25 Dec
2025
25 Dec
'25
12:47 a.m.
-----Original Message-----
From: Jon Elson via cctalk <cctalk(a)classiccmp.org>
Sent: 24 December 2025 23:26
To: cctalk(a)classiccmp.org
Cc: Jon Elson <elson(a)pico-systems.com>
Subject: [cctalk] Re: Hot Video Shift Register on VT100
Looking at the 74S299 datasheet, they show current draw as
140 - 225 mA, which gives 700 mW to 1.125 W dissipation. That SHOULD run
hot. Your other unit that doesn't run hot must not be a 74S299. If I read the
datasheet right, they say it can tolerate running in still air a 70C.
I just double checked and on the other unit it is a 74S299N, identical to the one that
gets hot in the VT100. I suspect it is OK for it to get hot and maybe I should just stop
worrying about it. But it is puzzling as to why this one gets hotter. I will get my VT101
back soon and I can see how that compares.
Thanks
Rob