6 Slot – Memory test on power up giving error
Address Write Read
00008000 5555 55FF
Checking with Mame, the memory chips in question were only small, so looking at the board revealed two DIL 5814’s. Chip select signals to these were toggling as expected, so I needed to identify which ram chip was which. Using the test probe I shorted pins 11+12 on one chip, powering on the board now gave read as 51FF so I was looking at the wrong chip. Replacing the other (with a 2018-35) sorted the problem.
No picture, Hole blown through LOPT. Had problems tracking down replacement – little tip given to me by Hantarex engineer – you can use the LOPT from an MTC9000 as long as you cut pin 2 off. (If you leave it connected, you will get a direct short to GND)
Totally dead, no screen display (blank white screen). For this I used the Fluke Z80-S2650 adapter to check out the ram and rom, and located two errors. The rom mapping was incorrect, with a large range of locations returning random values. Examining the board (since I have no schematics), all of the chip select lines meet up…
No Sound. Signal at output of SN76477 pin 13, follow through to input of sound amp, then from output until we reach electrolytic capacitor used to decouple connection to speaker. Signal going in, nothing coming out – replace capacitor sound back to normal. Only drawing a few pixels of player balloon sprite. Following the schematics,…
No display – When move board, display flickers – go around board pushing each chip in turn, when press on 2E picture appears. Pin 16 rusted, only just in place. replace chip – picture back to normal. No star display. Board had been hacked to play an alternate game, pin 15 on chip 2B had…
Screen filled with coloured lines, unstable, no sync (see above) – check clock signals from horizontal and vertical scan generators (74161’s at 2R,2S,3R,3S) – no signal feeding into pin 2 of horizontal generators. Follow trace back to 7474 at 3N, signal going in, nothing coming out – replace chip and screen display back to normal….