a4000 wierd memory problem : help!

[amigaman1]

Howdy guys,

Managed to score a second a4k 030ec rev b motherboard which seems to have some quirks with the memory banks;

- When I first powered it up it locked up at a yellow post or got past that to an occasional guru then rebooted and repeated the process
- I took it apart to try and isolate the devices, unplugged the hd etc. I pulled out one of the simms so it was left with just a four meg stick and hey what do you know.. boots straight into wb but comes up with half a meg of chipmem
- ok, pull out the remaining 4 meg stick, it powers on but locks at a green post. !! argh.

There's minor signs of the nicad leaking but it's confined to a really small area and hasn't touched any other tracks..

anybody got any ideas??..

[Thomas]

Well, depending on board revision, the A4000 has either four RAM banks and chip ram soldered to the motherboard or five RAM banks with one of them holding 2MB chip ram. If your board has five banks, you have to let the chip ram in place, otherwise it won't boot. Green screen means there is not enough chip ram.

Bye,
Thomas

[amigaman1]

thanks for clarifying that, I took a closer look at the mb and it makes a lot of sense. My next question is why would it yellow screen with a 2 meg simm in the chip slot or does that suggest the simm is most likely kapuut? If so will I need to find another 2 meg to replace it or will a 4 suffice?.

Thanks again.

[Thomas]

If you don't have any device connected and no floppy disk in the drive it should at least show you the floppy animation. If it shows the yellow screen before that, something is wrong.

Well, in your first post you wrote that you had only the last memory chip in place and it showed you 512KB of memory. AFAIK even if you place a 4MB chip in the chip-ram socket, at least 1MB of it should be recognised. So this suggests that the chip is damaged indeed.

I am not sure how the memory logic reacts if you fit something different than a 2MB chip into the chip-ram socket. But I think if you put more than 2MB there, the full possible 2MB should be available.

Bye,
Thomas

[Doobrey]

amigaman1 wrote:

There's minor signs of the nicad leaking but it's confined to a really small area and hasn't touched any other tracks..

 You can`t really tell just by looking at the surface alone.
The motherboard is a 4 layer board, so the battery can leak and "tunnel" along the tracks of the middle layers, eating the copper as it goes, get the battery out ASAP, if not sooner, then look up some old posts on here about cleaning up the board.
 When it does boot, does the clock function properly? (Can you save the time settings OK ?), normally on a battery leak, the clock and/or the chip memory get it :-x

 The only other things I could think of..
 1. Duff 2mb SIMM
 2. Dirty contacts on the SIMM
 3. Bad contact cos of a broken SIMM socket, CBM managed to get hold of some real crap quality sockets at some point.
 4. You didn`t do the ritual blood sacrifice of rubbing your knuckles on the Zorro riser  :-)

[Castellen]

There are 3 PCB tracks that run right through the real time clock area which often get corroded open circuit and can cause memory problems.
Look at the underside of the modtherboard, at the beack end of the U850 SIMM slot, and you can see there are 3 tracks running to 3 vias which are right beside the RTC battery, but under the edge of the SIMM socket.

Use a multimeter to test the integrity of the tracks from the SIMM slot to their destination.  They run to vias beside U216, so it's enough just to test them to that point.

Don't forget to clean the edge connectors on the SIMMs and the pins in the sockets using isopropyl alcohol to make sure there isn't a poor connection caused by dirt/grease.


Information on RTC battery replacement:
http://amiga.serveftp.net/Battery.html

And RTC fault finding/repair:
http://amiga.serveftp.net/RTCrepair.html

[amigaman1]

Thanks for the feedback everyone.

OK, i've got this really bad feeling that when I take the motherboard out i'm going to find corroded some tracks

Because I have 0 electronics know how, is there anyone in the melbourne australia area I might be able to commision to try the battery swap in hope of rescuing my ailing a4k?

[Castellen]

Well New Zealand is closer to you than Perth, so I'm almost within the Melbourne area :-P

If you can't find anyone else, I do component level motherboard repairs and PCB track repairs.

[A4000Bear]

Melbourne, Australia???

You are in luck, because there are tons of Amiga enthusiasts here who know about leaky batteries.

I suggest you bring your machine to one of the usergroups here, someone will be able to look at it for you.

MAUG meets on the 1st and 3rd Thursday each month, 8pm in the Moonee Ponds Neighbourhood Centre, Kellaway Ave, Moonee Ponds.

AUG meets on the 3rd Sunday each month 2pm in the Moorabbin Arts Centre, next to the Moorabbin station.

In the meantime, check out my site, there is a link to some info about leaky batteries at the top.

www.starnet.com.au/davem/amiga.html

[amigaman1]

I've meant to try and make it to one of the meetings for a while now but they always seem to clash with my work schedule.

If I delicately wrench that nicad of the board in the meantime its not going to do any harm right..?

Ok, 50 bucks to anybody in melbourne who's got the time and resources to swap battery and clean up the MB, how does that sound?


 

[elendil]

50 bucks? Come on, you can do that yourself, really

At least, depending on what you want, you can easily just cut the battery 'holders' and throw the battery to hell. This, of course, means adding a similar battery will be harder, but you don't want to do that anyway.

From the tons of posts about battery leakage, it appears that what people mostly do is wire a couple of wires to the battery terminals and then attach the new battery somewhere away from the motherboard.

Me, I just soldered the old one off, and resorted to using a timeserver

BTW: I am assuming it's the barrel-type battery that I had - were there any others for the a4k? And also I don't know anything about amiga repairs, but removing the battery without reattaching a new one won't damage anything (on the a4k, at least).

Sincerely,

-Kenneth Straarup.

[amigaman1]

talk about gung ho, I took your advice and with some careful plying lifted the battery out of its mountings, cleaned the terminals and area thoroughly, cabled everythig back up boot into wb and hey! 2 meg chip 4 meg fast!!!!!

Thanks for your input everybody, totally chuffed.

Cheers.

[elendil]

Woot!

Congratulations

Sincerely,

-Kenneth Straarup.