Atari Mega ST 1 Rev 1 no boot

[HigashiJun]

May sound stupid, but do you have the correct cable ?

[rubber_jonnie]

Yes, all reverted ... but no onscreen duplicated on serial for sure

Is your cable a null modem cable? It needs to be.

[Dwh18]

Yes, all reverted ... but no onscreen duplicated on serial for sure

Is your cable a null modem cable? It needs to be.

Bought it as a null modem.... might try with another one

[rubber_jonnie]

Can I suggest you get some photos of the areas you've repaired when removing the RAM expansion and also a video of what you see during the boot on your terminal.

[olivier.jan]

If you have a little serial to usb adapter (like ftdi232), you can connect RX and TX to pin 8 and 9 of the MFP (and GND anywhere on the motherboard’s ground), it will work directly at 9600 bauds.

[PhilC]

If you have a little serial to usb adapter (like ftdi232), you can connect RX and TX to pin 8 and 9 of the MFP (and GND anywhere on the motherboard’s ground), it will work directly at 9600 bauds.

That's a great tip actually and helped me fix something totally unrelated and non Atari

[Dwh18]

If you have a little serial to usb adapter (like ftdi232), you can connect RX and TX to pin 8 and 9 of the MFP (and GND anywhere on the motherboard’s ground), it will work directly at 9600 bauds.

Ordered this one

IMG_4372.jpeg (192.12 KiB) Viewed 534 times

[Dwh18]

Did some more digging and noticed u35 and u32 are different than U36 and U33. Is this supposed to be like this?

[PhilC]

Did some more digging and noticed u35 and u32 are different than U36 and U33. Is this supposed to be like this?

Are they the 74LS244 & 74LS373 chips? If so you should have two of each.

[olivier.jan]

The adapter you have should work, what I was mentioning are the little usb to serial (not RS232) like this: https://amzn.eu/d/dCjUFvn.

Anyway, if you want to check : Pin 8 of the MFP is TX while pin 9 is RX. So, if the diag cart is sending dat, you should see activity on pin 8 when you start the ST. You can test also the other direction: if you type data in your serial terminal it should generate activity on pin 9 of the MFP.

If you have an oscilloscope, checking will be pretty easy. With a multimeter, set on DC, you should see some voltage variations when there is activity.