Atari Dunk Shot to Tehkan World Cup Update 3

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Mar 022019
 

I’ve got a few minor things to do but I’m classing this project as finished.

Outstanding jobs are

  1. Fit Power Switch
  2. Swap Opto boards on the player 2 side as the controls are a bit jittery
  3. Mount the PCB in the cabinet
  4. Take a look at the PCB on a test bench as it has developed a small graphics issue

Paperboy PCB Repairs

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Feb 202019
 
Paperboy on the bench

A fellow arcade collector asked me to take a look at a Paperboy and Championship Sprint PCB as their cabinet had been standing idle for a long time. I intended to look at my own Championship Sprint and convert it to Paperboy so it seemed the ideal time to look at all three.

The first task was to visually inspect the boards and I found a number of problems, and ended up replacing corroded connectors, missing clock crystals, broken roms, dead rams, and various problem sound chips.

The second task was to setup a test bench without the need for an Audio Regulator 3 and Atari power brick which takes up lots of space! This was challenging because the PCB uses odd voltages like +15v, -15v and +10.3v DC. I had previously been told that if the +15v was not exact, this would stop the board from booting.

After a lot of experimenting I found that the PCB would run off a single switcher for test bench purposes. +12v DC is fine for both “Power OK” (10.3v DC), and as a substitute for +15v. In order to get sound, and for inputs to work, you need to have -5v DC which is derived from -15v on the PCB. To bypass the -15v you can clip -5v to the -5v end of the capacitor marked C140 and this worked fine. I then added a small +5v amp that connected to the audio pins at J15 on the CPU board, so I could hear the sound.

The next challenege was to find a way to display the output of the game as this uses a medium resolution monitor, and they are not common. I found that it was possible to use an Acorn CRT monitor (AFK18 or AFK52) or an LCD like a NEC AccuSync LCD 1770 nx

I also found that for the different monitors you also had to put inline resistors on the Red/Green/Blue to get the perfect image.

For the NEC – 270 Ohms
For the Acorn – 33 Ohms

I was now in a position to power up the boards and see if they worked.

My PCB

On my own PCB I had a number of issues.

1) The sound was not working, and sometimes I would get a 6502 communication error – The 6502 error was caused by a bad rom socket @ 2C.  If the roms or sockets are faulty @ 2A-2C it can generate this error.

2) On the self test, parts were missing on the scrolling playfield test, there were no colour gradients visible and I was missing the individual colour grey. In-game the same parts were missing – This turned out to be a fault with the Q2/Q3 transistors in the colour intensity section.

Paperboy was looking better!

The next problem was the audio. I had music and sound from the audio chips but it was distorted. Initially I thought this was an issue with the LM324 @ 9J/K.  I tested pins 10 with an audio probe and the sound was good, but was distorted on pins 8 and 9.  I isolated the pin 8 output by lifting the leg of the cap @ C64 and used an audio probe on the other leg of the cap.  The music was still distorted. So I replaced the Op Amp, but still had the same issues! The problem could only be in a small number of components and in the 2.5v adjust section. I measured the voltage at one end of resistor R105 and got 5 volts as expected.  I then measured the other side expecting something like 2.5v though a 1K resistor, but got 0.64v, so this is where the problem was. I had a look at components R105, R104 and C91, and all of them had corroded legs so decided to replace them all, and sound and music was now as expected but the speech was twice as fast!

This one took me quite a while to figure out.  I checked pin 8 on the Speech chip with an audio probe and the speech was also twice as fast at this point, so confirming that the fault was somewhere before the LM324 amp.  I thought it might be a fault with the speech chip itself but it was good, and all voltages to it were fine.

Obviously this was a timing issue, but I had no clue where to look, as it wasn’t clear to me on the schematics how the clock circuit in the speech section was all tied together. I brought up the datasheet for the TMS5220C and noted all the pins used by Paperboy.  The one that really stuck out for me was the OSC @ pin 6 which was the oscillator input, as it looked like the clock pin at pin 3 was not used by Paperboy. The datasheet also mentioned that the oscillator needs to run at 640khz. 

So I got the scope out and connected to pin 6 and measured the wave and it was reporting as 1.25Mhz, which when converting to Khz is twice as fast, so I was on to something! I then looked in the Tclk, and T1clk section with the scope taking measurements and this was still reporting as 1.25Mhz to the LS163 @ 4D.  I also confirmed that both pin 2 was 5Mhz and pin 12 was 1.25Mhz.

