Pang – JAMMArcade.net

Pang repair log #4

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!

Pang repair log #3

PCB Repair Logs, Repair Logs Comments Off

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

Pang repair log #2

PCB Repair Logs, Repair Logs Comments Off

Jun 162015

Got a friends Pang PCB here for repair.
He had carried out the ROM swap (made by ArcadeHacker) to desuicide it but he had no output although we could hear it playing blind.
The board is very clean and a visual check revealed nothing.
On powering the board up I got this screen

I could also hear the board did play blind so that’s a good sign.
I like to make little schematics for boards when I’m working on them and they don’t have any available and I quickly came up with this.

I started probing back from the RED pin on the JAMMA edge connector and soon came to a RAM chip at location 8C. Probing this chip and its counterpart gave me some odd looking signals which I got suspicious about.
These chips are CXK5814 SRAM chips and they seem the be the most unreliable RAM by comparison.
One of the RAM’s had all its data lines stuck LOW while the other chips data lines were all dead despite all the enable lines working as they should and the address lines active.
At this point I was certain they were dead but one last test was to ‘piggyback’ a known good RAM chip on top of the suspected bad one. I chose the one with the dead data lines to avoid potential contention and I got a partial image on screen.

I desoldered both the RAM chips and replaced them. I didnt have any spares in my RAM bin but found a couple of skinny 6116 RAM’s on a scrap bootleg board.

Fitting these I now got this wonderful sight.

Job done.