May 052017
 

A friend of mine sent this pcb to check why the background was all messed up

I immediately noticed  in demo mode that all the characters fell down in an endless loop because they couldn’t walk on the platforms

After searching for the fault in the video board for some days, I decided to test all roms starting from the program ones.

Program rom 04 didn’t match with anything in Mame and after checking the pattern I saw it was full of garbage.

 

After reprogramming with a good dump, the game was restored perfectly.

It seems rom 04 has only the layout of all levels because even without its presence the game is booting

 

Apr 232016
 

The game booted perfectly but was missing some parts of graphics , road and cars

 

MadG3

MadG5

 

Upon closer inspection, there was a missing bprom in position 14k.

MADg8

 

Since I had a working Mad Gear, I borrowed the bprom and installed on the faulty Mad Gear just to see if the chip was taken away because the game had other problems.

To my surprise, with the bprom in place, the game was perfectly working with all graphics in place.

It could have  been an easy repair but bproms are discontinued since 30 years and nowadays they are nearly impossible to find empty: they are otp chips so once programmed they cannot be erased!

In any case I did a research on ebay and there was no one selling the same kind of bprom needed for Mad Gear which is a 82s129 (equal to 6301 or 7052, depending on the manufacturer).

Next step was to find a way to reproduce it.

Bproms have small capacity but they have a fast access time (less than 50ns) and for that reason they are used often for decoding graphics.

Some OTP roms, such as 27256 or 27512 , have fast access times and can be used in place of bproms by just burning the binary file into them but the problem is that you have to build an adapter because the pinout is different and also the size of the chip itself is much bigger.

The other solution , more elegant and less invasive , is to reproduce the content of the Bprom into a GAL (Generic array logic). This has been done before by other people to reproduce some bproms but they had programming skills which I don’t have.

My friend Caius some months ago pointed me to a blog of a guy who programmed an alternate software for the TOP2005 chinese programmer which had also the ability to produce equations for a GAL out of a  bprom file.

Turned out that this was exactly what I had been looking for!

So first of all I would like to give full credit for this wonderful program to the guy who goes by the name of Elgen.

His blog is: http://elgensrepairs.blogspot.dk/

Facebook page: http://facebook.com/ElgensRepairs

Most important the software to convert bprom to GAL equations can be downloaded from here: https://bitbucket.org/Elgen/u2pa

Now back to the problem: my wish was to reproduce the bprom into a gal without building an adapter.

So I ran Elgen program on the bprom file taken from Mame which produced the GAL equations.

I then started the program WINCUPL by Atmel (can be downloaded free from here: http://www.atmel.com/tools/WINCUPL.aspx ) in order to produce the JED file (fuses list) out of the PLD equations (source code)  so that a programmer could burn the GAL chip.

On the WINCUPL program I declared the inputs (addresses) and outputs (datas) in the same pinout standard of the original bprom chip so that I could avoid bulding an adapter:

82s129

We don’t have to worry about CE1 and 2 because normally they are tied to GND

After copying and past the equations produced by Elgen program into the PLD project of WINCUPL and minimizing the equations using Expresso algorithm I got this:

MadG2

Since the equations were not complex in this case, I could use the smaller 20 pins GAL chip, a 16V8 instead of the bigger 24 pins 22V10.

You can see that the GAL file used only 2 data lines instead of the 4 of the bprom file.

At this time you can notice that the BPROM chip is only 16 pins while the GAL 16V8 is 20 pins.

After compiling succesfully I got my JED file to be used in a common programmer supporting PLD files:

MadG

 

With the way I declared inputs and outputs, I could install the GAL chip on the socket, leaving out 4 bottom pins.

In order to power it, I only needed to solder a jump wire from pin 10 to pin 8 for the GND! Very easy and less invasive!

 

MadG4

 

Now the smoke test:

MadG6

 

MadG7

 

Game fully restored!

Again I would like to thanks Elgen, without his program I couldn’t repair this game, but more over, it’s a very important tool for everyone who has missing or broken Bproms because they are really near impossible to find empty nowadays

 

 

Pang repair log #4

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Apr 042016
 

9 years ago I got a Pang for my personal collection. It was still with original battery and I carefully changed it with a new one because I didn’t like the wire wrap mod to desuicide it.

Unfortunately 1 year ago while testing the kabuki desuicider the game didn’t boot anymore, steady blue screen.

After testing succesfully the kabuki desuicider on another board it was clear my Pang developed a problem.

For more than a year I never managed to repair it until I got a Fluke 9010A which showed a problem on the z80 bus, the READ signal was not driveable.

I immeditely noticed that it had a very low resistance to gnd.

Near the Z80 there is a resistor network 4,7kohm.  the read signal was connected to a pin of this network which had only a resistance of 427ohm.

pang

I decided to desolder it and install a new one but the game didn’t boot.

I decided to let the game rest for some more time until one day I discovered that the game sometime booted , sometimes not but when it booted it crashed soon after.

Upon closer inspection I discovered that I soldered very loosy a pin of the network resistance!

After resoldering it better , the game booted without problems!

 

Ghosts ‘n Goblins repair log

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Apr 042016
 

Got this bootleg board for a repair.

The game could be played with music and sound but had a problem on the text layer:

gng2

gng3

 

I started probing around until by shorting carefully  pins of some TTLs I found the circuit of the text layer on the upper board.

A 74LS86@5J had all its output in the grey area (2.2V):

 

gng1

 

Changing it with a new one solved completely the issue:

 

gng4

gng5

 

Pang repair log #3

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Mar 232016
 

I desuicided this original PCB but after booting up I got this

Pang Pang2

 

After checking rams and buffer they were all good.

Just to avoid any doubts I dumped without convinction all the graphics eproms which normally are very reliable.

To my surprise when I lifted eprom PWE02 with the pcb in operation, the parts of the background corrupted turned to black revealing that at least the problem was connected to the circuit around the eprom.

Placing the eprom on my programmer I got this:

Foto 20-03-16 10 00 58

 

Turned out that the VCC pin of the eprom was making bad contact internally.

Burned a new eprom and the problem was fixed:

Pang_fix

 

A picture of the bastard before going to the bin:

eprom