exxos's Atari, Amiga & retro forum

No 3d printing required, seems I'd already run off a set of short stand offs and had them stored away, so the floppy got mounted just fine. Wiring harness is now made for the battery box, so I need to test that out too.

I've decided that a new reset switch is in order, as this one is all kinds of wobbly, so that's on the way along with a PS/2 mouse from exxos' store :) If I find a spare PS/2 mouse in the meantime, well it doesn't matter, I'll have a spare.

In the meantime I need to get a Gotek in. It was good to test with a real floppy, since you can observe the behaviour better at bootup, but for flexibility I want the Gotek.

The last thing to sort is the oddest. The diag cart reports 4MB consistently now. It was flip flopping between 2MB and 4MB until I tweaked the MMU socket, now diag cart says 4MB consistently. BUT, the diag cart RAM test does report errors.

Running Sysinfo shows 2MB, with bank 0 seemingly ok, no sign of bank 2. More RAM tests required I think, and I do have lots of spare RAM if repairs are required.

One more discovery, it seems like the PSU isn't all it's cracked up to be, as additional load, like a floppy or my CosmosEx seems to cause an inability to boot and weird instabilities.

Hooking up a re-capped STFM PSU seemed resolve this, so I also tested a spare Meanwell, and it works just fine with that, so I'll replace the PSU with that next.

Once the power instabilities are resolved, it's going to be working out why only 2MB out of 4MB is seen by TOS, so I'll run the diag cart memory test, see what's what.

If somebody more familiar with Megas than I am can advise on the memory bank layout for these machines, I'd be grateful of the help, as I'd only want to replace anything that is faulty, not everything.

Bank 0 seems fine then. Have you tested piggyback the ram chips on Bank 1? It might work depending on if the chip(s) that is faulty is not shorted inside. You just fit a ram chip on top with friction so that the legs touch each other. Depending on how many you have you can try piggyback all of them on bank 1. Otherwise just do 1 at the time and turn on the computer in between and test it with diagcart.

What does the diagcart says is faulty?

Bank 0:
U40= bit 0
U41= bit 1
U42= bit 2
U43= bit 3
U44= bit 4
U45= bit 5
U46= bit 6
U47= bit 7
U48= bit 8
U49= bit 9
U50= bit 10
U51= bit 11
U52= bit 12
U53= bit 13
U54= bit 14
U55= bit 15

Bank 1:
U60= bit 0
U61= bit 1
U62= bit 2
U63= bit 3
U64= bit 4
U65= bit 5
U66= bit 6
U67= bit 7
U68= bit 8
U69= bit 9
U70= bit 10
U71= bit 11
U72= bit 12
U73= bit 13
U74= bit 14
U75= bit 15

I think I got this right above. Hopefully someone will correct me otherwise.

Thanks DoG, I'll have a look at this tonight when I get home from work.

Ok, Meanwell PSU hooked up and working nicely. Needs a bit of a tweak to get the wires looking nice, but so far it works, so happy:

Ok then,let's have a look at the RAM goings on I say to myself. Nope, PSU suddenly dies when I plug in the floppy, so I trace whats going on back to freyed power connections for the floppy. Ok,that's fixed. Now can we look at the RAM? Yes? Yaay finally.

SYSINFO shows bank 0 is working, so happy days:


Nothing at bank 1 though through TOS, but Diagcart shows 4MB installed, and test run shows the following:


So, based on the info DoG provided, it's U69 that is dodgy.

Next thing I need is some suitable RAM chips, since I have only STFM RAM chips spare, so I'll have to go on the hunt for TC511000P-10 chips so I can try a piggyback test.

This sort of crap makes me very annoyed :cussing: :cussing: :cussing:

rubber_jonnie wrote: 30 Oct 2019 23:14 This sort of crap make me very annoyed :cussing: :cussing: :cussing:
Insanity_or_Insult.JPG

Jon, if you can't find any reasonable let me know and I'll send you a couple.

PaulJ wrote: 31 Oct 2019 00:17

rubber_jonnie wrote: 30 Oct 2019 23:14 This sort of crap make me very annoyed :cussing: :cussing: :cussing:
Insanity_or_Insult.JPG

Jon, if you can't find any reasonable let me know and I'll send you a couple.

Thanks Paul, I made some enquiries last night, hopefully I'll hear back today, so I'll let you know. As always, the level of help to be found on this site is excellent.

I might have a couple spare too RJ, if you need them then PM me.

rubber_jonnie wrote: 31 Oct 2019 07:50 Thanks Paul, I made some enquiries last night, hopefully I'll hear back today, so I'll let you know. As always, the level of help to be found on this site is excellent.

When I got my first mega it had a bad chip but in the main bank of memory so it wouldn't boot. Luckily the diagcart was able to identify the bad chip via the serial port. I had a hard time finding the chip at a reasonable price. All the single chips were from people attempting to get rich. So I ended up ordering two lots of 8 from different manufactures. Both lots work great so I ended up with some extra's. :D