Lifeforce repair log

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Aug 062016
 

Received this Lifeforce PCB for a repair:

DSCN4031

Board suffered from a backgrounds issue, screen was filled of blocks of garbage instead of correct tiles.Here a comparison with MAME snapshots.This in the title screen:

title_comparison

This is the in-game :

ingame_comparison

A video for a better understanding:

The hardware uses the famous ‘GX400’ video board :

DSCN4032

The peculiarity of this board is the lack of ROMs, all the graphics is generated by logic of TTLs and custom ASICs.Anyway I has a good starting point since the owner assured me the customs were all good so the problem was TTL related.So I started to check for abnormalities with my logic probe.All was good until I found some 74LS157 with stuck inputs.According schematics they come from a 74LS273 @12B:

74SL273@12B

As you can see this TTL latches data bits from a 6464 SRAM  @15B which is addressed by the custom ‘0005291’ @20D (probably a tilemap generator).Probing it with a logic analyzer confirmed the outputs were all stuck low or high (only one gate was analyzed but all other were confirmed stuck as well with my oscilloscope) :

74SL273@12B_logic_analysing

So confident I removed it (I forgot, obviously it was from Fujitsu):

DSCN4033

Once tested out-of-circuit, it failed miserably:

74SL273@12B_failed

Fitted a rounded  machine-tooled socket and a good chip:

74LS273@12B_new_fitted

And:

fixed

Once again Evil Konami has been defeated!See you in the next chapter of this neverending battle…

 Posted by at 11:00 am

Out Zone repair log #4

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Aug 032016
 

Another Out Zone PCB (this time on usual ‘TP-018’ hardware) on the bench:

DSCN3960

Board was in good shape but I noticed it was heavily reworked on solderside, a lot of ICs were replaced and PCB was not cleaned from solder flux residuals:

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Besides, some ground pins of JAMMA edge connector were partially missing or burnt (sign that something gone shorted) and a 100 nF mylar capacitor was missing.I promply restored all of them:

DSCN4022

Board booted into game but some sprites were wrong (more than a palette problem it seemed to me an issue related to data bus as if sprites were missing some layers) :

sprite_issue

When I went to read the four 1Mbit ROMs containing relevant data I noticed devices were put in wrong sockets:

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Silkscreening under the sockets clearly tells where these MASK ROMs must be placed:

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But also with ROMs in correct position some sprites were still wrong.I started to test the part of circuit involved in sprites generation and all was fine until I came across two data lines shorted on a 6264 RAM @10A :

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The two data lines are connected to the sprites generator custom ‘FCU-2’ and to inputs of a couple of 74LS374 so the short was present also on them.Lifting a pin of the custom didn’t clear the short.

DSCN4044

Obviously due the not high resolution of a simple multimeter I could read always a dead short on each of this component.So I decided to use my Polar Toneohm 850A short locator (essentially an audible milliohmmeter) in order to locate the minimum resistance point.

1,110 Ohm measured on the two shorted data lines (pin 12 and 13) of the 6264 RAM @10A:

DSCN4007

Around 700 mOhm measured on the two pins of the custom ASIC ‘FCU-2’:

DSCN4009

19.3 mOhm on the 74LS374 @19E

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17.2 mOhms on the 74SL374 @19C and beep was squeeling at higher frequency :

 

DSCN4011

So I was approaching to the short, it was in the area of the two 74LS374.On part side I didn’t notice anything abnormal so I went to inspect the solder side and after some time I find the culprit:

pin13-pin14_74LS374@19C_bridge

Two pads connected to  inputs of the two 74LS374 were bridged, a ‘kind’ gift of previous repairer.I warmed up my soldering iron and removed it.Powered up the board again :

fixed

Board 100% fixed.Mission accomplished.

 

 Posted by at 11:27 pm

Snow Bros repair log #2

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Aug 012016
 

A quick fix for a PCB that seems to develop always same issue judging from my experience and other repair logs.Received this Snow Bros for a repair:

DSCN3977

It was playing fine but some sprites suffered from flickering (it’s hard for my camera to capture this, see from second 5 of below video)  :

Maybe you can understand better from this picture provided me by the PCB owner:

snowbros02

The sprites are generated by the Pandora custom chip which read data from a MASK ROM and write them to four 4464 (64K x 4bits DRAMs) :

sprites_circuitry

When I went to probe these dynamic RAMs with my scope all was good except one data line (D2, pin 3) of the one @IC24, signal was weak and stuck high compared to an healty one:

data_line_4464_IC24_comparison

Confident I removed the chip which failed when tested out-of-circuit:

41464@IC24_failed

Installed a socket for a fresh chip:

DSCN3980

and tested again the board:

DSCN3981

No more sprites flickering and game 100% fixed.

 

 Posted by at 10:19 pm

Terminator 2 repair log

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Jul 242016
 

Got this board from Muddymusic.
Board was filthy when I got it and most IC legs were a nice shade of green. I decided to clean this up first.
20160722_194239

After a good clean the board came out OK, not great but definitely much better. I noticed that a socketed RAM chip had one of its legs hanging out the side of its socket.
20160722_194750

Not sure what effect this would have but I reseated it properly before powering it up.
I replaced all of the single wipe sockets on this board as I really don’t like them.
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20160723_115551

Next up was the power up test and I was greeted with a yellow screen which eventually turned mostly red and stayed that way. I could see the game was booting at least.
20160722_194824

From this point I can be sure the palette circuitry was at fault. Looking at the schematics you can see there are 2 x CXK5856 RAM chips responsible for the palette RAM.
t2_palette

In my experience these RAM’s have been the most unreliable so I desoldered both of them straight away and both of them failed spectacularly when tested out of circuit.
I replaced them and fired up the game.
20160723_151652
20160723_151700
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All seems to be working fine now.
Also dumped all the PAL’s from this too and hopefully will be getting them tested soon.

Devil World repair log

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Jul 212016
 

Got this Devil World PCB as non working. This game is running on a Konami Twin 16 hardware. It is a two layer board with the first one devoted to CPU/sound and the second one to GFX/video. The two faulty/replaced chips were on the video board and are highlighted in red.

devilworld1

Luckily the board was booting and got stuck on the RAM/ROM test screen with ROM #18 reported as bad (chip #1 on the board picture above).

devilworld2

That ROM is part of a 4 ROMs row which contains the GFXs. They are 40 pins Konami chips and looking in MAME I could see that they were 512kb MASK ROMs. I tried dumping it with my programmer but was unable as it found one dead pin. Compatible EPROMs for these are 27C400 so I burned one and replaced it.

The game was now booting but with a color problem on some tiles.

devilworld3 devilworld5

After a deep look at the video board I could find a Fujitsu 74LS153 located at 10H (chip #2 on the board picture above) with floating outputs (while inputs had healthy pulsing signals). I piggybacked it and got everything corrected. I desoldered the faulty one, put a socket and replaced it. Board is now working perfectly.

devilworld4 devilworld6

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