At this point I had a look at a working Speech board, and it was 1.25Mhz @ pin 12 so this was correct.  However it then went to the LS74 @ 4C/D.  This had a clock pin @ pin 11 from the LS163 which was 1.25Mhz, but the output pins @ 8, 9, and  data 12 showed 640Mhz, whereas my faulty board was showing 1.25Mhz at all these pins! 

This would conclude that the fault was at the 74LS74 because this should be dividing the clock signal and it is not doing so.  I changed the LS74 but this sadly did not fix the problem! The fault actually turned out to be the chip before the 74LS74 @ 4C/D. The 163 at 5D had a missing 1.5mhz signal @ pins 9 and 15, and also double speed @ pin 13 (2.5mhz instead of 1.25mhz). Replacing this chip fixed the issue

I then noticed a problem where the left coin input was permanently on. I tracked this down to no voltage beyond the resistor at R118, so input was permanently low. Replacing R118, and the input was now working as expected.

Strykr’s boards

Strykrs Championship Sprint PCB had a couple of faulty roms, but nothing major at all to report. His Paperboy CPU board was also good, but the video board had a number of problems after replacing a faulty rom:

(Blue actually looks Purple on screen but blue on camera!)

I checked the transistors in the blue, green and intensity section and found no issues, so I was a bit stumped as I was sure this was a straighforward colour problem. The resistors also checkeded out ok. So I thought I would independently check the colours to see what was what. All the solid colours checked out ok, on each output, but I noticed that both red and green were broken on the intensity section, when looking at them independently. Blue was fine. Also when all the colours are combined blue, and green show incorrect colours, but red is ok. So as the problem seems to be shared by red and green I thought I would check to see which chips it might use for both. I came up with 12L and possibly 13K thinking one of these must be at fault, but found no issues with those on a logic probe and piggy backing them. So I started tracking backawards looking at the independent colours R0-3, G0-3, B0-3 on the 374’s @ 12K and 13H I initially found no issues with those using a logic probe so dug out my scope and starting looking at the signals.

What I noticed was that R0-R3 had a very weak signal, so I tracked that back further to CRD12-15 on the 374 @ 12J, and then back to the color ram addressing and data buffers. I checked pins 11-14 on the 2149 @ 11H and found the same issues, and then tracked back further to the 244 buffer @ 10H and found that this chip had a decent input from the playfield section but had no output at this buffer as you can see below:

Input
Output

I piggybacked a 244 @ 10H hoping this would resolve the issue but sadly it didn’t although I know piggybacking buffers generally does not work. The good thing is I could clearly see an issue, so I thought I would also try and piggyback the 2149  colour ram @ 11H to see if this was affecting the buffer output rather than the buffer being faulty and voila…..colours corrected!

Unfortunately changing the colour ram only fixed half of the issues.  The intensity section was still broken and the in-game colours were still wrong….but looking better!

This made me think that *potentially* other colour rams were faulty, so I started to look at them and found that 11J next to the faulty ram also had weak signals, so I decided to replace both.

2149 ram is really expensive and looks like it is hard to get hold of so I thought I’d try some 2148-45 in replace of the 2149-2’s

I was pleased to see that on power up the video board looked to be 100% fixed.  Both in-game colours were correct, and the video intensity check looked right.

Atari Dunk Shot to Tehkan World Cup Update 1

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Apr 022018
 

My conversion of Dunk Shot to Tehkan World Cup is going fairly well.

Firstly the external work on the cabinet is complete and ready for the artwork.

Here is a picture of where things are currently at:

Tehkan World Cup

Tehkan World Cup

The cabinet has been painted and has t-moulding fitted. The coin door has been coated and re-fitted, and the control panels have been mounted and screwed into place after also being coated.

After the artwork has been applied, the next steps will be to work on the internal parts of the cabinet. Fitting a monitor, power supply, game board and trackballs etc. Luckily I now have a working game pcb to mount in the machine:

Tehkan World Cup PCB

Tehkan World Cup PCB

Biggest video games raid in the UK

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Mar 222015
 

March 12th 2015 saw one of the biggest arcade raids for video games in the UK, right here in my home city of Manchester! Altogether around 90 cabinets were found including some really uncommon games. together with parts, manuals, and unreleased documents from Atari. Check out some of the footage I took below, whilst being a helper at this historical arcade event:

Arcade Raid

Apologies for the poor quality video. It was dark, and I only took snapshots at various times during the raid.