exxos's Atari, Amiga & retro forum

stephen_usher wrote: 26 Jan 2022 13:49

rubber_jonnie wrote: 26 Jan 2022 13:07

Yeah, I ordered the QL minerva ROM from eBay Germany and it turned out I was already chatting with the seller on the QL forum!!

Does the Overdrive run at 33Mhz bus speed?

It's been a while since I played with one, and the 486 I have is already a DX2/66, so I can't remember how they did it all.

Yeah, the Intel DX2's are 5V and the 66MHz part basically clock doubles internally.

:lol: I actually remembered it right :)

Is it a ZIF socket, or are you going to have to pry the old CPU out?

A 486 66mhz DX2 was my first PC, it was pretty good for Quake :D

rubber_jonnie wrote: 26 Jan 2022 16:12 :lol: I actually remembered it right :)

Is it a ZIF socket, or are you going to have to pry the old CPU out?

It's gently pry it out with an electrical screwdriver time.

stephen_usher wrote: 26 Jan 2022 16:23

rubber_jonnie wrote: 26 Jan 2022 16:12 :lol: I actually remembered it right :)

Is it a ZIF socket, or are you going to have to pry the old CPU out?

It's gently pry it out with an electrical screwdriver time.

I never liked those 'gotta pry it out' sockets :cussing:

They were the normal type until at least the Pentium era when you required coolers attached to the socket.

I couldn't get the machine to boot at all with the MRBIOS for some reason, but managed to get it to boot with the original BIOS eventually.

After a bit of toing and froing I managed to get the 486DX2-66 working. I had to straighten a few pins for a start.

I'm soak testing the M/B out of the case at the moment, using CheckIt running full memory tests.

Whatever the fault is it's getting worse. I can hardly ever get it to POST.

'Scoping the pins on the ROM, most of the time there is zero activity. When it doesn't start up the /CE pin either goes constantly low or constantly high with small glitches and there's no activity on any of the other pins. Sometimes there will be a small amount of activity for a second or two and then nothing. After repeated resets it will suddenly spring to life and behave normally.

Once the machine is booted it stable, which suggests the reset circuit. I wish I knew where it was and what components it used.

Another strange thing I noticed last night was that the 486DX2-66 is actually running at a third of the speed of 486DX-33 for some reason. :-/

stephen_usher wrote: 27 Jan 2022 09:47 Another strange thing I noticed last night was that the 486DX2-66 is actually running at a third of the speed of 486DX-33 for some reason. :-/

This one is certainly giving you the run around!!

Yeah. I'm not sure that it's worth much more work unfortunately as it seems to be degrading with every minute of run time.

I could replace all the jelly bean tantalums on the board and hope that it fixes things but there's no guarantee. If it is a tant then I just wish it'd die in a blaze of glory and get it over with.