Atari 520 STE - Joystick port failure

[Dlfrsilver]

Hello, i'm writing here because one of my friends (a musician) bought for cheap a 520 STE, and it appears that the joystick port UP position is stuck to "high". When he use a game, the sprite is permanently jumping up without stopping.

He has already reflowed the solders (they were broken, like most of the time). But this has not changed a thing.

What would you advise Exxos ? Could it be the beyboard buffer (74LS244) ?

Thank you for reading me

[rubber_jonnie]

Has the keyboard been tested otherwise and found to be working? Does the mouse port function as expected? Also, does the problem occur with the joystick removed?

I'd suggest that if the KBD processor is socketed, you remove and re-seat it, cleaning the pins on the chip and using Deoxit or Electrolube on the socket.

I'd also suggest a close up examination of the PCB for cracks and/or shorts using a magnifying glass, microscope or possibly use a multimeter in continuity mode.

[Dlfrsilver]

Has the keyboard been tested otherwise and found to be working? Does the mouse port function as expected? Also, does the problem occur with the joystick removed?

I'd suggest that if the KBD processor is socketed, you remove and re-seat it, cleaning the pins on the chip and using Deoxit or Electrolube on the socket.

I'd also suggest a close up examination of the PCB for cracks and/or shorts using a magnifying glass, microscope or possibly use a multimeter in continuity mode.

Ok :

- The keyboard is working from what said my pal, and also the mouse. The solders have been redone on both mouse and joystick ports.
- The problem occurs with the joystick removed.
- the IKBD MCU has been removed and replugged in its socket.

EDIT : with the keyboard PCB unplugged from the motherboard, the sprite is still jumping permanently ! so the problem is on the motherboard

[stephen_usher]

Does it happen with the mouse disconnected? Joystick fire is the same as mouse button 2.

Check for solder bridges on the mouse port in case mouse button 2 line is bridged.

I had something similar when using a "Tom" USB mouse to ST adapter. There was no diode on the button 2 line so it was compensating for the joystick button switch in the circuit, meaning that the joystick fire button didn't work.

[rubber_jonnie]

Has the keyboard been tested otherwise and found to be working? Does the mouse port function as expected? Also, does the problem occur with the joystick removed?

I'd suggest that if the KBD processor is socketed, you remove and re-seat it, cleaning the pins on the chip and using Deoxit or Electrolube on the socket.

I'd also suggest a close up examination of the PCB for cracks and/or shorts using a magnifying glass, microscope or possibly use a multimeter in continuity mode.

Ok :

- The keyboard is working from what said my pal, and also the mouse. The solders have been redone on both mouse and joystick ports.
- The problem occurs with the joystick removed.
- the IKBD MCU has been removed and replugged in its socket.

EDIT : with the keyboard PCB unplugged from the motherboard, the sprite is still jumping permanently ! so the problem is on the motherboard

It could be that there is a problem with the 74LS244, and it is cheap and relatively easy to replace, but it sounds a bit unlikely. I'd be looking for shorts, solder bridges or other damage.

[PaulJ]

You should take a look at the connectors where they are soldered onto the keyboard. They tend to have solder broken from the tension put on the them plugging and unplugging. Much more like likely than a defective chip.

[Dlfrsilver]

You should take a look at the connectors where they are soldered onto the keyboard. They tend to have solder broken from the tension put on the them plugging and unplugging. Much more like likely than a defective chip.

Sorry, my pal already redone the soldering of the connectors. And it appears that the problem appears even when the keyboard PCB is unplugged from the motherboard.

Possibly the ACIA 6850 ?

[tzok]

Keyboard IKBD is connected over serial line to the second (U201) ACIA. If joystick is permanently read up, then there is no other explanation than bad ACIA.

[Dlfrsilver]

Problem found and solved : it was the 74LS247 under the keyboard ! This shit was broken and not working. I advised my friend to replace it, he did it, and tada ! his STE is working again, both mouse and joystick !