Jun 082019

I got this Bombjack Bootleg board a while back when I just couldn’t find any original boards for my cab. I since got an original board for it but this bootleg has been left for repair since then.

It was sold as “graphic & sound issues” without more explanations. Lucky though, these bootlegs are identical to the original boards.

A first visual inspection reveals a few loose & broken filter capacitors and a couple of messy traces near the edge connectors. Hard to say without a magnifier if they’re broken. The caps won’t be an issue for now so let’s focus on the traces


I could do a quick continuity test but as it happens, somebody sent me one of those cheap chinese microscope things. They’re essentially a USB webcam , so this is a good opportunity to give it a test.

Indeed two traces were broken, a quick solder bridge will fix that. Handy little toy that thing!

Next, I had to make an adapter since the board didn’t come with one.

On these boards the video signal comes from a separate connector on the far edge of the board. You can already spot there’s an IC missing there too

This might explain the graphic issue.

But first let’s finally power the board and check what we get.

So our colors are off, some graphic information is missing. There’s no sound coming from the board either. The wavy effect on top of the screen is an artifact of my monitor being in need of a re-cap so we can ignore this.
Let’s first take care of that missing IC. Looking at a photo found online, this should be an LS174 flip-flop.

I then checked the schematics and this confirms it as a pair of these is handling the color signals. Our missing IC at 8B handles the blue and part of the green signal.

Let’s drop a fresh one and see if this restores our picture.

Now to address the sound issue. Probing my way from the amp back I eventually realized I’was not getting any signal. All outputs on the sound ICs (three AY-3-8910) were dead , I suspected the z80 controlling these.

Swapping it with a new working one restored the sound completely board … here’s a photo for proof :

In addition to this I did make a couple of mistake on my adapter, meaning the controls worked incorrectly. I spent some time trying to troubleshoot this till I double checked my adapter. ah well.  Another case where having another working set would prove useful.
Anyway the board is working fine now, but while I tidied a few loose capacitors around the board I spotted this unpopulated section of the bootleg board:

Silk screen and holes for two leds and resistors. Comparing to an original board and checking the schematics, these should be indicators for the 5v and 12v lines.

While this is not strictly needed it’s an easy thing to just add them . I went for a green 5V and red for 12V

yay . a fully working Bomb Jack bootleg.
And for those preferring the video format:

The New Zealand Story (bootleg) repair log

 PCB Repair Logs, Repair Logs  Comments Off on The New Zealand Story (bootleg) repair log
Apr 172016

Got this ugly bootleg for a repair.



Game had no sound and the jump button didn’t work.

First of all, this bootleg is known to have the picture upside down and I wonder why the bootleggers left the game in this state.



Since I had no white noise from the amp I checked the circuit near it and found a capacitor with a leg desoldered. Unfortunately the hole was completely rusted and I had to run an ugly wire to another point on the pcb to restore the sound.

To do: find a thinner wire 🙂




For the “Jump” problem I traced back from pin 23 of the Jamma connector to input 2A of a 74LS257 multiplexer.

The jump button of the second player, was connected to input 2B of the same 74LS257.

So those buttons has the ouput 2Y of the 74LS257 in common, so to check if the TTL  was working correctly, I ran the input test with the second joystick and infact also the second player jump was not working. The output 2Y was oscillating but evidently not in a correct way.


Given that the game has no first player and second player  playing at the same time, I opted with a simple but effective solution: I shorted 2A and 2Y togheter so that the first player button was connected directly to 2Y.

In this way when you press first player button you press also the second player one but for TNZS is not a big deal because you never play a co-op game 🙂



With this solution I could fix the game without bothering to replace the ttl chip

Oct 052014

Been doing a few bits with muddymusic’s Jumping PCB.
I wanted to see how the C-Chip substitute ROM was wired into the circuit so ive made a small schematic and reversed the address decoder PAL.

Jumping Schematics
click the pic for full size.

