Hi all

I’m going to be spending a week in Frankfurt with work at the start of December.

Is there anything arcade-related for me to see (Sunday to Thursday evening)?

Thanks for any information 

I've been doing some work lately on some faulty sound boards and old drum machines, and found it quite tricky to work out exactly what part of a circuit was faulty.  You can't really use a logic probe to help, and a 'scope can give difficult to understand readings.

I had a look around for an audio probe (which is used to probe parts of a circuit and hear what's going on), but couldn't find one at a reasonable price, so armed with the LM386 amp datasheet I set out to build my own.  A PCB was designed, plus around £7 of components later and I've a working audio probe.

The probe connects to the power supply of the circuit under test (usually the 0V & +12V of the sound section), you just need to plug in a pair of headphones as it doesn't have a built-in speaker.  The sensitivity and volume are adjustable, and you just touch the probe tip to the part of the circuit you want to "listen to".

It helps answer the "is the power amp or some other part of the sound circuit faulty" predicament as it can prove the working bits of a circuit to narrow down to where a fault actually is.

Photos of the one built unit are attached (the probe tip is a nail, until the proper tips I've ordered arrive from China!)

Bare PCBs are available if anyone is interested, £2 each plus postage

Moon Cresta seems to be one of those games people either love or hate.  I've fond memories of playing it in a hotel bar in Scarborough (North East England) back in the early 1980's so I think it's a pretty cool game.

It was never on my list of games to hack, but a throw away comment by Jase on UKVAC a couple of weeks ago about a high score save kit got me interested.

I've already made the modifications to the high score saving code (it wasn't too hard as the game already has a high score table and name entry routine) so it was just a case of copying them to and from NVRAM.  Not having a boardset (yet), I haven't confirmed this works so it's not ready to be released, but hopefully will be in the next couple of weeks.

Whilst doing the high score save hack I noticed it's another game with annoying freeplay mode, where it sits at the "press start" screen rather than going through the attract mode.  I decided to also do this modification (and been able to test in Mame) which is what the code below is for.  Basically when in freeplay mode, it still displays "free play" on the screen, but now cycles through the attract mode.  Just pressing P1 or P2 start, begins the game.

The hack has been done for the "mooncrstuku" ROMset, and as the addressing is different across different variants it will only work with that one.  The code itself is simple so could be adapted to the other ROMs by changing the absolute addresses, so I've also included the source below.

Changes to be made:-

ROMset mooncrstuku

ROM smc1f

#0030 3A 00 B0 E6 0C FE 0C C2 4D 01 3A 35 80 B7 C2 4D 01 3A 00 A8 CB 47 3E 01 20 0A 3A 00 A8 CB 4F 3E 02 CA 4D 01 32 32 80 C3 81 01

#00F4 C3

#0115 30 00

ROM smc6f

#2FCE (individual ROM address #07CE) C9

Source code

; enhanced free play @0x0114
call freeplaycode    ;intercept for hack @ 0x0030

freeplaycode: ld a,(0xb000) ; are we in free play mode?
and 12
cp 12
jp nz,0x014d     ; return to main code if not
ld a,(0x8035)
or a
jp nz,0x014d     ; don't add dummy credits if already registered
ld a,(0xa800)
bit 0,a              ; P1 button pressed
ld a,1
jr nz,addcredit
ld a,(0xa800)
bit 1,a               ; P2 button pressed?
ld a,2
jp z,0x014d       ; return to main code if not
addcredit: ld (0x8032),a    ; add 1 or 2 credits depending on P1/P2 pressed
jp 0x0181          ; return to main code

; 0x2fce = RET (C9)   ; don't jump to static screen
; 0x00f4 = JP (C3)    ; don't jump to static screen

I've posted this up on UKVAC as the board has evolved, but here's a bit of a summary of a single ROM/RAM board I've made for a number of Z80-based games.

At the end of last year I was repairing a load of Galaxian boards, some original, some boots, and found a lot of problems seem to be with the ROM daughterboard (which often goes missing) or the program RAM, so I wanted to design something to make troubleshooting a bit easier.

Buying the already-available single ROM boards for a number of games I own would work out pretty expensive, so I spent some time in January designing my own single ROM/RAM daughterboard that plugs into the Z80 socket and replaces the old ROM board and RAM (RAM is optional).  You just need to burn whatever version of Galaxian or clone onto a single chip, choose whether you want to use separate RAM or not and install it if you do, then remove the Z80 and plug it into the daughterboard.  Once this was working, it was time to extend to other games.

So rather than it just being dedicated to Galaxian, I tried to make the hardware as generic as possible.  The memory addressing for the ROM and RAM is handled by a GAL, and I fed multiple memory address lines plus various control signals into the GAL, so the board isn't restricted to just Galaxian, but other Z80-based games, you just need to reprogram the GAL.

It's so far been tested working with the following games:-

Galaxian (Namco, Midway and bootlegs)
Amidar
Turtles
Pacman (ROM only as the memory addressing is a bit "odd")
Scramble (plus other games on Scramble hardware)

Using a single board does away with the multiple ageing IC sockets that lose their grip over the years, and also reduces power consumption a bit as it uses just one ROM and not the multiple ROMs originally in place.

The final thing is for anyone who does home-brew game coding, or hacking games.  Burning a single ROM is a load easier than having to burn multiple ones.  Also the RAM on the board can be replaced with a Dallas DS1220 NVRAM module (apart from Pacman), so the home-brew coders can write their own high score save routine.

I plan to get this working with more games as time goes on, and also maybe refresh my old Z80 programming skills...

Hi everyone,

Hello from the south of England, long time collector since 2000, but new here, have been meaning to join for a while...

Mainly like the classics from late 70's / early 80's, especially Williams (my collection includes Defender, Stargate, Robotron, Joust, Turkey Shoot, Joust 2, and most recently Bubbles).  Also have around 30 other machines from various manufacturers, plus a couple of pins (Getaway High Speed 2 and Scorpion), about half of them work

Cheers, Phil.