A4000D - Yellow screen

[Tumbleweed]

After sorting out my A3000T no booting issues (now works fine after reverting back to 3.1 Rom from 3.2 and putting 3.2.1 Rom in my Deneb) Ive dug out my knackered A4000D.

This is my own machine from back in the day when it first came out. Its a 030 model from c1992. This machine has had its problems - battery leak and leaking caps. It would work (broken sound though) but would boot and it was my main Amiga for a few years until I got my 3000T. A while back c10 years the 4000D finally gave up the ghost. I had someone look at it for me. The caps were replaced and there was lot of other repair work to fix broken traces and the RTC circuit. When I got it back it booted to kickstart but then failed - black screen; yellow screen; green screen. I put it away and since then haven't thought much of it.

I dug it out last night and gave it a go - I'm getting a yellow screen; remove the chip ram and I get a green screen. Im not convinced the 2MB Chip Ram SIMM I have is 100% - its double sided but whether its working or not I don't know and cant test. Ive ordered a 2MB SIMM from Analogic. So that could be the issue or it could be more involved.

I had a look round the board and its not a pretty sight. Signs of corrosion in the RTC area (I'm going to wash down with vinegar). The resistors R895 show signs of corrosion.

Would these result in a 'yellow' screen?

Weed

   

[SACC-guy]

yellow is error trapping

I know this isn't much.. but it's all I've got

[RetroPassion]

If you get a yellow screen, your chip ram is fine, green screen means bad or missing chip ram. The issue maybe a simple thing of broken tracks around that area, as there is some green, clean it all up and start testing the area for continunity between compoents and VIAS. it will take time but worth it :-)

[Tumbleweed]

Happy New Year!.

Ive been checking over the board with my multi meter (Santa got me a new one). Continuity looks to be ok so far (i need to remove the coin cell battery holder to get to Pins 1 -5 of U177. Ive used Amiga PCB explorer as my reference guide together with Anthony Hoffman's guide to repairing the RTC.

What I have noted is the voltage on R994 is c2.52v the voltage on all the other resistors in that bank are close to 5v; 4.93 - 4.94v. PCB Explorer shows it should by 5v. Output from the PSU is ok close to +12v +5v all check out ok.

I have a set of diag ROMs arriving this week - plan is to install them and see what happens. I also have a new 2MB SIMM coming for the Chip Mem. The double sided SIMM I have I cant remember if its the original or not and I dont think Ive got an old motherboard I can use to check if its ok.

If U177 is knackered (Ive read that it is often a culprit) where can I get a replacement part and how tricky a job is it to de-solder the existing one and solder on the new one?

Weed

[RetroPassion]

Happy New Year!.

Ive been checking over the board with my multi meter (Santa got me a new one). Continuity looks to be ok so far (i need to remove the coin cell battery holder to get to Pins 1 -5 of U177. Ive used Amiga PCB explorer as my reference guide together with Anthony Hoffman's guide to repairing the RTC.

What I have noted is the voltage on R994 is c2.52v the voltage on all the other resistors in that bank are close to 5v; 4.93 - 4.94v. PCB Explorer shows it should by 5v. Output from the PSU is ok close to +12v +5v all check out ok.

I have a set of diag ROMs arriving this week - plan is to install them and see what happens. I also have a new 2MB SIMM coming for the Chip Mem. The double sided SIMM I have I cant remember if its the original or not and I dont think Ive got an old motherboard I can use to check if its ok.

If U177 is knackered (Ive read that it is often a culprit) where can I get a replacement part and how tricky a job is it to de-solder the existing one and solder on the new one?

Weed

Hot air and flux is the best way without risk of damage, if you need the chip we can send you one free of charge if needed.

[Tumbleweed]

Cheers Retro thats very kind.

I removed the coin cell battery holder and completed the continuity checks on U177 with my multi meter. All checked out ok.

I got a new 2 MB double sided SIMM during the week and the set of diag roms arrived today.   I fitted the 2 MB SIMM and the diag roms. The machine boots into Diag ROM. Ive not used this before but from what I can see on the opening screen it is seeing the A4000D as a 68040 (I replaced the original 030 board with a A3640 v3.1 which I know is working) with 2MB Chip Ram.

What tests should I run and what should I be looking for?

One other thing I noted the machine wont soft reboot. I get a black screen when doing so. I need to switch it off for a period 10 mins and then switch it back on. This was a previous fault that I had someone try to fix previously but they weren't able to. The M/B has a quite a few wire adds around the audio circuit (I guess these are repairs to broken traces) but also looks like the power connector has been removed and resoldered back to the board as I can see traces of flux residue on the underside of the PCB. Also the caps next to the connector have wire adds on the top-side of the PCB I guess these are fixing broken vias / traces.

