exxos's Atari, Amiga & retro forum

@dml ok so I had a soldering issue with the Max232 and the serial chip next to the CPU, this was preventing the comms from working.

What I did was to see if we had bus activity, which I did, so I'd check the data and address busses, if they are working, it's likely a fault with the serial chips.

Once you have the serial working then it will list each step, ie mfp ok, ram found at..... Etc.

Oh and that tiny chip next to the Eiffel chip I had the wrong way round as it was nearly impossible to see the pin 1 marking. I swapped it and then it all worked serial wise.

Also remove the 48mhz oscillator and put the 40 in, in case your atf1508 and the 68150 don't like the higher block speed.

PhilC wrote: 07 Jul 2025 10:52 @dml ok so I had a soldering issue with the Max232 and the serial chip next to the CPU, this was preventing the comms from working.

What I did was to see if we had bus activity, which I did, so I'd check the data and address busses, if they are working, it's likely a fault with the serial chips.

Once you have the serial working then it will list each step, ie mfp ok, ram found at..... Etc.

Oh and that tiny chip next to the Eiffel chip I had the wrong way round as it was nearly impossible to see the pin 1 marking. I swapped it and then it all worked serial wise.

Also remove the 48mhz oscillator and put the 40 in, in case your atf1508 and the 68150 don't like the higher block speed.

Thanks for the tips - will see what I can find in that order.

I did try changing the MFPs since they are socketed but wasn't sure if they were critical for the UART since it has its own path. In any case it didn't change anything.

Will follow things back from serial inwards.

dml wrote: 07 Jul 2025 10:32- Power LED turns on/off with power button.
- 5v / 3.3v / 12v confirmed on rails, various ICs.
- Booting with ISA video cards (tested 2) shows no activity. Video remains dark.
- No activity over serial @ 115200/N-8-1.

Isn't that great, now you are nearly in the same spot as I am with my Falcon. :D

When I watch the data lines on the 68752 near the CPU, I see some kind of activity after a RESET. Looks like something digital is happening but it is not very tidy so difficult to say more than that.

When I look at the MAX3245 however, I see the VCC pin is sitting at 5V when the schematic says 3.3v. (pins 22,23,26 all at 5V)

The COM1:TXD seems to float up to about 7.5v.

[edit]

Some corrections....

One of the MAX3245 (U305) reads 3.3v for VCC and 7.3v at pins 27/28, which seems to be there for driving the serial levels.

The other MAX chip reads 5v for VCC and 6.0v at pins 27/28.

[edit]

Don't see anything wrong around here. Will go back to checking clocks everywhere.


J106 is still open - is that important? Can't see what it is supposed to do from the schematic.

Also I'm not sure how to configure J105 etc. to run things at a lower 'debugging' clock rate for capturing logic etc.

dml wrote: 07 Jul 2025 11:59 J106 is still open - is that important? Can't see what it is supposed to do from the schematic.

It is an optional user jumper for Nessi for future firmware revisions I'm told.

Have you had a look at U304? It's one of those fine pitch things that are hard to notice open and shorts on. It's the one just to the upper left of the CPU.

Looking at the ATF1508...

It is coming out of reset.

BCLK/83 = 40MHz
BCLK_X2/2 = 80MHz
CPUX2/10 = LOW
CLKEN/12 = 40MHz (?)

RW/28 = some pulsing after reset

Some activity on address lines too.

sety wrote: 07 Jul 2025 12:57 Have you had a look at U304? It's one of those fine pitch things that are hard to notice open and shorts on. It's the one just to the upper left of the CPU.

Yeah I have been over all the small stuff several times with a microscope & pushed all the pins with a needle. Everything looks good. I'll do another round checking for shorts under the ICs but I doubt it.

[edit]

Yep no shorts/bridges where they shouldn't be on the small ICs. Only those which match the schematic.

Orientation of U101 and U102/105 (I cant remember which one) is correct? I walked straight into it and I'm not the first. They look identical but they mirror each other.

sety wrote: 07 Jul 2025 13:27 Orientation of U101 and U102/105 (I cant remember which one) is correct? I walked straight into it and I'm not the first. They look identical but they mirror each other.

Orientation correct - but I'll need to check the 74 ICs are all in the correct sites and not accidentally swapped over or something....

Found something..... update soon....

I found 2 dry legs on the RAM SIMM, fixed those, all pins confirmed on the RAM board. No change in results though.