your attached bios file is 961020S.BIN or Release 10/20/1996S (see https://theretroweb.com/motherboards/s/pcchips-m530#bios) Is that your boards current bios ?
The bios update file you use must match the bios chip type, yours being an S type (PcChip/Amptron naming) not an L type. Back then they used a few diff make/models of the bios chips that the bios files were not interchangeable.
refer to : http://web.archive.org/web/19980425122820fw_/ … _mainboard_bios about S and L bios types
I suggest you update to the Release 10/01/1997 S version first from theretroweb.com and see how it goes..
Use the included Award flash v5.2b, if it not work try Uniflash. edited for clarity. i think...

Thanks for the reply. I downloaded and flashed:

theretroweb.com/motherboard/bios/891001s-63e3d9a3ca34a965851111.bin

This is a big improvement, because now the motherboard can boot on the K6-3+ CPU. It doesn't detect it properly, but at least I can now boot and enable the cache and features from the command line with setmul or k6init.

Also, on my particular board the jumper setting for 55MHz is actually 75MHz, so now I have a 450MHz K6-3+! It is a huge speed boost over the original CPU.

The main issue at this point is that the "CMOS checksum error" is always present. The bios defaults allow me to boot, but I can't figure this out. I was getting a battery error, but I opened up the dallas module and attached a new battery. This cleared the battery error and I can see the seconds counting in the setup screen so I think the time crystal is working, but the "CMOS checksum error" persists. Is this definitely a bad dallas module, or is there something else to check before buying a replacement?

Thanks again!

Hmm were you getting the low battery - cmos checksum error before the bios update ? Have you tried clearing the cmos using the j1 jumper ?
Make sure power is off and jump it for a few seconds. Also running at 75mhz bus clock is an overclock, it could be part of the issue but unlikely....
What type battery are you using for the dallas ? Not all coin cells produce enough V's to supply properly, it needs be new and at least 3.0+ volts by multimeter when connected.
Also if you did not cut the one lead when dremeling the RTC the coin cell will drain thru the internal dropping the overall volts. .
added: If you load defaults and save, then turn power off for a bit then back on does it hold the defaults or go back to an error ?

The motherboard I got has essentially no labels, but I've identified it as an M530 because it closely matches the pictures here:

theretroweb.com/motherboards/s/pcchips-m530

In some pictures there is a battery holder and a different real time clock chip. Mine looks the same as V1.6b but came with no battery holder and a dallas module labeled:

dallas ds1287
real time
8813

If the "8813" means the module is from 1988, then it is clearly not the original because other parts on the board date to 1996. Perhaps the dallas module is incompatible? I peeled it open, removed the dead battery, and added a good 3.2v lithium cell. With the pins exposed now I can confirm continuous 3.2v on the battery pin.

Before any modification the post screen reported both the checksum and failed battery errors. With a new battery I only get the checksum error. With the new bios and new battery I still get the checksum error. On the new bios, with the battery removed I again get both the battery and checksum errors. With the dallas clock chip removed entirely there is no post. It will not save time/date or any settings, even with continuous power from the wall. It is nice that the default settings auto detect IDE and allow the board to boot.

The JP1 jumper does nothing. I can see the trace for the JP1 jumper goes straight to pin 21 on the clock chip socket, and the dallas module has that pin folded up and would be completely NC until I opened the module. The datasheet I found for the ds1287 shows pin 21 as the RCLR pin. It measures around 2.7v and grounding it doesn't have any effect.

I've started checking for bad connections between the module and elsewhere on the motherboard, but I don't know what I'm doing and there are no obvious problems. I'm thinking either the dallas module is bad, or it is not original and not fully compatible.

I have tried all the bus frequency settings, and they all work as expected except that the setting for 55MHz as identified by the silkscreen label is actually 75MHz (hapilly 😀 ). This agrees with the datasheet for the CMA8860 clock generator when there is a -75 in the part number.

I am enjoying upgrading and tinkering with this board. It's nice to find others with similar interests. Cheers!

I have two updates to report with this board. First, I believe the Dallas DS1287 is not fully compatible. The other pictures I've found show a Houston Tech HT12888A being used. I saw a video from vswitchzero about a similar problem on a Gigabyte GA-586ATV Socket 7 motherboard, where the machine could boot with a Dallas RTC module but not save any settings. So I installed a necroware BQ3285 module and that fixed it. I can now save BIOS settings, date/time, etc.

Also, I flashed M520_J2.BIN from Jan Steunebrink. This modified BIOS for the M520 works on my M530, correctly identifies the K6-2/3+ and enables the features I previously had to do using k6init/setmul. My board has a UMC UM8670F chip on it, and this seems to be BIOS-compatible with the UMC UM8663 used on other versions.

I've maxxed out the RAM and I'm now installing linux. Thanks to everyone in the community for helping to make this possible!