Jan 182019

Received from Germany this Gundhara PCB, a top-down shooting game released in 1995 by Banpresto:

According to the owner the PCB suddenly developed a graphical issue.When I powered it up I could actually see some colors problem, the BLUE one was ‘bleeding’ in some parts of graphics:

After a quick check on PCB I could figure out the palette circuit made of two 6264 (8K x 8-bit) SRAMs, a custom (S-DIP 42 pin) marked ‘X1-007’ (which probably contains some latches or flip-flops) and three SIL resistor arrays configured as R-2R ladder to perform the final conversion from digital to analog (DAC)

Color palette circuit

When I probed the two 6264 SRAMs I found weak signals on some data lines of the one @U39, here is a capture from scope comparing the signal with an heathy one :

Good signal on left, bad on right

Sure enough I desoldered the chip, it indeed failed the out-of-circuit testing :

Installing a good chip fixed the issue, board 100% working again.Job done.

 Posted by at 9:03 pm
Jan 142019

Received today from Germany this Guardians PCB, also known as Denjinmakai II, a horizontally-scrolling beat-em-up released by Banpresto in 1995)

According to the owner the game played totally ‘bind’.I could confirm it as soon as I powered the board up :

Board playing ‘blind’

But, as you can see from above video, I was able to restore some graphics by pressing down this surface mounted custom ASIC (QFP 208 pins)

Judging from the heatsink on its top this custom ASIC acts as a GPU generating most of the graphics and video signals too.At a closer inspection I found many lifted pins on all four sides.An example :

I promptly reflowed the IC, this gave me a steady picture but all the graphics were scrambled and, judging from the blueish screen, the RED color was missing too :

Looking at solder side of the PCB I noticed a long and quite deep scratch passing across some traces:

Scratch on solder side

Inspecting the area with a microscope and doing a continuity check with my multimeter confirmed that some traces were severed and other caused unstable contact:

I patched and reinforced the traces with some AWG30 wire :

Traces repair

This lead to few improvements, graphics were still scrambled so I moved on to troubleshoot the lack of RED color.This was pretty easy to fix as the board had a quite clear damage that broke the trace which carries the signal to JAMMA edge connector :

Damage on PCB

As for bad graphics, I decided to double-check the previously reflowed custom ASIC and found a solder bridge shorting two pins:

Solder bridge on reflowed ASIC

Removing it fixed the issue and board completely.Repair accomplished.

Board finally fixed
 Posted by at 10:34 pm
Dec 312018

Some time ago I made a reproduction of the Jaleco ‘JK-03’ custom SIL used for inputs handling on some Mega System 1 PCBs but at that time I was not able to test it due to the lack of a proper PCB hence I asked for some volunteers.You can read the post here:

Today I can report the reproduction is fully working thanks to the test carried out from the user ‘Astro X’ of AP forums on his Saint Dragon PCB with missing ‘JK-03’ (actually an hack was installed as workaround) :

Thanks again to him for the feedback.

 Posted by at 6:59 pm
Dec 302018

I received for repair a quite rare original Spelunker PCB (on Irem M62 hardware).Board is a three stack one made of a top board (which carries most of sound hardware) :

SOUND board

A middle CPU board (specific for each M62 game) :

CPU board

And a bottom VIDEO board :

VIDEO board

The PCB had severe GFX faults, the sprites were only lines vertically stretched all over the screen:

All the sprites circuit lies on bottom VIDEO board which is the same for all games that run on M62 hardware.Looking at Kung-Fu Master schematics I could figure out that data bits from sprite ROMs are fed into the custom marked ‘KNA6034201’ :

Custom ‘KNA6034201’ in DIP40 package
Custom ‘KNA6034201’ schematics

The inputs were all active but most of outputs floating:

So the custom was most likely internally faulty.Luckily I have done a reproduction of this component some time ago.You can think of it like a 24-bit parallel to serial shift register:

I removed the custom and installed the reproduction:

‘KNA6034201’ repro

The sprites were back but not perfectly as they were lacking of lines and misplaced too:

Sprites not yet perfect…

The sprite line buffer consists in two 2k x 8-bit static RAMs (Toshiba TMM2018 used here) :

Sprite line buffer

Probing them revealed on both a floating address line (pin 1, A7) :

Address lines are generated by the surface mounted custom ‘KNA6074601’ :

Custom ‘KNA6074601’

Its pinout/implementation from Kung-Fu Master schematics :

I had no other choice than replacing this part so I asked the owner to look for a donor board.He found and sent me a Vigilante PCB which carried the ‘KNA6074601’ on bottom board :

Vigilante donor board

I removed the faulty one and soldered the spare back :

‘KNA6074601’ reworking

This restored the correct sprites:

Sprites and board finally fixed

Board 100% fixed.Job done.

 Posted by at 10:07 pm

64th Street – A Detective Story repair log #2

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Dec 212018

Got from Portugal this mint 64th Street – A Detective Story PCB, a beat ’em up released by Jaleco in 1991 :

The board simply booted to a static garbage screen:

At a deeper analysis both 68000 CPUs were not resetting properly on power up :

On the main one there was no transition from LOW to HIGH state, /RESET line went staight HIGH :

On the sound CPU both /HALT and /RESET lines were stuck LOW:

I traced back the lines to a typical power-on reset circuit based on the TL7705 voltage monitor IC which I replaced with no luck:

The circuit is made of few other components, specifically there are two 0.1uF mylar capacitors connected to pin 1 (REF) and pin 7 (SENSE)

I got few Ohms when I measured resistance across their terminals (after detached one leg from circuit), they were almost shorted :

I replaced them :

Board successfully booted into game with no further issue :

Repair accomplished.

 Posted by at 11:08 pm