Subelectro Hunch Back. PCB Repair.

After nearly a year of being in s pile of boards that needs fixing, I spent some time tonight fixing my Subelectro Hunch Back board. With reference to this thread on the UKVAC forum from when I originally purchased a Subelectro cab with this board in.

I had this board fixed by a repairer when I first got the cab, but on its return it lasted not more than a few hours before having jumpy graphics and eventually not booting correctly with a black screen displaying 'CREDIT 0' and making a constant audio tone. 

Failing graphics

Corrupt title screen

Fast forward to having a bit more experience and a few tools, my first port of call was to verify the ROM'S. The board has eight CPU program ROM's and two graphics ROM's. Of those, three of the eight CPU ROM's claimed to be blank or wouldn't verify against the on-line Romident tool. Both of the CPU ROM's also didn't verify correctly, I re-burnt a complete set of new ROM's tonight and upon power up the game booted and played correctly. My test monitor struggled a bit with the video sync on the far edge of the image, but it will display fine on an arcade monitor. Makes a change having an easy fix like this!

Images below of the working game.

The Subelectro Hunch Back board, running on Galaxian hardware.

Atari Return Of The Jedi. PCB Repair.

I recently acquired an Atari ROTJ PCB in an untested/unknown state. First up I had to make an adapter so It could be wired into my JAMMA test rig.

Upon 1st power up the game loaded and played but had some colour issues with the display and also all the foreground sprites had horizontal line missing from the graphics.

The first photo below show the speeder bike having horizontal lines missing from the graphic, the colours of the trees and the ground also didn't look quite right and seemed to be missing the colour brown

All text and other graphics seemed to display correctly.

The screen below also showed some colour error (Green hue over complete screen) along with missing lines in the Deathstar graphics.

After spending a fair amount of time using my logic probe to find a faulty IC I didn't really make any headway into the issue. I then decided to put the game into test mode to see if the diagnostics would point me in the direction of the fault. Well the game wouldn't go into test mode and seemed to stick on a Magenta/Pink colour screen when switched into test mode. Not a great help I thought... I decided to read the Manual for the game and sure enough a Magenta screen when set to test mode indicated a fault in the Colour RAM section of circuitry. As it turned out a RAM at location 12R was faulty. Initially I piggyback a new RAM on top of this one and the colours came back but it still wouldn't flip into test mode. So I swapped the IC anyway and on power up the colours now looked good and the board went into test mode.

No green Hue on the screen below now, but the missing line now quite visible.

The Atari schematics for this game are nicely laid out, I deduced that the fault was in the Motion Object Horizontal Line buffer areas of the circuit. Again more probing around and Its was not clear what was wrong, I don't like shot gunning parts on a large scale, I like to know what is causing the faults, so I took a break from the logic probe and went for a visual inspection of the solder side of the board and then I noticed something....

Pins on a 74LS163 in the Horizontal line buffer section had been bent over and looked like they were tightly presses into a track from another pin. I used my multimeter in continuity mode and confirmed that some pine were shorted together. I uses a scalpel to lift the pins away from the track which they seemed to have been squashed into. Upon powering up the sprite issue had gone and the game was fully working.

The pins that were shorting were pins 1 (Reset/Clear), 2 (Clock), 3 (Input A) & 4 (Input B).

Note to self to save time in the future, begin board repairs with a good visual inspection especially if the board has been stored for years with an unknown history, anyway the board is work and I'm well chuffed. 

Fully working Game images below.

UPDATE* 03-01-15

I forgot to show an image of the offending pins which caused the sprite issue. It was in device location 5N the board. See image below, I think something has scraped over this IC in the past or been squashed up against something whilst in storage.

Apple I replica computer build

My wife kindly purchased me a replica Apple I kit as a Christmas present, (the kind of present where I buy it and she pays me and wraps it up. lol!) The Apple I was the first computer designed and engineered by Steve Wozniak &  Steve Jobs. 

The kit is a replica made by Briel Computers. Inside the package was the following items: Blank PCB, Components & a CD containing build instructions, software and some original Apple I info.

Contents of the Apple I replica kit.

After a quick read of the build guide, I installed the components in what I deemed the best order.

Passive components, Power switch, Crystal USB->Serial headers installed.

                           

All IC sockets, PS2 and Video Phono connectors installed. 

IC's and USB to Serial adapter installed.

So that was all the components installed, I double checked that everything was installed the correct way around. The first check was the 3.3V from the USB adapter, this is used so you can a) power the computer and b) connect a terminal program from a computer to send files and type code. There is an onboard PS2 connector to plug a keyboard in directly or even an ASCII keyboard connector which the Apple II used (I think).

So the 3.3V was good, next up was the 5V line which powered all the IC's. Again this was good so I hooked up the monitor.

1st power up, the screen is full of garbage.. this is what's expected. Yes!

