PCB Repair Logs Section Z
|Pin Out||Section Z|
Forum Thread: Section Z PCB Repair
Symptom: No video output, not even a valid Sync signal
Cure: Bad outputs on the LS161 at 4K on the top board – replaced IC
Symptom: No text, power bar, speed bar, etc
Cure: Bad outputs on the M58725P-15 at location 8F on the top board, replaced with a 6116 (same chip type, different manufacturer and part code)
Symptom: Vertical white lines through the whole display
Cure: Re-seated mask ROM at location 3B on the lower board
Symptom: Sprites broken up and some parts appearing in the wrong places, on the main game area and below the CREDIT line. Sprite movement also jerky
Cure: Bad outputs on 2114 RAM at location 13C on the lower board – replaced RAM
Symptom: Some background graphics missing (the grey ‘pipes’/ducting in the centre area on the first level for example), also on the first level the top and bottom edge background graphics are a simple grey and green colour, instead of the normal cyan (with red and yellow button details). Etc.
Diagnosis: Thought there were bad outputs on the LS174 at location 9D on the bottom board, but was wrong (pin 2 was high, should have been low) as I then found that the clock input to this on pin 9 was missing and, using a good board (in case of broken tracks) tracked that back to pin 3 of the LS175 at 7A which had a bad input on pin 4 – this comes from pin 7 of 7B (an LS138) and it turned out that the connection between this pin and pin 4 of 7A was broken
Cure: Re-linked broken connection as detailed above
Symptom: Won’t boot, no video, no sync, no clock on pin 6 of main Z80A CPU at location 4E on upper board.
Cure: Bad LS161 at location 4G – replaced IC
Symptom: Short horizontal dashes appearing and flickering in random places all over the display, most prevalent on screens with more text
Cure: Dead output on pin 2 of the LS273 at location 10G – replaced IC
Symptom: No sound
Cure: The sound section on Section Z has it’s own Ground which isn’t connected to the boardset’s main Ground – simply Grounded either pins 26 or D
Like Ghosts ‘N’ Goblins, these boards are a pig to fix as there are no available schems and no visible traces. Because of this, tracing back connections involves using a DMM with an audible continuity test and doing a continuity check with one DMM probe on the pin you want to trace back, then running the other DMM probe across all the pins on all the chips and other relevant components until you find where the pin goes. A pain!
Horiz and Vert Sync signals are combined in the LS08 at location 8K on the top board and output on pin 8 – then to resistor R1 and out to the sync pin on the edge connector
Horiz and Vert address counters from the LS161’s at locations 4K and 5K
Z80 at location 4E – Was trying to track down the absent clock, ultimately gave up, but here are my findings as far as I went: Clock is obtained from pin 5 of the LS367 at location 1E. No input on this IC on pin 4, traced this back to pin 11 of the LS32 at location 8J. This didn’t have an input on pin 12, so traced this back to pin 3 of the same IC. Inputs to this on pins 1 and 2 – 1 should be active, 2 low, but 1 was low and 2 was high. 1 goes to a pin on the rightmost inter-board connector (nearest the main edge connector). Pin 2 is fed from pin 9 of the LS74 at location 7J which was fine but didn’t have an input on pin 13. Got bored after this, too much back-tracking!