AR2 sense disabling and info
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First published in 2001? in the Antique Amusements Magazine (AAM)
Subsequently bandied around the internet as an anonymous text file.

Originally written by :
Andrew Welburn 
http://www.andys-arcade.com

BEGIN

This article is semi-techie, don't worry if you don't understand it, you don't have to be able 
to :) It gives you an idea as to what games companies did when re-developing an old idea. 
Also, my interperetation of how these things works may not be technically correct, but it fits 
the situation, i'm not classicly trained, and therefore do not adhere to such sensible rules 
:) I just want to get games going again like you do :)

Ok, so you've got yer new (old) atari video game, and it doesn't work..

Surprise, surprise.. You've done the neccesary steps to determine that
the fault lies in the Regulator/Audio board (AR2 or AR1). How do you
fix it? well.. first off, there is 2 main types of AR1/AR2 boards
that come in classic era atari videogames, called the AR1 and the AR2. 
In the 70's in atari's infinite wisdowm, this job was actually done on the game pcb itself. 
This meant the logic PCB could get very hot, taking actual game logic out with it. The 
complaints were basically that if the regulator section did go down, it meant the whole game 
pcb had to be removed and replaced.. a costly excercise.. Atari split the section off, made 
the game pcb logic do just the game logic and the sub-power assembly was located on its own 
board, thus was born the Regulator/Audio board (AR1/AR2)... This was cheaper and quicker to 
replace for the operator.

Anyhow, Atari started this trend from Lunar Lander onwards.. Lunar Lander, Asteroids and 
Asteroids deluxe (atari's first three vector games) and Football (4 player) all used the AR1. 
While audio amplification, and some voltage regulation was done on this seperate AR1 board, 
there was still a relatively large amount of power still regulated on the game pcb itself (36v 
AC) which still caused some problems occasionally. After Asteroids Deluxe, they re-designed 
this AR1 configuration, by simply extending the board, regulating the 36v AC on there and 
piping 22v AC to the game pcb instead, much better.. This configuration was to prove so 
versatile, atari stuck with it from 1980 through to about 1984. From there it morphed into the 
AR3, and from there came the 'new' switcher.. but that's a story for another day... lets stick 
to AR1/AR2.

So anyway, as the time progressed, parts of the AR2 became redundant. Instead of redesigning 
the boards, Atari simply omitted the redundant parts leaving parts of the AR2 bare. 

Now, for collectors today that can be a bit annoying. When someone says they have an AR2 board 
spare, you often have to try and work out what revision it is to see if it'll work in your 
machine :) below is a list of which games used what revision boards, its not complete, but 
what i've been able to ascertain :

A034485-01 - Asteroids, Asteroids Deluxe, Lunar Lander, Football (4 Player)

A035435-01 - Atari board versions of Xevious, Pole Position I + II, DigDug

A035435-02 - Battlezone, Centipede, Crystal Castles, Liberator, Quantum, Red Baron, Star Wars, 
Tempest, Warlords, Return Of The Jedi, Arabian, Black Widow, Major Havoc

A035435-03 - Missile Command, Monte Carlo

A035435-04 - Gravitar, Millipede, Space Duel

A035435-05 - Namco Board versions of  Pole Position I + II, Xevious, DigDug

A035435-06 - Kangaroo


Now, you think, why is this important to me?? Well, you might not be able to find the precise 
revision for your machine, this is a handy cross-reference. In all honesty, if in doubt, use a 
revision -02, if you have one of these, it will work on ALL of them, and they are the most 
common :) Golden rule? The later the revision, the more parts they strip off.. with the 
exception of the -01 which is the least populated version, no idea why it got the -01 
revision.. When re-thinking the design, certain things were taken into consideration, cost to 
produce, pros and cons.. so you find that the -03 board is actually loaded like an -02 baord 
but without the numerous test points... pros.. cheaper/quicker to produce, cons... you can't 
hook equipment onto the test points.. big deal :) well.. you say that, because after the -03, 
they went back to using the -02 as operators didn't like the idea they lost the test points.. 
the customer is always right eh? 
The -05 and -01 revisions may seem a little odd, its the same game, why two different board 
versions?? well, those games listed were actually licenses that atari bought off of Namco 
(japan). Atari made up the cabinets and filled them with either namco boards or their own 
boards, either to meet demand quickly when it had a japanese release timed with a european 
release or what i don't know :) Anyway, some cabinets had namco boards, and some had atari
boards, the namco boards always had the audio amplified on the game PCB, like the rest of the 
industry by this point, but Atari insisted that their version of the board would require 
external amplification, et voila, one revision of the AR2 had the audio amp section on it, the 
other didn't..

Ok, history lesson over... HOW DO YOU FIX THEM?

Well, a lot of people go for shotgunning the entire board, you can buy 'kits', much like 
monitor cap kits, which contain all the critical components on the board. Regardless of the 
problem on the AR2 you buy a kit and replace everything accodring to the instructions. This is 
good in a way if you don't want to hunt down the problem and fix it manually, besides the AR2 
has a number of large capacitors which like all electrolytic capacitors can dry out, causing 
irregularities, or drifted values. The downside? well its a good afternoons work to do it 
properly, and you might get away with only spending £2 fixing it rather than £10. Or you might 
just like a challenge :)

My way? ahh, it may be a bit of a bodge if you want to call it that, but it works for me, and 
even if you do fit a 'kit' to your board i would reccommend carrying out this further mod 
anyway....

