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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: Motormouth on August 15, 2011, 04:39:28 AM
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I have recently purchased an 4000 Rev B motherboard,
I am having an odd problem. It is memory related. All the simm slot appear to be functional, and all the fast ram memory are 4 meg simms (or a total of 16 megs)
The problem I am having is the amiga is only addressing 1 meg of ram from each simm.
Or a max of 4 megs?
If I put in one simm I get 1 meg of ram. If I put in two simms 2 megs of ram.etc.... even if they are 4 meg simms.
the jumper J852 is set, as it should be, to 4meg or 1Mbit x32 (not 1meg or 256Kbitx32)
I have verified that the middle leg is getting 5 volts and the Ramsey pin 12 is getting 5 volts (it would be 0 volts if it were set to 1meg).
AIBB and sysinfo, both confirm only 4 megs of ram.
Anyone have any similar issues? How did you solve?
Online it appears usually battery acid issues take out simm slots or the U891 chip killing all the memory, not this issue.
Is there another signal I should be looking for, perhaps the _BUFEN signal or _WEO?
If so what should it look like?
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this is just a shot in the dark,but i had a similar issue long ago on a 4000 that someone had stuck A1200 roms in for some unknown reason,it will boot with 1200 roms but you will get trouble like you describe. if memory serves the chip ram showed up fine but fast always had a problem.Just something to check.
i would suspect the simms you are using off hand otherwise.Can you try it with 2-8MB simms instead of the 4-4MB simms?
dirty/tarnished simm slots could do this,but i would suspect you would be getting odd size ram reports.
Has the board you are working on been battery damaged in any way?
mech
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this is just a shot in the dark,but i had a similar issue long ago on a 4000 that someone had stuck A1200 roms in for some unknown reason,it will boot with 1200 roms but you will get trouble like you describe. if memory serves the chip ram showed up fine but fast always had a problem.Just something to check.
i would suspect the simms you are using off hand otherwise.Can you try it with 2-8MB simms instead of the 4-4MB simms?
dirty/tarnished simm slots could do this,but i would suspect you would be getting odd size ram reports.
Has the board you are working on been battery damaged in any way?
mech
Thanks for the ideas. the roms appear to be a4000 3.1 40.68
I tried your idea of the 2-8mb simms. One in bank 1 (slot 2) and one in bank 3 (slot 4), I get 4mb of fast ram. If I put in one 8mg simm into bank 1 (or the 2nd slot) I get 2megs of fast ram. So the problem is unfortunately consistent.
As for the battery damage it is very minor. I did check the U891 74LS245. it appears to be working. It appears to have been cleaned. Just in case I cleaned it more. All the simm slots seem to be ok.
There are only a couple of socketed things on the motherboard. One is the cpu slot. I put in a A3640 from one of my A3000, to see if that was the problem. I had the same issue.
The A4000 came with a -09 buster. I put an -11 in it. Again same problem.
Arrggg.
It appears be something annoying minor. I have to admit this is frustrating.
I am going to hook it up to an Oscilloscope after work tomorrow. If I only knew which look for. I found the A4000 Rev B schematics on line. I wonder if the problem is somehow the ramsey? or a single simm slot line?
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Did those 4MB SIMMS come with A4000 Rev B? If yes we can assume they should work.
Those 74LS245 chips between CHIP RAM bank and daughterboard bank that are one of the hottest ICs when looking operational A4000 Rev B with thermal camera. Possibly because of this heat one of those chips may fail. I know at least one case where changing one or more of those ICs solved all motherboard Fast RAM issues. So my point is that it may not be only U891. He used this chip as replacement:
http://fi.farnell.com/fairchild-semiconductor/74f245sc/74f-fast-ttl-smd-74f245-soic20/dp/1014088?Ntt=101-4088
One other case I have read about had failed clock latch chip (possibly killed because of excessive heat while desoldering battery). Also causing Fast RAM issues.
In the past my motherboard had a cut in traces under BANK 4 caused by battery leak by recless previous owner. If it looks like battery has never leaked this is ofcourse not your case either.
My experience is that EDO simms are used in A4000 motherboard it may see only one fourth of the SIMM. For example 8MB EDO shows 2MB RAM. EDO SIMMs work in most accelerator cards however. But I assume your memory is not EDO if it came with the motherboard.
