Drive 2 connection not working on Apple Disk II Interface Card

[macinbot]

I have an Apple Disk II interface card where Drive 2 connection does not work. Interface card is in an Apple IIe.

I have two Disk II floppy drives. Connecting either one to Drive 1 connection and the drive functions fine. Connecting either one to Drive 2 and it will not function.

Obviously hooking one to the Drive 1 connection, and the other to Drive 2 connection, Drive 1 will work and Drive 2 will not.

My Disk II interface card uses PROM P6 341-0028-01, and PROM P5 341-0027.

When I obtained this Apple IIe, one of the Disk II drives did not function due to the previous owner misaligning the pins and the card connector. This was resolved by replacing 74LS125 chip in the drive and the drive now works fine.

 

[bigmessowires]

The pins on the D1 and D2 connectors should all be identical except for the enable pin, so you can test for continuity between them to make sure D2 is good. The enable signal is on pin 14 and will be different. See here for the schematic showing how the two enable signals are connected: https://www.bigmessowires.com/2021/11/12/the-amazing-disk-ii-controller-card/ It could be a bad PCB connection, or a faulty 74LS132 at A2, or a bad 9334 at C2.

Give the previous owner's history, I would start by replacing the '132 at A2.

 

[macinbot]

The pins on the D1 and D2 connectors should all be identical except for the enable pin, so you can test for continuity between them to make sure D2 is good.

Give the previous owner's history, I would start by replacing the '132 at A2.

Thanks ^^^^

Testing the continuity is good between all pins D1/D2 is to rule out bad PCB connection, yes?

 

[Arbee]

Right, that would rule out a bad solder joint or damaged trace (those both are generally rare on boards of that vintage, but it's the easiest thing to check first).

 

[macinbot]

The pins on the D1 and D2 connectors should all be identical except for the enable pin, so you can test for continuity between them to make sure D2 is good. The enable signal is on pin 14 and will be different. See here for the schematic showing how the two enable signals are connected: https://www.bigmessowires.com/2021/11/12/the-amazing-disk-ii-controller-card/ It could be a bad PCB connection, or a faulty 74LS132 at A2, or a bad 9334 at C2.

Give the previous owner's history, I would start by replacing the '132 at A2.

Tested continuity between all connection pins. All read through, except pin 14, which had no signal/tone.

Replacing the 74LS132 made no change with the problem. Chip was a used (or maybe NOS) chip from reputable seller on eBay. Ordered 2 and tried both, but nothing changed on the card problem reading the second drive. (see attached pic with replacement chip installed and old one above).

Order a 9334 chip next or maybe something else to check?

 

[bigmessowires]

How are you testing that Drive 2 doesn't function? You can't boot the computer from Drive 2, that's normal. You'll need to boot from D1 and then try a command like "CATALOG,D2".

You could try replacing the 9334, but that seems like a lower probability point of failure. If you have the tools, just watching pins 4,5,6,8,9,10 of the 74LS132 while you attempt to access Drive 2 will quickly tell you where the problem lies. It's a pretty simple circuit, just two NAND gates. Either one of the inputs is wrong, or the NAND itself is misbehaving.

From a practical standpoint, Disk II cards are common enough and cheap enough that I'm not sure it makes sense to invest too much effort troubleshooting this one, unless it has sentimental value to you.

 

[macinbot]

How are you testing that Drive 2 doesn't function? You can't boot the computer from Drive 2, that's normal. You'll need to boot from D1 and then try a command like "CATALOG,D2".

LOL at me for not remembering how drives function on the Apple II 40 years later. My recollection was that on power up the Apple II would poll BOTH drives. Obviously not. "CATALOG,D2" does indeed bring up a catalog of the contents of Drive 2. The assumptions we all make when helping people, like "Oh, he certainly would go poking around in electronics land before first knowing how to access the drive from the system OS." You would think that'd be the case. So you'd think.

Anyway... All Disk II drives and the respective controller now function just fine. Thanks for that last obvious, but incredibly important, kernel of information.

 

[macinbot]

While I'm here... Is there a program that does a drive read/write test function for the Disk II drives? I was thinking I could use Copy II Plus or similar to confirm it is all working fine, but maybe there's a specialized program?

 

[bigmessowires]

Hehe, we've all been there. Glad it's working! I don't know of any Disk II tester programs but someone else might. I think if you can copy a disk with it, then you're good to go.