Asteroids PCB, not sure where to start

ieure

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I was playing this a couple days ago when it went dark. Symptoms:

- P1/P2 buttons on solid
- Spotkiller on
- PCB power LED on
- +5v is spot on
- Doesn't respond to test switch
- Emits UFO noise constantly

I swapped it into my AD cab and it's doing the same thing. Thoughts?
 
Game board problem, I'd start with checking the program EPROMs/sockets and if self-test won't even run then the CPU RAM at D2 and/or E2.
 

I don't have a logic probe. I did read through that, and I didn't see anything that described my problems. I seem to recall seeing a more extensive list of problems/solutions at one point, but I can't find it now.

Game board problem, I'd start with checking the program EPROMs/sockets and if self-test won't even run then the CPU RAM at D2 and/or E2.
Yup. I reseated everything that was socketed, no change. How do I test the RAM? It's all soldered, which sucks.
 
I don't have a logic probe. I did read through that, and I didn't see anything that described my problems. I seem to recall seeing a more extensive list of problems/solutions at one point, but I can't find it now.


Yup. I reseated everything that was socketed, no change. How do I test the RAM? It's all soldered, which sucks.

Try swapping out the CPU and check the crystal is not missing or broken. If all fails send it to ROAD.RUNNER, he's the shit with Asteroids boards. You can try piggy backing RAM if you want, I was able to fix a couple boards trying that but it's a crap shoot. Also a side note, if you hear beeps and tones when powering it on it's almost always bad RAM.
 
Well, I think it's basically nuts to own these games and not know how to fix 'em, so… What probe should I pick up and how do I use the damn thing?
 
Well, I think it's basically nuts to own these games and not know how to fix 'em

I agree with that sentiment.

Amost anything that comes up when you google 'logic probe' will work fine. Some people prefer models with an audio output. Search the forums here for a couple of detailed logic probe discussion threads.

As far as how to use it... start with the sticky thread in this subforum, "how to fix PCBs" or something like that. A logic probe is really a very simple device; all it shows you if what you're touching is "high" (roughly 5V) or "low" (roughly 0V) or "pulsing" (quickly changing between the two states). The real trick is understanding digital logic, the devices in question, and the schematics of the game you're testing... in order to know what a given point "should" be doing.
 
I agree with that sentiment.

Amost anything that comes up when you google 'logic probe' will work fine. Some people prefer models with an audio output. Search the forums here for a couple of detailed logic probe discussion threads.

As far as how to use it... start with the sticky thread in this subforum, "how to fix PCBs" or something like that. A logic probe is really a very simple device; all it shows you if what you're touching is "high" (roughly 5V) or "low" (roughly 0V) or "pulsing" (quickly changing between the two states). The real trick is understanding digital logic, the devices in question, and the schematics of the game you're testing... in order to know what a given point "should" be doing.

Thanks for the advice. I picked up an Elenco for $15 on Amazon. No audio, but oh well. I read through that thread as well… Seems like it covers the fundamentals, but I just have to get in there and screw with it.

Also re-located the big list-o-Asteroids issues I was talking about: http://usbdesigntech.com/asteroids/asteroids_pcb_troubleshooting_notes.htm

My problem isn't on it, but just reading through it gives me a good idea of the stuff I should be looking at.
 
OK, here's my short course in logic probe use:

Put it in "TTL" mode if it has a "TTL/CMOS" switch.

First you need to hook it up to power: +5V and GND. These old Atari boards are very handy in that they usually have several +5 & GND test lugs to clip onto. On other boards, often a large 5V filter cap is a good place to clip on. Sometimes, I take mini-clips to grab +5 & GND from a TTL chip, and clip the logic probe onto the other ends of those leads.

Then touch the tip of the probe to each of the points you have clipped on (+5 & GND). You should see a "high" and "low" indication on them.

Now you're ready to start probing. The main thing to try to be careful of is bridging two neighboring pins with the logic probe tip. Most times it's harmless, but there are cases you can do some damage by accidental jumpering.

With a dead game, the first things to check are the CPU's reset line and clock signal(s). The reset line should be briefly (fraction of a second) low at power on or after pressing the reset button, then stay constantly high. If it's stuck low, or perodically "blips" low, there's a problem with the reset circuit or watchdog circuit... or a problem somewhere else causing the code to go "off the tracks" and then the watchdog does it's job and resets. With the clock(s), all you can do with a logic probe is check that it's pulsing (not steady high or low). After that, check the data lines and the low address lines (A0-A7 or so); all of them should show some sort of activity in a working game. Higher address lines (A8-A15) may nor all be active, depending on the game design. Beyond that, some game-specific knowledge will likely come into play, to check INT and/or NMI lines, etc.
 
Spent some quality time with this PCB last night & tonight. Still don't really know what I'm doing, so any guidance or advice would be appreciated.

First thing I did was check voltage into CPU pin 8 (Vcc), 4.77vdc. Tweaked AR1 to get 5.00vdc at the +5 test loop. This brought Vcc up to 4.95, but didn't change the symptoms.

