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It’s a breadboard adapter. Kool work.

Time to design a whole PSU from scratch to fit the machine. Lmao.

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yeah obix knows what he is doing, I would have just cut up a 20pin extension cable and ground the green power on cable. lol

PSUs in servers of this time tend to be finicky TBH, I'm not socked it has problems.

Hey makes me happy you all enjoyed the photo :D

The adapter started out to be a quick cut/twist/green-to-ground, but I discovered this PSU was made specifically for the 720 with a few oddities (to me anyways). It's primary power is on the 3.3V rail and secondary to that is the 5V, the peripherals are pretty standard (accept the primary peripheral power cable has the red/yel swapped for 5V/12V, that could have been bad). The issue was I needed to monitor the voltage levels on all the rails while it was running to see if they were staying in tolerance and specifically the PWR_GOOD pin to catch it's level when the machine powered off. I wasn't sure if the PWR_GOOD voltages would be the same as they traditionally are as so many other things seem to be unique, wasn't able to find any pinout documentation for the PSU. Anyway, I don't think repairing it will be bad, just take some time walking through the circuit following basic SMPS principles.

The next gotcha was the CD-ROM. It was detected in RAID controller and externally seems to spin up and sound as expected, however no data. So I put in on another machine and still nothing. Opened it up hoping for a simple clean-and-lube but found the laser diode is completely dead, it does have an adjustment pot. but that diode is gone. I found another SCSI CD-ROM and that did the trick. I don't have a lot of experience with SCSI but it seems odd to me that it was configured with the CD-ROM connected to the RAID controller as its SCSI controller, but it works.

Now to get access to the HHD's in the RAID. The controller says the array is good, has an 8GB logical drive created out of the available ~12GB of the RAID-5, but that's as close as I've gotten to it, still says un-bootable and not accessible from other boot methods w/o the RAID/SCSI drivers. I got the IBM ServerGuide 3.1.1 cd set images now, but the boot disks it wants to create for installing a new OS are all some proprietary compression and are in 2.88MB images... the one thing I don't have, any 2.88MB disks. Maybe find a way to "span" two 1.44MB floppies? The problem there is I haven't discovered the compression format IBM used...

So, not sure what direction to go now, maybe pull the drives and build the OS on the drives using another machine then attempt to re-install...?

I'm not shocked by the yellow 12v and red 5v for the peripherals being swapped, I seen that in a lot of servers form this time frame. Not sure why they did this, its odd to me but regardless its good that you checked.

On a side note the PWM/tach cable on a lot of fans from this time frame had blue for its cable and 12v was yellow vs modern fans having yellow for the tach and red for the 12v. so if you ever get a old fan with a blue wire on the 3pin the yellow cable is hot/12v or in some cases 5v. Best to always check on systems this age as cable colors were not a standard yet.

The disks themselves aren’t special (beyond being really high end). Microsoft and many UNIX distributors also used them.

You have two approaches: You can use a 2.88mb disk.
Or you can use a flash to floppy converter. I use one for SD cards but you can also find usb stick converters as well.
Fyi, don’t make the mistake of creating multiple drives in a single flash media. It won’t work on a system that old. Use a separate flash drive for each disk.

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booting from usb isn't a option on something that old without something like a grub boot disk. unless if you're talking about a gotek in witch case it would work. as for the disks... i thought 2.88 disks were something completely different and it was 1.7mb disks that were a custom format on a regular disk?

the way i always did things was to ether burn off a os disk to a cd or put a drive in another system to copy the setup files then boot from a dos floppy and run the installer.

Exactly. A flash to floppy disk converter.


They are completely different. What you’re thinking of is the retail disks for, eg Microsoft DOS and Windows 3.x/95. Which are 1.44mb disks with a slightly larger payload compressed with, I believe, deflate, and an RTS.
The two eighty eights are actually that value when using FAT16. They’re 4 point Something raw.

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ohh gotcha, I thought you met booting right off a USB drive. The 1.7mb disks were a custom file system layout if I recall I think called DMF. I know you could put far less files or was it folders on it but the payload was larger, IDK I mostly used LS drives and phase discs back then. A LS drive would format a 1.44mb floppy to hold 32mb, so I never much used 1.44mb or 2.88 disks.

Wow, some good info in the conversation, thanks!


I agree, got several milk crates full of those cooling fans and there are all sorts of variations in the wire color coding, even more confusing when that fourth 'tach' wire is added. With the Server 720 I just didn't want to chance booger'ing it up if the feedback/PWR_GOOD voltage was intended to fluctuate in a lower voltage range, so I went a little overboard in attempting to monitor it.


I've never used one of those but have been very interested in acquiring one and trying it out. Sounds like they will work on these old systems as long as the USB format is correct? (I've wasted days on trying to create bootable media for machines of this era, now I've collected quite the floppy/CD image library.) That formatting is actually my current challenge...

IBM used these <address>.ADF files to describe the various hardware like ISA/PCI and RAID controllers, then stores this info for the BIOS to pickup at boot, once I got the matching .ADF files loaded that opened things up. Now the drives connected to the RAID controller are accessible, formatted to RAID-5 with a single FAT16 partition of 2GB out of about 12GB ( trying to avoid more complexity atm between LBA and old software ). This morning I've got to see if I can come up with some drivers for the SCSI CD-ROM like ASPI2DOS.SYS to bring it all together...

The Gotek products suggested above are fairly entry level. They are prebuilt to do one single job very well. I actually have two audio keyboard adapters.


What you’re looking for (or could possibly make) is a a usb to floppy drive converter, not a pre-coded unit. These are actually miniature embedded computers.

The better ones have a whole host of prebuilt selections that are switched or button presses and all you do is make your selections and put the disk image on a fat 32 or ext formatted flash drive.
It’s the hardware equivalent of mounting virtual disks in the os.


My primary unit also allows custom uploads to be installed, like British 3” disks and camera disks. So even when it chokes, if the format specs are out there you can make it work.
Check out CDW, Amazon, etc.

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