I have an A310 machine here which I thought was working fine! Just opened it up, chucked out the old batteries and gave the contacts a clean and replaced, DEL-power on and everything else looked great!
It had no FDD. So I took one out of a donor, and when I tried to read a disc, the FDD LED lit up and stayed on. The machine became unresponsive but the mouse still moved ok, a reboot fixed it. I tried another FDD and the same thing happened![:(]( "Sad")
So I got out the oscilloscope and noticed that when I probed pin 1 (CS) of the 1772-02, I saw a decaying voltage followed by the machine crashing. My theory is that either IC46 or the 1772-02 are goosed and have such a high impedance that the probe is drawing the current? Not sure if that makes much sense but maybe somebody can tell me if that's possible!
Anyway I got a logic analyzer as I wanted to check IC46 in case that was at fault.
I attached probes to 1 (/PRE) and 2 (/PWE) and 3 I wanted to see if 3 was driven HIGH when either input went LOW. It didn't it was just permanently HIGH. So I tried 9 (/S1) and 8 (since 10 is 5V), again 8 is permanently HIGH.
I did also try attaching pin 6, the output to the 1772-02's /CS expecting the machine to crash like it did when I put the oscilloscope on there but it didn't, it just stayed HIGH too.
I am going to break out these pins to a breadboard and replicate the function of the IC46 NAND chip using a 74LS00N I have here and see if it works as it should. Probably not necessary, but I am just learning here and want to make totally sure I don't pull out a good chip.
Cheers!
Nic
It had no FDD. So I took one out of a donor, and when I tried to read a disc, the FDD LED lit up and stayed on. The machine became unresponsive but the mouse still moved ok, a reboot fixed it. I tried another FDD and the same thing happened
So I got out the oscilloscope and noticed that when I probed pin 1 (CS) of the 1772-02, I saw a decaying voltage followed by the machine crashing. My theory is that either IC46 or the 1772-02 are goosed and have such a high impedance that the probe is drawing the current? Not sure if that makes much sense but maybe somebody can tell me if that's possible!
Anyway I got a logic analyzer as I wanted to check IC46 in case that was at fault.
I attached probes to 1 (/PRE) and 2 (/PWE) and 3 I wanted to see if 3 was driven HIGH when either input went LOW. It didn't it was just permanently HIGH. So I tried 9 (/S1) and 8 (since 10 is 5V), again 8 is permanently HIGH.
I did also try attaching pin 6, the output to the 1772-02's /CS expecting the machine to crash like it did when I put the oscilloscope on there but it didn't, it just stayed HIGH too.
I am going to break out these pins to a breadboard and replicate the function of the IC46 NAND chip using a 74LS00N I have here and see if it works as it should. Probably not necessary, but I am just learning here and want to make totally sure I don't pull out a good chip.
Cheers!
Nic
Statistics: Posted by nicf82 — Fri Mar 29, 2024 8:13 pm