Great write up. I always enjoy the troubleshooting process as much as the fix.
Given that both chips failed at once I would have guessed a static discharge at the external connector. U19 has some direct and unclamped connections to the outside world but U21 has buffers and diode clamps on all lines (except pin 5 which only has a buffer). It could be that U19 and U21 were the most sensitive though. Jeff Birt From: M100 <[email protected]> On Behalf Of Terry Stewart Sent: Thursday, August 20, 2020 4:16 AM To: [email protected] Subject: [M100] Our experiences repairing a faulty RS-232 circuit in a NEC PC-8201a Hi Guys, Philip Avery and I had fun fixing my NEC PC-8201a recently. I always write these things up as I'll invariably forget what I did when I want to revisit these things later. Anyway, if you are interested here is the article in two parts... https://www.classic-computers.org.nz/blog/2020-07-16-nec-pc8201a-rs232-repair.htm Part two is linked from part 1. Regards Terry (Tez)
