exxos's Atari, Amiga & retro forum

I recently obtained a Falcon that appears to be in pretty sorry shape. Looks like I'm missing several ICs:

U51 - BIOS and GEM ROM? Where can I get a replacement? Or is it possible to burn my own ROM?
U52 - What chip goes here?
U33 - Motorola Math coprocessor - Is this normally empty?
U64 - MK48T87B is supposed to go here? Is there a particular variant (-24?) that I need?
U63 - Prior owner did a very odd mod here. Anyone know what it's supposed to do? Is it reversible?


I'm comfortable with soldering and putting chips back the board, but I'd like to get some pointers with what to tackle first and what's optional.

I'm guessing U33 is optional, U64 can be tackled after I get a basic bootup, whereas U51 and U52 are required to boot?

From a quick look... you're missing TOS ROM (you can burn your own, sure, but that specific EPROM is harder and harder to find), ACIA (replaceable from an ST), NVRAM. That FPU socket looks suspiciously different (all my Falcons have a brown plastic one) so this may be another source of trouble. There are certainly some PCB traces destroyed and that mod is a clockpatch but looks like sh*t indeed, I would remove it completely and use Exxos's one.

Is it possible to boot the Falcon at all without any/some of these items for testing purposes? I'm going to have to order several of these from overseas. Ideally I'd like to get a a sign of life from it before I spend a considerable amount of money on parts (and wait a month or or longer for them).

I would say no, it is not.

Not sure what "overseas" means for you but you know that Exxos sells most of the missing IC (also RAM), right?

Yep everything @mikro says is correct...
just my take on it:

U51 - TOS ROM buy from Exxos store
U52 - This is ST Microelectronics ACIA, there are two on the board. The other one that *is* on your board is in the top left corner under the PSU area, it has two lifted pins see? Those pins will need putting back inside their sockets or patched. But yes get the same chip as that. You'll need to find somewhere to source it, check ebay, st-freakz, jays retro computers etc...
U33 - Motorola Math coprocessor - Yes this is normally empty.. just keep it empty for now.
U64 - This is NVRAM, buy a new one from Exxos store.
U63 - You gotta get rid of all that crap and fit an Exxos clock patch instead.
info: https://www.exxosforum.co.uk/atari/last/ ... /index.htm

Also in the U64 image, there is a picture of a resistor soldered to the motherboard and then soldered to a black wire - there is a missing inductor here, L102? I think. This will need replacing. I'm not sure of the value though, perhaps it can be bridged.

Also2 you are missing resistor R217 just above U63.

Do not do *anything* else till you get all this sorted. Before installing a new ACIA or NVRAM make sure you socket them. Before installing a socket clean up all the vias out with solder wick and test all the traces 100% first.

And be prepared for problems. You gotta ask yourself why someone left a Falcon in this condition to begin with, it was a highly modified Falcon with a bus-speeder. If you're lucky, the reason might be that the bus-speeder failed or caused instability, the owner may have attempted to remove it but was beyond their skills/depth. With luck you might have a lovely Falcon after this.

Then report back ;)

Just a minor correction, I do actually sell ACIA's as well.

https://www.exxosforum.co.uk/atari/store2/#0105

@exxos Ah that's good, I wasn't 100% sure if the ST and Falcon ACIAS were the same.

Steve wrote: 04 Jan 2022 15:18 @exxos Ah that's good, I wasn't 100% sure if the ST and Falcon ACIAS were the same.

Yep. Other than brands, and the supposed faster "B" versions, not much else variation wise AFAIK.

Awesome help. Thank you guys. I'll get to ordering some parts slowly putting things back.

Preliminary checking of the power supply (with no load on the output side) seems to indicate that it's bad as well. Is it best to troubleshoot and fix components or replace the power supply with a modern one? Any suggestions on a good replacement?

sirpete wrote: 07 Jan 2022 12:10 Awesome help. Thank you guys. I'll get to ordering some parts slowly putting things back.

Preliminary checking of the power supply (with no load on the output side) seems to indicate that it's bad as well. Is it best to troubleshoot and fix components or replace the power supply with a modern one? Any suggestions on a good replacement?

A modern PSU is always a good thing, but you may want to try checking your PSU under load before ordering anything.