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Possible 'Base 64K memory failure' on a 286 build

andrew_241

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Oct 23, 2008
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Location
Southeast Michigan, United States
Hello!

As I mentioned in this thread, I've built a 286 computer. I went and got some DRAM chips (4C1024E-10 18-Pin DIP, 1M x 1, 5V, made by Micron, 36 in total) for onboard memory of 4 MB. Unfortunately, when I powered on the system, the screen did not come up, so I connected the speaker, and heard a repeating series of three short beeps. The board, a BAM/12S, is equipped with an AMI BIOS. According to this, the beep code I'm encountering means 'Base 64K memory failure'. I've tried removing all the chips, replacing the first chip in bank zero with other chips, and leaving only bank one filled. I'm starting to think that maybe the DRAMs I got are incompatible with the board. According to the manual, I need 411000-10 type DRAMs. In another thread, I find that 511000 is a compatible part, and according to this, the Micron 4C1024 is an equivalent part.

So assuming the memory is the wrong type (I don't know what else could be wrong, as I've checked and double checked that all the jumpers in the system have been set properly), where could I get actual 411000s?

Thanks!
 
My 286 motherboard also calls for 411000 DRAMs. I ended up buying THESE 511000 DRAMs from Jameco. They aren't cheap, but they work perfectly on my 286 motherboard as well as my Intel AboveBoard Plus 8 memory board,

Well, I went ahead and got 36 of those chips from Jameco, but unfortunately, I still get three short beeps as soon as the power is turned on. Since I haven't had luck with either set of memory chips, maybe it's not the memory after all.

Any ideas on what could be wrong?
 
Have you double checked jumper settings for memory configuration? Also, some boards have sockets for other types of memory for alternate configurations. Make sure those are empty if they exist on your board. If that's all correct for the type and amount of memory, then you'll need advice from someone more experienced than I.
 
Check the motherboard traces for damage and all the sockets are in place and no capacitors have failed. It doesn't take much to prevent a motherboard from working.
 
Have you double checked jumper settings for memory configuration? Also, some boards have sockets for other types of memory for alternate configurations. Make sure those are empty if they exist on your board. If that's all correct for the type and amount of memory, then you'll need advice from someone more experienced than I.

There is a DIP switch bank on the motherboard. There are two possible settings for the DRAM configuration I have installed, and I tried both of them, but no luck.

Check the motherboard traces for damage and all the sockets are in place and no capacitors have failed. It doesn't take much to prevent a motherboard from working.

I looked at the traces on the board, and there doesn't appear to be any damage that's visible. All the capacitors on the board are really small, but all of them look to be undamaged. The BIOS battery has been replaced, with the new one soldered on by someone experienced with such things, but that's the only modification. I made sure the battery was of the same type.

Here is a picture of the board's memory chips and surrounding area: IMG.jpg
 
Since my motherboard is similar to what you have, I took a look at my configuration to see if there is anything that might help.

Mine has 18 "KM41C1000AP-8" 80ns chips in bank 0 (the lower three rows), with DIP switches 6, 7, and 8 set to OFF, ON, ON for a configuration of 640KB base + 1,408KB XMS. JP5 is closed for a zero wait state. (Hmm, my manual actually says to use 421000-8 chips)

So for your 36 411000 compatible chips, DIP switches 6, 7, and 8 should be set to OFF, OFF, and ON for 640KB base + 3,456KB XMS. Because you are using 100ns "-10" chips instead of 80ns "-8" chips, you will have to open JP5 for one wait state.

Some of the modes let you use memory above 640K as EMS instead of XMS, but most programs are happier with XMS mode.

And if you are wondering what ram speeds are appropriate, here is what I recall was the general rule for PCs like these:
4.77mhz CPU - 200 Nanosecond ram ("-20")
8mhz CPU - 120 Nanosecond ram ("-12")
10mhz CPU - 100 Nanosecond ram ("-10")
12mhz CPU - 80 Nanosecond ram ("-8")
Of course, you can usually use faster ram in slower machines.
 
