English Amiga Board - View Single Post

Daedalus · 08 March 2018, 10:27

I don't have the rev 5 schematics to hand, but on the ref 6 schematics, that looks like an EMI suppressor - the small 3-legged components that are placed on almost every I/O pin on the A500. This part is simply a resistor and a capacitor arranged with the resistor in series with the signal and the capacitor between the signal and ground. The values of the resistor and capacitor parts vary with the type of signal involved - it looks to me like that part is connected to pin 7 of joystick port 1. That would make sense, as that line carries +5V power and so has the current available to burn it through if it shorts. If that's the case on your board, check for a short between pin 7 and ground. If there is none, a 4.7 ohm resistor should do the job just fine, as that's what is used for that job in the A600 and 1200.

08 March 2018, 10:27	#16
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,335	I don't have the rev 5 schematics to hand, but on the ref 6 schematics, that looks like an EMI suppressor - the small 3-legged components that are placed on almost every I/O pin on the A500. This part is simply a resistor and a capacitor arranged with the resistor in series with the signal and the capacitor between the signal and ground. The values of the resistor and capacitor parts vary with the type of signal involved - it looks to me like that part is connected to pin 7 of joystick port 1. That would make sense, as that line carries +5V power and so has the current available to burn it through if it shorts. If that's the case on your board, check for a short between pin 7 and ground. If there is none, a 4.7 ohm resistor should do the job just fine, as that's what is used for that job in the A600 and 1200.