Asteroids game board debugging

joetechbob

Member
Joined
Oct 26, 2011
Messages
168
Reaction score
2
Location
Fargo, North Dakota
Hi all!

I picked up a non-working (but clean) Asteroids off of a regional auction site. Before I purchased the machine I was able to go take a non-thorough look at it and found that when turned on it made a loud buzzing noise, had both P1 and P2 buttons lit solid and no video (but had neck glow on the monitor--spot check light was on though). Looking online I saw others had hit a similar issue before and it sounded like it tended to be a low 5V line going into the game PCB.

When I got the game home, I did some basic diagnostics and did find that the 5V rail on the game PCB was low (around 4.5 volts). I then adjusted the regulator to give around 4.95 to 5 volts on the power rails (and Vcc legs on spot checked ICs). After resetting the game I continued to get the buzzing sound and solid P1/P2 lights. My next course of action was the following:

1) Pull all of the socketed chips, cleaned the pins and re-seated the chips.
2) Clean the edge connector with a pencil eraser
3) Looked for obviously bad solder joints--found a couple and ran jumper wires.

After doing this I fired the game back up and I was still getting the same issue. I then checked the RESET pin on the 6502A and found that it was low. I tried connecting the watch dog disable loop to ground, but that didn't seem to affect the state of RESET.

[Note: I have a digital multimeter with a basic frequency counter built in that is supposed to support measuring up to 10MHz signals.]

Next--after testing RESET--I checked the 6MHz tap and had my multimeter show around 4.8MHz. Testing the other divisions I saw 2.4MHz and 1.2MHz (can't test the 12MHz as my meter won't go that high). This was a bit of a concern, but I took it with a grain of salt as I am using a $100 multimeter to take this measurement. However, when I got to B4 I saw that the 3kHz and 12kHz pins were just outputting complete garbage (according to my multimeter)...I was reading anything from 45kHz to 75kHz on one pin, for example.

I double checked and re-checked power throughout and everything looked good. Long story short, I have a local collector friend who has a non-working Asteroids Deluxe board that he let me borrow. When I hook up that board I see almost the exact same measurements on the clock circuit, RESET is low, and the symptoms are more or less the same (makes a buzzing sound...P1/P2 lights are a different pin out on Deluxe so I didn't verify those).

I was hoping that the LS393 at B4 (counter) was going to be bad on my board (and thus causing the bad 3kHz and 12kHz), but what are the odds that someone else's board gives the same measurement/behavior?!? Is that a high failure chip/circuit? It seems almost like my power supply *is* bad (despite the solid 5V I'm getting). Perhaps it's noisy and I need to replace the main filter cap (big blue)? Has anyone else seen this before?
 
It is almost certainly a dead big blue, the giant capacitor on the main power supply. You can check the DC outputs of the PS for AC current to verify. My Tempest was doing the exact same thing and this got it running again.

Bob Roberts sells 'em for, I think, $12. It's probably a good idea to rebuild the AR1 while you're at it.
 
Have test mode working

Thanks for the tip!

Luckily the same friend who lent me the Asteroids Deluxe board also had several spare Atari power blocks. I popped in a new big blue and the oscillator is now humming along great. I even get test mode.

Short story long:
I had actually measured a 120 hz spurious signal on the regulated 5v line shortly after I posted my initial message. Since the buzzing sound also was lower frequency I downloaded a tone generator on my iPhone and set it for 120hz--it sounded exactly the same as the buzz off of asteroids. I called up the same friend that lent the spare board and he offered to let me borrow his set of several power blocks. When I got back--as a sanity check--I hooked up a switching power supply to just the game board and all the measurements looked good--reset, clock(s), etc. I was smiling after that :). I then swapped in a new big blue and was able to get into test mode. Now I'm grinning ear to ear :D.

In test mode I get a single chirp upon entering the mode--the same chirp one hears for a button press. Is that normal? I expected six high pitched tones for the RAM test...the Asteroids Deluxe is failing a RAM check and I hear 2 high pitch tones and one low pitch tone that don't happen at all on my board. Not sure if that's a good thing or if I'm just not getting a RAM check. Any thoughts?
 
In test mode I get a single chirp upon entering the mode--the same chirp one hears for a button press. Is that normal? I expected six high pitched tones for the RAM test...the Asteroids Deluxe is failing a RAM check and I hear 2 high pitch tones and one low pitch tone that don't happen at all on my board. Not sure if that's a good thing or if I'm just not getting a RAM check. Any thoughts?

With Asteroids, on entering test mode, it's normal to hear a single "chirp" (just like you then hear if you press a button in test mode). You don't get any RAM-check tones unless there's a problem. So the single chirp (and button-induced chirps following that) is a Good Thing.

Do you have any video output? There should be a crosshatch pattern on the screen and some letters & numbers. The manual explains the meanings of the display (dip settings and possible EPROM errors, IIRC).

PS: if you don't already have it, the manual & schematics can be found here: http://arcarc.xmission.com/PDF_Arcade_Atari_Kee/Asteroids/
 
Playing blind

That's good to hear. I'd since had a chance to run everything again out of test mode and the game appears to be playing fine--albeit blind as I don't currently have a working monitor (that's now my current project).

Thanks for the link to the manuals. I've got a few things, but that site is a lot more complete.
 
Monitor working

Update: I got the monitor going so I now have a working asteroids. Thanks everyone!

One more question: the game plays great and without issue, however, when I run test mode the screen shows a page fault error.

Anyone ever see the game run perfect but have test mode fail?
 
Update: I got the monitor going so I now have a working asteroids. Thanks everyone!

One more question: the game plays great and without issue, however, when I run test mode the screen shows a page fault error.

Anyone ever see the game run perfect but have test mode fail?

Try playing some 2-player games. Pay carefull attention to each players score and number of ships remaining, etc. Make sure nothing funny happens.

The "page select" error relates to the RAMSEL line. The RAMSEL line controls swapping of page 2 and 3 or RAM. Pages 2 & 3 of RAM are (I think) used for player-specific data storage.
 
The easiest way to tell if your big blue is bad, is to put your meter on AC volts and measure the voltage across the cap. AC should read very low, like .001 if you are reading .1 its going, if you read more than .3 its bad, if you read 1vac its toast.
 
Back
Top Bottom