Help with a Williams (Robotron) I/O board problem.

GaryMcT

Active member

Donor 2011
Joined
Jun 4, 2009
Messages
2,346
Reaction score
24
Location
Carnation, Hawaii
One of the inputs (movement up) didn't work on my friend's Robotron. We swapped I/O boards with his Stargate to see if that was the problem, and it is the problem. I checked the resistors that are the first thing that you hit when you hit the I/O board and they seem fine. I'm not sure how to test capacitors with the equipment that I have (fairly new at electronics). What would you do next to debug the problem?

Thanks!
Gary
 
I would check the inverter at IC6 next. Make sure the input to the inverter is correct first by check the voltage at pin 7 - it should be around 5V. When you move the joystick up, it should go to 0V.

Now check the output at pin 6. It should normally be around 0V, and when you move the joystick up it should go to 5V.

I had the same problem on my Joust awhile ago (only it was "P1 move left" that stopped working) and the inverter IC was the culprit.
 
Any fix for this? I have a bubbles with same input problem I think. Cocktail version and both sides just go right together or left together weird!!
 
Unfortunately, the 6821 PIA commonly causes problems. The input tests in the diagnostics will usually show when this is the case. If the diagnostics shows Invalid Switch, then my experience has been that the PIA has an internal short.

The 74LSx57s don't typically go bad, however as already stated, be sure to check the 4049 inverters. The inputs should be high and outputs should be low. Switches pull the inputs low and set the outputs high. You can easily check this with a DMM.

I like to put my DMM on the diode setting, clip the + lead to the ground and then check the output pins of the ICs with the - lead. All outputs should show a standard diode voltage drop of around 0.7 volts. If you are seeing a dead short or open, that IC is likely bad. Do this with the board disconnected and not powered, of course.

Kirk S.

P.S. I fix Williams stuff...
 
Back
Top Bottom