark!), and am working through these bad RAM boards. One of them is so bad, however, that it prevents the machine from booting! If I have it plugged into either slot, even with Mark's test ROM in there, the machine displays a black screen, and the Space Warrior lamp comes on. There is a buzzing sound in the speaker.

So, I clearly have a chip with a stuck address line or something, and I'm about to go probing, but I just figured I'd see if anyone else had ever run into this before.

-Ian
 
I'm going through and fixing Gorfs... I burned a copy of Mark's test ROM (thanks Mark!), and am working through these bad RAM boards. One of them is so bad, however, that it prevents the machine from booting! If I have it plugged into either slot, even with Mark's test ROM in there, the machine displays a black screen, and the Space Warrior lamp comes on. There is a buzzing sound in the speaker.

So, I clearly have a chip with a stuck address line or something, and I'm about to go probing, but I just figured I'd see if anyone else had ever run into this before.

-Ian


Yep, have a few of them with the same symptoms. They are in my "I will get to those later" pile.
 
OK, I fixed that bad RAM board. Turned out to be a nearly shorted capacitor on the board, the one between +12v and ground. Measured 48 ohms.

I was also able to successfully identify and replace the faulty RAM chips on all of my bad RAM cards. Problem is, that I don't have enough chips to fix all of them. I looked up the datasheet of the 4027 and modified a 4164 to suit. (the extra /CS line on the 4027 isn't actually used on Gorf, it's tied to /RAS). Using that modified 4164, I get flashing, dashed yellow lines through the screen. Oddly enough, Mark Spaeth's diagnostic ROM passes the test just fine like this. Also, the game will work - your ship doesn't automatically explode when it appears. The game plays fine - but with flickering yellow lines.

So, it would seem that the timing is different between the 4164 and the 4027... Tried a 4116 too - same problem.

So, anyone know anything about the DRAM timing on Gorf? I'm off to do some digging to see what other DRAMs might be compatible...

-Ian
 
I was also able to successfully identify and replace the faulty RAM chips on all of my bad RAM cards. Problem is, that I don't have enough chips to fix all of them. I looked up the datasheet of the 4027 and modified a 4164 to suit. (the extra /CS line on the 4027 isn't actually used on Gorf, it's tied to /RAS). Using that modified 4164, I get flashing, dashed yellow lines through the screen. Oddly enough, Mark Spaeth's diagnostic ROM passes the test just fine like this. Also, the game will work - your ship doesn't automatically explode when it appears. The game plays fine - but with flickering yellow lines.

4027 latches the output on the rising edge of /CAS and holds the output through /CAS high. 4116/4164 tristate when /CAS is high.

Astrocade is designed poorly, and the video circuit reads out data w/ high /CAS, so the video output gets whatever trash is residually left on the bus.

During CPU access cycles, /CAS is asserted so the CPU has no problem reading/writing the RAMs, so the RAM tests pass.

(Just to keep some dumbass from coming in and trying to say I'm wrong -- It might be /CAS instead of /RAS, I can't remember, but it's one or the other -- I haven't looked at 4027 DRAM timing in a while, and I"m not going to dig to find my notes to answer a question here).
 
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4027 latches the output on the rising edge of /CAS and holds the output through /CAS high. 4116/4164 tristate when /CAS is high.

Astrocade is designed poorly, and the video circuit reads out data w/ high /CAS, so the video output gets whatever trash is residually left on the bus.

During CPU access cycles, /CAS is asserted so the CPU has no problem reading/writing the RAMs, so the RAM tests pass.

Ah hah. That makes perfect sense. Thanks Mark. I guess I'll have to actually use the right part then :)

-Ian
 
I am also having dashed yellow lines in my Wizard of Wor. Do yours look like this? http://www.youtube.com/watch?v=DgDhDW9JSvw I will be watching your post in hopes of fixing my game as well.
Good luck,
Scott

I can't play YouTube videos at work, but I'll check on it when I get home. The lines I was getting when I had the wrong RAM chip installed were different from the ones I was getting with failed RAM. They were thinner, and flickered a lot faster. I already fixed the RAM boards - I was just searching for a more plentiful substitute for the origninal RAMs. Failed chips on these RAM cards are very common - which is why Dave and Mark took the time to write test utilities.

-Ian
 
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