exxos's Atari, Amiga & retro forum

Not sure if it helps but I did try the one working Amiga floppy I have (Line of Fire I think it is) and that appeared to run ok

I also tried a Gotek with a few games (possibly Speedball to check the audio worked ;)) and they seemed ok too.

stephen_usher wrote: 02 Feb 2025 18:56

rubber_jonnie wrote: 02 Feb 2025 14:38 No real difference using that range. Crashes quick and has to be rebooted.

Something is very wrong there then.

Maybe one of the higher address lines isn't behaving correctly somewhere so writing to a location where nothing is supposed to be is changing something at a lower address where something important lives.

That's certainly possible. I've spoken to the seller of the RAM expansion and he says it was tested and worked. It was only £10 ish so I'm not bothered if it doesn't work.

I do see what looks like there's normal activity across all pins now though so it's quite odd.

Need to go back to the memory schematic and see what I can find.

JezC wrote: 02 Feb 2025 19:28 Not sure if it helps but I did try the one working Amiga floppy I have (Line of Fire I think it is) and that appeared to run ok

I also tried a Gotek with a few games (possibly Speedball to check the audio worked ;)) and they seemed ok too.

It's all very odd. I've prepped the RAM positions for an onboard upgrade this evening, but I won't do it just yet.

rubber_jonnie wrote: 02 Feb 2025 20:40 That's certainly possible. I've spoken to the seller of the RAM expansion and he says it was tested and worked. It was only £10 ish so I'm not bothered if it doesn't work.

If the machine crashes in the same way without the card in the trap door then this is discounts the card.

stephen_usher wrote: 02 Feb 2025 20:50

rubber_jonnie wrote: 02 Feb 2025 20:40 That's certainly possible. I've spoken to the seller of the RAM expansion and he says it was tested and worked. It was only £10 ish so I'm not bothered if it doesn't work.

If the machine crashes in the same way without the card in the trap door then this is discounts the card.

Very probably yes. I'll try it again before I go to bed and pay more attention.

stephen_usher wrote: 02 Feb 2025 20:50

rubber_jonnie wrote: 02 Feb 2025 20:40 That's certainly possible. I've spoken to the seller of the RAM expansion and he says it was tested and worked. It was only £10 ish so I'm not bothered if it doesn't work.

If the machine crashes in the same way without the card in the trap door then this is discounts the card.

OK, so I tested late last night and these are the results:

Memory range 0xC00000 to 0xD7FFFF

Trapdoor RAM installed - The memory test flashes up for probably less than .5s then the machine crashes with flickering and glitching.

No trapdoor RAM installed - Crashes instantly with no indication of a RAM test starting with on screen glitching etc

Memory range 0008000 to 000fffff (This range was shown in another memory map I looked at)

Trapdoor RAM installed - The memory test flashes up for probably less than .5s then the machine crashes with flickering and glitching.

No trapdoor RAM installed - The memory test flashes up for probably less than .5s then the machine crashes with flickering and glitching.

I'm not sure why there seem to be conflicting memory ranges but 0xC00000 to 0xD7FFFF shows a size of 1.5MB in ATK and 0008000 to 000fffff shows a size of .5MB in ATK.

In other news I decided to pull Fat Agnus out of the socket to double check the socket pins, the chip pins and give it another scoosh of contact cleaner. The bad news is that the IC is super tight and came out but with a lot of resistance and the PLCC puller slipped. Back in the socket it'll either boot to the 'Insert Workbench' screen or it completely crashes with a software meditation.

I've ordered a new socket to be on the safe side but it's a pain, and I'm hoping it isn't Fat Agnus. It seems unlikely that the IC is bad as it seemed to work fine before, but I'm now wondering if the socket is part of the problem.

0.5MB / 1MB Fat Agnus chips are cheap. They made millions and there were lots and lots of spares when CSG closed.

2MB Fat Agnus chips have run out practically everywhere, the only real source is/was dead A500 plus motherboards and now you can get replacement motherboards everyone is holding onto theirs driving the price to more than the cost of A500 plus.

alexh wrote: 03 Feb 2025 12:43 0.5MB / 1MB Fat Agnus chips are cheap. They made millions and there were lots and lots of spares when CSG closed.

2MB Fat Agnus chips have run out practically everywhere, the only real source is/was dead A500 plus motherboards and now you can get replacement motherboards everyone is holding onto theirs driving the price to more than the cost of A500 plus.

Mines not an A500+ so I expect a normal one would do, but I think the socket is bad as it goes.

What about 00000000 to 0007ffff ?

It is probably the socket, these tend to give issues with pins that are bent or cracks, for testing you can clamp the socket a bit and see if the issues change.

You could try to remove the Agnus again, inspect the socket for cracks and then bend the pins in the socket so they make better contact.

If you want to replace the Agnus, the 8372a is the best for this machine(1MB chip), unless you want to go all out and get an expensive 2MB Agnus and an adapterboard..

The 8372a is a PAL/NTSC switchable unit, so that is something you do not have to worry about.
8371 is a 0.5MB chip unit, it will probably work out of the box, but 0.5MB chip isn't really enough IMHO.
The 8375 has many variants, most of them will not work without an adapter and there are specific NTSC and PAL units.

Maximilian wrote: 03 Feb 2025 17:07 What about 00000000 to 0007ffff ?

I did a full ram test on the onboard RAM and it came out just fine.

Maximilian wrote: 03 Feb 2025 17:07 It is probably the socket, these tend to give issues with pins that are bent or cracks, for testing you can clamp the socket a bit and see if the issues change.

I'm certain it's the socket, as soon as the new one arrives I'll get it replaced.

I did do this, including pin adjustment, but it seems worse every time the Agnus comes out and goes back in. it's worse.