Amiga 1200 not booting up

Pior · 06 August 2022, 18:25

I have a A1200 Rev2B motherboard that I hoping to get some guidance on. This is a bare motherboard with nothing attached but a set of good 3.0 roms it will not boot up.
It has been recapped and no damage to the board or tracers. The led power light stays dim when you first turn it on, sometimes it may flash to bright but back down to dim but the screen just stays black. On the first power up it will also flash the floppy Led even though there is not a floppy drive attached. When I stick in the my good DiagRoms and go to boot it the power light will go from dim to bright and just stay bright no flickering, I also get a full red screen on the monitor. and then the power Led will just flash evenly. I tried the DiagRom with Serial hookup with putty but never starts showing any data.
I checked U49 for 5v which I get from pin1 to pin 2. and all reset points seam to check out ok but I do not get any 5V signal on Gayle 39 or the CPU pin 22. Could this be a a Bad CIA?
Does anyone out there have any recommendations or next steps to take..

solarmon · 06 August 2022, 20:00

How are you checking the reset signals? Using a multimeter or a logic probe or oscilloscope?

Using a multimeter is not the best, as you are not really checking for 5V voltage, but whether the signal is HIGH or LOW, and whether and when it changes. A multimeter will probably not be quick enough to show the change in signal. It is recommended to use at least a logic probe, otherwise an oscilloscope is ideal.

This diagram of the reset signals may help:

https://sites.google.com/one-n.co.uk...-reset-signals

06 August 2022, 18:25	#1
Pior Registered User Join Date: Aug 2022 Location: CRESTLINE Posts: 2	Amiga 1200 not booting up I have a A1200 Rev2B motherboard that I hoping to get some guidance on. This is a bare motherboard with nothing attached but a set of good 3.0 roms it will not boot up. It has been recapped and no damage to the board or tracers. The led power light stays dim when you first turn it on, sometimes it may flash to bright but back down to dim but the screen just stays black. On the first power up it will also flash the floppy Led even though there is not a floppy drive attached. When I stick in the my good DiagRoms and go to boot it the power light will go from dim to bright and just stay bright no flickering, I also get a full red screen on the monitor. and then the power Led will just flash evenly. I tried the DiagRom with Serial hookup with putty but never starts showing any data. I checked U49 for 5v which I get from pin1 to pin 2. and all reset points seam to check out ok but I do not get any 5V signal on Gayle 39 or the CPU pin 22. Could this be a a Bad CIA? Does anyone out there have any recommendations or next steps to take..

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06 August 2022, 20:00	#2
solarmon Registered User Join Date: Dec 2018 Location: UK Posts: 1,715	How are you checking the reset signals? Using a multimeter or a logic probe or oscilloscope? Using a multimeter is not the best, as you are not really checking for 5V voltage, but whether the signal is HIGH or LOW, and whether and when it changes. A multimeter will probably not be quick enough to show the change in signal. It is recommended to use at least a logic probe, otherwise an oscilloscope is ideal. This diagram of the reset signals may help: https://sites.google.com/one-n.co.uk...-reset-signals

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