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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: patrik on November 25, 2003, 03:41:21 AM
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Hi everyone!
I have a friends A4000 here which I have been trying to fix. For a long while, the trusty old A3640 cpucard was used in this machine without any problems until a while ago when he got himself an Apollo 4040 card. It was then the fun(?) stuff began... the machine refused to work with motherboard fastmem installed and if you had the machine turned on for a while and rebooted it, it would freeze after the reboot - no crash or anything just still as ice (with no motherboard fastmem installed). The funny thing is that if you just didnt reboot it, it would be running totally stable for as long as you pleased.
I told him I could give it a look and se if I could do anything about it.
I found out that if you ran the machine with the Apollo-card unpopulated only having fastmem on the motherboard the machine would boot and work for about 1 min until it started to go slower and slower and slower until it just stopped... letting a big fan blow over the board and motherboard from the powersupplyside of the A4000 (without drivebays) seemed to solve the problem. I have spent many hours looking for bad solders, resoldering parts of the Apollo and parts of the A4000 motherboard, cooling components selectively. I really thought it was the Apollo-card that was bad because the computer had worked so fine with the A3640 and focused mainly on that. At the end, after pulling my hair with the Apollo, I began focusing on the A4000 motherboard and found out that it was the ramsey-chip that was the bad guy. If it is cooled _A LOT_ it works perfectly with motherboard fastmem installed and there are no freezes at reboots (with or without motherboard fastmem installed). Though that much cooling isnt possible in the A4000 case so I resorted to a mounting heatsink on the ramsey-chip and attaching a little fan in the gap between the daugtherboard and the frontplate to blow air underneath the Apollo on the ramsey-chip. With this fix motherboard fastmem cant be installed (If you for example use bustest (http://www.aminet.net/util/moni/bustest.lha) and test the speed of the motherboard fastmem the system will become slow or freeze) , but if no motherboard fastmem is installed the system works fine and always reboots - no freezing or anything. That is very good as now the machine is usable again (ponder the inconvenience it is, not being able to reboot the machine ;)), the only backside is that motherboard fastmem cant be installed.
Now I am curious if anyone else has had any problems with the ramsey-chip?
/Patrik
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Never seen that exact problem myself, but have seen various ICs go faulty where they misbehave when heated up.
You did well to find the problem, not so easy to track down!
Fitting a heatsink/fan to the faulty device may not be the ideal soloution as I've found these kind of faults can get worse over time.
Best bet is a replacement. It's soldered to the PCB in the A4000D, so you'll need some SMD tools to steam a replacement on.
Should be easy enough to find another, I have a few spares here if needed. From memory the A4000D Ramsey was mainly revision 07??
Better not fit an earlier revision (like from an A3k) as there may be compatibility problems.
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@Castellen:
Yes this is indeed not a good solution, as you say the ramsey is probably prone to become worse. But if it works a year it is a extra year of A4000 usage for my friend :).
The ramsey in this machine is indeed revision 7 (-07 is printed on the chip) :). I have never tried surface soldering a PLCC, but I have done some various other surface soldering and think I am skilled enough to solder a new ramsey to the motherboard , alternatively a socket. Though removing the faulty ramsey from the motherboard would be much more difficult than attaching it or a socket (atleast this is my impression) :(. Do you have any tips regarding how to do PLCC desoldering?
/Patrik
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Was also wondering if the Apollo-card could be generating signals of less quality than the A3640-card and thus making the ramsey misbehave easier.
Has anyone experienced an Apollo-card making their systems unstable?
/Patrik
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Do you have any tips regarding how to do PLCC desoldering?
I don't have any on desoldering, but here's a webiste that explains how to do surface mount soldering with a toaster oven..
http://www.seattlerobotics.org/encoder/200006/oven_art.htm
:-D :-D :-D
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@Wain:
That doesnt sound too healthy for the rest of the motherboard :D.
/Patrik
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Hmm, as far as using a toaster oven for SMD soldering goes, I would not reccommend it!
Didn't look at that website, but you can appreciate that solder melts at 250-350°C and very close to Ramsey are plastic connectors which have a much lower melting temperature. You do the maths :)
PLCC soldering is a piece of cake once you get used to it. Fortunately the the pitch and spacing of the component legs in the A4000 are very large, making the job even easier.
You can do the job with a "pyropen" if you're careful, but better to use a proper hot air or infrared SMD soldering tool.
Remove the faulty device by first gently pre-heating the area, then focus on the pins of the device, moving the SMD tool in a circular pattern.
Gently apply upward pressure under one corner of the device. Suddenly the solder will reach the melting point, and it will lift off.
Using a hand soldering iron and solder wick, clean all solder off the pads and clean away residue with isopro alchohol.
At this stage you can fit a PLCC socket, or a new device.
Sockets are tricky and you need to have a small nozzle for the SMD tool to solder it on without melting the socket.
It's easy to fit a new device straight to the PCB. Run a ring/bead of fresh solder paste over all the PCB pads, you usually need slightly more than you think.
Place the new device on the board, getting polarity correct and lining up each pad perfectly.
Use the SMD tool to melt the solder on a couple of pins in one corner only.
Check again everything is still lined up perfectly. Then heat all the solder paste all the way round.
Carefully inspect all pins for solder shorts and unsoldered pins.
Unsoldered pins can be fixed by applying a tiny bit of solder paste and re-heating.
Small shorts can be fixed by heating the pins and running a needle or tiny steel spike between the device's pins.
Solder shorts underneath (and larger ones) are cleared by using a hand soldering iron with solder wick.
Once finished, check again for solder shorts, clean away flux with alchohol and power up the system.
Hope that helps :))
Anthony.