A4000 boot question

[Castellen]

I remember reading somewhere that A4000 actually needs a keyboard or mouse connected to work, don't remember which or if both. Can anybody confirm that?

That is not correct.  The A4000D will boot without keyboard, mouse or Zorro riser board.  Obviously needs a working CPU board, both clock source jumpers set correctly (both INT for A3630, both EXT for nearly everything else).

Has it had battery corrosion?  There's a few common problems that corrosion can cause with the RTC and fast memory interface which can stop it booting.

Remove the chip memory SIMM (nearest to the centre orf the board), you should get a green screen at power on.  If not, then you probably have issues with CPU board, ROM or some other hardware issue.

[Castellen]

I think he means "a green screen"....

Good spotting, I did mean green screen.  Will fix the previous post.

[Castellen]

The previous owner sent me pictures of it running, it was through Amibay and I have no reason to doubt him.

Fair enough, the A4000 board has been recently tested so good chance it's a CPU board problem if that's of unknown origin.

Check the ROMs are in the correct sockets, that's another common mistake.  Perhaps they were swapped out and the pair was exchanged in the sockets.  Also make sure they're not in backwards, i.e. pin 1 is in the correct location.  Though that often causes permanent damage to the ROM.

Also make sure both oscillator modules are fitted, there should be a 50MHz one and a 28MHz one.  The 50MHz one is required when you're using an A3630 and clock source jumpers are set to INT.

With just CPU board, ROMs, chip memory SIMM and nothing else connected to the board, it should boot to the insert disk screen after about 30 seconds.

[Castellen]

Check that the ROMs are in the correct sockets (not exchanged) as this will also cause the symptoms you're seeing.

This photo shows where they should be, note the Commodore part numbers, i.e. 391513-xx should be in socket U175.

Failing that, you need to get a known good CPU board, or get your A3630 checked by someone with a working A4000.

[Castellen]

No, they're manufacturing date codes (January 1993 and Decemeber 1992).

Next you need to get someone to check your CPU board, or find a known good one to test with.

[Castellen]

Is the 50Mhz crystal (8 dil square) on the A4000 mobo needed for function even if CPU card is using external clock - in other words does it set the Amiga internal clock?

No, the main board 50MHz oscillator module is not used at all in external clock mode.  

So yes, that might be a problem.  On some boards the 50MHz oscillator was socketed, and because it's socketed it often means that people *have* to play with it.  If it gets put in backwards (rotated by 180 degrees) then it usually causes permanent damage to the oscillator.  Pin 1 is indicated by the one square corner on the edge of the metal can.  Pin 1 on the main board is indicated in silkscreen on the top side, and by a square pad on the bottom side as was the standard in C= PCB CAD.

It's easy enough to test if you have an oscilloscope or frequency counter - you should always have 25MHz on both INT pins of both clock source headers.  As I recall, there's a D-type flip flop or something used to halve the 50MHz clock frequency to 25MHz, and a delay line used to generate the quadrature clock (same frequency but phase shifted).  It's uncommon for those parts to develop problems however - so most likely a bad A3630, they sometimes get leaking electrolytic capacitors too that cause corrosion damage.  Or maybe a bad 50MHz oscillator.