Robotron Repair Logs

I picked up a couple of Williams ROM boards from eBay. They were listed as “untested,” which basically means “not-working.” I plugged them both in my test rig and sure enough, they’re not working. Both boards are 5771-09840-00 Rev A boards (one with Joust ROMs, the other with Robotron 2084 ROMs), even though both boards are jumpered for Robotron 2084. I’ll eventually get around to posting the logs for both boards but I’m concentrating on the Robotron 2084 ROM board first.

Robotron 2084 ROM board – 5771-09840-00 Rev A

Meticulously inspected board and ensure there were no loose connections or broken leads on the resistors. No problem areas were noted.

Plugged ROM board into a known working CPU board:

  • no rug pattern
  • no lights on ROM 7 segment LED display

Checked voltages to board:

  • Good +5V & ground to board from power supply

Checked voltages at board components (EPROMs, resistors, and capacitors):

  • DC voltages at all capacitors/resistors is at +1.3V
  • DC voltages at EPROMs +1.3V
  • DC voltage on + post at C46 is +5V
  • DC voltage on + post at C25 is +1.3V

Replaced 100uF 25V capacitor at C25 and retested voltage:

  • Good +5V + post at C25
  • Rechecked DC voltages on EPROMs, capacitors, and resistors–all good at +5V
  • Determined bad C25 capacitor

Inspected ROM chips by pulling them out and reseating them:

  • Three of the 2732 ROM chips lost pins when pulled from the board
  • Burned a new set of 2732 ROMs
  • Reseated both Special Chips 1 & 2
  • Board will now boot to a rug pattern, but continuously watchdogs
  • Determined bad set of EPROMs

Checking voltages on all Integrated Circuits (ICs):

  • All DC voltages are +5V

Jiggling the ribbon cable to the CPU board makes the screen flicker and random text appear:

  • I need to replace the ribbon cable on the ROM board

I ordered a Hakko FR300 desoldering gun from Japan so I can do some resoldering work. Currently awaiting its arrival. I’ll update this log when that happens.