IBM PC/XT (Model 5160): Part 3 (Booting into Cassette BASIC)
26It boots! The original symptoms were no video & no beep when booting - according to the list of POST steps this would indicate it's failing before step 21 when the video card is initialised.
https://minuszerodegrees.net/5160/post/5160%20-%20POST%20-%20Detailed%20breakdown.htm
And from what I can see on the diagnostics ROMs it's looking quite likely that BANK 0 is failing - using a dedicated ROM to test this (TEST6099) indicates pretty much all of the 4164s have failed except for one. This is the step 15 test.
Supersoft diagnostic ROM (from the 80s):
https://minuszerodegrees.net/supersoft_landmark/Supersoft%20Landmark%20ROM.htm
Ruud's diagnostics ROM (modern, based on Supersoft):
https://minuszerodegrees.net/ruuds_diagnostic_rom/Ruuds%20Diagnostic%20ROM.htm
TEST6099 ROM (tests just BANK 0 or the BASE 16/64KB):
https://minuszerodegrees.net/5160/code/IBM%205160%20-%20Some%20test%20code%20for%20U18.htm
Replacing these suspect DRAMs and the machine finally boots to cassette BASIC with just a "601" error because no drive controllers are connected.
Progress!
I have upgraded the BIOS to the latest version (9-May-1986) and will try the drives next.
The Persyst "Time Spectrum 384" multifunction card requires some repair due to the Varta battery corrosion - replace some resistors and IC sockets.
Components of this machine:
[1] Twin half-height 360KB 5¼" floppy drives
[2] Single 20MB hard drive (Tandon TM-262)
[3] MDA video card
[4] Persyst "Time Spectrum 384" multifunction card: 384KB RAM, RTC, parallel & serial ports
[5] Floppy drive controller with external floppy connector
[6] Hard drive controller
[7] IBM Model 5151 monochrome (green) screen
More videos on troubleshooting IBM PCs & compatibles:
https://www.youtube.com/playlist?list=PL5pwokf56wMLjhEgssoRyZJO1VWeQ09ij