Connect like this:
http://www.playtool.com/pages/psuconnectors/atpic.jpg

Miphee wrote:

Please insert photos of said components.

Already edited the question, hopefully it's helpful.

tip: don't push them straight down. Start angled, leaning towards the memory so that the... I don't know what they're called, small plastic thingies maybe 🤣 can make it to the holes

try putting them at a bit of an angle at first guiding the notches on the plug into the grooves of the connector

you should also consider removing the battery from the board while you have the chance 😀

Here's what I'd do.

1. Remove that battery ASAP.

Take everything out of the case, and test it all out of the case.

3. Make sure you plug in the power supply properly. The two black cables should be together. If you plug them in wrong (which is doable) it'll kill everything.

Thanks! I did try leaning it, but hopefully now that I know it should fit I'll manage it. The plastic clip should be facing the other way compared to how I'm holding it on the photo, right? Towards the camera, not the RAM slots?

About the battery: noted, thanks for the warning. Already ordered a replacement but it will take some time to get to me; wasn't sure if I can wait until then or if I should remove the battery right away. If I remove it and don't put anything else instead, will I be able to boot and use the computer? Just not save the CMOS settings?

I didn't want to remove the motherboard from the case, didn't see the point. What would that accomplish? I did take it out to check its other side and make sure nothing is stuck underneath it or some such.

By the way, I wanted to test just the PSU alone first, but it may not be safe running it without any load, right?

VioletGiraffe wrote:

By the way, I wanted to test just the PSU alone first, but it may not be safe running it without any load, right?

It depends, some AT PSUs won't start if there is no load, one such such example would be the PSU on the IBM 5170 PC AT, if no hard drive was present then the PSU would not fire up, so a dummy load (in the AT's case, a resistor on the 12V rail) would be needed to trick the PSU into starting up (the motherboard alone wouldn't draw enough power)

So it's always wise to plug in a hard drive (ideally an old MFM hard drive, but an IDE hard drive will do) to a spare molex from the power supply you want to test.

Thanks for all the help. I can't believe how difficult it is to put an AT connector into place, makes you appreciate modern physical interfaces.

For all I know this is correct, but just in case can you please verify I connected it properly?
https://i.imgur.com/ZCo2s6h.jpg

And another two quick questions:
1. Is either of these two 3.5" Fdds better than the other?
2. I have an expansion card providing hdd, fdd and com interfaces. The fdd ribbon cable has two very different connectors on its business end :one plugs into the older 5. 25 FDD, the other looks like IDE and can be plugged into a 3.5 FDD. Can I plug both in at the same time? The Fdds don't seem to have any master /slave selectors. Also confusing is the fact that both this IDE-like FDD connector and the other two HDD connectors are missing a key so they can be inserted into an HDD or FDD both ways, which seems wrong.
Photo: https://i.imgur.com/SCq7jYP.jpg

1. Yes, the power cables are correct.
2. The floppy drives don't have a master/slave jumper and many older cables don't have a key. I don't want to complicate things more since there is more than one way of configuring A and B drives, some 5.25" drives have "drive select" jumpers and cables do vary. They may have double connectors for both A and B drives, a double connector for a single drive, just two connectors for both types actually enforcing the configuration, a twist or no twist etc. Just post a complete photo of the FDD cable and we'll tell you what to connect where. As a general rule check out the photo below (not mine). You can have of course both a 5.25" and a 3.5" drive connected at the same time, as long as the cable allows it -not all cables support 2 drives. One goes before the twist and is B:, the other goes after the twist and will be A: (don't use one pair for both drives no matter how much it seems convenient for cable management and don't forget to declare them correctly in BIOS). This is a common scenario/cable, if yours looks different then a photo is necessary to continue.

Much appreciated, very useful info on the twist and the drive letter assignment. My cable has a twist between the 3.5" IDE-like connector and the older-style 5.25 connector, so based on what you're saying it's OK to have both as long as I figure out which is the correct orientation (as I mentioned, all my IDE connectors are not keyed). Is there a rule of thumb for figuring out the right orientation? And can connecting it in reverse harm anything?

And sorry, forgot to include the picture for the question #1 - these are the two floppies I'm choosing between, do you think one is better than the other?
https://i.imgur.com/o2qqg63.png

VioletGiraffe wrote:

Is there a rule of thumb for figuring out the right orientation? And can connecting it in reverse harm anything?

Don't worry about the floppy ribbon orientation, you won't damage anything. Connect the drives one at a time to rule out other problems and determine the orientation: If you connect it wrong, the floppy light will stay on the whole time. In rare cases the PC might not even start. Just switch it and you're done.
Also almost always the 5.25" connector has a key, it's weird that yours doesn't. For early 3.5" connectors that was common though.

You're right, the 5.25" one has a key, but all the HDD and 3.5" FDD connectors don't.

Well, wish me luck, going to plug everything in and power up the system. Hope none of the magic smoke comes out!

It's alive! IT'S ALIVE!!!!

Can't make either of the two 3.5 in FDDs work, though. The 5.25 drive works but I have no bootable 5" diskettes nor any way to create one.
According to the ribbon cable diagram above: if I only use a single connector, the one before the twist, will this drive be A: because it's the only drive in the system? Or will it be B: because the connector before the twist is always B:?

To test a 3.5" drive connect it alone on the last connector, the one furthest away from the I/O card. That should be A: and declare it as such in BIOS too.

Unfortunately, this ribbon cable won't let me do that as its two connectors are different - one only fits a 5.25 drive (this is the further out - last - connector), and the closer one fits 3.5" drives. I'll see if I maybe have another FDD connector lying around since 15 years ago, although there's not much hope. Once again, I really appreciate your advice!

Connect it to one of the connectors after the twist... that's whay konc meant to say.

precaud wrote:

Connect it to one of the connectors after the twist... that's whay konc meant to say.

I understood that, but I can't do that because the connector after the twist only fits a 5.25 drive, and I need 3.5. The 5.25 drive does work, but I don't have a boot able diskette of that type.