Problems with an XG-1 gun and the 7800: stuck on autofire?

[+GoldenWheels]

I got an untested XG-1 gun from ebay recently. Price was right (enough).

 

Upon plugging it into my 7800 for Crossbow (only gun game I have) and in the choosing a path screen (and level one for that matter), the gun just fires. All the time. I can aim, and the cursor moves, it is firing where I aim. It just won't STOP firing.

 

Any ideas? I'm not using an extension cord in this case. Straight into the system. Trigger seems to be fine; that is, it is not stuck in the "fire" position and it seems to be depressing the switch fine inside. Click, click...damn thing just won't stop firing!!!

 

(I have an XE but no Bug Hun or Barnyard Blaster to test it there with.)

[+David_P]

You should be able to test the trigger on the XE. I think the trigger is the same as the joystick trigger, so try:

 

10 GRAPHICS 0

20 PRINT STRIG(0)

30 GOTO 20

 

RUN the program with the gun plugged in to the first port, then watch to see it the value is changing when you pull the trigger or not.

[+GoldenWheels]

You should be able to test the trigger on the XE. I think the trigger is the same as the joystick trigger, so try:

 

10 GRAPHICS 0

20 PRINT STRIG(0)

30 GOTO 20

 

RUN the program with the gun plugged in to the first port, then watch to see it the value is changing when you pull the trigger or not.

 

D'oh! I don't have a keyboard for it!

[+Mitch]

You should be able to test the trigger on the XE. I think the trigger is the same as the joystick trigger, so try:

 

 

No, the trigger on the gun is the same as up on the joystick.

 

Mitch

[+GoldenWheels]

So I guess I have to buy an XE gun game and see if it works? Is that the only way to fish this out?

 

I opened the gun up and it LOOKS fine.

[+Stephen Moss]

I do not know about this specific model however a typical light gun circuit consists of a phototransistor and resistor, a switch and a logic gate, usually either a 7400 (NAND) or a 7408 (AND).

The switch acts as a gate placing one of a gates two inputs into the correct state to allow output of the phototransistor to change the output of the gate.

 

Clearly the output from the light gun appears to be holding the input to the VCS stuck in either the High (+5v) state or the Low (0V), typically Atari inputs are active low.

Some light guns have an autofire switch, if that is true for this model ensure it is in the autofire off position and check the switches are function correctly by measuring its/their resistance.

 

For two pin switches you should get approximately 0 ohms when it is one position and infinity when in the other, for three pin switches you should get approximately 0 ohms between the center pin and one end and infinity between the centre pin and the other end which should swap when the switch is in the opposite position.

 

Change the switch if it appears to be defective, it the switch appears to be OK then there may be a bad solder joint on the logic chip, try re-heating the joints and adding a little extra solder.

 

I can not give more specific instructions without access to a circuit diagram (preferred) and/or a detailed description of how it operates.

[+GoldenWheels]

Stephen I appreciate your input a lot but sadly 95% of it is over my head.

 

I can safely say there is no auto-fire switch. I can say (which I learned here) that the XG1 is not a typical light gun but more of a light pen. The difference I don't actually understand myself but I guess is the reason you can't just use, say, a Sega gun with an Atari.

 

Dollars to donuts says I have to break down and buy the Best light gun. Too bad as my goal was to have all "official" Atari gear, but I just can't find the XG1 at a fair (to me) price and I read that (anecdotally at least) the Best gun performs better anyway.

 

I really wanted to paint the XG1 black though....I wonder if I can transfer the best guns guts to the atari casing!