A1200 Dim Led, Black screen :-(

[nadoom]

Hello Chaps,

I am having a right mare trying to find out what is wrong with an A1200 I have acquired. Its a 2B mobo, and when power is applied from a good working PSU, I am only getting a black screen , led remains dull.

Power seems to be reaching every where, +12,-12 and +5 is ok.
My oscilloscope is showing that all the address lines show no activity, so its as if it isn't starting at all.
None of the chips get hot, alice gets a little warm.
There is now CCK4 signal to the crystal so i am thinking budgie may be nackered?

Your suggestions would be really useful.  I am a mid level noob (although I have built a A500++ and a floppie A2000), good at sticking stuff on a motherboard but find it hard to know where to start with actually diagnosing issues.. so if any of you have some ideas where I can  make a start please let me know?

Cheers

Nad

Thanks in advance!

[nadoom]

Hey,

I am going to be recapping it very soon, just waiting on the caps, however nearly all the caps are related to things other than the black screen ( or so I read ) so i think i should still get something from it other than the black screen?

Its got 3.0 Roms, I've tested these in a working A1200 and they do work fine.

Diagrom hopefully will help, I am waiting for 2 x EPROM to arrive for that, I only have 1 EPROM at the moment ( for A500 Diagrom) so it doesn't work in the 1200


Thanks for your replies

[nadoom]

Hi I gave it all a good clean, and also resoldered the connection to the rom's, still getting a black screen.  Very strange, what else could it be? CIA's maybe?

[nadoom]

A chap on amigalove pointed me in the direction of the reset and halt signals on the 68020.. They were both low, so came across this helpful diagram:

https://imgur.com/hiDZrS7

So I tested U49 which is a voltage detector apparently. basically it was outputting 1V rather than 5V so this turns out to be the issue.

I tested the theory by connecting pin 1 with pin 2 so that line was 5V and the A1200 Led went bright and it the kickstart 3.0 screen was shown!!

Turns out its fairly common:

https://www.tsb.space/knowledge-base/replace-amiga-cd32-1200-voltage-detector-with-a-tc54vc/

Thanks to everyone that helped out, also to Amigakit guys for moral support :-D

Nad