Here are the equations for the address decoder too. Ive renamed to the pins to something more suitable for human consumption.
/* Inputs */

Pin 1 = A23;
Pin 2 = A22;
Pin 3 = A21;
Pin 4 = A20;
Pin 5 = A19;
Pin 6 = A18;
Pin 7 = A17;
Pin 8 = A16;
Pin 9 = A15;
Pin 10 = A14;
Pin 11 = A13;
Pin 13 = FC0;
Pin 14 = FC1;
Pin 23 = FC2;

/* Outputs */

Pin 15 = CA12; /* A12 of C-Chip replacement ROM */
Pin 16 = CA13; /* A13 of C-Chip replacement ROM */
Pin 17 = CA14; /* A14 of C-Chip replacement ROM */
Pin 18 = CA15; /* A15 of C-Chip replacement ROM */
Pin 19 = LROM; /* Chip enable for other ROM’s */
Pin 20 = A; /* Pin 1 of 74LS138. Input A */
Pin 21 = B; /* Pin 2 of 74LS138. Input B */
Pin 22 = C; /* Pin 3 of 74LS138. Input C */

/* Equations */

!CA12 = !A23 & !A22 & !A21 & !A20 & !A19 & !A13 #
!A23 & !A22 & !A21 & A20 & !A19 & !A18 & !A17 & !A16 & A15 & A14 & !A13 #
!A23 & A22 & !A21 & !A20 & !A19 & !A18 & !A17 #
!A23 & A22 & !A21 & !A20 & !A19 & !A18 & A17 & A16 #
A23 & A22 & !A21 & !A20 & !A19 & !A18 & !A17 & !A16 & !A13 #
!A23 & !A22 & !A21 & !A20 & A19 & !A18 & !A17 & !A13 #
A23 & A22 & !A21 & A20 & !A19 & !A18 & !A17 & !A16 & !A15 & !A14 & !A13;

!CA13 = !A23 & !A22 & !A21 & !A20 & !A19 & !A14 #
!A23 & A22 & !A21 & !A20 & !A19 & !A18 & A17 #
A23 & A22 & !A21 & !A20 & !A19 & !A18 & !A17 & !A16 & !A14 #
!A23 & !A22 & !A21 & !A20 & A19 & !A18 & !A17 & !A14;

!CA14 = !A23 & !A22 & !A21 & !A20 & !A19 & !A15 #
A23 & A22 & !A21 & !A20 & !A19 & !A18 & !A17 & !A16 & !A15 #
!A23 & !A22 & !A21 & !A20 & A19 & !A18 & !A17 & !A15;

!CA15 = !A23 & !A22 & !A21 & !A20 & !A16;

!LROM = !A23 & !A22 & !A21 & !A20 & !A17;

!A = !A23 & !A22 & !A21 & !A20 & !A19 & !A18 #
!A23 & !A22 & !A21 & A20 & !A19 & !A18 & !A17 & !A16 & A15 & A14 #
!A23 & !A22 & A21 & !A20 & !A19 & !A18 & !A17 & !A16 & !A15 & !A14 & !A13 #
A23 & A22 & !A21 & !A20 & !A19 & !A18 & !A17 & !A16 #
A23 & A22 & !A21 & A20 & !A19 & !A18 & !A17 & !A16 & !A15 & !A14 & !A13;

!B = !A23 & !A22 & !A21 & !A20 & !A19 #
A23 & A22 & !A21 & !A20 & !A19 & !A18 & !A17 & !A16 #
!A23 & A22 & !A21 & !A20 & !A19 & A18 & !A17 & !A16 #
A23 & A22 & !A21 & A20 & !A19 & !A18 & !A17 & !A16 & !A15 & !A14 & !A13;

!C = !A23 & !A22 & !A21 & !A20 & !A19 #
!A23 & !A22 & !A21 & A20 & !A19 & !A18 & !A17 & !A16 & A15 & A14 #
!A23 & !A22 & !A21 & !A20 & A19 & !A18 & !A17;

The A, B and C outputs from the PAL feed into a 74LS138. In order to select the C-Chip substitute A and B must be HIGH and C must be LOW. From the equations (or just looking at the MAME source code) we can work out that the C-Chip ROM lies at address 0x80000.

So, not a great deal of info but its pretty interesting all the same.