Background, I've been working on a Williams System 11 F-14 Tomcat board, which has been had quiet a few bad components. Several of the MC6821 PIAs have been bad, several more that I haven't yet desoldered are probably also bad.
I was looking into testers on the market for these chips and have only found the neoloch tester and a few other pricier options. Today, just by luck I discovered that the more expensive XGecu T56 programmer can test these chips. Since it uses the same software as my cheaper T-48, I was curious why I couldn't test on mine. It turns out that the T-48 lacks the hardware to provide Vcc to pin 20 of the programmer. So I started playing around with my programmer and applying external power to pin 20. I only have a very small sample size of 3 PIAs that I can test, but it identifies my two known bad ones as defective. It identifies the one PIA that I *think is good as normal. I have no idea if I am doing something stupid that could damage the programmer or the PIAs, but it seems like it is working.
If anyone else is feeling particularly brave and has one of these cheap programmers, plus a spare MC6821. Apply 5V external power to pin 20, ground to pin 1, and then run a logic test. I suppose it might be wise to bend pin 20 upward out of the ZIF socket so that you're not sending external power directly into the programmer (I honestly didn't think of doing that until right now).

I was looking into testers on the market for these chips and have only found the neoloch tester and a few other pricier options. Today, just by luck I discovered that the more expensive XGecu T56 programmer can test these chips. Since it uses the same software as my cheaper T-48, I was curious why I couldn't test on mine. It turns out that the T-48 lacks the hardware to provide Vcc to pin 20 of the programmer. So I started playing around with my programmer and applying external power to pin 20. I only have a very small sample size of 3 PIAs that I can test, but it identifies my two known bad ones as defective. It identifies the one PIA that I *think is good as normal. I have no idea if I am doing something stupid that could damage the programmer or the PIAs, but it seems like it is working.
If anyone else is feeling particularly brave and has one of these cheap programmers, plus a spare MC6821. Apply 5V external power to pin 20, ground to pin 1, and then run a logic test. I suppose it might be wise to bend pin 20 upward out of the ZIF socket so that you're not sending external power directly into the programmer (I honestly didn't think of doing that until right now).




