Got this Sunset Riders PCB for a repair:
Gameplay and graphics were OK but music was accelerated and distorted:
Music is generated by the YM2151 sound synthesis chip widely used in many arcade systems:
For first I checked its clock input pin and measured frequency was fine (3.579 MHz) :
When I piggybacked a good chip on it correct music tempo was restored:
Replacing the chip fixed the issue completely.
This is one I fixed some time ago but still worth posting here.
Problem 1: The display would exhibit streaks of grey lines mostly around sprites as the pcb warmed up & progressively get worse over the period. Symptoms would sometimes completely disappear after 10-15 minutes.
Note the grey lines around the sprites.
After inspecting the board there didn’t appear to be any bad connections. I suspected an intermittent component fault.
I didn’t have any freeze spray so I cooled off suspect chips ( I used some ice wrapped up in a sealed plastic bag to avoid any leak ) and found cooling the transistor @ Q4 on the video board would reproduce the above problems. I replaced the faulty 2sc1815 transistor at Q4 on the video board which cleaned up the video sync signal.
Problem 2: Game boots sometimes, other times it does not start and boots to junk.
Probed 6502 address pins, found that all were stuck high whenever the game failed to boot. All other signals looked OK. I tried substituting the main CPU for the sound CPU ( a 6502 as well ) but the symptoms were the same.
I traced the RST signal from the CPU to a 555 timer. There appeared to be a problem with pin 8 from the inverter at 9C to the trigger of the 555. Whenever the game booted to junk pin 8 of the inverter was floating & my logic probe was not registering the normal RST behaviour you would expect. I suspected a bad LS04 at 9C and planned to replace it.
Removed the LS04 at 9C. Pin 7 which is the ground pin was crushed under the IC. In other words it completely missed the plate thru hole ( it was blocked with solder ) during manufacturing and wasn’t making good contact with the ground pad. This game would have been faulty since the day it left the factory & explains the chip’s intermittent behavior.
Re-installed the inverter & re-tested with good results, no more booting to junk!
Just a quick fix for a Shadow Warriors PCB I had since many years but never looked at:
Gameplay was fine but all the backgrounds GFX were scrambled and messy:
This is the part of circuit which generates the backgrounds, located on video board:
Luckily EPROMs and RAMs were socketed so I first tested the latter and found a bad one @3D (a Toshiba T5563 pin to pin compatible to a generic 6264) :
Replacing the bad chip was enough to clear the issue.
I got this Major Title 2 PCB for cheap from ‘Smitdogg’ of MAME team:
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He said me board had some GFX issues.Actually when I powered it up I got no sprites at all:
For first I checked the sprites EPROMs with my logic probe and found no activity on all pins.These four sprites MASK ROMs on video board are addressed by the ASIC “GA22” on CPU board :
I probed it and all its pins were silent too.I tried to reflow it without luck, sprites were still absent.Then, looking at the board, I noticed an open jumper ‘J3’ right hear the GA22 ASIC:
Looking at other M92 CPU boards I could see that this jumper was always closed to position ‘B’ (so with central and right pins shorted together).So I did it on my board too:
and sprites were magically restored!
Now the technical explanation.The jumper is actually for selecting which clock signal must be delivered to the sprites generator ASIC “GA22”.If closed in ‘B’ position, ASIC will receive a clock signal of 26.6666 Mhz (which is the correct value for most of M92 games) :
If closed in ‘W’ postition, the ASIC will get a 18.000MHz signal (no sprites with this configuration) :
Last issue to fix was some audio background noise:
I quickly traced it to a missing 47uF 16V electrolytic capacitor @C213 in analog sound section:
End of job.
Got this NebulasRay PCB ( converted from another Namco NB-1 game) from my friend Josef for a repair:
For the uninitiated the game is a vertical shoot ’em up released by Namco in the 1994.It runs on Namco NB-1 platform.Here are the specs:
Board actually booted but didn’t pass the disclaimer screen:
As said, main CPU is a 68EC020.Probing it, revelead a good activity until it got stuck on the above screen, at this point most of control lines were going to high impedance state terminating the BUS activity.So, there had to be some trouble in the main code execution but, given the hardware complexity and lack of documentation, I was pretty lost.
I started to do some tracing on PCB so I could locate the WORK RAMs ( two Toshiba TC551001 @5C and 6C):
I figured out that they were not addressed directly by main CPU but through the near custom C351 (which is actually the custom sound CPU).I replaced both RAM but without luck.So, I removed the custom C351 and checking traces underneath it I found two breaks which I patched with some tiny wires:
With this fix the board passed the initial disclaimer screen but went straight into test mode although dipswitches were set to off.I quickly traced this to a missing 74HC253 multiplexer @4F:
Finally the board entered in game but all sprites were wrong :
Object RAMs are two Mitsubishi M5M5256 @20M and 21M:
A closer inspection revealed some loose pins that I promptly resoldered.In this way all sprites were restored except for jailbairs on some of them (like game title ):
All sprites ROMs are on the small daughterboard in form of 8 MX29F1610 FLASH devices :
Since the board was a converted one, they were hand soldered not in professional way (let’s say so..) so I reflowed them.Graphics and sound were perfect now but some inputs were missing or stuck like reported in switch test:
The inputs circuitry is so designed on this kind of hardware : JAMMA connector pin is connected to some EMI filter arrays , then to some custom CUS93 resistor arrays, then to some 74HC253 which combine inputs into outputs that go to the ASIC C160 (which is the I/O chip):
After some tracing I could pinpoint the faults in two bad CUS93 resistor arrays @2L and 1F:
Besides, there was intermittent contact between some pins of JAMMA connector and EMI network filter array @1K:
Board 100% fixed.End of (long..) job.