Stockedde wrote on 2021-08-19, 10:05:Hi! […]
Show full quote
Hi!
I have picked up a J-Bond A450C-G 486SX/DX motherboard.
Exact one: http://www.win3x.org/uh19/motherboard/show/8487
Closest on Stason, mine doesn't have the DX2 option or JP1, CPU speed select: https://stason.org/TULARC/pc/motherboards/J/J … -486-CACHE.html
Never used and looks great. However there is no oscillator or RAM.
As far as I've understood, the oscillator frequency should be the same as that of the CPU. Is that correct?
Usually for a 486 that's correct. Certainly looks like it here.
Can't really find the one on the picture on Win3x (Koyo kco-110s 33.000mhz), but what should I look for? And where?
Any oscillator with same form factor/pinout and desired frequency, and where... good electronics places like Mouser, Reichelt or whatever exists where you are. Or failing that eBay, which takes longer and is a lottery (generally used sometimes remarked parts) but can be very cheap.
As for the speed... depends on your CPU. With an SX/DX25, DX/2-50 or DX/4-75 Overdrive you want 25MHz, with an SX/DX33, DX/2-66 or DX/4-100 Overdrive, you want 33MHz, for a DX40 or DX/2-80 go with 40MHz and for a DX50, 50MHz.
Or go for multiple crystals so you can swap them and try different speeds...
There is a jumper JP50 (between CPU and NPU) for 33 or 50 MHz. What does that do? Let's say I have a 25 or 66 MHz CPU, how do I set it?
It's a clock halver for the Weitek NPU. Those things were rated to max 33MHz, so if your CPU bus speed was max 33MHz, you fed it full bus speed, and if your bus speed was over 33MHz you only gave it half the clock ticks. The jumper has no effect without a Weitek 4167 co-processor installed.
The mobo is advertised (in this ad at least) as having EDO SIMM: https://www.ebayshopkorea.com/itm/A450C-G-Soc … B-/184727476114
Haven't found detailed specs, but can you tell by looking at the board if it is EDO or FPM? or will either work?
What memory is supported is determined by the chipset, so if you can identify the chipset and find its datasheet, you will find what memory technology it accepts, and which chip densities.
Here that's complicated by the fact it look relabeled here, at least, in Pentium days Soyo used to relabel Via chipsets as Eteq. This isn't a Soyo board, and it doesn't look like a Via chipset either, but googling that ETC82C4901 doesn't get me anything resembling a datasheet (and does give lots of Soyo hits) so something similar seems to be going on.
However this board is an early 486 board with 30p SIMMs; I've never seen 30p EDO SIMMs and chances that a board with only 30p SIMMs has a chipset that supports EDO is very slim indeed. Just go for regular FP SIMMs, preferably 60ns if you want anything over 33MHz.
