Working on Robotron, Centipede, and Tempest!

slicknick13

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So, I'm just getting back into games after a long while (like, RGVAC was cooler than a web forum long).

Anywho, I decided to dig into this stack of dead boards I've been carrying around with me and I figured I'd pick some expert brain about my problem children.

These are all on a test bench with a switcher and a JROK RGB to component board except for the vectors, which are in a space duel cabinet. I've got a USBee locic analyzer for poking around.

Set 1: Robotron:
This boardset is dead, no video, no 7 segment LED, watchdogging like craziness. I put new sockets in for the decoder ROM 6 (corrosion), the CPU (corrosion), and replaced the RAM with 4164's. I can hold reset and watch the CPU write to the reset address, see ROM 12 get selected and write data back to the CPU. Taking a look at 5G to see what's going on in the watchdog ckt, I see that pin 3 is held low. Tracing that all the way back to 4G, I see why. A10 and A11 are in lock step, so that pin never gets decoded. Frustrated, I'm thinking, Why no video? I can trace that all the way back to a Screen Control signal that's doing nothing. That ends for me at the 6821.

I need to walk away from this set for a while, or at least until I can pick up another set to compare against. But if anyone has any suggestions..

Set 2: Centipede:
Havent touched this in a while, but it's next when I get a new edge connector. Plays blind, but I get nothing but a yellow screen. Any preliminary suggestions?

Set 3: Tempest:
I got this set when I was young and a hot shit, thinking I could fix stuff. I replaced all of the sockets and ram (didn't use sockets!) and apparently made a mess of the whole shebang. This set should probably be scrapped, but it's one if my firsts, and now its a challenge. I went around and pulled all of the sloppy sockets and poorly installed vector RAM out. I then went ahead and fixed all of the traces I ruined way back. Checked for shorts and continuity on the soldered in program RAM since I don't want to mess with that yet, I slapped new vector RAM and sockets in, and put one program ROM socket back in with a 27256. This is the way it sits and is, of course, watchdogging. Now I remember back when I was fixing a couple of Asteroids boards you could split the VSM from the program side to at least get that working first. Is this the case with Tempest? I'd love to be able to just the the program to start with no vectors or aux board and ease myself into this one.
 
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I was wrong about the Robotron, Screen Control comes from 3A on the ROM board. Trace it all the way back and again, It's because A10 and A11 are pulsing together.

I'm assuming that the program is starting to run but not getting far enough along to being up the screen or start talking to the 7-segment LED. I guess I should start looking for RAM trouble? Maybe 3B, 3C, 3G?
 
I retitled your thread so it would get the attention of folks that work on those boards.

RJ
 
I retitled your thread so it would get the attention of folks that work on those boards.

RJ

Hey, Thanks! You even kept the emphasis exclamation point.. lol

On tempest lift pin 6 on R9 ls244 this will seperate the vsm from the program.

I knew it could be done.. I'ma bring this one back to life. It's just been sitting there laughing at me for too long now...
 
On the Robotron:
- Try recrimping the ribbon cable connectors on the ROM card. When people remove the ROM card they pull the ribbon cable and that causes the wired to pull away from the IDC connectors.
- verify that you are getting both clock signals at the 6809 CPU chip. If you have corrosion as far as the decoders, you probably have corrosion around the crystal.
- check the buffer chips (1D, 2D, 2G and 1D) to make sure the address lines are being buffered correctly.
- check all of the 7474s. For some reason, these flake out all the time and since they generate the clock signals and well as the timing to the RAM, it only take one to cause the symptoms you are seeing.

ken
 
On the Robotron:
- Try recrimping the ribbon cable connectors on the ROM card. When people remove the ROM card they pull the ribbon cable and that causes the wired to pull away from the IDC connectors.
- verify that you are getting both clock signals at the 6809 CPU chip. If you have corrosion as far as the decoders, you probably have corrosion around the crystal.
- check the buffer chips (1D, 2D, 2G and 1D) to make sure the address lines are being buffered correctly.
- check all of the 7474s. For some reason, these flake out all the time and since they generate the clock signals and well as the timing to the RAM, it only take one to cause the symptoms you are seeing.

ken

I replaced the ribbon cable. One of the first things I did after reading all the threads I could find.

Both clocks look good. The corrosion isn't battery leakage, it must've sat outside of a cabinet. It's all isolated on the side of the board with the headers, up to about column C.

As far as I can tell, all of my buffers look good.

I did find a bad 7474 at 4D. After I replaced it I finally at least got something on the screen, though still not a hint of anything on the 7 segment display:

photo.JPG


The watchdog really cooled its heels too. It's pulsing a lot slower. About every 128ms (off the top of my head). Right along with the R/W line, which seems like more than a coincidence. Something to dig into tomorrow.
 
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