exxos's Atari, Amiga & retro forum

That's interesting.

I have a F030 mainboard which went through scary repairs and while it seems to work fine as it is, it gets really unhappy with any accelerator installed. I'm pretty sure there's a resistive track somewhere to/from the combel chip that got all the rework - so I started mapping out all the track resistance readings. I got through a bunch and they all read about 1.5R on whatever meter I was using - and then I got bored. It's a lot of pins and a lot of scrolling around the service guide :)

I was just using a normal DVM and should maybe have been using something better - but still interesting to see what devices people come up with for this kind of thing.

SteveBagley wrote: 23 Jun 2025 00:34 The Milan schematics are on dev-docs.

Where ?

It says "Milan 68040 PC Board Layout (Rev 1.3) [2-13-2001]" but it is really "Schematic and Layout".

alexh wrote: 23 Jun 2025 09:45 It says "Milan 68040 PC Board Layout (Rev 1.3) [2-13-2001]" but it is really "Schematic and Layout".

Oh yes thanks

D2 was 1R to GND before viewtopic.php?p=130165#p130165

So I cut this pad has at least it would give a little bit of area to solder blob over later...


And behold, no more short to GND !


I cannot find D2 (ISA bus) going anywhere else really other than the ISA slots... Starting to like more and more that that big chip has died... Very odd that it doesn't get red-hot though..

Only other thing I can think is to check that the IC actually has power.. But I don't think is really important as D2 is outright shorted to GND anyway.

Looking on evil bay and the chip I found, there is a slight number variation which I need to figure out next because the one the board is PC87308-IBO and the one on evilbay is PC87308-IBN

Hopefully it will just be something dumb...

Currently there does not seem to be any mention of those numbers in any datasheet :roll:

exxos wrote: 23 Jun 2025 11:02 Currently there does not seem to be any mention of those numbers in any datasheet :roll:

I find in most cases, as the numbers become letters and appear more towards the end of the ID, the less important they are :D

Except when that isn't true of course. :p

Anyway, great find re. the short on that pin. Are you sure the short isn't something to do with the board though? Did you follow the short, cutting the track right up to the IC? Does it go anywhere else under the IC, maybe to the back of the board again? Just in case...

dml wrote: 23 Jun 2025 11:41 I find in most cases, as the numbers become letters and appear more towards the end of the ID, the less important they are :D
Except when that isn't true of course. :p

Yeah, would be nice to actually confirm im not going to get a IC which is 5 mm smaller in size than the one I have all something like that! :lol:

Are you sure the short isn't something to do with the board though? Did you follow the short, cutting the track right up to the IC? Does it go anywhere else under the IC, maybe to the back of the board again? Just in case...

It's not just that one pin though it is basically all the databus from the flash...

Looking at the schematic it doesn't really go anywhere else and I even buzz around the board to make sure. Mostly just a pullup resistor pack and the ISA bus (nothing is plugged into the slots) so there simply isn't anything else on that track.


The vias mostly seems to go downwards towards the flash. So I don't think it can be a PCB fault as it would have to have various faults on 8 data lines.

That flash databus only seems to go to the 2 big chips. Its obviously not the other big chip as the fault vanished. Doesn't seem to be any other tracks under the big chip but hard to tell.But I don't see anything else in the schematic anyway..

I got a new reply from Uwe,

Hi Chris,

as far as I remember -IBO und -IBN were the PC BIOS the are configured
for and doesn't matter for Milan.

The data sheet of the PC87308 exists somewhere here in printed form,
but I don't know where.

And if I remember correct you can also use the later pin and function
compatible PC97308.

I've attached the data sheet of the PC87307/PC97307 which is almost
identical and I think you can use it as as well.

We switched from the PC87308 to a PC9730? for the REAC060 about 2005
but I can't remember if it was the 307 or the 308.

I think you can remove the Super I/O and the board should start up
without it. At least you should see the correct pattern on the ISA bus.

Kind Regards
Uwe

I was wondering about removing the chip as its just a IO thing..

But first I really need to remove the first PCI slot because it very much in my way :(

...this is where you find a tiny coin jammed in the ISA slot :)