Uploaded March 2023 | Updated September 2026, 3 weeks ago

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Part two in my quest for 8 MB of RAM on my Radio Shack TRS-80 Model 16B! In this video, I perform four modifications in Tandy Technical Bulletin TB 12/16B:44 on the 6 MHz “short board” 68000 CPU card. These upgrades enable the DMA burst mode functionality required to use XENIX 3.x un-patched, as well as correcting PAL and other issues that were revised on 8 MHz versions of the 68000 board.

Music (in order)
None – just me prattling on endlessly.

Chapters:

Project Intro / Attempting Boot of XENIX 3 (0:00)
The Mod Kit (1:46)
A Look At The 68000 Card And Mod Process (3:02)
U48 PAL Upgrade and U36 Prep (5:45)
Knife-to-Board: BERR and WAIT Modifications (8:12)
First Test Boot…And Failure! (13:43)
Second Attempt…It Works! (15:08)
What’s Next / Outro (16:22)

I do these videos unscripted, so I apologize if the in-the-moment descriptions of things are a bit scattered. If you have any questions/comments about this video, you can find me in any of these fine locations:

The Tandy Discord Server
The CoCo Nation Discord Server
The TRS-80 Color Computer (CoCo) group on Facebook
The CoCo Crew Podcast group on Facebook
On the Vintage Computer Forums (vcfed.org)
The TRS-80 Models I-4/4P Group on Facebook
Tandy / Radio Shack Model II /12 / 16 / 16B / 6000 Owner's Group on Facebook
Twitter (I'm TJBChris there...)
The Level29 BBS (I'm TJBChris there, too.)
Particles BBS (Guess who I am here? Yeah, TJBChris.)

Thanks for watching!