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EMDarrow
February 28th, 2017, 10:07 PM
So, my Vectra QS/20 has two banks for RAM, four slots each. I have five sets of four 1mb sticks that all detect fine in the bank 0 slots and give the system 4mb of RAM. But when I try to put two sets in- four sticks in bank 0, four in bank 1- it won't even POST. Ive tried mixing and matching chips as well: no issues there, but only if I load bank 0. Once I drop sticks in bank 1, nothing. Monitor doesnt even get a signal. There are no jumpers on the system related to RAM that I can find.

Am I missing anything I can try? Or is there just something wrong with the board and bank 1 is borked?

Stone
March 1st, 2017, 02:11 AM
Or is there just something wrong with the board and bank 1 is borked?That's the obvious answer. :-)

Is that a DX or SX?

EMDarrow
March 1st, 2017, 05:45 AM
Is that a DX or SX?

SX, but does have a 387.

Stone
March 1st, 2017, 07:28 AM
SX, but does have a 387.387 is irrelevant here. The SX/DX notation represents the bus width -- not the processor/coprocessor relationship.

A 386SX has a 16-bit bus so there are only TWO SIMMs per bank, same as a 286. So, if you have 8 SIMM slots you have 4 banks of 2. Try it with just two in bank 0 and you'll see what I mean.

With two in bank 0 and two in bank 1 you have 4 MB.

So it would seem the problem is in bank 2 or 3 since when you fill them the board craps out.

Try putting 2 SIMMs in bank 2 and none in bank 3.

Then try putting 2 SIMMs in bank 3 and none in bank 2, just for fun to see what happens.

EMDarrow
March 1st, 2017, 07:53 AM
A 386SX has a 16-bit bus so there are only TWO SIMMs per bank, same as a 286. So, if you have 8 SIMM slots you have 4 banks of 2. Try it with just two in bank 0 and you'll see what I mean.

With two in bank 0 and two in bank 1 you have 4 MB.

So it would seem the problem is in bank 2 or 3 since when you fill them the board craps out.

Try putting 2 SIMMs in bank 2 and none in bank 3.

Then try putting 2 SIMMs in bank 3 and none in bank 2, just for fun to see what happens.

This contradicts the documentation on the processor board (http://th99.classic-computing.de/src/m/E-H/30891.htm). I dont have the optional RAM expansion board, so I just have the eight RAM slots, listed as bank 0 and bank 1 (A0-A3 and B0-B3 on the board).

If I try starting it with less then four sticks in (one in each bank 0 slot) it wont start, though in this case it does give warning beeps. Same happens if I populate all four bank 0 slots but only 1, 2 or 3 bank 1 slots. Also happens when I populate two bank 0 and two bank 1. I also tried populating just the bank 1 slots, but same result: beeps and no POST. Not sure what the beeps represent, but in this context Im assuming memory error or insufficient memory population.

After all this I put the sticks back in bank 0 and it starts right up, reading 4mb.

Stone
March 1st, 2017, 07:56 AM
This contradicts the documentation on the processor board (http://th99.classic-computing.de/src/m/E-H/30891.htm).DUH!!!

It's a DX... NOT an SX!

EMDarrow
March 1st, 2017, 07:57 AM
and I did find my first mistake here: it is in fact a DX. I just assumed since it had a 387 installed it was an SX, but no, both 386 and 387 are listed as DX-20.

EMDarrow
March 1st, 2017, 08:02 AM
Is there even a point to the 387 if the CPU is a DX? There are jumpers for disabling the NPU.

Stone
March 1st, 2017, 08:16 AM
Is there even a point to the 387 if the CPU is a DX?You need to reread my previous post:


387 is irrelevant here. The SX/DX notation represents the bus width -- not the processor/coprocessor relationship.

A 386SX has a 16-bit bus so there are only TWO SIMMs per bank, same as a 286. So, if you have 8 SIMM slots you have 4 banks of 2. Try it with just two in bank 0 and you'll see what I mean.

With two in bank 0 and two in bank 1 you have 4 MB.

So it would seem the problem is in bank 2 or 3 since when you fill them the board craps out.

Try putting 2 SIMMs in bank 2 and none in bank 3.

Then try putting 2 SIMMs in bank 3 and none in bank 2, just for fun to see what happens.To repeat... a 387DX does NOT have a coprocessor. You're confusing that with a 486DX which does have a coprocessor.

EMDarrow
March 1st, 2017, 08:23 AM
To repeat... a 387DX does NOT have a coprocessor. You're confusing that with a 486DX which does have a coprocessor.

Wow, Im just missing things left and right, sorry for being difficult.

I guess this was a learning experience if nothing else, though Im back to square one. Looks like the board is faulty, at least WRT the RAM slots.

Stone
March 1st, 2017, 08:57 AM
Yup, the nomenclature is a Royal PITA and leaves much to be desired.

Here's a summary:

486DX = 32-bit core, 32-bit bus, math coprocessor.
468SX = 32-bit core, 32-bit bus, no math coprocessor.

386DX = 32-bit core, 32-bit bus, no math coprocessor.
386SX = 32-bit core, 16-bit bus, no math coprocessor.