Risks with trial-and-error testing RAM chips?

[boggit]

I recently bought a Baby AT 286 motherboard (OCTEK Fox II, rev 3.0) off eBay that I installed in my IBM 5160 case.

* The motherboard looks like this:

* The motherboard came equipped with no Dip RAM, but with two SIMM cards slotted in (one 1mb and one 640kb, if the BIOS memory count is correct).

* The manual for the motherboard has the following to say regarding Dip RAM:





* As it happens, I have some 44256 and some 41256 chips lying around: One set from a non-working JUKO Turbo XT board (100 ns, if I've understood it correctly) and another set (four 44256 and two parity ones) that I purchased recently that are 70 ns.

* I'm not sure what the correct DRAM ns is for this motherboard, and the manual doesn't seem to specify it.

QUESTION: If I were to plug in either set of Dip RAM chips to trial-and-error test if they work, do I risk damaging the hardware or something, or is the worst thing that could happen that the RAM chips won't work and that I'll have to unslot them again?

 

[eswan]

You've got 2x 1meg simms in bank 0, 286 motherboards typically either ignore the 384k in the Upper Memory Blocks or possibly uses it to 'shadow' the roms. You should be able to use 4x 44256 and 2x 41256 in the bank 1 dip sockets to give a total 2.176 meg (2048+512-384).
It's either/or per bank on simms vs. dip, won't damage anything, might not work properly, won't see any extra ram.

 

[boggit]

You've got 2x 1meg simms in bank 0, 286 motherboards typically either ignore the 384k in the Upper Memory Blocks or possibly uses it to 'shadow' the roms. You should be able to use 4x 44256 and 2x 41256 in the bank 1 dip sockets to give a total 2.176 meg (2048+512-384).
It's either/or per bank on simms vs. dip, won't damage anything, might not work properly, won't see any extra ram.

Excellent. Thanks!

EDIT: I just want to add that the 01664 kb RAM count on startup is what is shown regardless of whether shadowing is turned on or off. Not sure if that makes any difference in the context of what you are talking about, but just FYI:

 

[boggit]

Update: None of the chips worked. RAM error beeps on both sets, both with and without parity ram installed.

 

[Svenska]

* I'm not sure what the correct DRAM ns is for this motherboard, and the manual doesn't seem to specify it.

The speed depends on your CPU clock speed. You need 60ns (16 MHz), 80ns (12 MHz), 100ns (10 MHz), 125ns (8 MHz). Faster memory will work, but won't improve speed.

I wouldn't use such a board to test DIP memories. The hardware is already quite complex, and you won't get far with broken memories. It's better to test on 8-bit systems which often can get somewhere with faulty memory (e.g. diagnostic ROMs), at least far enough to tell you which chip is broken. (Testing one chip at a time still requires the other 12 bits to be known-good.)

Your 100ns chips will probably all fail in this board, they are far too slow.

I just want to add that the 01664 kb RAM count on startup is what is shown regardless of whether shadowing is turned on or off.

Correct. This board does not allow remapping of the 384 KB upper memory to extended memory. But it can use it for ROM shadowing, which can be useful.