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

   

[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

[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

[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

[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

[Tumbleweed]

I might just incur the cost of getting a proper rework station. The guy in New Zealand fixed my A3000T a couple of years back. Top job too. Board looked brand new when I got it back and he helped me when I had a couple of teething issues when I re-installed it in the tower - I messed up refitting the ZIPs.

Ive got a 2000 & 3000D that need recapping and a A1200 thats 'dead' - black screen no sign of life so might just might be able to justify the cost.

Weed.

[Tumbleweed]

That look like it will do the job. Its similar to one I was looking at on Amazon. I'm in UK so found this one on ebay:

https://www.ebay.co.uk/itm/255844036734?hash=item3b917e307e:g:K-oAAOSwHYZjfx3f&amdata=enc%3AAQAHAAABEA41IEMvOn9XcvsOaMj3kN%2BRAxMpMmTBHG%2BJjzGnUpSiyWivfuos5YsCm3xI4ue7fmGCnuRtb2%2B2J%2Bz3YP1x0Lgv0cqwu%2BBssT%2BlHKkq2BIE84Wqw8t40r9wpSttl8jseh9%2BAXRFnbExZfdr2WrlQDNard78AK8fVDkeEw7ezk6jzaE7ybpEQrf0BNYmv6fmLPZ5LN3fiVkDVg47KfAKr7be12f0i1kMidjFMfJ0vknCbKoV6Sc8pc7Fwd9bE7mhiDg%2F8txI4hvQPoFPS4W3xq%2BW0z9tjJEIT7%2BuB4arSZHdRWJuMEWjB8f0oy4C4VYbdTWHfe%2BxJLI25vVWoRvrEXVWjEabCVnHaGgG3%2BOkYS4b%7Ctkp%3ABFBM4sCpm7Zh

The one on Amazon I was looking at was this one:

https://www.amazon.co.uk/Soldering-Temperature-Stabilization-Function-Electronic/dp/B08YD66SXZ/ref=sr_1_2?crid=2VUX6G0U65A6I&keywords=YIHUA+862BD%2B+SMD+ESD+Safe+2+in+1+Soldering+Iron&qid=1673725925&sprefix=yihua+862bd%2B+smd+esd+safe+2+in+1+soldering+iron%2Caps%2C74&sr=8-2

Both look similar. Think I might go with the one you suggested if it does the job and it is more within my budget.

I checked all the traces from U975 and U976 respectively. U975 connectivity was all good. U976 wasn't (least Im not sure).

U976 Pin 14 to the resistor R989 ok; resistance 4.68 ohms; voltage 4.77v (Amiga PCB explorer puts resistance at 4.75 ohms and voltage at 5v). My readings look ok compared to that (?). Connectivity from R989 to J975 Pin 11 - none. No connectivity at all. Is this ok? And also what is header J975 for?

U976 Pin 10 to the resistor R992 on the underside of the board ok; resistance 4.63 ohms (that seems a tad low Amiga PCB explorer has it at 4.75 ohms). Voltage I measured at 4.9v (Amiga PCB has it at 5v) that seems ok. However no connectivity to J975 pin 5. None. Is that ok?

And I made a discovery when I turned the board over to check R992 - there is no capacitor at C177. One of the Pads has gone too.

Nevertheless I have been able to play with it - have got the OS installed and hooked up a Iomega ZIP100 to it that I got off ebay this week. I have it connected to the net using my plipbox (borrowed from my 3000D) however it seems temperamental. Sometimes it works sometimes it doesn't. Could be a problem with the parallel port or me being dumb in setting it up.

Cheers for your help.

Weed

[Tumbleweed]

I dug out an old soldering iron, not a quality modern one, and was able to address some of the the things I had identified.

R994 had lower than expected voltage.  My multi meter measured c2.4v when Amiga PCB showed it should have been closer to 5v. There was no connectivity between the resistor and the 5v rail. I fixed  it by adding a blob of solder between Pin 1 and the via #1795. Multi meter now reads +5v.

R975 (underside) wasn't connected to ground. I fixed that by adding another blob of solder between Pin 2 and via #11570.

Booted up and still only 16 colours in WB; ATK shows I still have probs with Alice - 'AGA Alice with bad Lisa ID'. So still some ways to go.

Weed


 

[Tumbleweed]

Hi all,

After a lot of connectivity testing, de-soldering, resoldering I got my A4000D back to booting with full AGA. The intial non-boot I reckon was down to a knackered Buster. I replaced the Rev 09 on the board with a Rev 07 one from my A3000T. Machine booted but no AGA. 16 colours only. I ordered a Buster 11 and installed A4000D booting happily into WB but still no AGG. Amiga TestKit reported "WARNING: AGA Alice with bad Lisa ID".

Lots of googling later I narrowed possible cause down to U976 by following "Chucky" A4000D repair guide. I ordered replacement parts for U975, U976 and U177 plus some 4.7K resistors and some new ceramic capacitors.
   
Lots of youtube later I de-soldered U976. Checked connectivity - the vias under the chip. Hmm not all good. Long story short after checking all connectivity from U976 and repairing broken traces on the top-side and the bottom-side, replacing a resistor and a cap along with U976 Ive got it working with AGA. its been almost 10 years' since this machine worked and I thought it was gone for good.

Wife will be happy too as she can now get the kitchen table back!

Weed