Repair Logs – Page 77 – JAMMArcade.net

Wolf Fang: Kuhga 2001 repair log

Jan 282016

Some days ago I had on the bench this Wolf Fang: Kuhga 2001 PCB (known outside Japan as “Rohga – Armor Force”) , a good-looking horizontally scrolling shoot ’em up manufactured by Data East in the 2001 :

Wolf_Fang_PCB

When I powered it up, I was greeted by this screen.

missing_SYNC

It was a clear lack on SYNC signal confirmed also by a measurement with a frequency counter on pin 13 solderside of the JAMMA connector.So, given the absence of schematics, I started to trace back the signal with a multimeter but couldn’t find where it was generated.Visually inspecting the board I found a suspicious crack over a trace :

RSCN1560

My multimeter confirmed the trace was really severed.After patching it, the SYNC signal was restored but there were jailbairs on the sprites:

jailbairs_sprites

Sprites are stored in some 42 pin MASK ROMs :

sprites_MASK_ROMs

I visually inspected the area and found another broken trace on solderside which lead to a data line of these MASK ROMs:

RSCN1570

I promptly patched it with some AWG30 wire:

RSCN1572

and sprites were restored:

sprites_fixed

But after this I realized that sound was missing at all.Diverting the audio signal to an external amplifier, I could hear both music and sounf FXs but there was no output from the TA8205AH amplifier on PCB :

TA8205AH_amplifier

So I decided to remove and replace it but , as for my previous Pitfall II repair, I was wrong, it was good.Looking at its datasheet, I could figured out how its mute circuit was made:

TA8205AH_mute_circuit

Checking the 220uF 16V electrolytic capacitor connected to pin 8 of the amplifier gave me a dead short across the terminals.So I desoldered and test it out of circuit having confirm it was really shorted:

220uF_16V_shorted

Replacing it restored full sound.End of job.

Atari Asteroids repair log

PCB Repair Logs 2 Responses »

Jan 282016

I was recently sent an Asteroids PCB which I had previously bought back from the dead, the PCB had developed distorted vectors but still running.

Here is what the TEST screen looked like, the actual diamond shape was perfect but text was oversized and distorted;

IMG_20160128_242023439

The actual GAME mode looked worse;

IMG_20160128_241959634

Check out the giant asteroid!

I knew the problem was in the Vector State Machine (VSM) area, specifically the area which is responsible for handling object vectors, so I looked there first.

It was not long until I found a decoder (LS42) at 7E which seemed to have some pins stuck LO;

IMG_20160128_242035901

I desoldered the decoder;

IMG_20160128_242531687

I tested the decoder in my IC tester;

IMG_20160128_242615090

I then socketed and replaced with a fresh decoder;

IMG_20160128_243027782

Asteroids now fully working;

IMG_20160128_243034333

IMG_20160128_243046130

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