First, a little bit of a theory lesson.. what does the AR2 do? well, it supplies the game PCB 
with a nice clean set of voltages, +5v -5v +12v +/-22v and 10.3v unreg. It also amplifies an 
audio signal from the pcb to drive the main speakers in the cabinet. Now the +5v supply is the 
nifty bit, and really, the most important bit. +5v drives the main game logic. Now, 20 year 
old game PCB's don't like to have the +5v jumping about going from roughly +3.5v to +6.5v, 
they want a nice steady +5v they can rely on. This is where an OLD AR2 falls on its face.. 
Atari thought it'd be cool to make the AR2 intelligent. Bad move. We all know what happens to 
inteligence as we get older ;) 

Anyway, the best way to think of it is this.. the AR2 pumps out +5v to the game board, but 
also has an extra feed coming from the game board to the AR2. The AR2 then measures what 
voltage is coming back from the game PCB. If there is a difference, it cranks up the output a 
little bit to compensate for the loss. Loss of voltage is expected in a few metres of wiring 
running round a cabinet, and plugs/edge connectors. But what happens 20 years down the line 
when you have tired old wiring, and dirty oxidised connections that you either dont think to 
clean, or can't clean efficiently? the AR2 isn't doing anything wrong really, its doing its 
job, but it assumes that there shouldn't be more than a 0.1v voltage drop in the wiring in a 
cabinet. If the connections are so dirty, or have accidentally been broken or whatever, the 
AR2 keeps cranking up the voltage to try and match its output. What can happen is you can see 
the voltage going up and down as the AR2 tries to keep up. if you measure the voltage on a 
game pcb and see the +5v going up and down, be scared, this is when components fail.

Solution: fool the AR2 into thinking everything is hunkey dorey...

How? where the lines for the +5v leave the board and where the return (sense) lines come back 
in, simply tie them together. By tying them together at the output, the AR2 will be reading a 
return voltage of precisely what voltage its just put out.. simple.. it isn't measuring a loss 
and therefore wont try to compensate. The easiest way to do this is to locate J7, this is the 
connector responsible for the +5v output and return. Turn the AR2 over onto its back and 
solder onto the reverse where the pins for the connector are in place. see diagram 1 for 
instructions on where to put in the links. Use something like fuse wire or a component lead to 
solder over them, something pretty thick, it can carry a bit of current, so make it thick on 
the safe side.. The idea is to tie pin 1 to 2 and pin 3 to 6 remember to translate the diagram 
in reverse when you flip the AR2 over :) the top side of the AR2 board should be labelled 
which pin is which. 

The only other thing i usually do is replace the 2N3055 power transistor that sits right in 
the middle of the massive heatsink, they are the main powerhouse for the +5v it appears, so 
you want that to be nice and reliable. They are really easy to find, general purpose kinda 
component, they still make them today so usually about £1.50 that will cost ya. Remember to 
make sure when fitting a new one in that the case doesn't touch the metal heatsink, there is a 
little rubber insulating mat inbetween the transistor and the heatsink.. it is there for good 
reason, it is a heat conductive layer that electrically insulates at the same time. Just make 
sure it goes back on properly :)

Bingo.. that's all i usually do, and that has kept my 4 machines which use an AR2 happy :)

common faults? well if burnout has occured in the past, its often apparent that R29 and R30 go 
nuclear, often bursting into smoke and cratering the board. if you can botch a repair in, 
replace them and carry out the steps above and you shouldn't have any more problems.. some 
people say that R30 should be swapped with a higher wattage resistor, i've personally not done 
that as its better for that resistor to smoke than the little regulator (Q1) which is 
virtually unobtainable. 

Once you've suitabley rectified the AR2, all that remains is to install it in your game and 
power her up.. Of course, now is the time to go round and clean/replace those edge connectors, 
and check for shorts or broken wires. I know its tedious to clean/inspect everything, but hey, 
you want your game to last yeah? do it then :) once installed in the machine and powered on, 
put your voltmeter on the GND and +5v test points ON THE GAME PCB and read off what the board 
is getting on the +5v line. Adjust R8 on the AR2 to get a nice +5.00v - +5.10v reaching the 
game board and you're all set :)

If you neglected to clean the edge conectors and you close the back door disturbing the 
wiring, you could now have knocked that nicely measured +5v to something else... go clean them 
connectors :) If you hadn't carried out the afformentioned mod, now is the time the AR2 would 
probably be squeeling and spitting smoke. If you appear concerned by how hot the 2n3055 gets 
after such a short time of being turned on, don't be, look at the size of the heatsink its 
bolted to :) 

ok, just briefly things to look at if you have certain symptoms :

*lack of -5v - check Q9 (7905) bolted to heatsink
*lack of +12v - check Q8 (7812) bolted to heatsink
*lack of audio, or distorted audio in speaker 1 - check Q5 (TDA2002)
*lack of audio, or distorted audio in speaker 2 - check Q7 (TDA2002)

enjoy

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