4mb STFM SMD Ram upgrade - FAILS TO BOOT :(

[exxos]

Thanks, I'll give it a try in the morning - unsoldering the switch wouldnt help test it?

Yeah you could do that or just unsolder the wire, doesn't make any difference.

[rubber_jonnie]

Hi @Lurch the black foreground is usually a sign of a memory issue, so id investigate that first.

As PhilC says, a border with a black or black/corrupted central screen area is memory without much doubt. You could verify with a diag cart, but I've seen this enough times to be fairly sure. The colours are not really relevant here, but the picture is.

as exxos suggests, dropping it to 1MB only will help to understand just what is going on.

When looking for solder bridges, you must also consider if you've removed all the old RAM (Not just the spots where the pins connect), are there any solder bridges at the old RAM locations, either underneath or on the top of the board.

This also looks very similar to a problem I had with a Mega 4, and it was the data lines from the CPU to the MMU, 2 were broken. Buzz out all the lines going to the memory card to check for shorts between the connections and also to GND, and also buzz out the data lines from the CPU to the MMU. If you have a logic probe, then use that to check the state of the data lines at the CPU and the MMU. Any that have a different state, or don't buzz out could be bad and require fixing.

I've attached a ZIP file with a word doc in it that has all the pinout information you need for the CPU and MMU data lines.

[Lurch]

ok, I removed the single wire AND the 1-4mb switch.

STILL wont boot :(

However, instead of having white dots in the black screen area (as in picture above) - the black 'paper' is now solid black.

So, should I now remove the ram upgrade and check all the previously populated ram IC points for a short?

(The black foam it ships with - having that covering the pins while testing the board wont cause anything will it - I'm reasonably sure its non-conductive?)

[rubber_jonnie]

The black foam is conductive, so remove it.

Before you de-solder everything, flip the mainboard and test for shorts on that side, it could save you some work.

[troed]

However, instead of having white dots in the black screen area (as in picture above) - the black 'paper' is now solid black.

This means that you have different memory errors in different banks - which unfortunately is an indicator that there's more than one fault to find.

/Troed

[Lurch]

Hi,
I've removed the 4mb ram upgrade, cant see any obvious problems on the board.

I'm wondering, would the board power up with 0mb ram?

Thanks

[czietz]

I'm wondering, would the board power up with 0mb ram?

Without RAM, TOS won't boot and you will not get any meaningful screen output. The diagnostic cartridge is able to output error messages over the serial port even on a board completely without RAM.

[Lurch]

Without RAM, TOS won't boot and you will not get any meaningful screen output. The diagnostic cartridge is able to output error messages over the serial port even on a board completely without RAM.

I've had a quick seearch for diagnostic carts, but not really found anything useful - I'd like to purchase one from the UK if possible

[exxos]

I've had a quick seearch for diagnostic carts, but not really found anything useful - I'd like to purchase one from the UK if possible

Those are in my UK store... click SHOP in the navbar.

[rubber_jonnie]

@Lurch If you're getting a diag cart, I'd also suggest you get a null-modem cable. Diag cart is here: https://www.exxosforum.co.uk/atari/store2/#0165

If the ST can't display on screen, which without memory is likely, then you can connect the null modem cable to a PC with a serial port an use a terminal app like Teraterm to see the diag cart output over serial.

You can power on without RAM, most likely you'll just see a white border and black central screen.