Testing a 1488 line driver...

[Gene Buckle]

I've got an Ampro Littleboard that I'm trying to bring back to life. 
Sometime last year it quit transmitting data on Port A (the console port) 
so I shelved it until I had time to look at it.

I've checked the Z-80 DART with a logic probe and I'm seeing data coming 
out of Port A (Pin 15 on the DART) when the machine boots up.  I check the 
input pin on the 1488, and get the same sound (the logic probe chirps with 
each state transition) as I get out of the DART.  However, checking the 
output of the 1488, I don't get anything.  Since I don't want to blow my 
probe apart on 12V, I used an LED to watch the output on the 1488.  The 
LED lights the instant I attach it to the output and doesn't flicker or go 
out when I reboot the computer to make it send data out the port.

The Port should be running at 9600 baud, so I should see at least some 
flicker activity on the LED if the 1488 is toggling the output pin.

Before I spend the time to replace the 1488, I'd like to hear from you 
folks if the chip is actually bad.  Is what I'm seeing indicative of a 
dead 1488?

Thanks all!

g.


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