400 K Floppy Drive Repair Components

Professor Lund,

Great to see you posting here on TinkerDifferent!

I was trying to swap out capacitors in my two Carts after reading your post, but suddenly the entire website shutdown...



I guess I will need to wait until tomorrow.

Tariffs have wreaked havoc across all my Mouser Carts, I must say. It's very frustrating.

The site is working today, but even though I have the site set to the Japan region (where I live), I am getting the same message...



That indicates it may not be sold anywhere, which is very odd.

Swapping out the caps is going to take time because the ones in my cart originally were the best caps available at the time. Now I am finding inferior ones. They will work, but have higher ESR. For example, consider the specs of one of the 22uF caps in my 400K Drive OA-D34V-22 Cart, with ESR of 270m-Ohms and 350mA Ripple Current:


An in-stock 22uF cap with the same physical size and lead spacing and capacitance has higher ESR, as evidenced by the tiny 50mA Ripple Current:


Sometimes choosing a higher voltage cap will reduce the ESR, but there is an upward limit to that because there will come a point when you won't be able to find a cap in the physical size you need, and if the cap is too big, it won't fit. That's why it takes time to find good replacements. You need caps that fit into the space on the PCB, have the right lead spacing, and also have good specifications (105°C, low ESR where possible, etc.).

Because I need to get read to go to work now, I will need to examine this later.

Professor Lund,

I've spent a number of hours on this, both yesterday and today. This issue has become really complicated due to Mouser having killed off the right caps, so this post is long and messy as a result.

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Just to correct and clarify your opening post, the Big PCB on the 400K drive only requires HALF the quantity of caps you mentioned (for a single 400K drive), so the following is correct:

Big PCB:

3pcs of 47uF (stock specs: 16V, D=6.5mm, H=8mm, Lead Spacing=2.0mm or 2.5mm)

2pcs of 22uF (stock specs: 16V, D=5.1mm, H=8mm, Lead Spacing=2.0mm or 2.5mm)

That applies to both Carts listed under my video — two carts because 400K drive types and PCBs differ...

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The capacitor-related differences between the two 400K drive types appear on the Small PCB, and the 0.22uF in an aluminum electrolytic type is nowhere to be found on Mouser as of today.

I am, however, able to find in-stock 0.22uF caps in solid Tantalum LEADED form here:


The big issue is that the HEIGHT of the stock cap is 5.8mm or so. Those solid leaded Tantalum caps are 7mm to 7.11mm tall. By far, they are the BETTER cap though because they won't need to be replaced. And although I have no idea if the working voltage is 5V or 12.5V across that cap, even if it is 12.5V, the solid leaded Tantalum caps linked above are rated for more than double that working voltage (35V or 50V) which means you're safe.

So the question is, can you buy the solid tantalum cap and make it fit? Probably because the other caps on that SMALL PCB are 7.0mm.

For now, this is the one I will pick as it is D=4.4mm:

But here's the issue. The stock cap LEAD SPACING is 1.5mm, and that tantalum cap is 2.54mm. That means the cap would stand up on its legs, further increasing its height off the PCB, which I think may pose a problem. But perhaps you could lay down that cap on its side to make it fit, because it is not adjacent to other caps in the area.

That very well might work, but perhaps ONLY on this PCB type...



But it doesn't appear possible to "lay down the cap on its side" if you have the following Small PCB type...



Nevertheless, I have swapped in that tantalum cap on both of my SMALL PCB Mouser Carts, because that's all we have!

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The 1uF capacitor I had chosen in my carts previously was the best. 20mA Ripple current and low ESR. All the aluminum electrolytic caps in the physical size we need are only 10mA Ripple current, which means about double the ESR...


However, if we do with this 1uF cap as I did with the 0.22uF cap and go with leaded Solid Tantalum (which again has enough voltage headroom to be safe), this one would be my pick...


I've added that to my two Carts. And because it is isolated from other caps, you MIGHT be able to lay it down on its side to make it fit. This is speculation on my part, but it's the best I can do, since I don't have that cap.

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Both of my Mouser Carts are now complete with no out-of-stock caps as of this writing:

• Mouser Cart for newer OA-D34V-22: https://bit.ly/3dl56B9
• Mouser Cart for older OA-D34: https://bit.ly/2zSpzyy

I believe strongly in helping out my fellow vintage Mac enthusiasts as much as humanly possible, in large part because I have the “do to others as you would have them do to you“ philosophy. I myself have a lot of help through the years, so when I have the ability to help someone else, I want to do my part.

I also try to get answers for people in a timely manner because I myself don’t like to be kept waiting for many days or weeks. I had hoped to get back to you in 24 hours, but the complexity of the problem caused it to be two days, so I apologize for that.

In answer to your question about whether the perfectly sized electrolytic capacitors that I had selected previously in my Carts will become available again, sadly, due to tariffs and a lot of craziness that’s been going on this year, I really have no idea. Best to assume they won’t be in stock again.

With that said, the capacitors I selected yesterday are the best I could find at this time.