AR1 Sense Mod?

jeffsgames

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I have an Asteroids cocktail that has an AR board that has a burned diode at CR3. I did an AR1 repair kit from Bob Roberts, but it didn't come with the diode. This looks like it is the same problem as the Resistor on the AR2 that has a problem from the sense circuit. Does this board have that same Sense circuit, and would it be a good idea to replace this diode with a jumper to disable it like in the AR2? I see all kinds of info on the AR2 mod, but nothing on the AR1.

Any advise? Thanks!
 
Does this board have that same Sense circuit? I see all kinds of info on the AR2 mod, but nothing on the AR1.

Yes, the AR1 has a sense circuit very similar to the AR2.

Your burned diode is telling you that there's significant resistance in the +5V path from the AR board to the PCB. Check your connectors, pins/terminals & edge traces.

I am unqualified to advise on how to do a "sense mod" as I've never done one. I personally choose to repair the as-designed power paths, and leave the sense circuit intact.
 
Yes, the AR1 has a sense circuit very similar to the AR2.

Your burned diode is telling you that there's significant resistance in the +5V path from the AR board to the PCB. Check your connectors, pins/terminals & edge traces.

I am unqualified to advise on how to do a "sense mod" as I've never done one. I personally choose to repair the as-designed power paths, and leave the sense circuit intact.

+1

I try to keep things the way they were intended as I am not an EE. I do some mods as a temp to diagnose the problem with the boards.

An example where I had to replace a mod was on my Galaxian that I am having a terrible time with. There was a mod with the clock circuit and when I remove all that was done and replace the parts I had no clock. I looked at the mod a previous tech grounded pins 1 and 15 of a 74ls368. When I replace that mod I had my clock back. That was probably a repair but I had no idea at the time.
 
The sense mod on an ARII definitely has both good and bad points. On the good side, the board can't blow itself up if the connector to the game PCB works loose or gets high resistance in the +5 path. This reduces the likely hood of having to re-do the ARII fixes over and over, and reduces the probability of burning traces to the main PCB.

On the down side, the ARII is no longer able to adjust itself automatically to changes in the PCB - if the connector gets a little bit high resistance, the +5 on the PCB could drop down enough that the PCB won't work well.

I've personally done the sense mod to my ARII because I didn't want to replace the PCB connector right now (it's pretty loose), and I don't want the ARII blowing itself up if the thing works loose again.

If you've got time to fix it right (replace or re-pin the PCB connector), then you really don't NEED the sense mod. If you don't have that time, then the sense mod is going to save you some diodes and soldering till you can.
 
I've personally done the sense mod to my ARII because I didn't want to replace the PCB connector right now (it's pretty loose), and I don't want the ARII blowing itself up if the thing works loose again.


Just an FYI......if your connector pins have lost their tension....You will burn up the motherboards "fingers" (regardless of sense mod, or not).

This is why I HATE the sense mod. IT WILL NOT FIX A SHOT CONNECTOR. This is an urban myth, perpetuated by internet mis-information. The sense mod IS NOT a fix at all. It's a band-aid.

Here's the hard facts.....when the pins inside an Atari edge connector lose their tension several things will happen: the two "sense" resistors on the A/R II board will burn up (on an A/R I board, it will be diodes)....sometimes only one will burn if caught in time. Next, you can burn up the motherboard's "fingers". This is happening because the edge connector has lost it's "spring tension", maybe the motherboard's fingers are oxidized......basically, where the edge connector and the motherboard connect, this connection is no longer "solid". This is the problem, and THIS needs to be addressed. So, what happens if you do the sense mod and do not address the actual problem? Well, let's examine what you just did. By doing the sense mod, you just jumpered the sense circuit to 5VDC. So, the A/R board is now using an additional path to send 5VDC to the motherboard.....seems like a GOOD idea, right? Well, in theory it is....but there's a fatal flaw in this theory. YOU DIDN'T REPLACE THE EDGE CONNECTOR'S PINS. We already know the edge connector's connection point is compromised. If it wasn't, you wouldn't have had the sense resistors burn. So, what are the consequences of what you just did. Since you didn't replace the edge connector's pins, they are still a weak point. They are still going to generate heat. So, instead of burning up one or two 1¢ resistors.....you're going to burn up your motherboards edge connector's fingers. This will take a bit longer, since the sense mod spreads the 5VDC line out over a few more wires.....but the nature of how the sense circuit works, the connection point of these (additional wires) has already been comprimised.