After a quick press of the 'clear' button followed by the 'reset' button I'm staring at and "@" sign, this is the Apple I prompt, you are now in Woz Monitor mode, here you can set and view memory locations and program directly to the 6502 processor. The ROM that comes with this Replica has Apple Basic installed, back in the day you would have to build a Tape interface and load it into RAM from Cassette. To get into basic, you type E000R and hit return. There's also an assembler called Krusader built into the ROM, this is a assembly language dev tool for the Replica I which can be run from location F000R. This is what I'm going to be looking into once I've finished playing with some of the existing software releases for the Apple I.

A very basic Basic program!

I'll post some more updates, if/when I make any progress with anything that may seem remotely interesting.

Regards, Smart.
                         

Atari Jet Fighter. What's the score?

So another week goes by and my Jet Fighter board has another failure, these 40 year old 74 series logic seem to be dropping on a regular basis from being powered on for a few hours here and there...

This this when I started a game, the scores didn't reset to '0' for either player, when I scored some 'hits' on the other Jet the score moved in an odd sequence something along the lines of 2,3,2,6,4,11.

Out comes the operation manual and my printed schematics. The scores are initially generated by two identical circuits comprising a 7493 binary counter, Pins two and Three which are linked to the 'START' signal are used to reset the counter to zero when the game starts. Pin 14 is the counter input which is pulsed when either Jet is 'Hit'. The output pins hen count upwards to a maximum of 15 and pass on to some more circuitry.

Jet Fighter Score Counters

After playing a few games I noted the following... the score was being reset every time a game was started, just not to zero, and it was actually counting, just not in a sequential order, I made the assumption that these two counters would not be the issue as having two different IC's fail at the same time was improbable, If one of these had failed it would seem more likely that one of the scores would stop working and not both at the same time.

The next part of the circuitry that relates to the scores is shown below:

Jet Fighter Score selecting

The 74157 at location A5 receives the signals from the two 7493 counters. I used my logic probe to test the pins of this IC. Pin 1 was pulsing away as expected and the input pins were all the in the same logic state as the output pins from the 7493 counters. There are  four output pins used which feed into a Prom which selects the Score number data, by my testing, pin 12 which is output 4Y on the datasheet was stuck high all the time. Quickly piggybacking a new 74157 cured the scoring, but did seem to have a side effect of resetting the game a short while after stating a new game. Anyway once socketed, I put in a new 74157 and we're back to fully working again. My IC tester confirmed that output 4 of the IC was faulty.

Missile Command PCB fix

Board location E5 - 74160 dead output at pin 12 and other outputs suspect.

Confirmed as faulty in IC tester.

Fixed! :)

Arcade Garage 1.0

Well after close to four years, all the cabs I own are (touch wood!) working, Well I need a new starter for my Tempest Fluorescent light, but thought I best capture them while they all do work. My current line up consists of:

Fire Truck, Jet Fighter, Electrocoin Midi with a dual JAMMA adapter playing Pac-Land & Wonder Boy, Tempest Cabaret, Centipede Cabaret, Hang-On and Pole Position.

On the way to getting my current lineup I’ve also owned the following cabs: Lethal Enforcers, Cruis’n World, Missile Command Cabaret, Asteroids Cabaret, a Popeye Pachislo & 2 JAMMA cabs.

Photos below and a video, sorry for the lack of commentary but I’ve got a stinking cold at the mo and the vocals don’t sound too good.

ATARI Hot Wheels!

Tempest. Board repair.

This board failed on me back in March, and I briefly looked at it but didn't really have the enthusiasm to fix it at the time, fast forward six months and here we go again...

So upon re-testing the boards, the X axis output had stopped working, this was caused by a failed TL082 at location D/E12 on the main AVG board, pin 7 wasn't outputting anything, I fitted a new socket and replacement IC and had a stable output again, back to where I was six months ago.

Last week I got stuck into this fault again, (Crazy vectors and Showing Mathbox error in test mode) I have spent a good few hours probing with a scope and logic probe to try and track down where the issue was, I got the schematics printed onto A1 paper at work, I even de-soldered all the proms from another Tempest AUX board to double check my proms had verified correctly, which they had.

Now, convinced that it wasn't a Prom/Bitslice/Socket or Interlink cable, I honed in on the remaining IC's in the Mathbox area. E4 a 7408 (quad 2-Input AND gate) got my attention, now I'm not really proficient enough in fixing boards to understand what was wrong but pin 6 which drives the clock input of B1 (374) didn't look pulse correctly on my logic probe, the frequency of the pulsing was all over the place and the HI/LOW LED's were going 'mental' in an odd way. I tried piggybacking a known good chip onto the 7408 to no avail, not deterred I de-soldered it and put a socket on the board. I then tested the IC in my Programmer which also tests 74 series logic, and sure enough one of the gates reported faulty. I put a new 7408 in and BOOM! The game is working again!

I have ordered new TL082's, MC1495's, trim pots for X/Y size/position adjustments and will fit these when the arrive to hopefully improve the reliability of this board, but for now I think I'm due a few credits. :)