Today I’ve dumped the only PAL from a Truxton II/Tatsujin Oh PCB.Original device was a registered but unsecured PALCE16V8H so I could read it straight in my programmer.Dump is not tested since the PCB is not working but should work on a PALCE16V8 target device or a GAL16V8.Any feedback is welcome.
Had on the bench this Marchen Maze PCB (Namco System 1 hardware) :
On the power up I was greeted by this screen:
The RAM @D6 is a 6264 located on CPU board (fault was surely on this board since I succesfully swapped a good one) used in pair with another one @E6 , both are adressed by the near custom ’48’ which is a sprite address generator:
For first I went to replace both RAMs (sometimes the board booted showing an error also on the one @E6) but this didn’t cure the problem as well swapping a good known custom ’48’ had no effect.Probing these RAMs revealed some address lines stuck high.Looking at the schematics of Pac-Mania (which runs on same hardware) I figured out that adress lines from custom to RAMs are driven by two 74LS365 @H6 and @L6.
Parts mounted on the PCB were from Fujitsu which means high chance of failure:
After a quick test with my HP10529A logic comparator (which confirmed me troubles on all outputs) I decided to remove them.They both failed in my programmer:
This cleared the error on startup so board successfully booted into game but sprites were all blocky:
Judging from the kind of fault on screen, this, more than an addressing issue, had to have something to do with data.Always looking at schematics I noticed that data bits from the custom ’48’ and RAMs are routed to two 74LS377 @A3 and @A4 :
and from these to the custom ’39’ sprites generator:
Piggybacking the two 74LS377 I could partially restore sprites :
This lead me to remove and replace both.The desoldered ones failed when tested out of circuit :
Sprites back again in all its glory and board 100% fixed!
Some days ago I had on the bench this original Pitfall II PCB:
Board booted but all characters/texts were missing and also sound was totally absent:
I started to check the circuit around the six tiles/characters ROM and found nothing of abormal until I came across a 74LS273 @IC39 with missing clock on pin11:
As you can see from the above picture someone had already socketed it but broken the trace going to pin 11, he tried also to patch this but didn’t make a good work ending up there was no perfect continuity (45 Ohm measured) between this pin and above pad :
Once established connection, all missing characters were back again:
So I moved to troubleshoot the lack of sound.Putting my fingers on solderside pins of the LA4460 amplfifier didn’t produce any noise at all so I was sure that it was bad since I could get sound from its input (pin2) connecting it to an external amplifier but nothing on its outputs (pin 7-9).So, I removed the amplifier and put a good one back:
But I was wrong, still no sound at all.So, I went look at schematics of Choplifter that, though runs on different Sega hardware (System 2 while Pitfall II is on System 1), shares the same audio circuitry:
I had not taken into account the pin 6 of the LA4460 which is called ‘MUTE’.This pin when tied low, like its name says, mutes the outputs.So, I went to probe it on the board and, indeed, it was stuck low.I could trace it back to pin 16 of a BA12003 @IC129 (a Darlington transistor arrays) :
The input (pin 1) was low so signal was not inverted internally (like schematics show) and outputted high :
I desoldered and tested it out of circuit where it failed:
I replaced it with a compatible ULN2003:
and sound was back again.End of job.
Added japanese version of Laser Ghost to the list. This version is untested on real hardware for now.
Got this Taito Megablast for a repair:
When I powered it up, I was greeted by a solid black screen, /RESET and /HALT on main 68000 CPU were stuck high.A visual inspection revealed that JAMMA connector was oxidized.Once cleaned it, the board booted:
As you can see both tiles and sprites had sever issues, besided the sound was all garbled and scratchy:
So, for first I went to dump the devices containing tiles/sprites (three 40 pin MASK ROMs 27C400 compatible) and audio samples (two 32 pin MASK ROMs 27C040 compatible) and dumps were not matching the MAME ROM set for the ones @IC32 (sprite data), IC58 (tiles data) and IC29-IC30 (audio samples data) :
Loading my dumps in MAME I could reproduce the issues more or less accurately:
Replacing these bad MASK ROMs with the equivalent EPROMs fixed completely the game.
