exxos's Atari, Amiga & retro forum

Looking at the schematics, a lot of the ROM address and select decoding is being done by U2, a PAL16L8. That would be another place I'd look to make sure that's doing the right thing and isn't selecting both ROMs at the same time or something silly like that.

stephen_usher wrote: 26 Feb 2022 20:51 OK, the pinout for the OS ROM is the same as a 27C128 which should mean making a replacement is easy, as would be verifying the contents of the original.

As it goes, it's not the actual OS ROM that's the problem, as I've tested it in my 800XL and it's fine, same for the BASIC ROM, so no need to replace either.

The same goes for U2, what Atari refer to as the MMU, that's tested and working in my 800XL too, so I know it's not the IC that's the problem either, so it's something to do with the connections to it or logic relating to accessing it.

It seems the delay line is fine too, though my modern replacement also tests fine in the 600XL which is good to know.

So I need to check all the tracks and any address/data/select lines/logic are good for the OS ROM, as it clearly isn't getting far enough to call BASIC, but it is getting far enough to hand off to the Star Raiders cart.

I have read that Star Raiders is sometimes referred to as a diagnostic cart, and it seems it jumps into that much earlier than most other cartridges, a bit like the early detect for a cartridge in the ST.

Hopefully get some more done on it this afternoon, but at least I know all the main ICs and video circuitry work, it's just the start up initialisation that's failing.

Had any time to look at this wee beasty since yesterday morning? I'm hoping for good news. :-)

stephen_usher wrote: 28 Feb 2022 19:56 Had any time to look at this wee beasty since yesterday morning? I'm hoping for good news. :-)

I have had a look, but it's proving to be a bit of a head scratcher!

It looks like the original 16KB was bad, as it has shown more signs of life since I did the 64KB upgrade, and of course poor Sally had expired too. Data and address lines buzz out all ok.

It still won't boot to BASIC, however it does boot and run Star Raiders as I mentioned previously, but also the Bounty Bob Strikes Back cart runs, too, so assuming this means BBSB runs in a similar manner to SR, it means I know the following.

1. Since I have a display and the game is running, these ICs are fine:- CPU (Sally), GTIA, Antic.
2. I have sound, so Pokey is good.
3. I have joystick controls, so that part of the PIA is working.
4. Since Star Raiders needs the first 8K of RAM to work, plus the Self Test shows 16K OK before it crashes, it looks like at least 8KB is working, probably 16KB which should be enough to run BASIC as far as I know.

In addition to that, all of the other ICs have been swapped for new and no difference. I also know the BASIC and OS ROMs are fine as they work in the 800XL, as does every other major/custom IC.

I did wonder if it might be a problem of the OS running, but BASIC not starting, but after some comparisons with the 800XL, I still think it's the OS failing to start fully.

The 800XL starts like normal with the BASIC ROM removed, but then jumps to the self test at the point BASIC would normally load. Star Raiders and BBSB both run fine with the BASIC ROM removed on the 800XL too.

The 600XL on the other hand never gets to the self test unless I hold down the option key at boot. Even then it jumps direct to the RAM/ROM check and not the self test menu.

It could still be RAM related, and I need to check all of the activity on the pins on both RAM chips, see how they look too.

The diagnostics available for the 600XL are not great I have to say, but I'm off to look for some 800XL docs, since the boot to OS then BASIC should be identical.

It's driving me slightly mad!

I don't know a thing about those systems, but is there any "special diagnostic ROM" or a "diagnostic CART" that would start as soon as possible and more resilient to hardware condition than the standard self test of the standard ROM ?

I ask because recently I watched a video from "noel's retro lab" where he builds a remake of an amstrad CPC, and at one point, he use such cart and rom.

sporniket wrote: 01 Mar 2022 06:09 I don't know a thing about those systems, but is there any "special diagnostic ROM" or a "diagnostic CART" that would start as soon as possible and more resilient to hardware condition than the standard self test of the standard ROM ?

I ask because recently I watched a video from "noel's retro lab" where he builds a remake of an amstrad CPC, and at one point, he use such cart and rom.

I have a Super Salt diagnostic cartridge, however that doesn't start unlike Star Raiders.

There are other carts that plug into the PBI edge connector, rather than the cartridge port, so I'll do some research on those, see if they work like a dead test cart.

@sporniket

So, it looks like the SYS-CHECK V2.2 cart is what I'm looking for, it seems to be a dead test type affair, all I have to do now is find somewhere selling it.

@rubber_jonnie have you looked at the 800XL Sams technical manual, its a lot more helpful than the Atari one. Hopefully it'll be somewhat similar in circuit layout


http://www.atarimania.com/documents/Ata ... ervice.pdf

PhilC wrote: 01 Mar 2022 09:12 @rubber_jonnie have you looked at the 800XL Sams technical manual, its a lot more helpful than the Atari one. Hopefully it'll be somewhat similar in circuit layout


http://www.atarimania.com/documents/Ata ... ervice.pdf

Thanks, I was going to go and grab that but been a bit busy, I shall have a look. It seems there is no equivalent for the 600XL.

Just fired an email off to Jürgen van Radecke, seems he makes the Sys-Check V2.2, so will get that to add to my arsenal :)