Non-booting A600

[ajk]

Hi guys,

I've got an A600 board here that just does not want to boot. I have so far:

- replaced all electrolytic caps
- replaced U14 and U36 relating to the reset circuit
- installed sockets for U7 and U8, and tried different combinations of CIA chips
- checked (though not in any great detail) that there is activity in Agnus and 68000 pins
- tried different ROMs, including the Logica Diagnostic one

But always I get the same result - a light grey (possibly white, hard to say) screen. The Logica ROM goes through the motions showing all kinds of colours an then also ends up with the light grey display. The caps lock LED lights up for a brief moment when booting, and the system does respond to a ctrl-a-a-reboot.

The board looks very clean, only very slight dullness in some solder joints near the caps. Can't see any obvious damage beyond that.

Any suggestions as to how to track down the fault?

[jimbob]

Is this a different diagnostic ROM from the one you have?

http://www.diagrom.com/

Looks very useful for a partially booting board. (oh, a new version announced as I posted - http://eab.abime.net/showthread.php?t=84560 )

Sounds like the boot process is getting quite far if it stops at light grey so 68k is likely ok. Does the floppy drive click?

[ajk]

I have only tried the Logica ROM. I do know of Chucky's ROM too, need to burn one when I have EPROM equipment at hand next.

The floppy drive motor energizes when the system is started, but it doesn't click or do anything if a floppy is inserted.

[Zetr0]

@ajk

Originally Posted by ajk

Hi guys,

I've got an A600 board here that just does not want to boot. I have so far:

- replaced all electrolytic caps
- replaced U14 and U36 relating to the reset circuit
- installed sockets for U7 and U8, and tried different combinations of CIA chips
- checked (though not in any great detail) that there is activity in Agnus and 68000 pins
- tried different ROMs, including the Logica Diagnostic one

But always I get the same result - a light grey (possibly white, hard to say) screen. The Logica ROM goes through the motions showing all kinds of colours an then also ends up with the light grey display. The caps lock LED lights up for a brief moment when booting, and the system does respond to a ctrl-a-a-reboot.

The board looks very clean, only very slight dullness in some solder joints near the caps. Can't see any obvious damage beyond that.

Any suggestions as to how to track down the fault?

After reading this my first thoughts are about the keyboard MPU, should that be damaged or more likely the 3.5MHz lead-based oscillator not be pumping this will hold the Amiga in a ROM reset state.

Its a cheap fix if it is the MPU clock - I would start there.

[ajk]

Interesting. Is it possible for the ROM to be held in reset by itself? I have checked the reset line of the 68000 and that does go high a short time after power on, as expected. There is also activity on the _ROMEN (_CS) line of the ROM itself.

[Zetr0]

@ajk

The Keyboard MPU will hold the system in RESET if the 3.15MHz resonator is not functioning.

[ajk]

@Zetro

Yes, but what does the situation look like on the bus? The system reset line is correctly held high, on at least some of the chips including the 68000. Would it still be worth getting a keyboard controller and swap it out? I haven't got a replacement in stock. I'd just like to be sure that it is indeed the culprit, before buying one.


I checked just to be sure - the oscillator seems to be providing the correct frequency: