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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: bolt on April 09, 2011, 10:16:28 AM
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Hi!
I've got an Amiga 500 where the mouse and joystick ports have stopped working properly. The mouse only goes right and down, and the joystick only goes left and right.
From searching on google, I found that the problem might be the multiplexer, or the Denise chip.
I replaced the Denise chip with one from another, working machine, and desoldered the 74hc157 mux and replaced it with a brand new one. The exact same issue remains :furious:
I then started logic probing the board, and found that while both X and both Y signals from the mouse, and all 4 directional signals from the joystick reach the mux, only left and right from the joystick port and only 1 signal of each axis from the mouse exit the mux.
Thus I get the idea the mux isn't switching between the inputs as it should. I followed the A/B input from the mux to pin 6 of an "octal tranceiver" next to Denise. The connection to the transceiver has a resistance less than 1 ohm, so that should be fine.
I don't know enough about the hardware to determine what should be providing the input to the transceiver, or what else could be wrong.
Can any of you help? Anyone who has had similar issues?
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Check that R404 is 120 Ohms and if that is fine, replace U33 (74F04).
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The signal involved is named _CCK and comes from Agnus. So you could try swapping that out also.. In case another chip is shorting it out, it also goes to Paula and the external expansion slot.
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The signal involved is named _CCK and comes from Agnus. So you could try swapping that out also.. In case another chip is shorting it out, it also goes to Paula and the external expansion slot.
CCK comes from Agnus. _CCK comes from the 74F04 inverter at U33.
If the problem was the CCK clock from Agnus, it's likely there would be other problems besides the mouse/joystick as CCK is used by Paula, Denise, and Gary.
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Could be...
Also might be the 74HC245 at U41 loading it down.
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Thanks for all the suggestions. I'll give these a shot and report back :)
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If the problem was the CCK clock from Agnus, it's likely there would be other problems besides the mouse/joystick as CCK is used by Paula, Denise, and Gary.
All other functions seem to be working fine. Games which only require right/left/fire can be played, sound works and everything.
I will try with the Agnus chip from the other machine anyway though, just in case.
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Check the 8520s.
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Check that R404 is 120 Ohms and if that is fine, replace U33 (74F04).
I cannot find the R404. Do you know where it's located?
I can find all others in the range R402-R406 however.
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CCK comes from Agnus. _CCK comes from the 74F04 inverter at U33.
If the problem was the CCK clock from Agnus, it's likely there would be other problems besides the mouse/joystick as CCK is used by Paula, Denise, and Gary.
The spare Agnus I have looks to have some damaged pins anyway, so I'm not able to replace it.
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Check the 8520s.
According to first reply in this other thread they are not related to the problem, but I changed them anyway, and it did not help:
http://www.amiga.org/forums/showthread.php?t=51194
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I cannot find the R404. Do you know where it's located?
I can find all others in the range R402-R406 however.
What revision is your motherboard?
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What revision is your motherboard?
6A
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Still can't find the thing :/
I might be blind, however... :confused:
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Still can't find the thing :/
I might be blind, however... :confused:
Not blind. Revision 6A boards don't seem to have R404. That might have something to do with it.
Check if the connection between pin 4 on U33 and pin 1 on the 74HC157 is Ok and make sure that pin 3 on U33 isn't shorted to ground.