Atari 520 STFM - Issue 4x Multi TOS Upgrade

[DigitalSkunk]

Hey guys, I am probably overlooking something silly, but I am a bit stuck.

Just some background on this machine:
I upgraded to a new Exxos PSU, main cap, video fix, and 4MB RAM upgrade. I forgot to get the DMA/BUS fix resistors on that order, but they should arrive soon. All the previous upgrades were successful and the ST was stable before performing the ROM upgrade.

• I got PP's TOS Improved 2 versions, and Atari's original TOS 1.04, 2.06

• On 2x 27c4001 EEPROMs

• A17 and A18 (Pin 30, 31) are TOS toggles. This seems to be working? Switch off has both pins at high, 5v. I used 33ohm resistors I had laying around, is this high enough for protection?

• With both switches grounded, A17 and A18 low, it successfully boots TOS 1.04 original.

I can't get the other three versions to boot, and am not sure what to check next.

• I have a strange revision of 520 STFM, ROMs are under the PSU, 2 chip version.

So, to be less cramped and reduce the chance of ROMs, GAL shorting to the bottom of the PSU shield, I actually installed the GAL on top of the 68k, and ran a fairly long CE1 line from GAL 15 pin to Pin 22 of new ROMs.

• Pin 24 on new ROMs are pulled up from the socket, connected to GND on mobo. (OE)

• Under pin 24, I ran A16 to Pin 2 of new ROMs.

• GAL pin 15 CE1 is running to Pin 22 of both new ROMs. This pin is inserted in the socket still.

• When I unsoldered the CE blob jumper on the board, TOS 1.04 original quit working also until I soldered it back on 1M pad.

• A16 and A17 pads are still soldered on 1M like stock.

I hope this is enough info to start. Thanks in advance for any help anyone can offer. I am rather confused at this point. lol

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[DigitalSkunk]

Ok, update! My resistor networks came in and now all mandatory fixes have been applied to my ST (BUS resistors, DMA pull-up for drive access, Exxos PSU, main cap replacement, video cap replacement, and I removed an old 4MB RAM upgrade in favor of the cleaner Exxos one). It is very stable.

There is some issue happening with the GAL chip or how I've connected it to decode the additional address space for TOS 2.06. TOS 1.04 boots perfect.

• My toggle switches work. When 1.04 is running, switching either of them causes it to halt. On reset, it keeps the same display it had previously.

• Whenever I switch back to select TOS 1.04 again, it successfully loads on reset again.

• Whenever I try to boot TOS 2.06 or TOS 1.04 Improved, just sits there with a white screen.

• No bombs. It seems it can't see the proper address to boot from so it just sits there not loading anything on the white screen.

• I tried modifying the configuration of the CE, A16, and A17 solder jumpers but anything but the current configuration (as pictured, all three have 1M position shorted) prevented even 1.04 from booting.

Honestly, I am tired of fighting with this. But this is the last internal upgrade I have planned. I would just get the Exxos TOS 2.06 decoder, but it won't fit under my PSU on my strange mobo revision so making this part easy is out. lol Feeling a little defeated at the moment.

:(

[Steve]

Sorry I can't provide any advice on this TOS switcher... If the Exxos dual tos switcher doesn't fit, perhaps the Sidecartridge would?

[exxos]

It sounds like your switching with the power on ? You always need to power off,switch , power on.

[DigitalSkunk]

It was mostly a curiosity to see how it would behave.

When I power completely off, change toggle switches, power on it just sits at the white screen for every version except 1.04.


I have to be missing something with the GAL pin connections or maybe I connected to ROMs incorrectly:
Inputs:
A23 = 1,
A22 = 2,
A21 = 3,
A20 = 4,
A19 = 5,
A18 = 6,

AS = 8,
RW = 9,
ROM2 = 19,

Outputs
CE1 = 15, %E00000-E3FFFF and FC0000-FEFFFF to both new EPROMs pin 22 %

DTACK = 17; % Via diode - soldered to GAL %

I have the OE on both new 27C4001 EEPROMs connected to GND. (Pin 24) GAL CE1 output goes to pin 22 on both.

Pin 24 is pulled up so it doesn't go in the sockets. On original ROMs, this is A16. I grabbed this from the empty sockets to the left and ran to Pin 2 of new ROMs.

I tried the DTACK diode in both directions. No change.

CE1 output from GAL is that long striped wire going around the shifter can. I have seen many setups like this, so I don't think the signal is getting interference/garbled?

I'm not seeing anything SUPER obvious anyway... :mrgreen:

[DigitalSkunk]

Sorry I can't provide any advice on this TOS switcher... If the Exxos dual tos switcher doesn't fit, perhaps the Sidecartridge would?

Thanks for the reply, Steve!

I'm 99% there so I will eventually get this figured out on the internal ROMs. Especially with some more experienced eyes on it helping out! :)

I am considering their multi device side cart: https://sidecartridge.com/products/side ... -atari-st/ sometime with the RPI Pico. I Still haven't decided which route to go with wifi connectivity once these TOS issues are figured out!

[rubber_jonnie]

As exxos said, switching the toggles with power on is not going to just flip from one TOS to another, it doesn't work that way, much safer to power off then back on again and toggle with power off.

I'm assuming you're trying to use the GAL for either toggling the address lines to hit 1 of 4 TOS images or to do the decode for TOS 2.06.

I don't think it's working as you think it is and if you're not using it for the TOS 2.06 decode, I doubt 2.06 will ever work.

[exxos]

I do actually have a new decoder board in my basket. It will decode TOS104 / TOS206 space. This one can solder on top of the CPU. So it should fit those more problematic machines. Though I can't say when it will "make it to store" yet though. A few weeks probably.

[DoG]

Could you draw a schematics of this? Where did you get the jed for the GAL from? Something you wrote yourself?

[DigitalSkunk]

As exxos said, switching the toggles with power on is not going to just flip from one TOS to another, it doesn't work that way, much safer to power off then back on again and toggle with power off.

I'm assuming you're trying to use the GAL for either toggling the address lines to hit 1 of 4 TOS images or to do the decode for TOS 2.06.

I don't think it's working as you think it is and if you're not using it for the TOS 2.06 decode, I doubt 2.06 will ever work.

The GAL chip is specifically for decoding TOS 2.06 and larger ROMs. Both the GAL and the EEPROMs were programmed by PP.

The two toggle switches are actually completely separate from the GAL, and connect to the two highest address lines of the ROMs.

I am making up a circuit diagram real quick so that the setup is more clear! Will post as soon as I get it together.