Reset Circuit
Posted: Sat Dec 12, 2020 8:41 am
Hi,
what is the component corresponding to the NE555 of the A500 on the A2000?
Thanks
G
what is the component corresponding to the NE555 of the A500 on the A2000?
Thanks
G
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I found a Rev6.2 which apparently has no damage, the battery seems to have been removed in time, but when turned on it gives a black screen. Somebody told me that the problem could be in the reset circuit and he thought it was the NE555 which is a chip that provides the reset signal to 68000 and start the A2000, but on the A2000 NE555 is not there, but it should correspond to the LM339.GadgetUK164 wrote: ↑Sat Dec 12, 2020 10:23 am PST518B - It's connected up to an LM339. Either of those could cause reset problems.
I believe the 339 is used to reset based on the keyboard clock signal (ie. when you press Ctrl+Amiga+amiga) and perhaps has a "power good" type thing going on too where it can influence a reset?
It is confusing coming from the A500!
Edit: The above is for R6, the older boards use different components:-
LM2901 - U20
7438 - U16 (related to _HLT)
7407 - U12
As soon as I turn on the A2000 it is at 0V and after one second from switching on it goes to about 5V and remains like this ..GadgetUK164 wrote: ↑Sat Dec 12, 2020 8:46 pm Yes, the reset should go low on power on, then high as it comes out of reset.
Yes, I could try, although I believe DiagROM assumes that some components are functional in order to boot. I don't think it starts regardless ..GadgetUK164 wrote: ↑Sat Dec 12, 2020 11:51 pm That's correct! It will go low for a second or so, then high. So it sounds like your reset is OK. It's probably corrosion related or a failed 245 on the buster side. Try running DiagROM!