exxos's Atari, Amiga & retro forum

stephen_usher wrote: 25 Jan 2022 09:53 It feels as if everything is in courier limbo at the moment.

I'm waiting on the delivery of not only the QS8888 but also ISA/PCI BIOS post diag card (looks like Chinese eBay seller pretending to be in the UK) and a 486DX2-66 "Overdrive" CPU. Then there's the package I sent to someone yesterday.

Sigh

I know the feeling!!

Well, in lieu of the other stuff arriving I went in search of a newer BIOS for the machine.

After wasting a couple of AT27C512R chips on incompatible BIOS images I came across the archive of MRBIOS bios images. These are generic BIOSs aimed at specific chipsets and seem to cover all bases. There was a UMC48X with local bus and Weitek socket. That works a treat and has far better support for IDE in that it can read the drive details. It still can't do LBA unfortunately though, even though it's from 1994.

However, it does do a full check of the cache at power on and notices that something bad is afoot. This is far better than the original AMI bios which blindly tries to use it.

The one down side is that the user interface used to configure things is far less intuitive.

Bother! The second (larger) hard drive has just failed in the 486.

Oh well, it was the noisy one and with this new BIOS I may be able to get the 10GB ex-iMac drive usable instead.

Another issue which appeared last night was that it's getting harder and harder to boot the machine after it's been off for a while.

The power output from the PSU is fine, so it has to be the motherboard.

Previously it's just been a case of switch on and then press the reset button. Now it's taking longer and longer after power on to react to the reset button reset to initialise the video and POST. Sounds awfully like a capacitor, but there are no electrolytics on the board and tantalums generally don't fail that way, they either explode after going short or not work at all.

I really need this POST board to arrive to do any more diagnostics here.

P.S. I rescued the twin system to this a couple of years ago and it had the same (needing to press reset) start-up issue.

stephen_usher wrote: 26 Jan 2022 08:22
P.S. I rescued the twin system to this a couple of years ago and it had the same (needing to press reset) start-up issue.

Interesting that they both have the same issue. I'd have thought capacitor too, but with no eletrolytics where do you go with it! Could it be a failing IC in the reset circuit?

I'm assuming that the PSU is good at this point?

POST board should help, fingers crossed it arrives soon.

rubber_jonnie wrote: 26 Jan 2022 09:45 I'm assuming that the PSU is good at this point?

Yeah, all voltages are spot-on, all the power rails are clean and the "power-good" line comes up correctly.

stephen_usher wrote: 26 Jan 2022 10:46

rubber_jonnie wrote: 26 Jan 2022 09:45 I'm assuming that the PSU is good at this point?

Yeah, all voltages are spot-on, all the power rails are clean and the "power-good" line comes up correctly.

Bit of a head scratcher that.

Well, the 486dx2-66 Overdrive processor has arrived.

Looked at the From address on the label and surprised that it's from Dave Stevenson, the person who runs the main Memotech resource web site and who produces the CFX add-ons. It's a small world.

stephen_usher wrote: 26 Jan 2022 12:09 Well, the 486dx2-66 Overdrive processor has arrived.

Looked at the From address on the label and surprised that it's from Dave Stevenson, the person who runs the main Memotech resource web site and who produces the CFX add-ons. It's a small world.

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.

rubber_jonnie wrote: 26 Jan 2022 13:07

stephen_usher wrote: 26 Jan 2022 12:09 Well, the 486dx2-66 Overdrive processor has arrived.

Looked at the From address on the label and surprised that it's from Dave Stevenson, the person who runs the main Memotech resource web site and who produces the CFX add-ons. It's a small world.

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.