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 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,…
Ran through self test OK, came up with chequer board screen and then reset most of the time. Occasionally would start game, but with credit noise continually playing and credits rapidly counting upwards. This is caused by CPU 4 (E5) not running properly. checked the eprom and ram (C5,D5 and E5) and ram was faulty….
Boots up, and plays, but incorrect sprites – most noticeable little bug changes into ‘END’ at one point. Check 74ls138 at 8n, controlling graphics banking, and pins strobing. Replace chip and now uses correct sprites. Quiet missile sound and explosion sound. Both of these effects use the op-amp chip, LM324 at 7T. Replace this chip…
In normal mode, just had a blank screen. Enable test mode and you instead get an error message showing that the ROM test had failed (even though the rom itself checks out OK with correct content) This is because the custom Atari SLAPSTIC chip is not functioning correctly. It is used to page banks of…
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…