I can also verify adding 8MB SIMM memory to BANK 1 and BANK 3 is correct. I use similar setup for my two A4000 motherboards.
Not really helpful but hopefully you find the failed part eventually.
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Thanks for the ideas. the roms appear to be a4000 3.1 40.68
I tried your idea of the 2-8mb simms. One in bank 1 (slot 2) and one in bank 3 (slot 4), I get 4mb of fast ram. If I put in one 8mg simm into bank 1 (or the 2nd slot) I get 2megs of fast ram. So the problem is unfortunately consistent.
As for the battery damage it is very minor. I did check the U891 74LS245. it appears to be working. It appears to have been cleaned. Just in case I cleaned it more. All the simm slots seem to be ok.
There are only a couple of socketed things on the motherboard. One is the cpu slot. I put in a A3640 from one of my A3000, to see if that was the problem. I had the same issue.
The A4000 came with a -09 buster. I put an -11 in it. Again same problem.
Arrggg.
It appears be something annoying minor. I have to admit this is frustrating.
I am going to hook it up to an Oscilloscope after work tomorrow. If I only knew which look for. I found the A4000 Rev B schematics on line. I wonder if the problem is somehow the ramsey? or a single simm slot line?
Its sounding more and more like a broken/bad trace somewhere. can u ohm them out from ram slots to chips and see? or u mentioned a scope,may be the ticket there.
please let us know what you find!
mech
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Possibly MA9 bad? Check continuity from PS/2 pin 9 to Ramsey pin 83 or possible short to GND or Vcc. Make sure pin 12 is high for 4 MB banks.
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@Motormouth , did you resolved the problem? suddenly I have now here the same problem too :( ...the only thing I did was replacing U891. So the RTC should not have anything to do with the fast ram or? In fact it was working before the replacement. I hope I don't look to bad now :shocked:
the jumper J852 is set, as it should be, to 4meg or 1Mbit x32 (not 1meg or 256Kbitx32)
I have verified that the middle leg is getting 5 volts and the Ramsey pin 12 is getting 5 volts (it would be 0 volts if it were set to 1meg).
same checked here. But the board just get 1MB out of 4MB from each simm.
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If jumper 852 is set correctly, you can try use larger simm in fast slots and chip slot and switch J213 and J213 to 8MB and try what change. I noticed, that in my Amiga, when using larger simm on original setting simm wasn't recognized correctly, when set those jumpers to 8MB my Amiga had 2MB chip and 16MB fast.
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You mean J213 & 214, the "free sex and beer" jumpers actually did something?
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Its sounding more and more like a broken/bad trace somewhere. can u ohm them out from ram slots to chips and see? or u mentioned a scope,may be the ticket there.
please let us know what you find!
mech
This RAM Simm problem is very common and symptomatic of battery corrosion ruining traces near the slots as mechy says. Sometimes you cant see it because its deep in the layers of the board. Take the MB out and inspect it underneath and neutralize all corrosion/acid. changing CPU and/or buster makes no difference generally with Ram trouble.
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If jumper 852 is set correctly, you can try use larger simm in fast slots and chip slot and switch J213 and J213 to 8MB and try what change. I noticed, that in my Amiga, when using larger simm on original setting simm wasn't recognized correctly, when set those jumpers to 8MB my Amiga had 2MB chip and 16MB fast.
wow thats the first time i've heard of something like this..
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I came across this thread because a 4000D motherboard I bought with "repaired battery damage" would only recognize 1 MB of RAM in each slot (occupied with a 4 MB stick). Gave up on the answer after a lot of traces tested and went ahead and installed it in a case; out-of-the-blue, all the memory was recognized correctly! Best guess, it needed proper grounding to work.:idea: Still keeps chitty time though. :confused:
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I wonder how many of these problems are caused by J852 falling off :)
(For the record, it should be pins 1-2 for 4MB SIMMs)
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maybe a little later :) but i had this problem until today.. it was related to the _FAIL signal. The wire from psu wasn't stable so ramsey was forced to see 256k x 32 dram like j852 was shorted in 2-3 position. Hope it helps...