🛠️ In this video, I demonstrate a diagnostic ROM I developed for Commodore 2040, 3040, and 4040 disk drives. I created this while trying to fix a problematic 3040 drive and thought it might help others working on these vintage machines.

💡 The ROM performs zero page and static RAM memory tests and uses the drive’s LEDs to indicate what’s wrong - making it easier to identify which chip has failed without needing specialized equipment.

What’s in the video:

  • 🔧 Why I made this diagnostic tool for my drives
  • 📖 How to use it
  • ✅ Testing in a working drive to show normal operation
  • 🔍 Demonstrating what happens with a faulty 6532/RIOT chip (causing zero page RAM issues)
  • 💾 Showing how it identifies bad static RAM chips
  • 🔢 Reading the drive’s device ID and reporting it via LED flashes
  • 🔌 Installing it both as the primary ROM ($F000) and alongside stock DOS 1 ROMs ($D000)

The ROM has been useful for my own repairs, letting me quickly pinpoint which components needed replacing. Is my 2040 now the World’s largest1 2114 static RAM tester??? 😄

Timestamps
00:00 Intro
00:11 Why?
00:31 What’s in this video
00:49 2040 Architecture Overview
02:08 Diag ROM in action
02:54 Zero page failure
03:42 Static RAM failure
05:07 Running alongside stock ROMs
06:37 Source assembly
06:58 Wrap-up

Links:

If you’re working on old Commodore drives, hopefully this helps save you some debugging time. 💾

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