If your sense circuit is fine, and you're doing the sense mod as "preventative maintenance".......keep this in mind.....the sense resistors are the weakest point in the link. They almost always go first. You see the edge connector on these motherboards burning up because someone keeps replacing the resistors, and nothing else......so, at some point, the edge connector starts to burn (after all, it is the actual problem). So, your preventative maintenance just disabled your "early warning sign".

If you're going to do the sense mod.......at a bare minimum, replace the grounds and 5VDC pins in the edge connector (or have fun with a cooked motherboard in the future).

Rant over! (now go fix your edge connectors)

Edward
 
I definitely plan to replace the edge connector pins right away. I might even jump some direct power leads to the PCB to ensure solid connection like I did on my Pole Position.

I've always thought the Sense mod would prevent too much voltage from being sent to the PCB. I've always done that for a safety fix. I thought it would prevent the AR from passing too much voltage to the PCB, even if it wasn't passing 5V. I can live with too little voltage going to the PCB and having to adjust or repair the AR, but what I don't want is the AR trying to send too much voltage because it thinks there isn't enough. Is this logic incorrect?
 
I definitely plan to replace the edge connector pins right away. I might even jump some direct power leads to the PCB to ensure solid connection like I did on my Pole Position.

I've always thought the Sense mod would prevent too much voltage from being sent to the PCB. I've always done that for a safety fix. I thought it would prevent the AR from passing too much voltage to the PCB, even if it wasn't passing 5V. I can live with too little voltage going to the PCB and having to adjust or repair the AR, but what I don't want is the AR trying to send too much voltage because it thinks there isn't enough. Is this logic incorrect?

You're on the right track. A properly working sense mod will detect voltage drop and adjust accordingly. Now, when you disable the sense mod....the A/R board will not increase the voltage. Here's the problem (if you don't fix the edge connector).....say the A/R board is working properly....pumping out 5.05 volts DC to the motherboard. That 5.05V is a constant....never changing, but......you have weak pins in the female connector housing. So, you have 5.05VDC going from the A/R board and up to the weak pins. Because the pins are weak, they are only "transferring" 4.85 volts DC to the motherboard "fingers". This point of voltage loss is going to generate heat. As it heats up, the connector pins will lose more tension and "bite" less.......thus generating (even) more heat......thus degrading the connector pins (even) more. At some point, say hello to a burnt motherboard! This voltage loss and subsequent heat generation will happen regardless of sense mod or not.

Edward
 
You're on the right track. A properly working sense mod will detect voltage drop and adjust accordingly. Now, when you disable the sense mod....the A/R board will not increase the voltage. Here's the problem (if you don't fix the edge connector).....say the A/R board is working properly....pumping out 5.05 volts DC to the motherboard. That 5.05V is a constant....never changing, but......you have weak pins in the female connector housing. So, you have 5.05VDC going from the A/R board and up to the weak pins. Because the pins are weak, they are only "transferring" 4.85 volts DC to the motherboard "fingers". This point of voltage loss is going to generate heat. As it heats up, the connector pins will lose more tension and "bite" less.......thus generating (even) more heat......thus degrading the connector pins (even) more. At some point, say hello to a burnt motherboard! This voltage loss and subsequent heat generation will happen regardless of sense mod or not.

Edward


OK with that scenerio if the sense circuit is still intact, won't you still have the problem with the heat generating on the connector pins? But in that case won't the AR board send EVEN MORE voltage increasing the heat even more? I guess that's the main concern I have. Obviously if the resistor burns way before that heat buildup then great, but if not would there be a potential issue?

One more quick question. Can the traditional R30 resistor be used on the AR1 board instead of a diode, or do I have to have a diode in that circuit?
 
