2/10 serial port B won't transmit from Tom Stepleton on 2017-10-19 (lisalist1)

From: Tom Stepleton <stepleton_at_email.domain.hidden>
Date: Fri, 20 Oct 2017 01:21:57 +0100

Hi folks,

As of now my Lisas and their peripherals are nearly completely recapped---only the Widget and the Twiggy drives are left to do. Naturally I will be taking it very easy with those. I found that nearly all of the power supplies had at least one leaky electrolytic capacitor in them, and the power filter caps were also looking pretty distressed. Replacing the caps and the trimpots on the video boards resolved some display instability issues as well. *Let this post be a warning: if you haven't done it yet, it's time to think about recapping your Lisas!*

Anyway, with the covers off my machines, I thought I'd try to investigate a problem with my 2/10 that I first mentioned here a few years ago. Serial port B can receive data, but it can't transmit.

I've managed to verify the continuity of both the TX and RX lines all the way from the DB-25 port through to the 26LS30 and 26LS32 chips on the I/O board, and then from those to the 8530. I'm guessing the fault must be in one of these three chips, but before I try to get my friend to bring his oscilloscope over, can anyone think of anything else I should investigate? If not, then besides the data lines, is there anything that my friend and I should check out on the I/O board?

(I guess I could swap the 8530 between Lisas to see if that changes anything---but I hate to pull big chips unless I need to; I'm always worried about bending pins.)

Thanks all. Recap those Lisas!
--Tom

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Received on 2017-10-20 11:19:44