[cctalk] Re: Hot Video Shift Register on VT100

[Rob Jarratt via cctalk]

> -----Original Message-----
> From: Jon Elson via cctalk <cctalk@classiccmp.org>
> Sent: 24 December 2025 23:26
> To: cctalk@classiccmp.org
> Cc: Jon Elson <el...@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