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Re: Amiga 2000 stopped working...
Posted: 14 Jun 2024 16:49
by stephen_usher
My hunch is that the system is halting as soon as the ROM code tries to do any I/O.
Given that the first thing that DiagROM tries to do is write to the serial port but the Kickstart ROM probably does a memory test first would be why one runs for longer before stopping.
Re: Amiga 2000 stopped working...
Posted: 14 Jun 2024 16:57
by BennehBoy
So that circles back to a bus error then? And maybe those LS245s?
Re: Amiga 2000 stopped working...
Posted: 14 Jun 2024 17:24
by terriblefire
:!:
stephen_usher wrote: 14 Jun 2024 16:49
My hunch is that the system is halting as soon as the ROM code tries to do any I/O.
Given that the first thing that DiagROM tries to do is write to the serial port but the Kickstart ROM probably does a memory test first would be why one runs for longer before stopping.
But since he's measured ROM /OE and it never goes low it's not. It's not even enabling the ROM to execute code
Re: Amiga 2000 stopped working...
Posted: 14 Jun 2024 17:32
by Kepler
This is interesting...if I remove U300 and measure the voltage at pin 2, it reads 0.45v at start up. If I insert U300, it measures 5v at start up...
Actually, now that I have seen and read the previous posts, this is correct behavior.
Re: Amiga 2000 stopped working...
Posted: 14 Jun 2024 18:05
by BennehBoy
You said you tried all the custom IC's in another board... what about the CPU? EDIT, although it wouldn't explain OE on the ROM...
Re: Amiga 2000 stopped working...
Posted: 14 Jun 2024 18:07
by Kepler
I wish I had missed that and it was the cause of this grief...but it was the first IC I replaced. ðŸ˜
Re: Amiga 2000 stopped working...
Posted: 14 Jun 2024 22:24
by terriblefire
Kepler wrote: 14 Jun 2024 18:07
I wish I had missed that and it was the cause of this grief...but it was the first IC I replaced. ðŸ˜
Is there any way you can capture /AS low and ROMOE at gary at the same time on your scope? trigger on the falling edge of /AS once .. if you could hold the machine in reset with the power on beforehand that would be even better.
Re: Amiga 2000 stopped working...
Posted: 15 Jun 2024 03:24
by Kepler
Capturing both would require two leads presumably?
How do I hold the machine in reset with the power on?
Re: Amiga 2000 stopped working...
Posted: 15 Jun 2024 13:39
by terriblefire
Kepler wrote: 15 Jun 2024 03:24
Capturing both would require two leads presumably?
How do I hold the machine in reset with the power on?
Short the reset line to ground until you are ready or if you have a helping hand hold CTRL-AMIGA-AMIGA , set the scope to trigger then let go.
Re: Amiga 2000 stopped working...
Posted: 15 Jun 2024 13:57
by stephen_usher
@terriblefire given that the OP is reporting different symptoms depending upon which ROM is installed, do you think it may be a good idea to perform this test without either ROM installed, just in case the fault is being compounded by the ROM chip(s)?