Checked RESET pin on CPU. High, not pulsing, indicating that the watchdog is not triggering. All address bus (AB) lines are low. All data bus (DB) lines floating. Clock output 1 is high, 2 is low, and clock input is low, explaining why the board won't boot.

Moved to the clock circuits. No clock output on the 9316 counter @C4 pins 12, 13, or 14, which all measure low. Moving to the input on pin 2 shows this low as well, pointing to Y11, a 12mhz crystal, or something in its circuit.

Checked Y11, which looks like it has been replaced at some point. Found input low and output floating, moved to the LS04 inverter @B5. Vcc & GND test fine. Schematic shows pin 13 (6A) grounded through R32, which should bring 6Y on pin 12 high. However, pin 12 measures low. This output feeds the crystal, explaining the lack of clock.

I suspect replacing the LS04 at B5 will solve my problems, but I don't have one handy. I'm also not sure if I need to remove some components (or legs of components) from the circuits to accurately test them. Advice on whether I should try other tests before attempting to replace B5 would be greatly appreciated. This is my first board repair, and I'd prefer to at least destroy all the traces & pads replacing the correct component.
 
Your logic sounds very logical to me :) Swap that sumbitch out. Do you have a parts board somewhere you can steal the chip off of, if you're too impatient to wait for the chip to come in?
 
Order the chip and sockets (and maybe some other common spares like 74s, 157s, 191s, etc) and while waiting for it cut the legs of the suspect chip as close to the chip body as possible (leave enough to grab later). It's really not worth it to try to save it and risk damaging the board. Once it's cut the remnants of each leg are much easier to remove one by one. What I do is have my clippers hovering over the remnant on the parts side of the board, then I heat it up from the solder side. When the solder melts I quickly grab and remove the leg in one motion. If you're too slow the clippers will leach off some of the heat and harder the solder. If that happens let go with the clippers and try again. It's a quick but gentle motion - if it gets stuck you don't want to force it and pull up a trace. Once all the legs are out you can go back with a solder sucker and get any remaining solder out of the holes, then solder in a socket and plug in the chip.
 
Your logic sounds very logical to me :) Swap that sumbitch out. Do you have a parts board somewhere you can steal the chip off of, if you're too impatient to wait for the chip to come in?
I have two untested boards in the mail, but I'm hesitant to cannibalize from boards that could be repaired. I think I should track down parts.

Order the chip and sockets (and maybe some other common spares like 74s, 157s, 191s, etc) and while waiting for it cut the legs of the suspect chip as close to the chip body as possible (leave enough to grab later). It's really not worth it to try to save it and risk damaging the board. Once it's cut the remnants of each leg are much easier to remove one by one. What I do is have my clippers hovering over the remnant on the parts side of the board, then I heat it up from the solder side. When the solder melts I quickly grab and remove the leg in one motion. If you're too slow the clippers will leach off some of the heat and harder the solder. If that happens let go with the clippers and try again. It's a quick but gentle motion - if it gets stuck you don't want to force it and pull up a trace. Once all the legs are out you can go back with a solder sucker and get any remaining solder out of the holes, then solder in a socket and plug in the chip.

Interesting. I was thinking it might be good to heat up from the parts side of the board to avoid burning the traces on the bottom. I'll give your way a shot and perhaps experiment on a junk board to find a technique that works for me.

My main concern is that something else in the circuit could be pulling that pin low. Clipping and testing the output of that inverter should prove/disprove that theory, yes?
 
The local Fry's has the parts I need, but I'm not going to make it there until the weekend. All the online places I've checked want $10 to ship an up-to-1lb package, which is crazy.

Any favored places I should check out? I tried Mouser & Digi-Key. Bob Roberts doesn't sell the LS04.
 
I picked up the LS04 & socket locally, installed them without doing too much damage to the PCB, fired it up and... Exact same problem. I checked everything for continuity & shorts with my multimeter (before powering it on), and it looked fine.

Guess I'm going to go over it again with the logic probe, but I suspect the crystal at this point... And of course I didn't remember to grab one when I was out.

Any other suggestions?
 
A pair of untested boards arrived today, which gives me something to compare against. One booted with some scrambled vectors… All the in-motion objects were all over the screen, but the copyright, score etc were fine… And the P1 LED was flashing intermittently / too fast.

Second one booted okay, though there are some weird drawing issues. Not sure if it's the monitor or PCB.

In any case, I went over both the working board and my non-working board with a logic probe. Main thing is that both pins of the crystal on the working board are reading low on the probe, while on the non-working board, one measures low and the other is floating. Now, I don't know why both pins would measure low — I'd expect one high, one pulsing, but maybe I don't understand how these things work and they don't use TTL levels. But the current theory is bad crystal, so I'll swap that.

I was going to run the scrambled vector board through its self-test, but after grabbing it to slot back in the cab, the crystal literally fell off the board. So I'll be getting a few of those next.
 
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