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Olivetti M21 (M24) Dead motherboard PAL IC

Conventional Memories

Conventional Memories

Experienced Member
Joined
Sep 26, 2020
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So, while I was cleaning the corrosion off of the motherboard of my M21 I must have accidentally put one of the PAL IC's in the wrong way around (IK, stupid), unfortunately this than led to it frying itself.
Now I don't have any experience with PAL's and GAL's, but is this something repairable? Have these IC's been read out / reverse engineered?
To be more specific, it is chip "8H" on the motherboard. 20220913_224032.jpg
 
Your best bet is to borrow the PAL from someone and then clone it. (Not a simple procedure, but years ago, I acquired the AT&T 6300 which was missing a PAL from the video board and devised a way to clone it--buried in one of my blog entries, assuming they still exist).
I can't even make out the part number on yours; if it's registered PAL, it can be more difficult. I'm not aware of anyone working out all of the PAL equations, but I haven't checked in years.
 
Chuck(G) said:
Your best bet is to borrow the PAL from someone and then clone it. (Not a simple procedure, but years ago, I acquired the AT&T 6300 which was missing a PAL from the video board and devised a way to clone it--buried in one of my blog entries, assuming they still exist).
I can't even make out the part number on yours; if it's registered PAL, it can be more difficult. I'm not aware of anyone working out all of the PAL equations, but I haven't checked in years.
Click to expand...
Ohh OK thanks, I've had a look trough your blog posts and although it's a lot of work. It does seem doable.

So now I'll just have to find someone with a m21 or m24 to borrow the pal from.
What does the sticker on the PAL mean? Is this a revision number? And if so does that mean I have to clone the exact same version?
 
The sticker serves to distinguish this PAL from the other PALs on the board. It may be version-dependent, but it's impossible to read the one on your PAL.
 
I'm relatively sure it was "PL48" but that seems to be a different number in every other picture of motherboards I can find online, It's always PLxx, so that seems to indicate that there are revisions and they might not all be compatible on my motherboard.µ
 
Hello, yes, there are at least two versions of some of the PAL. It is recommended to swap some PALS when updating from BIOS 1.0/1.1 to later revisions. It is possible to read theses PALs and to copy them, @pevalcas did that already, but currently he can not.
 
1ST1 said:
Hello, yes, there are at least two versions of some of the PAL. It is recommended to swap some PALS when updating from BIOS 1.0/1.1 to later revisions. It is possible to read theses PALs and to copy them, @pevalcas did that already, but currently he can not.
Click to expand...
Ohh great, so that means there are already some digital images out there somewhere? Any idea where I could find those? Also, any way to tell what bios rev I have from the sticker ("RB2")?
Thanks ;)
 
Unfortunatelly I don't know, pevalcas did not shared them with me and he used to have a harddisk crash a year ago where he lost much. But if he was able to do so, why not anybody else with a device which can read PAL chips? Unfortunatelly I don't have such a device.
 
Here are the PALs. The 8H has different versions:

I included the latest PL52. Being a PAL16R8 you can replace it with a GAL16V8,
programmable with a cheap Chinese programmer and convert the file with PAL2GAL.

I can also get you the PL48 if you want, but the PL52 should work.
 

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  • PAL_M24_1.43.zip
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Here is a complete set from a 1.1 motherboard, should be identical to yours. I am also including a GAL version.

I can also send you a programmed gal, but you'll have to wait until I travel to Europe. It's a pain in the neck to fill a ton of
custom forms for a gal.
I am pretty sure that you can find someone "local" with a TL866 and a GAL16V8. It takes 3 minutes...
 

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  • PAL_M24_1.1.zip
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tpaxia said:
Here is a complete set from a 1.1 motherboard, should be identical to yours. I am also including a GAL version.
Click to expand...
Great, thank you. I was afraid I was going to have to find another machine to dump the PAL from.
I'll have to check and see if I have a compatible GAL somewhere that I can program.

Anyhow thanks, you saved me a lot of work. Now let's hope the rest of my M21 works. Apart from some Varta damaged traces the rest of the internals look to be in great condition.
 
1ST1 said:

tpaxia, thanks a lot for this!​

Click to expand...
NP. I have a complete set of M24 PALs you need the others.

I bought an AT&T 6300 to build a z8001 board for it, but it had non compatible PALs, so I bought an 1.43 motherboard and then found the rest…
 
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Conventional Memories said:
Anyhow thanks, you saved me a lot of work. Now let's hope the rest of my M21 works. Apart from some Varta damaged traces the rest of the internals look to be in great condition.
Click to expand...
These pals are difficult to dump. I had to buy a labtool48 just to do that…

Dump the bios and we can compare it with other versions “in the wild”…
 
Thanks again!!! Once I had the new GAL in there the M21 booted straight up into DOS 2.11 from its HDD.
20230305_155315.jpg
tpaxia said:
Dump the bios and we can compare it with other versions “in the wild”…
Click to expand...
Of course, I've attached a dump of my BIOS.

Next up:
1: Check for a loose connection, because as soon as I put it right side up it gives me a DMA error when booting. ("DMA Timer Fail:03")
2: Check the keyboard matrix, half the keys aren't working.
 

Attachments

  • Olivetti M21 BIOS.zip
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I have just checked with pevalcas through chat.

Your M21 shows a 1701 error and you say that it has DMA problem. PL48 is a verry early version! Your BIOS shows 11B, also he has never seen before. We both think that you have a very early M21 with very old PAL set and Beta BIOS.

The 1701 is some kind of harddisk or controller error, same meaning as at IBM https://minuszerodegrees.net/5150_5160/hdd/1701_possibilities.htm . Did the harddisk work before you burned (and replaced) the PAL?
 
1ST1 said:
I have just checked with pevalcas through chat.

Your M21 shows a 1701 error and you say that it has DMA problem. PL48 is a verry early version! Your BIOS shows 11B, also he has never seen before. We both think that you have a very early M21 with very old PAL set and Beta BIOS.

The 1701 is some kind of harddisk or controller error, same meaning as at IBM https://minuszerodegrees.net/5150_5160/hdd/1701_possibilities.htm . Did the harddisk work before you burned (and replaced) the PAL?
Click to expand...
The picture is from when I first plugged in the new GAL it was still on it's side to access the MB, I did not have power plugged in to the MFM HDD. that explains the 1701 error.
After this I hooked everything back up and it booted straight in to DOS from the HDD.

Then I put the M21 bottom panel back on and put it back horizontally and it didn't boot anymore only displaying: "DMA Timer Fail:03"
So sow it's working in some orientations and not in others, that leads me to believe that there must be a loose connection somewhere.

I have no idea when the last time this machine worked was, when I got it the Varta battery had leaked all over the motherboard so it must have been a while ago.
 
You can remove the battery, it has no big usage, it's only time/date, and the M21/M24 BIOS has several 19xx/Y2K bugs, so it will not display current date of year 2023 correctly.

Anyhow the M21 (and M24, M24SP) are timeless beauties!

For the DMA error, it looks like you have to check the correct seat of the Intel 8237 DMA controller and 765 floppy controller in it's socket, and maybe also the connection between the mainoard and the "U-board" graphics card and the bus converter where the harddisk controller is plugged in.
 
Great, thanks for the tips. I'll take it apart fully when I have some more time. Maybe some deoxid in those old single wipe sockets and reseating all the boards wil clear up the issue.

As for the battery, I already put in a 4F capp. I prefer those as a drop in replacement for these vartas, those will outlast a computer like this and don't need replacing unlike a cr2032 and diode mod. Also not a big chance of leaking on the long run with a modern cap unlike most battery types.
 
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