REV 3 - REV 5 - The beginning (ST536)

[exxos]

The 330R load seems to help a lot and doesn't seem to upset the voltage by anything significant.

There's a whole layer for GND anyway..

gnd.PNG

[exxos]

Just found one problem. If I press down slightly on the SR98 transformer the ST resets :roll:

Second problem - if I heat the PLD after a few seconds it also locks up. I wonder if that's the same issue as to why fast-slew doesn't work :shrug:

Thing is - I don't know if heating the PLD up even works on the original TF536 at this point. It could be "normal" :shrug:

EDIT:

Fast slew doesn't change the behaviour ..

[exxos]

Being running GB6 for the past few hours and will leave it on overnight again...

20251121_215302.jpg

20251121_215339.jpg

[exxos]

Left on overnight..

20251122_093842.jpg

Will leave it off for the weekend and see if it still works on Monday!

[exxos]

3 days turned off.. Left it running GB6 this-afternoon and hit 76 loops..

Running front bench...

20251124_181618.jpg

[coonsgm]

Looking good!!

[exxos]

There's some current modifications to the ST536 288XL series to address some issues I found the past weeks.

https://www.exxosforum.co.uk/atari/last ... tm#MOD2025

Most as mentioned before. A poor 100MHz clock drive to the SDRAM and 3.3V power issues. There is a new firmware on the same mod section which must only be used after doing the mods. Going back to other firmwares will damage stuff, so don't do it !

I am also working on another respin of the board. I am using a new regulator which should be better and the 3.3V rail will be split into a dual rail powered by 2 regulators instead of one. More HF bypassing caps (typically 4.7nF) will also be added.

BETA testers please do the mods and see how you get on. There could still be issues, but I feel they are hardware related not firmware related now.

Before the mods, it would run for hours at a time.. leave it off a while, go back and unstable again. Currently its been working fine this past week and running several hours on TTram tests and GB6.

[coonsgm]

Looks like I have my Saturday project here.

1 - Swap the 144 to the 288
2 - Make the mods listed
3 - flash the new firmware
4 - Test test test....

[coonsgm]

There's some current modifications to the ST536 288XL series to address some issues I found the past weeks.

https://www.exxosforum.co.uk/atari/last ... tm#MOD2025

Most as mentioned before. A poor 100MHz clock drive to the SDRAM and 3.3V power issues. There is a new firmware on the same mod section which must only be used after doing the mods. Going back to other firmwares will damage stuff, so don't do it !

I am also working on another respin of the board. I am using a new regulator which should be better and the 3.3V rail will be split into a dual rail powered by 2 regulators instead of one. More HF bypassing caps (typically 4.7nF) will also be added.

BETA testers please do the mods and see how you get on. There could still be issues, but I feel they are hardware related not firmware related now.

Before the mods, it would run for hours at a time.. leave it off a while, go back and unstable again. Currently its been working fine this past week and running several hours on TTram tests and GB6.

Looking at the mod and for the most part it looks really straightfoward.

The one question I had is about the 4.7nf capacitors. The note says "Solder a 4.7nF 0603 capacitor across every small cap on the bottom of the PCB." Does this mean to replace the existing ones or add the 4.7nf side-by-side?

IMG_3887.jpeg

[exxos]

The one question I had is about the 4.7nf capacitors. The note says "Solder a 4.7nF 0603 capacitor across every small cap on the bottom of the PCB." Does this mean to replace the existing ones or add the 4.7nf side-by-side?

The 4.7nf is in addition to the existing caps..

Just solder them on the side of the ones already on the PCB..

Be careful though as it doesn't take much for the caps to unsolder off the board while trying to solder the new caps on!

Would be useful if you could scope before and after on that pin I sent to you in pm a couple days ago to see if there is any noticeable difference afterwards..