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More 2600 Technical Fun - Player 2 shoots constantly



Here is an issue that I've seen before in one form or another and I thought I would talk about it here while working on a earlier era 2600 heavy sixer last night. The system was sent in for refurbishment. In this case that is all the original electrolytic capacitors being replaced out, new DC power jack, new voltage regulator etc. But a problem was reported and confirmed during testing of the console.

What was the issue? In this case it was an issue with the player 2 controls. Specifically, player 2's fire button was always registering as being pressed. Easiest game to demonstrate this was Air-Sea Battle as when you reset the game to start, player 2 is constantly shooting the entire time even without a controller plugged in. Part of the refurbishment process is changing some components near the joystick port per an Atari service bulletin from back in the day for ESD protection.

It is the last part in regards to the ESD protection that needs focus, because it was found that static electricity from players hands when inserting and unplugging the joysticks, would cause static discharge to the joystick pins. Luckily for most this is pretty harmless but one component in particular on the heavy sixers is very sensitive to this and prompted Atari to create the service bulletin to address it.

The specific component to be checked is labeled as A203 on the main board. While the original IC chip has an Atari PN labeled on it, the chip is a bog standard 4050 IC that was common on the 8-bit line, 5200, some 2600s and lots of other devices. So common in fact, that the 4050s are still made today. However, on the heavy sixers, the trigger lines (Fire button) goes through the 4050 chip and in turn relayed back to the TIA. The most basic way it works is that +5v is always present on pin 6 of the joystick port which is the trigger line for each controller. When you press the fire button, you ground this connection causing the +5 to drop to near 0. This is what is referred to as going from Hi to Lo and is how the system knows when controller inputs are being used. In the case of this 2600, pin 6 from joystick port 2 was not showing any voltage from it and as a result, this was being interpreted by the logic in the system as if the fire button was already being pressed down. The basic troubleshoot process here is to verify the traces from pin 6 back to pin 7 on the 4050 IC chip and ensure there are no broken traces. If that checks out, then the culprit is down to two component at that point being The 4050 IC or the TIA itself. 

Anyway, per the service manual flow charts and because I found no issues with the traces on the board, I removed the original 4050 IC chip, installed a socket and new 4050. Let it burn in test for several hours last night and verified that player 2 is now behaving properly and not so short tempered.

So in this case it was an easy fix but also a warning on why ESD was and still is an issue to this day. In this case, an errant spark from someones hand in the past damaged something internally in the 4050 IC causing it to no longer function properly in regards to the player 2 fire button.

Replacement 4050 IC installed in new socket however, I did eventually replace this 4050 out also with a new Ti branded one as this on would cause graphic visual issues after a while.




Just a pic showing the soldering work after installing the new socket and 4050 IC chip.




Here is one of the new cap+diode component fixes applied to port 2 at location C237 as stated in the Atari service bulletins. There is another component set like this on the player 1 port C236 location as well.



Edited by CrossBow
Fixed pic rotations. added additional information

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Awesome write up.  I'm such a nerd that the minute I saw the symptom, I knew it was the 4050 chip. 

You've done a beautiful job on that repair.  Using a socket and really nice soldering.


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