exxos's Atari, Amiga & retro forum

Ah, ok - will see what resistors I can find...

Makes sense as I can see on another ST (which was a 1040 originally) that has a Marpet memory upgrade fitted & there are these 3 resistors cut at one end & connected to +5v on a big electrolytic cap.

Though I doubt that will be the end of the saga, it seems worth a go later this evening!

Thanks all - will report back with any news when I can.

@JezC No worries, the tech team is ready and waiting :)

rubber_jonnie wrote: 06 May 2020 17:36 @JezC No worries, the tech team is ready and waiting :)

@rubber_jonnie Thanks - much appreciated.

Didn't manage to try pulling up the RAS/CAS signals last night (couldn't find suitable resistors but will search more later).

Instead, I looked at another failing system, this is a 520STM with a C070859 board (SMT GLUE & MMU) which wasn't showing the outer/inner display areas at boot.
Popped in the DiagROM EPROMs (I'm beginning to think that a DiagROM cart would be handy at this point!) & no RAM faults reported...will upload the results here later (and also the results for a boot on a good machine for reference) but I'm wondering if it's a fault on the display circuitry somewhere as much of the rest of the core circuitry appears to be running OK.

Hoping that the long weekend will give me a bit more time to progress the repairs (and even get more done with the first H4!) but there are plenty of non-retro tasks to tackle as well...

JezC wrote: 07 May 2020 08:43 I'm beginning to think that a DiagROM cart would be handy at this point!

I'd say that getting a diag cart would be useful, it's way easier than switching the ROMs round. I can't recall where I got mine from, but mine does have the advantage of having some LEDs, so that when you boot to the diag rom it it flashes like a HDD activity light.

It might not seem like much, but if you don't see the light, it's a pointer something isn't right in ROM land.

Also it's worthwhile getting a diag cart, @exxos has them in his store, that has the offical Atari diagnostic tools, which are referenced in the service manuals. It makes it easier to cross check, and also outputs to serial.

Black Cat Hardware have empty 64kb and 128Kb cartridges you can use with TerribleFires diagrom.

Otherwise is exxos diag cart with original Atari test rom AND gembench AND memtest really great.

rubber_jonnie wrote: 07 May 2020 10:31 I'd say that getting a diag cart would be useful, it's way easier than switching the ROMs round. I can't recall where I got mine from, but mine does have the advantage of having some LEDs, so that when you boot to the diag rom it it flashes like a HDD activity light.

It might not seem like much, but if you don't see the light, it's a pointer something isn't right in ROM land.

Also it's worthwhile getting a diag cart, @exxos has them in his store, that has the offical Atari diagnostic tools, which are referenced in the service manuals. It makes it easier to cross check, and also outputs to serial.

@rubber_jonnie I think you've mentioned more than one cart in your various posts (one refernce to cartman & another to one from gossuin.be - though the latter might just be the test leads etc.?
One has some LEDs on it which show some simple diagnostic 9and sounds helpful)..

I think I'd probably want something like the board that @exxos does but without the EPROM so that I could put my own collection of programs on it (Atari diagnostic for ST/STE & Falcon, TF DiagROM for example)...

I got a bit further with the third non-booting system, looks like it's only seeing the first 128k of RAM instead of the whole 512k. So I'd hazard a guess that one of the address lines is faulty ;)

Better download the schematics & see where it goes. :roll:

DoG wrote: 07 May 2020 10:44 Black Cat Hardware have empty 64kb and 128Kb cartridges you can use with TerribleFires diagrom.

Otherwise is exxos diag cart with original Atari test rom AND gembench AND memtest really great.

@DoG Thanks for the links - the external cart for my own EPROMs sounds handy!

Better see what else I'm still short of for the first H4 & then see what is left (i.e. how little) in the budget... :(

@JezC I find that the schematics can be a a hindrance due to their poor quality. They do have their uses, but I'd suggest buzzing out the address lines, it's quicker, and it'll give you a more accurate picture of what's going on.

rubber_jonnie wrote: 07 May 2020 20:39 @JezC I find that the schematics can be a a hindrance due to their poor quality. They do have their uses, but I'd suggest buzzing out the address lines, it's quicker, and it'll give you a more accurate picture of what's going on.

@rubber_jonnie Ok, thanks for the warning.
I was hoping to work out which address line it was (and whether for row or column address) & use the schematics to trace all the nets on that memory bus...but maybe I should re-think that approach.

Something to ponder overnight. :?

@JezC Good luck whichever way you decide to go.