exxos's Atari, Amiga & retro forum

stephen_usher wrote: 10 Mar 2022 15:10

rubber_jonnie wrote: 10 Mar 2022 14:57

I returned it to stock and it won't even run Star Raiders. It could be faulty RAM, but it could also be something else.

I'd still return it to stock and then use the diagnostic cartridge. Being able to Star Raiders with expansion may be taking you on a wild goose chase where it's using RAM that the rest of the system can't see or use initially.

I did, it didn't work. As for the RAM on the Syscheck, I had that disabled when I did test it, but stock 16KB and without Syschck, all I get is a black screen and not even Star Raiders works.

:-(

I'd start returning to stock machine and replacing the 16K ram chips.

You said you are using a two chips ram upgrade. You might have an incompatible Antic. Unlikely that both ANTIC ares (you said you swapped all main chips). But just in case, exactly which ANTIC part numbers are you using?

Also, the new MMU is an original Atari chip, or is one of the newer ones?

I believe that Syscheck requires 64K. But again, I'd start with just replacing the old RAM chips.

ijor wrote: 10 Mar 2022 15:44 I'd start returning to stock machine and replacing the 16K ram chips.

I'd have to source some replacement 16KBx4Bit chips first.

ijor wrote: 10 Mar 2022 15:44 You said you are using a two chips ram upgrade. You might have an incompatible Antic. Unlikely that both ANTIC ares (you said you swapped all main chips). But just in case, exactly which ANTIC part numbers are you using?

Yes, 2x 64KBx4Bit in place of the original 16KB chips with additional wiring as per the image below (Not my machine, but the same setup):


I just tried swapping the Antic from my 800XL again, see if it made a difference, but it didn't. They are both marked C021698-1 dated 1983.

ijor wrote: 10 Mar 2022 15:44 Also, the new MMU is an original Atari chip, or is one of the newer ones?

I have 2 originals, one each from my 800XL and the 600XL. Both test fine in my 800XL

ijor wrote: 10 Mar 2022 15:44 I believe that Syscheck requires 64K. But again, I'd start with just replacing the old RAM chips.

OK, I just wen't back to look at the email Jurgen sent and he says when the 600XL is stock and 16KB, it will error on the 16KB boundary, which is what it's doing, despite having 64KB installed.suggesting that the machine is not seeing above 16KB.

Also, in the Sys Check manual it suggests a black screen is bad RAM, so bad that the OS can't load, which is what I have.

Minor update, just to be sure I said the right things. I reverted to the original 16KB of RAM and I get a black screen on boot with the bare machine. Pressing Option does not take me to self test in this config.

Neither Star Raiders nor Bounty Bob work in this configuration.

SysCheck instantly fails the RAM test, so it's not seeing the first 2KB RAM, which gets tested first according to the SysCheck manual, otherwise it would continue up to the 16KB limit, then fail based on what Jürgen said.

Running SysCheck with its own OS and RAM, it all runs through the OS self test memory check just fine.

There has to be a RAM problem.

I will source some 4416 RAM just to be sure from the 16KB side, but it seems like it isn't seeing the first 2KB of RAM, possibly not the first 16KB, but it does see 16KB with the 64KB RAM expansion fitted, enough for the carts to run, but nothing that can be used by the on board OS.

rubber_jonnie wrote: 10 Mar 2022 16:30 I just tried swapping the Antic from my 800XL again, see if it made a difference, but it didn't. They are both marked C021698-1 dated 1983.

Ok. Yes, they are the newer ANTIC revision. Should be fine.

I will source some 4416 RAM just to be sure from the 16KB side,

That sounds like a good idea to me.

.. but it seems like it isn't seeing the first 2KB of RAM, possibly not the first 16KB, but it does see 16KB with the 64KB RAM expansion fitted, enough for the carts to run, but nothing that can be used by the on board OS.

Please forgive me if I'm saying something that you already know. But note these ram chips are not separated by address, but by data bits. I'm not familiar with the upgrade you installed, but in the original 16K configuration each chip outputs 4 bits for every single address. Sometimes a RAM chip doesn't work at all, and then that bit (or bits) is stuck at a fixed value. Sometimes it works mostly well and only specific cells on the ram chips are damaged.

ijor wrote: 10 Mar 2022 17:59
Please forgive me if I'm saying something that you already know. But note these ram chips are not separated by address, but by data bits. I'm not familiar with the upgrade you installed, but in the original 16K configuration each chip outputs 4 bits for every single address. Sometimes a RAM chip doesn't work at all, and then that bit (or bits) is stuck at a fixed value. Sometimes it works mostly well and only specific cells on the ram chips are damaged.

Indeed, I get what you're saying, I was just trying to ascertain is it ROM or is it RAM and through the use of the SysCheck, I changed my opinion from ROM to RAM, and it turns out that was the correct thing to do.

I just looked at activity on the RAM address lines with the scope and A7 was very off. It was pulsing, but the voltage was very low, about 2 volts.

So, I removed both RAM ICs and the A7 line came back to life, so I popped one in then the other, sure enough, one of the RAM ICs was pulling down A7, so I removed it.

Not having any spare 16KBx4bit RAM, I dropped in one of the 64KBx4bit ICs in not expecting it to work, but lo and behold, I have a working 600XL!!! I swapped out the working 16KBx4bit IC for one of the other 64KBx4bit ICs, and it's still all good.

So, we are working happily as a bog standard 600XL with 16KB RAM! I can boot to BASIC, the built in self test works just fine and it passes the SuperSalt RAM tests and the self test RAM test, though not the SysCheck RAM test because it expects 64KB of RAM.

I'll run the full battery of SuperSalt tests tomorrow.

:girldance: :girldance: :girldance:

Next I need to make the 64KB upgrade work (It currently doesn't, I don't know why), and then I can look to install the U1MB from my 800XL, and I'll probably also move the VBXL and PokeyMax to the 600XL as it is such a nice small form factor it'll be perfect for setting up on my retro bench in place of the 800XL. I'll return the 800XL to stock configuration.

I'm really pretty happy with the result, once again a bit of luck goes a long way!!

rubber_jonnie wrote: 11 Mar 2022 00:06 Not having any spare 16KBx4bit RAM, I dropped in one of the 64KBx4bit ICs in not expecting it to work, but lo and behold, I have a working 600XL!!! I swapped out the working 16KBx4bit IC for one of the other 64KBx4bit ICs, and it's still all good.

Great news! I can imagine your satisfaction. 8-)

You know. I had forgotten, but this thread reminded me that my very first Atari was a 600XL :)

Yay! At last! 🙂

Great result @rubber_jonnie

Glad you have sorted that one at last.

Kudos