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
Jan 112019
 

I recently aquired a few Robocop PCBs, and this particular one seemed to be working fine at first glance. Eventually however, I realised that certain sounds seemed to be missing from the attract mode.

In particular I noticed Robocops speech as he rolls off the Prime Directives was not there. A closer look playing the game revealed further sounds missing, like the groans from the enemies as you kill them and others.

I then realised that is was just the ADPCM samples that were missing.

So I looked at the CPU board where most of the final digital and analogue circuits are. First I checked the DACs and found no samples present, so went further back to the large YM2203 sound chip. I probed pin 19 of the IC and would have expected to hear the samples here, however I heard nothing except static.

Pin 19 circled in red
Pin 19 circled in red

I was able to determine that the ADPCM samples are stored in the EN02 ROM, so I popped this into an eprom reader and checked the content.

The eprom was corrupted, so I burned a new one and the samples were restored.

Another Robocop saved.

Jan 022019
 

Today I’ve uploaded the latest version of my BINman software.
This version is v4.3.2 and has had some rewrites and a few extra features added.
First is the ability to deinterleave the bytes of a file into nibbles.
Second feature added can be found under the “Special” menu. It was added as a request from a user. This swaps the nibble values from one byte and the adjacent byte then deinterleaves that file. For example an original file of: “12 34 AB CD” will output two files, one containing “13 AC”, the other “24 BD”.
Its not something I’ve ever had the need for but obviously someone wanted it so here it is.

As usual it can be found in the “Downloads/PC Software” section.

 Posted by at 7:04 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