🇦🇺 IBM PC/XT (Model 5160): Part 3 (Booting into Cassette BASIC) [TCE

It 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.
minuszerodegre...
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):
minuszerodegre...
Ruud's diagnostics ROM (modern, based on Supersoft):
minuszerodegre...
TEST6099 ROM (tests just BANK 0 or the BASE 16/64KB):
minuszerodegre...
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:
• IBM PC & Compatibles

[@joopidema]

Did not know about those diag ROMs. I will give those a try. There are also alternative BIOS ROMs. Makes the XT boot much faster.

[@Brfff]

I'm guessing if you remove a lot of the POST code then you could get it to boot much faster, i.e. don't check 640KB RAM every time you boot! Do you have any links? /Brett

[@skjerk]

Seven of nine😎

[@Brfff]

*groan* ... ;)

[@davidknoll]

Just take them all out and test them individually (with other equipment)

[@Brfff]

I'll definitely be testing the ones I've removed. Probably worth reseating the other ones. I'm working on the Persyst multifunction card at the moment - have removed all 384KB (to give the card a good clean with white vinegar) and will add them back in banks to see what works

[@Chriva]

Are they including the parity chip as part of the fault beeps? @18:00

[@Brfff]

I'm still not entirely sure ... according to the TEST6099 documentation there are only eight beeps (one for each data bit), and a failure of the parity bit is indicated the same as no data bit failures (0x00) ... ?!
"If the BASE 16KB RAM test has executed and FAILED, then a few seconds after power-on, you will hear a series of 8 beeps from the speaker.
Some beeps are short, some are long. Short corresponds to a 0. Long corresponds to a 1.
The eight beeps (eight 0's and 1's) make up a byte. The order of beeps is bit 7 to bit 0 (MSB to LSB).
For example, if you hear short-long-short-short-short-short-short-short, that is 01000000 binary, or 40 hex.
00 hex (00000000) = Failure of parity bit
01 hex (00000001) = Failure of bit 0
02 hex (00000010) = Failure of bit 1
04 hex (00000100) = Failure of bit 2
08 hex (00001000) = Failure of bit 3
10 hex (00010000) = Failure of bit 4
20 hex (00100000) = Failure of bit 5
40 hex (01000000) = Failure of bit 6
80 hex (10000000) = Failure of bit 7
Anything else indicates multiple bits. For example, 28 hex (00101000) indicates bits 5 and 3."

[@Chriva]

@@Brfff That manual was incredibly not helpful lol. Happy you got it sorted. Just went into curious mode when I noticed 8 beeps mentioned but saw 9 chips :)

[@IkarusKommt]

Now that is a terrible monitor....

[@Brfff]

What?! It's kinda growing on me ... nice, crisp, green text! I'm hoping to play some Pacgirl if I can get it to boot from one of the drives ;)

[@IkarusKommt]

@@Brfff I can literally see letters fading over several seconds...

[@Brfff]

@@IkarusKommt Yeah, actually I noticed that too

[@WacKEDmaN]

nice job!.. strange the rest of the ram is fine and it was only that first bank...

[@Brfff]

There's a little bit of greenish corrosion on the BANK 0 socket pins from the Varta battery leak ... maybe due to that?

[@WacKEDmaN]

@@Brfff yeah maybe even the sockets?.. have u got a tester for the 4164s? ..it maybe just corrosion on the legs/sockets causing them to be bad?..new clean leg chips are making better contact?.. might be something to check out..

[@Brfff]

For sure I won't be discarding the chips until I'm certain ... there's some uncertainty about the parity chip (see discussion with Christian @Chriva)

[@WacKEDmaN]

@@Brfff yeah i was thinking that too..if the parity bits arnt working it could show up as the ram chips failing..

[@joopidema]

Put some deoxit or contactcleaner in the sockets. And clean the RAM chip legs. Maybe the sockets are just the problem.