On Coronavirus lockdown for the past few days, what better way to spend the time, fixing 40 year old arcade circuit boards. Pulled out some Asteroids and Asteroids Deluxe boards, getting much better at fixing these, here are some repairs from the past week or so and a few other tips on fixing them.
Some things I do first on all Asteroids boards (haven't replaced all sockets on AD boards yet, so far they seem to hold up better).
- Replace rom and 6502 sockets (if original), just good preventative maintenance.
- Burn new roms (if original proms show any signs of brittleness), check rom and CPU sockets.
- Put game in self test, listen for Ram errors.
- Check clock and reset line on CPU.
- Test ALL Voltages, including regulators near the front of board, 8.2 VDC at 4016s in vector section.
- Start in-depth testing with Fluke 9010a if you're lucky enough to have one and confirm program code is running.
Asteroids Deluxe, Dead (3/16/20)
- Board doesn’t do much of anything, cleaned roms, processor, nothing on power-up, board was watchdogging. Actually a fun repair as I figured out most issues relatively quickly, but probably still spent 3 hours fixing this one due to multiple issues.
- Used 9010a to test roms, none of them passed rom test. Probed around on address lines, A7, pin 1 of roms stuck low. Input at 74LS244 (C1), pin 2 was active, output, pin 18 was stuck low.
- Replaced C1 and board now boots with video issues, asteroids stretched, video off.
- No activity on DACx8 line, pin 5 at D11 is stuck low. Output at D/E10, 74LS157, pin 4 is stuck low, inputs look okay.
- Replaced D/E10 and pin 4 is now pulsing, video still distorted, but maybe slightly better?
- No activity on DACx6 line, pin 7 at D11 is stuck low. Pin 6, D10 stuck low, replaced D/E10 again and picture much better, first “new” 74LS157 that I just installed was apparently bad.
- Probing around vector circuits, found pin 7 at F8, 7497 was stuck low. Replaced F8 to fix issue. Board now works...
- While typing up repair look over to see some large lines on screen, looks like player ship is now screw up.
- Quickly found output at 74LS175 at M6, pin 6 was stuck low. Replaced M6 to fix board, again.
- Board lasted a few more hours before developing video issues during bench testing.
- Found dead outputs at A10, 74LS157, Logic Comparator confirmed IC was bad, replaced it and picture improved, but still not right.
- Output at D10, pin 9 was high (74LS374), input was pulsing. Replaced D10 and image is back to normal (again).
- Guess what? Board developed issues again during testing.
- This time looked like something on the Y-axis before the DAC, took a little while to figure this out as all inputs to the DAC were pulsing, I was sure the everything the Y Position counters circuit was okay. Finally noticed to DACY7* input to the DAC was pulsing but not right (used scope to notice it). Replaced 74LS374 at B10 to fix the problem.
Asteroids Deluxe Beeps (3/16/20)
- Board beeps on power up, two high beeps, one low beep. Manual indicates bad 2114 ram at M3.
- Removed suspected ram, installed new socket and new ram and board works.
Asteroids, Dead Board (3/13/20)
- Installed new processor and rom sockets as preventative maintenance, board plays beeps constantly in test mode, it is watchdogging.
- Use 9010a to test rams and roms, everything checks out okay.
- Replaced L6 to lift pin 1 to isolate program code from vector generator, board plays blind.
- Replaced 74KS42 at E7 and 74LS175 at M7, thought they might be the issue, no change.
- Swapped out Prom at C8, board now plays blind (no more watchdogging).
- Replaced TL082 at A12 as piggybacking led to some vectors. Board now has some bad video.
- Replaced TL081 at B/C12 as piggybacking helped, slightly better picture, but everything now collapsed on Y axis, asteroids looked squished.
- Found bad output, pin 6 on 7497 at H8, replacing that brought picture back perfectly.
Asteroids Dead Board (3/3/20)
- Installed new processor and rom sockets as preventative maintenance, board plays blind, no Z output activity.
- Found bad leg (it wasn’t reaching board) 74LS109 IC at A9. (D8 pin 14, HALT line was not pulsing).
- Board now works but 00 in score are off on boot (kind of misaligned) for about 10-20 seconds. Voltage at 4016s was -8.4 VDC at boot. Replaced most caps in circuit and it seems to better, still a little high on boot, but calms down quickly.