Dead Amiga 4000 motherboard; what next

[PulsatingQuasar]

I bought a dead Amiga 4000 motherboard to fix. It was missing the ramsey so I soldered that back on.

If I remove the chip RAM I get a green screen. So I know the processor board is working and the ROM is also doing it's thing. If I stick the RAM back in the screen stays black. Well, not completely. If I turn the brightness and contrast way up on my monitor I can see there is a signal. I also get the white short line on the screen from powering up the 68040 so I know the CPU board is working.

No flashing lights and I can use Ctrl-Amiga-Amiga to which the Amiga responds with the power light going dim and coming back up. No diskdrive click.

The Buster, Gary and both CIA's stay cold.

The freaky thing is that I got it working once after spraying contact cleaner on the SIMM, ROM socket, power connector and CPU connector and after applying some pressure on the CPU board connection. But I haven't gotten it to work since then. So I think this might just have been a freak occurence.

How can I meassure either of the CIA chips is causing the Amiga not to boot?

It's either that or there is a PCB problem somewhere on the mainbord. There is no battery damage.

It's really odd that it worked once.

[PulsatingQuasar]

Because they are soldered down.

There must some kind of measurement I can do to find out if it's the cause of the not booting.

[PulsatingQuasar]

The jumpers are in the correct location. But I also tested with other 040 and 030 boards.

All capacitors have been replaced.

The only thing I can take off is the Super Buster 11 which I bought new from Vesalia because the board had a rev 7 buster. So I don't think it's that.

Where do you actually get 2 new CIA chips these days?
EDIT: Found them at Vesalia. I'll order a couple of them.

What is interesting is that the board has flexed a lot around the CPU connector. The connector has actually bended somewhat.

I could stick the CPU board on the motherboard and use a multimeter to test the connections one by one but if that is not it, it might be a broken trace or via. That's going to be hard to find.

[PulsatingQuasar]

Great tip about the PLCC socket.

The ramsey was indeed soldered off by the previous owner. I bought one from Vesalia and soldered it back on.

I also fixed jumper J500 and some traces next to the ADV chip since the previous owner took that off too.

I measured all the pins between the motherboard and a CPU board and they all make a connection so the CPU connector is not the problem.

I'll buy a bunch of those CIA's from Vesalia. Since they are a common cause for problems it never hurts to have a few spares around.

Next weekend a new try to fix this motherboard. :-)

[PulsatingQuasar]

Small update.

It doesn't look like the CIA chips are the problem. The problem still persists.

What I did next was to fit an 68030 accelerator because it is smaller. I then was able to feel the temperature of the Ramsey chip which within minutes gets warm/hot. That is not OK because on a working A4000 motherboard the Ramsey barely gets warm.

So I was afraid it might have been broken. So I cut it off and this time I soldered on a socket and put a new Ramsey in the socket but again the temperature gets warm/hot within minutes.

The only thing I can think of now is there is a short cirquit on the mainbord that kills the ramsey. I don't think I will continue to fix this board unless it's something obvious I can fix first.


Other Amiga 4000 mainbord problem:
I have another Amiga 4000 mainbord here which works but it doesn't see any fast ram from the mainbord or from a Fastlane Z3 expansion. Should I replace the Ramsey first and then some other chip like the Buster?

[PulsatingQuasar]

The motherboard that didn't see the fast RAM on the motherboard had 4 tracks that didn't connect anymore to U891 from the via's. I fixed that and it now sees the memory again. This board is fully working now.

The other one is still dead. I also looked around on a German forum and asked Amiga Center about a possible cause. It is clear it is a short cirquit that heats up the Ramsey but no obvious cause like a resistor that doesn't work anymore.

There is possibility that the Bridgette or one of the other RAM related chips is causing the short cirquit.

[PulsatingQuasar]

Whoohoooo.

Other Amiga 4000 mainbord giving a Kickstart screen now. The one with the overheating Ramsey.

On a German forum I read some people with a overheating Ramsey because of R79( below the CPU board connector next to the screw hole on the Ramsey side) having died. For me that was not the case. R79 measured it's exact value.

So after some measuring of the SIMM's and the Ramsey pins for a short cirquit I thought what if one of the tracks in relation to R79 has been broken and hey presto!! That was it.

The small 7 mm track between resistor R79 and the via at the side of the motherboard was broken. Don't know what the previous owner did to manage that but glad that was it.

Tomorrow I'll test to see if something else is broken. I hope not.

[PulsatingQuasar]

Did some more testing now.

All RAM banks are OK. Keyboard and mouse are working and the floppy drive is also working.

Haven't tested the harddisk yet but I don't think the IDE port is dead.

I have already changed all capacitors by new ones. Now only to add a new battery and this motherboard is fully functional.