OK with that scenerio if the sense circuit is still intact, won't you still have the problem with the heat generating on the connector pins? But in that case won't the AR board send EVEN MORE voltage increasing the heat even more? I guess that's the main concern I have. Obviously if the resistor burns way before that heat buildup then great, but if not would there be a potential issue?

One more quick question. Can the traditional R30 resistor be used on the AR1 board instead of a diode, or do I have to have a diode in that circuit?

Basically, in a nut shell......if the connector is weak (on power or ground rails).....it's going to burn. In a home use enviroment, a new edge connector should last a very-very long time (unless you're one of those people who leave their games on all the time). With the sense circuit intact....the weakest link is the 10 ohm resistors (on A/R II.....in your case the diodes on A/R I). They usually go first, but you can still get motherboard burn. This all happens very slowly. It takes quite awhile for those resistors (or diodes) to open up. While they're cooking, the motherboards edge connector is definately heating up. It ultimately depends on who long the problem is let go. Now, with the sense mod.....there's nothing left to burn but the motherboards edge connector (albiet, this would even take longer to happen....since the 5VDC and grounds are now spread out even more, using the sense circuit's connection points as voltage and ground paths to the motherboard). All of this assumes we're talking about a game WITH a new edge connector.

There is no right or wrong. Well, there is a wrong....not replacing the edge connector....and thinking you're not going to have issues:).

Edward
 
How about my other question: Can the traditional R30 resistor be used on the AR1 board instead of a diode, or do I have to have a diode in that circuit? Is the entire design the same or is it different enough that a diode must be used? I'm asking because I have several resistors but no diodes. I'll need to buy some if I plan to not do the sense mod. I've heard the layout and design are the same but I haven't looked at the schematics to verify this.

Also, Bob's AR1 rebuild kit says to "upgrade" the 1000µf capacitors to 3300µf. Does that sound right? They work, but is that "safe"?
 
How about my other question: Can the traditional R30 resistor be used on the AR1 board instead of a diode, or do I have to have a diode in that circuit? Is the entire design the same or is it different enough that a diode must be used? I'm asking because I have several resistors but no diodes. I'll need to buy some if I plan to not do the sense mod. I've heard the layout and design are the same but I haven't looked at the schematics to verify this.

Also, Bob's AR1 rebuild kit says to "upgrade" the 1000µf capacitors to 3300µf. Does that sound right? They work, but is that "safe"?

The AR1 & AR2 circuits, while very similar, are not identical aside from the R29/R30 vs CR2/CR3 difference (R1 & R6, at least, differ between the two). It'll probably work with resistors instead of diodes, but I won't guarantee it. However, the diodes in question are one of the most common types on the planet (1N4001). Go to Radio Shack and get some (1N4002, 1N4003 or 1N4004 will work fine as well, they just have higher voltage ratings).

The capacitors in question are in the audio amplifier circuit, not a voltage regulation circuit. They're the output coupling caps. Changing from 1000µF to 3300µF is certainly "safe". It may change the frequency response of the amp a bit... but it is safe (so long as it has the proper voltage rating and is installed correctly).
 
The AR1 & AR2 circuits, while very similar, are not identical aside from the R29/R30 vs CR2/CR3 difference (R1 & R6, at least, differ between the two). It'll probably work with resistors instead of diodes, but I won't guarantee it. However, the diodes in question are one of the most common types on the planet (1N4001). Go to Radio Shack and get some (1N4002, 1N4003 or 1N4004 will work fine as well, they just have higher voltage ratings).

The capacitors in question are in the audio amplifier circuit, not a voltage regulation circuit. They're the output coupling caps. Changing from 1000µF to 3300µF is certainly "safe". It may change the frequency response of the amp a bit... but it is safe (so long as it has the proper voltage rating and is installed correctly).

Interesting! Thanks for your help! I will run by Radio Shack on my way home from work tonight. This is REALLY helpful!
 
OK I picked up some of the diodes from Radio Shack and replaced the two on the AR1 board. I also added some power wires to the PCB for GND and +5V. I've started to make a new connector for the wiring harness. I got about 10 pins in and am calling it for the day. Should finish up later this week.

Thanks everyone for the help!
 
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