The Invaders – Zaccaria

Byadmin

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 at IC41, a 74LS156. Replacing this put the memory map back to normal (it seems to map all of the RAM and ROM areas). Having sorted the memory map, the Fluke revealed a couple of bit errors in the video ram. Replacing the two 2102 ram chips sorted the problem.

IC positions are marked with the bit number they occupy.

Oh, and the blank white screen – the chip select for the character rom was high, when someone had replaced one of the video ram chips before, they must have damaged the track. Adding a wire link returned everything to normal.

Similar Posts

  • Neo Geo

    Byadmin

    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….

  • Hantarex MTC9000/A

    Byadmin

    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)

  • Galaxian

    ByMichael Coates

    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…

  • Carnival

    ByMichael Coates

    Carnival on a Gremlin / Sega Vic Dual PCB. Just had blue bars on screen, although probing the Z80 showed it was trying to run code. Using a logic probe I discovered that the /WRITE signal of the ram chips was always high. This signal comes from a 74LS10 at U77. Checked this chip and…

  • Lady Bug

    Byadmin

    Board ID 8016 : Falcon version ? Static graphics on screen, dead – pin 24 low on Z80, /WAIT signal. Trace signal on board to 74LS74 at E7. Signal incorrect for inputs. Replace with new one, board fixed.

  • Mr Do!

    Byadmin

    Blank screen, Blanking line to output colour proms always enabled. Trace back to 74161 in timing circuit – output stuck, input clock all look OK – replace chip and picture appears. Blue video only – The video lines are controlled by three transistors near the edge connector, checking these revealed that 2 were not giving…