Falcon030 Repair

[jamesrhq]

I thought I'd document what I'm upto in trying to get this Falcon motherboard running again, incase it's useful to anyone, and more importantly such that people far more knowledgable than me might be able to help. :lol:

The overview is, it's a Falcon PCB I got from eBay some years ago when I bought two faulty boards. I repaired one, which was just some bad reflow work on the VIDEL on the board, and I'm now having a look at this one! It's is missing VIDEL and the SCSI controller.

After some initial investigation (viewtopic.php?f=29&t=7449&sid=3bafe00be ... 8fb18f48a9) it looks like it had a Phantom bus accelerator installed. All the mods required for the Phantom have been reverted and everything in general looks in good enough shape. I've moved the GAL's from my working board over to this one and am trying to see what happens without a VIDEL. The only thing a bit dodgy at the moment is the 3 clock path resistors have just been replaced with solder blobs. I don't *think* this will cause it to not run, but does need sorting.

So, what happens on power up? After reset the CPU runs for a couple of short bursts (measured via AS on the expansion bus) and then hangs. It's quite interesting --

RigolDS0.png

Yellow is reset. You can see it's really janky and bounes a lot before stabilising. I'm guessing this is "normal". Once it stabilises then the 68000 runs for a short burst, then reset goes low again. I'm running the Falcon diagrom cart here. So by the looks of it, the initial burst is TOS checking for the presence of the cart, jumping to it, then when reset goes low it's executing RESET on the 68k (which is the first instruction of the diagrom). Results are similar, but different, when running TOS.

The amount of CPU access after the reset always seems to be the same when running diagrom. When running TOS, depending on if it's a cold boot or a warm boot, the amount of CPU cycles varies before hanging. A cold boot runs for longer. I'm guessing it's some kind of handshaking of between VIDEL and COMBEL which is hanging the bus. So by the looks of it, I can't get any further until a new VIDEL is installed!

[jamesrhq]

More random trivia. I hadn't spotted before that COMBEL also has a DRAM controller in it (or at least partial along with VIDEL). I added a RAM board and TOS now runs for 200ms+ before hanging. Running diagrom is identical to before. So my guess is TOS is doing some more "memory stuff" before initialising VIDEL and causing the hang.

[Steve]

Might as well solder a new Videl in, it might just work. I don't think anyone's tried diagnosing a falcon without a Videl before, so it's not likely you'll learn anything without it. In my view anyway.

[jamesrhq]

Yes, agreed! I was trying to figure out if the combel was sound before ordering the videl, incase I needed to order both. To be honest, I can’t tell. It looks like it’s working given the cpu activity, but can’t tell 100%. So I’m ordering a combel and videl to be on the safe side given postage from the US!

[Steve]

@jamesrhq yeah good idea... and let's face it, you'll easily re-sell the Combel either here or on eBay if you don't end up needing it.

[jamesrhq]

Haha, very true! It's amazing Best are still selling spares, and at very reasonable prices given the scarcity. Parts have now been ordered, so lets wait and see what happens with a VIDEL installed. I'm mildly optimistic at the moment given the 68K is actually running to some degree.

[alexh]

Every time I order from BEST I get my package opened by customs, I have to pay VAT/Duty and a handling fee. Good luck.

[jamesrhq]

I wouild expect that to be the case, yes. :(

[chronicthehedgehog]

Get some TT Touch caps while your at it :D

[jamesrhq]

When looking through the parts Best have, I almost want to get a few of everything "just in case". :lol: You never know when these things will go out of stock, at which point repairing anything becomes a scavenger hunt.