Variation on A4000 dark gray screen problem

[gertsy]

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?

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.?

[gertsy]

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.

Okay so its not a video issue.  And by removing the ram you've shown the basic hardware and POST is working, so that's encouraging.
I guess you've tried booting with just chip ram.?
I think the flashing pwr light LED means there is a system error in general.  As that's what happens if you guru on restart.
Another suggestion is to remove the riser card and see what happens.  Rarely they can have issues but they usually cause addon card issues rather than system halts.
Finally take the MB out and check both sides carefully with a magnifying glass checking for component damage or bad joints. Then reassemble and verify your jumper settings:

Fucntion:            Jumper:    Setting:   Description:
CLK90 Clock Source   J100:1-2   X-X X      Internal (020/030)
                     J100:2-3   X X-X      External (040)
CPU Clock Source     J104:1-2   X-X X      Internal
                     J104:2-3   X X-X      External
ROM Speed            J151:1-2   X-X X      200ns
                     J151:2-3   X X-X      160ns
CHIP RAM Size        J213:1-2   X-X X      2 Meg
                     J213:2-3   X X-X      8 Meg (yeah right)
Enable Second        J351:1-2   X-X        No Second internal floppy drive
Internal Floppy                            or 1.76MB floppy drive
                     J351:      X X        Enable second internal floppy drive
                                           880k as DF1:
Redirect DF0:        J352:1-2   X-X X      Internal: DF0: and DF1: internal
                                                     DF2: and DF3: external
                                           External: DF2: and DF1: internal
                                                     DF0: and DF3: external
Enable DSACK         J850:1-2   X X        DSACK enable. Required if CPU is a
                                           68020. Also requires U860 and U152.
                     J850:1-2   X-X        No DSACK.
RAM Size             J852:1-2   X-X X      RAM size 1 Meg x 32
                     J852:2-3   X X-X      RAM size 256k x 32
Select NTSC/PAL      J212:1-2   X-X X      Select NTSC
                     J212:2-3   X X-X      Select PAL
VBB\MA10             J214:2-3   X X-X      Supplied VBB to ALICE
                     J214:1-2   X-X X      ALICE supplies MA10 for 8 Meg CHIP
                                           (NO it DOESN'T WORK!)
Select Sync on Green J500:1-2   X-X X      Sync on Green Disabled
                     J500:2-3   X X-X      Sync on Green Enabled
LISA Sync            J501:2-3   X X-X      Default
Select DAC Sync      J502:1-2   X-X X      DAC Syncs on Green
                     J502:2-3   X X-X      DAC used standard signal

[gertsy]

I generally find the opposite; the A3000 is full of low quality IC sockets that tend to cause various issues over time.

Anyway, sounds like you've tried pretty much everything you can.  The 2nd CPU board you tried - was that a known working one?

If you run out of the options, I can have a look at the board for you.  A couple of years ago I developed special hardware and software to report stages of software execution in A4000 ROM during boot which makes it possible to see exactly where the machine is failing during boot.  Then it's possible to proceed with a repair based on the clues it provides.

http://amiga.serveftp.net

Welcome back from Antarctica? Castellen, Hope you had an interesting time...

[gertsy]

Sorry to bump this year old thread, but I just had exactly the same situation that OP described, and it turned out to be something nobody mentioned yet in this thread. So for the next person to have this problem and search Google, check your VGA adapter:

Problem was caused by my VGA adapter which was just a straight cable adapter inside. When connected to my LCD monitor the A4000 displays only a dark grey screen unless I pull the chip RAM, then it shows a green screen. If I power it on with the monitor disconnected, wait a few secnds, and then plug the monitor, I see the "insert disk" animation and everything works as expected.

I was able to solder in a buffer chip to my adapter on the sync lines and now everything works fine.

Certainly seems to be exactly the same symptoms. The plugging in of the monitor after booting sounds like a great trouble shooting technique. Well done!

Another is to revert to a 15khz capable Commodore monitor and standard Amiga video cable. Which I think we all assumed orb85750 was already doing.  If not, and it is the same problem as you had, then it's a good reminder to always give an overview of your system and it's connectivity before relating the problem.  Removes a lot of educated guessing. Even electronics professionals like Castellan can't read people's minds from a post. Face to face maybe.

I wonder if Orb85750 ever solved his problem....