Repair Logs – Page 77 – JAMMArcade.net

Gryzor repair log #2

Jan 232016

A friend got a Gryzor PCB working but with problems on some of the sprites (mostly enemies and items with half of the horizontal lines missing).

The 4 GFX MASK ROMs were tested ok on another Gryzor PCB. Looking with the scope on the RAMs revealed nothing really suspicious.

I then piggybacked the RAMs around the GFX part and quickly found the faulty one.
It was the NEC 8644FU12 at location 14G. This RAM is a 4464 (64k-word x 4-bit, same type than the ones I replaced on my recently repaired Final Star Force).
Here is a picture of the PCB with the faulty chip highlighted in red:

gryzor2-1

Piggybacking it with a compatible TMS 4464-12 restored all the sprites.
In fact, the problem was so small that it was impossible to see any suspicious signal on any of the pins of that RAM with the scope (every signal looked healthy). I replaced the chip and obviously got the PCB running perfectly.

Here is a before and after picture:

gryzor2-2

Marchen Maze repair log

PCB Repair Logs Comments Off

Jan 132016

Had on the bench this Marchen Maze PCB (Namco System 1 hardware) :

Marchen_Maze_PCB

On the power up I was greeted by this screen:

D6_error

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:

custom48_D6_E6_RAM

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.

object_control_circuitry

Parts mounted on the PCB were from Fujitsu which means high chance of failure:

74LS365@H6_@L6

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:

74LS365@H6_@L6_failed

This cleared the error on startup so board successfully booted into game but sprites were all blocky:

blocky_sprites

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 :

object_datal_BUS

and from these to the custom ’39’ sprites generator:

object_datal_BUS_2

74LS377@A3_@A4

Piggybacking the two 74LS377 I could partially restore sprites :

sprites_restored

This lead me to remove and replace both.The desoldered ones failed when tested out of circuit :

74LS377@A3_A4_failed

74LS377@A3_@A4_reworking

Sprites back again in all its glory and board 100% fixed!

sprites_100%

Pitfall II repair log #3

PCB Repair Logs 2 Responses »

Jan 082016

Some days ago I had on the bench this original Pitfall II PCB:

Pitfall_II_PCB

Board booted but all characters/texts were missing and also sound was totally absent:

issue2

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:

74LS273@IC39_

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 :

pin11_resistance

Once established connection, all missing characters were back again:

fixed

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:

LA4460_reworking

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:

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) :

BA12003@IC129

The input (pin 1) was low so signal was not inverted internally (like schematics show) and outputted high :

ULN2003

I desoldered and tested it out of circuit where it failed:

BA12003@IC129_failed

I replaced it with a compatible ULN2003:

ULN2003@IC129

and sound was back again.End of job.

Megablast repair log

PCB Repair Logs 1 Response »

Jan 082016

Got this Taito Megablast for a repair:

Mebaglast_PCB

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:

issues

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) :

DATA_location

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.

fixed

Strider repair Log

PCB Repair Logs 1 Response »

Jan 072016

I received a CPS1 Strider for my personal collection (B and C board only) from my friend Roger this week. The board was sold as not-working, and when I fired it up, it was sure enough not working:

As you can see above, there were heavy jail bars present in the background sprites. Experience with CPS1 hardware told me one of three things was going on – bad C board, bad mask roms or bad/corroded sockets. The C board is the B-01 PPU variety, which is functionally equivalent to the B-21 PPU. Since I have known working B-21 boards on hand, this was an easy starting point. Swapping the board did not have any effect, so I knew it was either the mask roms or the sockets at fault.

In order to verify the mask roms, I removed them from my board, and set my Superpro 580u programmer to HN27c4000g (which are pin for pin compatible the HN6204P mask roms capcom used). Strider is a very strange board in that the etched rom numbers DO NOT match with the PCB. I turned to mame source code to determine which rom file correlated to which mask rom. Sure enough, the FIRST rom I tried to verify complained about Pin 12 not having connectivity. Some times when you read mask roms as eproms, there are pins internally disconnected, and that is OK. This was not one of those times. I referenced the HN27c4000g datasheet to determine that Pin 12 was actually for Address 0. This address line is 100% required for the rom to function.

Today happened to be my lucky day. I had ONE and only ONE 27c4000g eprom on hand. Burned the mame binary to the rom, popped it in Strider, and the game was back in action!

I played a few games, did not observe any other abnormalities. I wish all repairs could be this easy! Another great Capcom game has been preserved!

Older Entries Newer Entries