Brian E. Brzezicki
Copyright 2016
4/4/2016

Disclaimer
Use this at your OWN risk, do NOT sue me if it breaks your board... if your doing this your board is probably already broken though ;)

Game Board #1 4/04/2016

Problem:

  • Game did not work, LCD monitor did not sync
  • rom @ ic51 is missing

Troubleshooting/dianosis steps:

  1. Fluke 9010A RAM long test
    • 0x0000 - 0x03FF - OK
    • 0x4000 - 0x43FF - OK
  2. vsync and hsync bad, looking at hd46505 looks like it's not outputting correctly but let's first check memory
  3. Fluke ram short 0x0000 -0x03FF - BTS 0xFF @ 0x0000
  4. Fluke rom short 0x4000 -0x0bFF - BTS 0xFF @ 0x0400
  5. Something's not right. they cannot both be bad at all addresses all bits?
  6. read @ 0x5000 coming back as 0xFF
  7. lets look at the address selection circuit do a read on 0x2000 getting a messed up signal on IC14 (CE and OE) seeing a 1.4mhz signal!!!
  8. all ROM chips have 1.4mhz on OE!!! OE seems to be tied together! took second board off, still same problem.
  9. ugg on this board, #18 (OE) are tied together and 16 is OE!
  10. removed 2 previously repaired chips IC25 and IC26, this is near related signals.
  11. repaired trace under IC25, put in new socket and 74LS74
  12. installed a new socket and 74LS163 @ IC26
  13. no change, still getting 1.4MH signal.. actually I wonder maybe we should get this signal, actually yes?
  14. IC10 generates the RO2 signal, tested bad, replacing
  15. replacing poorly soldered IC22
  16. ok now getting reads at various ROM addresses
  17. ram test 0x0000 - 0x03ff still failing though, trying a new 6116, no change
  18. writing 0x55 to 0x0000 on loop, not seeing data come over
  19. buffers r/w signals verified, I am getting addresses
  20. replacing 72LS244 @ IC3 and IC4 now getting 0xff at any read :(
  21. never getting the address signal on reads all high
  22. all reads from RAM are coming back "DA"
  23. IC14 is always enabled
  24. 74ls00 @ IC42 seems bad it controls IC14's OE
  25. going to check eproms 15, 16, 17 OK, 12 and 14 missing, replaced 10, 8, 7 seems bad (32) 52 bad (16) 51 missing
  26. erased and reprogrammed 8 and 10 and the rest
  27. testing roms in circuit IC12 - 0x3000 1264 - ok IC7 - 0x4000 8Ad3 - ok IC8 - 0x5000 - 77D6 - ok IC9 - x6000 62f6 - ok IC10 - 0x7000 - 7992 - ok IC14 - 0x8000 - 02fe - ok ic15 0 9x9000 - f1e0 - ok ic16 - 0xa000 - 88b9 - ok ic17 0 0xb000 - eab8 - ok
  28. reads @ 0x0000 are pulling from ROM IC14 though it does seem that /OE goes high when the read/write happens need to check around IC #22 - problems with socket, signal propogation to buffers?
  29. replacing IC22 and soldering directly fixed the problem. vias were damaged had ot apply solder on the top and bottom to ensure continuity. immediately LCD synced
  30. game started booting
  31. lets's test RAM fully now
    • long 0x0000 - 0x03FF - OK
    • long 0x400 - 0x7FF - OK
    • long 0x0800 - 0x0bff - OK
    • long 0x1000 - 0x1fff - OK
  32. bad colors found - two problems
    • bad PROM @ I7
    • green video lines on adapter was bridged