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So for your 36 411000 compatible chips, DIP switches 6, 7, and 8 should be set to OFF, OFF, and ON for 640KB base + 3,456KB XMS. Because you are using 100ns "-10" chips instead of 80ns "-8" chips, you will have to open JP5 for one wait state.

I've tried powering on the board with JP5 both open and closed, and still nothing but beeps from the speaker. The manual for my board actually says that the memory access time when using a 12 MHz CPU is 100 NS.

Is it at all possible that replacing the BIOS backup battery with another of the same voltage, but higher amperage (by about 5 mAh), could render the board unbootable? Because that's the only thing that's been done to the board. I did have a 287 coprocessor installed, but the board still beeps regardless of whether it's installed.
 
A few other things you might try:
Try it with just bank zero populated.
Try it in non-turbo mode (JP7 open or turbo switch off).
If this the board is already installed in the case, check to see if any screws with over sized heads or metal mounts are shorting traces on the motherboard. Perhaps try powering it up when not in the case.
Re-inspect the motherboard for any scratches, debris, or corrosion on the traces or expansion slots. If you have any corrosion in the slot near the battery you might use a toothbrush to clean it out.
Try booting with no cards in the slots. If there is a problem with the cards, then you should get a different set of beeps (the error beep for no video found)

I'm probably remembering the timings all wrong, but I wonder why your manual says 100ns chips and mine says 80ns? Either way, it should at least boot.
 
A few other things you might try:
Try it with just bank zero populated.
Try it in non-turbo mode (JP7 open or turbo switch off).
If this the board is already installed in the case, check to see if any screws with over sized heads or metal mounts are shorting traces on the motherboard. Perhaps try powering it up when not in the case.
Re-inspect the motherboard for any scratches, debris, or corrosion on the traces or expansion slots. If you have any corrosion in the slot near the battery you might use a toothbrush to clean it out.
Try booting with no cards in the slots. If there is a problem with the cards, then you should get a different set of beeps (the error beep for no video found)

I'm probably remembering the timings all wrong, but I wonder why your manual says 100ns chips and mine says 80ns? Either way, it should at least boot.

Yeah, I've tried powering on the board with just bank zero populated, in non-turbo mode, with and without expansion cards, and have tried removing it from the case. Unfortunately, nothing seems to work. I'm about ready to give up on it and get a different board. I've been looking at this, and can simply take the CPU I have and plug it in, but it looks like the board from that site doesn't have any BIOS chips on it.
 
I'm about ready to give up on it and get a different board. I've been looking at this, and can simply take the CPU I have and plug it in, but it looks like the board from that site doesn't have any BIOS chips on it.
They claim the board is new so it must have the BIOS chips. However, I see two other issues. The barrel battery is bad and with that you usually get more than just a bad battery. Also, that board takes a PLCC CPU and you probably have the PGA variety.
 
They claim the board is new so it must have the BIOS chips. However, I see two other issues. The barrel battery is bad and with that you usually get more than just a bad battery. Also, that board takes a PLCC CPU and you probably have the PGA variety.

The motherboard I have has the PLCC CPU, not the PGA, so it will probably work with the other board. What sort of issues are there stemming from a bad battery? On the board I have now, I've definitely had issues, and the barrel battery was leaking, but was replaced.
 
What sort of issues are there stemming from a bad battery? On the board I have now, I've definitely had issues, and the barrel battery was leaking, but was replaced.
I've never seen one that didn't leak. And more often than not the leakage caused damage to the board and its traces. Occasionally the damage could be repaired but most of the time it was way beyond my capability.
 
I've never seen one that didn't leak. And more often than not the leakage caused damage to the board and its traces. Occasionally the damage could be repaired but most of the time it was way beyond my capability.

Exactly! I have been cutting out or removing all batteries from any PC I take in since I came across my first "exploded" one in person in about 2000ish. I usually even remove CR2032 batteries, I have never seen one leak in person, but I have heard second hand about it happening.

Most cases when I get around to fixing them I install a battery holder box in an area of the case where it can't damage anything if someone leaves old batteries in it to leak.
 
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