New year layout update

Welcome to 2016. New layout for the website. As you were...

Atari Jet Fighter PCB repair. Calling Virtvic to the cockpit

So Vic from Ten Pence Arcade Picked up a Jet fighter a while back, the Transformer in the cab was shorted so he decided to DC mod it with the help of a fellow forum member. After completing the conversion to DC Vic made a simple adapter to power the board and output its video signal. With not much luck in getting the game to show I offered to help Vic out and attempt to get the board working...

Once powered on with a 5V & 12V DC supply after converting from AC volatages we were presented with a black display on the monitor, after checking the clock signals around the board there looked like there was plenty of activity across the board.

I did a quick visual inspection and noticed that the 74165 at H4 had been inserted backwards in a socket. This was replaced ans inserted the correct way round.

No change to display.

Whilst probing around the board we found some bad outputs from a 7414 (Hex Inverter) at J9. This IC deals with input directly from the control sticks. I can't remember the exact issues but I'm guessing the inverting of signals wasn't correct on a few of the outputs.

Next I looked at the locations where the video signals were mixed together. A 7427 at C5 mixes the H Blank & V Blank signals along with 'PWR Reset' signal, this signal was low, it turns out this issue was an effect of making the DC conversion. The Power reset is triggered from a transistor which is on the AC side of the board and as we removed AC it was never triggering, well it triggered once when the board was powered up. I ended up tieing this signal to a 12MHz signal from the board (No notable side effects yet :) ), this falsly switched the reset signal and the video display now appeared. Well some of it did. We had a gray background and the scores showing but no Jets.

Part of the power reset circuit that we were now bypassing contained a 7474 at R3. This was confirmed as being faulty and replaced. Technically it is now being bypassed.

With the reset now taken it was time to find out why the Jets were missing.

This fault took me a few hours to track down.. The long & short of it turned out to be a faulty 7413 at D9. This is part of the circuit that detects when either of the player start buttons are pressed. Pin 8, the output section for the 2 player start button was stuck high, this placed a 74175 flip-flop further down the circuit in the wrong state. The 'START' signal for the game usually pulses and resets the game scores along with the Horizontal & Vertical position counters for the Jets, with it being stuck permanently on the location counters for the Jets were constantly being reset, happening so often that the video never showed on the display. When removed from circuit and checked in my IC tester it was confirmed as faulty.

Once socketed and replaced we have Jets on the screen during Attract mode.

Finally we could now see both Jets flying but one of them (Jet 2 -  White) had constant inverted video.

Black Jet looks OK, but White Jet's video is inverted

Pin 6 of the 7432 at K8 was stuck low, forcing the game to think that Jet 2 was constantly being blown up. This is usually a 1 second pulse which should occur when a plane is hit from a missile.

Socketing and Replacing the IC fixed this problem.

I hooked up the sound outputs to a speaker and we're certain getting game sounds. So we now have a game that looks to be working with audio & Video. Vic will fully test it when he puts in in his cab, I wouldn't be surprised if we has some small issues to deal with like Jet rotation or score counting problems which I've previously dealt with.

Short video below showing the board running in it's semi-complete state.

New Marquee Light

Strange find in my new Enduro Racer cab... So the marquee doesn't light up, lets take the monitor surround off and see what's going on,..This is not quite what I expected to see..

Quick Atari Jet Fighter Repair

So I moved my games around today making space for a new cab and upon turning Jet Fighter back on the score for the white Jet was missing form the display.

A quick browse at the schematics led me to the section below:

/Score1 is the Video signal for the black Jet score and it was pulsing away on my logic probe. /Score2 was for the white Jet and that output (Pin 3 of C3) was stuck high. I checked the input signals and they all looked good so I piggybacked C3 with a new 74LS00 and the score came back. 

I removed the bad chip, fitted a socket and popped the new 74LS00 in and everything is working again.

Sega Outrun in a Power Drift arcade cab.

Part 1.

My newest arcade cab I picked up was a Sega Power Drift, unfortunately both the CPU & Video boards had faults with the Custom IC's, this basically rules them out of being repaired unless swapping the parts with IC's from another Sega board set which very rarely come up for sale... So what to do with a really nice cab, put a cracking game in it that by my reckoning used the same cabinet hardware but different connector arrangement, yes its Sega's finest racer Outrun!

I started off by comparing the wiring pin outs in the back of the user manuals, once these were documented I set about transposing the pins from the Outrun board onto the Power Drift connectors. The Power Drift cab has a filter board that connects all of the cab wiring together, there are then another set of cables that connect to the PCB. This would mean that I just need to make a new set of cables from one side of the filter board to the Outrun PCB.

Luckily for me I had an Outrun loom that I could use therefore meaning I only needed to marry up the wires to the Power Drift filter board using new connectors. The connectors labelled 'AMP' on the Sega boards seem difficult to source, a company called JST seems to produce a very similar connector but I had trouble sourcing these, that's why I decided to use my Outrun loom.. I have ordered some IDC connectors which are a similar connector type as used in PC's for the IDE & SCSI cables. Once these arrive I will make another loom and provide info on what needs to be used as I'm guessing this will be the route anyone else thinking of doing this will go down.

Below is the connector layout that need to be followed:

Every cable with exception of Coin Switch 2 and Coin Meter 2 have been tested and confirmed as working.

Some info below on the connectors I used and where you can get them:

Here's a few photos on the looms I made:

 

The end result is that Outrun plays in my Power Drift cabinet with Force feedback from the motor shaker in the steering wheel mechanism along with all other game IO.

I will update this post with more info when I get the wiring looms remade with connectors that are readily available. If anyone can help with sourcing the JST type connector please get in touch.

Let me know if I can assist if you're going to made a  set of conversion cables, It should be pretty straight forward now the pin conversion is written done and proved to work.

Thank for reading, Mart.

Arcade Garage 14-07-15

Atari Pole Position. Now what's happened with the road!

Well after my last PP fix a short while ago everything was looking good and the game played fine until last week when I was shuffling my cabs around in the garage arcade... When I turned the cab on for someone to play (Hi Chris!) The road had again decided to fail. It looked like the track edge (red & white stripe) was covering the grass on the left side of the track, there was also something going on at the right side of the track edge.

I quickly swapped out the socketed custom IC's which are responsible for the track being displayed, it wasn't any of those :( 

After a checking some more signals I previously looked at with my logic probe I moved to the area in the schematic labelled 'Roadway Memory and Adders'. From the descriptive name it could certainly be an area I needed to look at. Not long into checking signals, I came across signal 'Σ3' (Sigma 3) which is an output from a 74LS283. There are six of these 'Sigma' signals which are mixed in a 74LS298 with some other signals, the output from that LS298 are the address lines of the graphics ROM which contain the track data. Signal Σ3 was stuck always high in comparison to the other Sigma signals which were pulsing away. I removed the IC put in a new socket and with a new IC inserted we were making progress! In honesty I thought this was going to be the 'fix' for the board, but it was apparent there was now something else wrong as shown below.

As you can see above the vertical lines in the track were staggered (i.e. Centre line in track dividing each half) I moved to the schematic section labelled 'Picture Data Memory Address Modifier' and quickly found an LS157 at location 4H with an output that was dead. The signal name was 'MUX2' and this is an input into one of the Custom IC's at location 5L. ( If this custom IC is removed the whole track will disappear) I removed the LS157 fitted a new socket and IC and we have a working Pole position again.