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Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 12:43
by HigashiJun
May sound stupid, but do you have the correct cable ?
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 13:05
by rubber_jonnie
Dwh18 wrote: 07 Mar 2025 12:20
Yes, all reverted ... but no onscreen duplicated on serial for sure
Is your cable a null modem cable? It needs to be.
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 13:59
by Dwh18
rubber_jonnie wrote: 07 Mar 2025 13:05
Dwh18 wrote: 07 Mar 2025 12:20
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
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 16:47
by 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.
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 18:43
by 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.
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 20:37
by PhilC
olivier.jan wrote: 07 Mar 2025 18:43
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 :D
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 21:31
by Dwh18
olivier.jan wrote: 07 Mar 2025 18:43
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
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 22:08
by Dwh18
Did some more digging and noticed u35 and u32 are different than U36 and U33. Is this supposed to be like this?
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 07 Mar 2025 22:11
by PhilC
Dwh18 wrote: 07 Mar 2025 22:08
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.
Re: Atari Mega ST 1 Rev 1 no boot
Posted: 08 Mar 2025 07:12
by 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.