Amiga 4000 - Stability issues

[tinner]

Following on my previous thread about weird entries in the EarlyBoot Menu link and explained by Piru I am now back to where I was - stability of the whole system. Although I thought it is now stable, taking the Ami to the living room (rather to keep it in the server room) caused the stability issue to strike back...

Hardware specs I am using to narrow down the random hangs is as follows (as you can see from the previous thread - pretty much everything has been removed for testing).
Amiga 4000D rev.B motherboard
new 2MB Chip Ram Simm (straight from AmigaKit)
new 450W PSU (with adaptor from AmigaKit)
Original C= daughterboard
ScanDoubler by arXon
Battery has been removed
Cyberstorm MK3 68060/50MHz (no PPC) with pair of matched (and tested) 16MB SIMMs (70ns). Memory is set as 70ns, free from errors and properly fitted. 68060 does not have a cooler on it but I am using 80mm fan directly on top of it and it never gets hot.
I have also tried various 68040/68060 libraries and setpatches - from both the original floppys, CSMK3 original floppies and the internet... they don't seem to fix anything
Everything is taken out of the tower case and not using the SCSI hdds I have at all... System boots of the old WD Caviar 340MB with classic system (3.1) on it. It is a default installation with nothing on it apart from the DOpus 4.xx
I have also managed to grab an original A4000 keyboard off ebay so I can confirm that whenever I get random freezes the CPU is still working as the caps-lock light works whenever I press it.

Description of the issue:
Random crashes with either Red or Yellow GURU, but most often it is just a freeze of a whole system.
Example 1 - copying files from a floppy using Workbench to the harddrive, system freezes and floppy's light stays on but the head does not move at all... caps-lock still works.
Example 2 - shortly after booting with no startup-sequence and simply issuing loadwb command (with all the necessary assigns, but no setpatch running). I get a window that Workbench task needs to be suspended (don't remember the exact description - but it's the one when a task hangs). Sometimes I don't even get to the Workbench - just freezes during boot.

I am loosing hope to actually make this beast reliable again... It seems that there is a hardware issue somewhere but apart from randomly replacing capacitors or perhaps buying a new mobo or CSMK3 I cannot narrow it down on my own... Any help would be greatly appreciated...

tinner

[motorollin]

Since it came back after moving it, I wonder whether something is not connected well and came loose when you moved it. Certainly loose CPU cards, RAM and other things can cause stability problems. So try dismantling the whole machine then carefully putting it back together, making sure everything is firmly connected.

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moto

[tinner]

Hello Motorollin,
I have - the whole machine is dissasembled at the moment and the CSMK3 is firmly fitted just as the daughterboard and all the SIMMs (both the chip one and two fastram simms).
I was suspecting exactly that... but there is no way something would not fit properly now as it is out of the case and I still experience the issues. Then again it is very confusing why it worked before the move... (with old PSU)

thanks for your suggestion though
tinner

[Damion]

Definitely check for any contact issues. Step 2 IMHO would be to replace all SMT caps before getting too carried away.

[motorollin]

tinner wrote:
I was suspecting exactly that... but there is no way something would not fit properly now as it is out of the case and I still experience the issues. Then again it is very confusing why it worked before the move... (with old PSU)

Can you try with the old PSU again? Maybe there is a problem with the new one or the adapter. Can you also check the voltages coming from the PSU to ensure it is providing sufficient voltage? Reduced supply can caused stability problems.

--
moto

[tinner]

Thanks for your replies.
Regarding the voltages - will check again, although it doesn't look like it... After I've moved the computer it was still using the old PSU, became unstable so then I wanted to try with a new PSU before posting here again. So the new PSU did not change anything. Regarding the SMT caps... How difficult is it to actually do it? And what kind of caps shall I purchase and which ones should go first? I suppose I will have to dig through some schematics first... but roughly speaking it looks like I will have to ask Anthony Hoffman to fix it for me... Does anyone know any place in the UK that could help me?

kind regards
tinner

[zipper]

My towerized A4000 has the biggest problems with abundant power leads - must be 20-30 plugs there and often an intermittent plug sends the puter into crash. And don't forget the MoBo power plug, the 5V pin is under heavy stress and tends to give up slowly.

[tinner]

Hello Zipper - that is a good point...
the power rating on the old PSU for +5V is 18Amps hence the nice fat blue wire going through it... However I was a bit surprised to see the AmigaKit's adapter to have a single normal wire for +5V... Then, on top of that I am using Micronik's tower that came with a "extension" cord from the PSU to the mobo and I am still using this on my testbed as the PSU is on the top of the tower while the mobo is on the floor next to it... I will put it side by side and run few tests... thanks again any other suggestions are more than welcome.

tinner

[Tumbleweed]

You say that the battery has been removed, but what about damage to the M/B? Have you got memory on the maindboard in addition to chip ram? If so remove it and reboot.

Have a look at the caps at the back of the board, at the ports - the audio caps tend to leak and can seriously damage your board. Have a look round there for signs of corrosion.

If you thibk the board needs repairing, Amiga Centre France can do board repairs and are alot closer than Anthony Hoffman. Amikit in the UK have just started up a repair service, might be worth a look. I haven't heard any reports about them. Amiga Centre France has a good rep and gets good feedback.

[tinner]

Thanks Tumbleweed.
I don't have any memory on the mobo apart from the Chipram Simm. The damage due to the leaked battery is minor - I will post some pictures when I get back home. I've went through Anthony's tutorials and from what he's put there it looks like the caps are ok (no sign of leakage). Actually - I have a great way of comparing that as I have another dead A4000D mobo with a lot of caps leaked and the one I am "debugging" looks brand new to that one. Well Thanks for the info - will post more info and try to test the caps on the mobo... BTW, from my previous testing (have a look at the other thread from my first post) the sound did not have any distortion whatsoever - everything was working as expected.

Well.. thanks again, your support is highly appreciated.
tinner

[Damion]

Hi Tinner,

Keep in mind, those caps often begin to leak long before there are visible signs. As the electrolyte is harmful to the pcb, replacing them now (while the board is still pristine) isn't a bad idea.

Anyhow, something to consider, if everything else checks out OK. Anthony Hoffman does excellent work and is reasonably priced.

 

[tinner]

Voltages checked.
+5V = 4.96V
+12V = 12.1V
-12V = -12.0V
-5V = -4.97V
I've also tried without the "extension" cable and it did not change a thing - still randomly crashing...
Quick comparison between the dead and good mobo proves that some capacitors needs replacing - the readings on both (checking the same cap with the right polarisation) gives completely different readings. So... Gotta PM Anthony Hoffman.

Again - Thanks everyone for help. I will post more info when I have it.

[ceaser]

I have a dead 4000 too but I just bought it so I'm really mad.  It is a grey screen.  That's all I get.  Is that what you're getting too?  Or you get nothing at all?  This thing wont even boot from the floppies I've tried.