Variation on A4000 dark gray screen problem

[orb85750]

I have an A4000 with a very clean motherboard, but it has a dark gray screen boot problem.  I disconnected everything.  Once the insert disk screen came up for about 10 seconds, but then it reverted to the dark gray screen.

I noticed that the PSU fan speed was all over the place, so I thought it might be the PSU.  I replaced it with a known working one.  I powered up and all seemed perfect for 30 seconds, but then the damn dark gray screen popped up again.  Since then, I have been unable to get it to work again at all.  I tried a different CPU card, but that didn't help.  All the chips/memory are secure.

Has anyone experienced anything like this before?  It seems to be so close to working.  I'm stumped.

[orb85750]

It smacks of a ram problem, maybe tarnished sockets. Be sure the chip simm is in the right socket and is indeed a chip simm.

Look the Pins in the psu plug over well, if 1 is tarnished or spread open a bit it may be a bad connection problem, usually on the +5v wire.

Reseat the A3640 accelerator board and make sure its on the plastic standoff pins.

Have the caps leaked on the A3640? they are known to eat a trace under the leaking caps at times.

check all jumper blocks. move them on the pins and be sure they are making contact.

Mech

I have another machine that's working, so I can move in known working
parts -- and I have done some of that (PSU and CPU card), without success.
I don't want to mess with my working machine too much or I might end up
with two non-working.

Memory & sockets look good.  I removed the fast ram, which did not help at all.

PSU is good.  I tried my other (working) PSU with same result.

Reseated A3640, no help.  Still same problem if I insert my working A3630 too.

No leaky caps anywhere, as far as I can tell.  The machine looks damn good and clean,
much better than my working machine.

All jumper connections checked.

THE POWER LED is flashing about once per second.  Does that have
any specific meaning?

Any other suggestions, anyone?

[orb85750]

Do you see a light grey screen before the dark grey.?
If not then I suggest your machine is not getting to the post test.

Taken from the Amiga 4000 Service Manual:

"Passed Test

Light Gray Initial hardware configuration tests passed.
  Initial system software tests passed.
  Final initialization test passed.

Failed Test

Red ROM Error - Reseat or replace
Green CHIP RAM error (reset AGNUS and re-test)
Blue Custom Chip(s) Error
Yellow 68000 detected error before software trapped it (GURU)

The system performs the following test sequence:

1.1. Delays beginning the tests a fraction of a second to allow the hardware to stabilize.

2.Jumps to ROM code in diagnostic card (if found)

3.Disables and clears all DMA and interrupts.

4.Turns on the screen.

5.Checks the general hardware configuration.

If the screen remains a light gray colors and the tests continue, the hardware is OK.

If an error occurs, the system halts.

6.Performs checksum test on ROMs.

If the system fails the ROM test, the screen display turns red and the system halts."


Does the sequence above occur or are you seeing dark grey from switch-on ?

Try booting with just the fast ram in the fast ram sockets and see what that does. any difference?

Then try booting with both mouse buttons held down.  Any difference?

Might be telling you to suck eggs but only make one change at a time each time you try to troubleshoot.

There is a minute chance that something is wrong with video set-up and you are dropping to a grey screen because logically that is what is being displayed.?

Thanks for the suggestions.

It goes directly to the dark gray screen -- no light gray seen at any point.

If I remove the chip ram and leave in some fast ram, I get a bright green screen.

Putting the chip ram back in, I'm back to the dark gray.

If I boot and hold down both mouse buttons, there's no difference -- still dark gray.

[orb85750]

I highly doubt that I have any jumper settings wrong, given that the machine did work very briefly the other day.  Even if I remove all the fast ram, it does not boot with the chip ram.  The daughter board was taken out and had no apparent effect.

Anyone else have any ideas as to how this machine was not working, then working very briefly, now not working no matter what I try?  

I can throw my A3000 against the wall and it will still boot.  These A4000 machines are very finicky?

[orb85750]

If anything A4000's are inhearantly more reliable than 3000's due to surface mounting.

The psu's are pretty good. The 3000 suffers from 20 year old sockets that tarnish and make bad contact. Thats being said i have had good success making either run reliable.

Its much like a used car, sometimes used computers have been treated badly or developed problems. Used is used

have you physically pulled the roms and reinstalled them, i have seen roms with a pin bent under that makes contact at times.

i still think you have a trace thats eaten under the A3640 or a contact problem on ram or cpu slot.


mech

Sure, maybe I've just been lucky with the A3000 and unlucky with the A4000 -- I'm not the original owner of any of these machines, so I know nothing about their histories.

How can there be a bad trace in the area of the CPU slot?  (How would that happen?)

RAM problem?  I do get a green screen when I remove the chip ram, then back to gray when it's installed.  The fast ram cannot be the cause (since it has been removed).  Wouldn't I simply get a green screen if there were a contact problem on the chip ram?

CPU slot problem?  Maybe that's where I need to concentrate.  I will also physically pull the roms -- haven't done that yet.

Thanks again.