Defender: 'Thrust' always on

[MonsterBash]

I did go over it a coupe times. The last time I completely removed the solder and the pin (pin 9) and it still stayed on.

Sooner or later it'll bug me enough and I'll figure it out

You mentioned reflowing the pins on the interface board before all this trouble started?

I'd go looking for a solder bridge on that board somewhere.

 

[cdjump]

i don't have the schematics handy, but if there's a debounce capacitor on the stuck input line, clip one leg and see if that fixes it. I'm seeing that more and more on mcr stuff.

 

[MonsterBash]

I'll have to look into that.

It's weird because the thrust isn't on all the time..only about 95% of the time. Kinda like playing the game..and taking your finger off the button for a second..then putting back on.

As the game got played (not just sitting in attract mode..but actually playing games) it was down to like 50% of the time on, and at one point almost cleared up all together. The more it was played..the better it got. During the whole time the thrust 'button' still worked from the CP.

Something else I was thinking about..the thrust 'button' is the only button on defender (minus the up~down joystick) that can continuously stay 'on' where the rest of the buttons are 'press for one action..then press again' (how cool would a rapid fire mod be?). I know nothing about circuitry but..this tells me that button is handled differently than the rest..and the problem probably lies where ever this difference is

i don't have the schematics handy, but if there's a debounce capacitor on the stuck input line, clip one leg and see if that fixes it. I'm seeing that more and more on mcr stuff.

 

[YellowDog]

I'll have to look into that.

...

Something else I was thinking about..the thrust 'button' is the only button on defender (minus the up~down joystick) that can continuously stay 'on' where the rest of the buttons are 'press for one action..then press again' (how cool would a rapid fire mod be?). I know nothing about circuitry but..this tells me that button is handled differently than the rest..and the problem probably lies where ever this difference is

There is no debounce capacitor on the Williams classic I/O cards. All debounce is done in software.

The most likely cause is either:
(a) the 4049 chip that inverts the ground signal is going bad, but is not quite completely dead.
(b) the 6821 PIA is going bad, but is not quite fried on that channel yet.
(c) there is a hairline crack on a trace or a cold solder joint
(d) there is an unintended ground connection on the thrust wire somewhere (solder bridge on the leaf switches, crack in the insulator between the leaves, someone used too large of a screw and bridged the leaves, a crack in the wire from the leaf switch allowing a ground contact, etc.)

ken

 

[andyman]

Might be an alarmingly obvious one but have you checked the thrust switch itself, ignore me if this has been done.

Andy.

 

[MonsterBash]

Yeah..

It does it with the CP cabling disconnected from the I/O board

Might be an alarmingly obvious one but have you checked the thrust switch itself, ignore me if this has been done.

Andy.

 

[Shavenyak]

There is no debounce capacitor on the Williams classic I/O cards. All debounce is done in software.

The most likely cause is either:
(a) the 4049 chip that inverts the ground signal is going bad, but is not quite completely dead.
(b) the 6821 PIA is going bad, but is not quite fried on that channel yet.
(c) there is a hairline crack on a trace or a cold solder joint
(d) there is an unintended ground connection on the thrust wire somewhere (solder bridge on the leaf switches, crack in the insulator between the leaves, someone used too large of a screw and bridged the leaves, a crack in the wire from the leaf switch allowing a ground contact, etc.)

ken

I had a success tonight, so I thought I'd share for anyone interested and the archives. My problem lately has been thrust stays on and the ship staying up (top of the screen). I don't know what a debounce cap is but there's a normal cap on the board near the ribbon cable. I replaced it (original) and I'm back in business. It's SO nice when it's an easy fix.

 

[ringwar]

The interface board doesn't have many chips. Look at the schematic, replace and socket the cheapest ic's first. If you haven't removed any ic's before, the easiest way is to clip the legs and pull one leg at a time while heating the solder.