exxos's Atari, Amiga & retro forum

PhilC wrote: 27 Jul 2021 13:34 @MP76 I don't think SJ2 needs to be made but maybe @exxos can correct me.

Ignore SJ2 its not required.

@DoG and @PhilC are right you need those two links. One on the 3V3 #2 socket and the one on the RTC chip area to get it to boot.

Thanks guys. :)

I don't know what ROM you are using. What is on it? Try removing the jumper on the ROM selection jumper on the left side of the board. Only TOS below 1.04 will work (192Kb).

You will also have to wait a while if no disk drive is attached.

Ha! Regarding the ROM, I got it from Exxos but because my hotmail security seems to have gone sky high it continually bins emails, including I assume my order confirmation.... I "think" it was the TOS 1.2/1.4 one, since then I've also gone into storage and pulled out the PLCC TOS from my Mega ST as I was fairly sure that was a TOS 1.2/1.4, swapping them out just gives a grey screen.

Correlation between the SIMM and MMU and other bits on the board have allowed me to confirm that all my soldering is "good", maybe I'll check for shorts next.

SO it's doing something - lit grey screen that's not booting, but does seem to accept a "reset" from the back button, hangs for a second or so and then goes back to grey screen.

I'm convinced this is going to be something really simple like a jumper issue.

There's some circumstantial evidence as well, I've tried booting on 512kB and I'm sure only 1 or 2 of the 74ACT244DW buffers is warming, when I go full 4MB all 4 of these chips are warming up (and when I say warming I don't mean roasting, just a subtle warm-up)

With the standard dual TOS PLCC from Exxos is it TOS jumper "made" or "open", I'll try again and wait a while as there's not floppy connected

MP76 wrote: 27 Jul 2021 18:26 With the standard dual TOS PLCC from Exxos is it TOS jumper "made" or "open", I'll try again and wait a while as there's not floppy connected

Open = TOS102
Closed = TOS104

But either should boot.

Thanks guys - I'll get there eventually :)

@MP76 do the simple walking around the pins of one of the 5V expansion ports with a continuity tester to see if you have any shorts. That’s a good starting point.

I've done a fair bit of belling out and fault finding in accordance with the original Atari 520 service manuals.

Learnt that PLCC's have a different pin layout to DIL's so pin 20 DIL may not be pin 20 on a PLCC for the same function, figured this one out from datasheets etc

Done all of the checks to see that I've got 32/16/8 Mhz on the required pins, I have.

Double checked the reset circuit and this appears to be working, eg HALT is high on the 68000 until the reset is pressed.

Next on the list is moving on to the video shifter - I have found something odd here. I'm using a mono monitor with the mono to VGA adapter cable that forces mono, and I've installed the force mono jumper and seen pin 30 of the shifter be low as expected, pulling out the jumper and putting in a standard RGB lead (or indeed NO video lead at all) pin 30 is still LOW, I'm expecting this to go HIGH.

Any thoughts?

I would try this fix as it causes reset issues...

https://www.exxosforum.co.uk/forum/viewt ... =10#p68030