Amiga.org
Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: sdyates on October 21, 2006, 03:49:21 AM
-
My A300 works very well other than this one small problem:
Playing F/A-18 Interceptor and another game.
It is as though someone in holding down the down arrow or joy down. If F/A-18, the jet ius always trying to pull up and eventually crashes.
I Aliens, the character always moves downward and in another, the action is similar.
I have OS3.1. Could it be that any of my chips may be bad? There ios no hardware damage from a battery leak and the battery is fine.
Thanks
-
Oh, I have a spare A3000 - any chips I could swap out?
-
Been a while, but IIRC the CIAs handle the joystick imputs.
-
I assume you have tried another joystick!
--
moto
-
lol - I have tried other joy sticks... and egt this... it happenes without a joystick or keyboard even hocked up ;)
-
Definitely the CIA or Paula.
--
moto
-
I assume you have tried these games on the other A3000?
-
I will try replacing paula and the CIAs...
And yes, I did try on another A3000. Definately an issue here somewhere.
Awesome guys. Gives me somehting to check before the webcast ;)
-
I replaced both CIAs and even put them in the right direction ;)
Replace Paula.
I replaced and tested each separately. There is no difference noticed.
Other ideas my find friends?
NOTE: The chips I replaced were from another machine where this problem did nto occur. This machine had 2.04.
-
What? All of the joystick/mouse *direction* inputs are read by U450 (Denise).
There are physically only 4 inputs to Denise, but 8 direction inputs from the two ports, so a multiplexer is used to sample between eight lines into four.
Download one of the many joystick testing programs from Aminet such as this one (http://www.aminet.net/package.php?package=util/batch/joytest.lha).
If the "stuck direction" problem occurs on both joystick ports, or more than one direction input, the problem is more likely to be between the multiplexer U401 and Denise, or the Denise input(s). Perhaps a bad socket contact.
If the problem is isolated to one direction input pin only, then you may have a problem with the multiplexer input (unlikely) or something between the multiplexer and the joystick port. Quite often the EMI filters tend to get cracked, but they usually tend to go open circuit so cause no direction movement. In your case, it sounds like there is probably a short to ground on the "down" input.
With the computer powered on but no joystick plugged in, you should be able to measure the same voltage on all direction inputs on the connector, i.e. pins 1 to 4.
Since each direction input is the same separate circuit repeated four times, you have three other references to compare against.
Schematic of the joystick I/O here (http://amiga.serveftp.net/Schematics/A3000_schematics/A3000_08A-Paula-Joystick.png) (bottom left corner) which may explain things a little better.
-
This is great info. I replaced the Denise right away as it was a simple task and the least timely.
I downloaded the application and found that there is certianly a problem getting inputs fromthe joystick port.
I am unfamiliar with U401, its location or if it can be removed witha vicegrip or not ;)
Which other parts could I swap out to diagnose? Or, will I know require a special vendor to do this?
Thanks for your help thus far
-
From memory, the U401 multiplexer is located behind the keyboard socket in the A3000D and soldered in. So no, don't remove it with vice grips :-)
It's not that common for the multiplexer to fail anyway, more likely to be something between the I/O port and the multiplexer.
You should be able to diagnose everything with a digital multimeter.
My advice is to compare the in circuit running voltages between the bad inputs and the good inputs. Most likely the faulty input(s) will be at 0V instead of 5V. Then you can turn off the power and use continuity/resistance measurements to find out what's going on.
-
Have you tried cleaning the joystick port pins with alcohol yet? K.I.S.S.
While cleaning check if all the pins are present and fully extended.