No I have it doing something more than a just a yellow screen I am a bit more hopeful that the board might be salvageable but given I am a novice at this its going to be a lot of googling and trial and error.

Weed

[Tumbleweed]

Screenshots of Diag ROM. First one with 2MB Chip Ram installed  on m/b; second one 2MB Chip and 4 MB fast installed on board; 3rd one RAM test - fails.

[Tumbleweed]

After a bit of thought overnight I replaced the rev 09 Buster with an older (rev 07) I extracted from my 3000T (I upgraded it to a rev 11). I booted the 400D using diag rom. This time its reporting 4MB of useable fast memory (last night it was showing 0 useable). I then swapped out the diag roms for 3.1 roms and powered on. After a few seconds it boots into kickstart. This makes me think Ive got an issue with Buster or something related to it.

A couple of questions:

- can you run a A4000D with a 07 Buster?

- I know the 07 doesnt support Zorro III bus masters, so maybe thats where the problem with the board is and by using the 07 Part it in some way 'fixing' the problem (?)

Can anyone give me some pointers as to what I can test for?

Weed

[cehofer]

FYI,

About 10 years ago, I found an A4000 MB on ebay yellow screening.  I started poking around on it and found and I don't know how they did this but Buster was installed 90 degrees out and forced into the socket.  I carefully  got it out and put it in correctly.  It booted right up.  At that time I was able to get a Buster 11.  So yellow is definitely Buster.   I was surprised by putting in the chip 90 degrees out didn't fry the board. 

Since then, I recapped it and still runs great!

[Tumbleweed]

Thanks cehofer. I managed to get a Buster 11 (from Analogic) arrived today and I fitted it. Machine boots fine. I still have an issue though - I am not getting AGA in workbench, Ive read that this could be a problem with the shift registers U975 and U976.

Ill do some more testing round these at the weekend when I have time. The area round these has been repaired previously could be broken traces or maybe they need replacing.

Machine boots and I was able to play Banshee so mouse and joystick ports are OK.

Weed

[RetroPassion]

I would remove those chips, test for continuity and replace with new, this saves a lot of time :-)

[cehofer]

Yes.  On another A4000D I have, I had to replace all 3 chips and trace repair by the battery because of leakage.  I actually lost one direction of mouse, aga, and real time clock.  It wouldn't find it and I could not save the time manually.  There is a trace that runs back to the ROMs I think that tells it that it is AGA capable.  It sounds like battery damage.  Even if it doesn't look that bad, over time the chemical reaction just keeps dissolving the traces.  I think I got the 3 chips on Ebay or Digikey.  It has been a couple years now.

It was scary and fun at the same time to desolder each chip with my new solder/heat gun station.  You have to use a heatgun.   I watched several videos on Youtube before attempting desoldering.  I think there is a guy that actually does the battery damage repair on youtube.  I have been soldering for years but that was my first at surface mount chips.

If you have battery damage, It can creep all the way to the through hole eyelets and damage the connection.  I recommend an ohm meter and ohm all the connections.  It looks like from your pictures that you have the battery damage creeping with the discoloration on the board.  Once you get the chips out, you can clean the board with alcohol.  BTW, It really sucks if it creeps to the right and damages the RAM socket.

[Tumbleweed]

Cheers Retro thats where I think I'm heading. I have checked continuity from U976, U975 and U177. All seem ok. My thinking is to get new parts for all three and replace the existing chips. Looks like a reasonably straightforward process provided you have the right tools - hot air de-soldering / soldering station.

Hot air seems to be the recommended approach but rework stations are quite pricey. But that said packaging and shipping the board to someone else is also quite pricey.  Or can you get by with a decent soldering iron and solder braid to remove the existing chips? Much more affordable!

Weed

 

[Tumbleweed]

Cheers cehofer. I got some IPA delivered today and have given the board a good clean. It looks a whole lot better now. I had cleaned it with vinegar first. Rest of board looks ok. I had the caps replaced a few years ago and they look ok.

Weed

[cehofer]

FYI,

Even after I fixed all the continuity of the traces and before I replaced the chips, it still didn't fix my problems.  I was really discouraged at that point.  It wasn't until I removed, cleaned and replaced the 3 chips that it fixed my problems.

I purchased my solder/heat gun station 4 years ago on ebay for around $250 US.  I did because I had 2-A4kT, 3-A4kD, and a CD32 to recap as well as their power supplies.  I wanted nice heat control to be able to recap the smd caps.  I am still not fully confident on using a heatgun to remove chips.  I purchased an IR table to preheat. 
There is a guy in NZ who is highly recommended and not cheap.  There is pretty much nobody in the US that does it that I am aware of.  I am scared that my stuff would get lost or damaged if I shipped it all the way to NZ plus the shipping would be outrageous.

The solder station was a good investment.  I have used it to repair a lot of other stuff too besides my Amigas.