SWIM PLCC to secondary disk drive header adapter

[tashtari]

So, I was thinking...

There are three Macs that have HD20/DCD support in ROM but do not have a secondary disk drive connector, internal or external, to wit the IIvx, IIvi, and LC II. On these machines, it's possible to connect a TashTwenty or Floppy Emu by means of clipping on to the !ENBL2 leg of the SWIM PLCC itself... but this is, of course, clumsy and cumbersome.

What if there was an adapter board that fit over the SWIM PLCC, using an inverted PLCC socket, and broke out the appropriate pins to a 2x10 header for a secondary internal drive header?

Not only would this be useful for HD20/DCD support on the IIvx, IIvi, and LC II, but it would (I think) make it possible to connect a Floppy Emu on a number of other Macs without disconnecting the internal floppy drive. That'd be pretty cool.

I'd love to make this myself, but looking at the PLCC sockets available for sale and eyeballing how they'd fit upside-down, it looks like the ones that would fit best are the surface-mount ones. In addition, to put the socket on one side and the 2x10 header on the other seems like it would require both parts to be surface-mount. Aaaand... I am, to put it mildly, not confident in my ability to do surface-mount soldering. Hmm.

What do folks think? Anyone interested in collaborating?

 

[Phipli]

So, I was thinking...

There are three Macs that have HD20/DCD support in ROM but do not have a secondary disk drive connector, internal or external, to wit the IIvx, IIvi, and LC II. On these machines, it's possible to connect a TashTwenty or Floppy Emu by means of clipping on to the !ENBL2 leg of the SWIM PLCC itself... but this is, of course, clumsy and cumbersome.

What if there was an adapter board that fit over the SWIM PLCC, using an inverted PLCC socket, and broke out the appropriate pins to a 2x10 header for a secondary internal drive header?

Not only would this be useful for HD20/DCD support on the IIvx, IIvi, and LC II, but it would (I think) make it possible to connect a Floppy Emu on a number of other Macs without disconnecting the internal floppy drive. That'd be pretty cool.

I'd love to make this myself, but looking at the PLCC sockets available for sale and eyeballing how they'd fit upside-down, it looks like the ones that would fit best are the surface-mount ones. In addition, to put the socket on one side and the 2x10 header on the other seems like it would require both parts to be surface-mount. Aaaand... I am, to put it mildly, not confident in my ability to do surface-mount soldering. Hmm.

What do folks think? Anyone interested in collaborating?

Are the unused pins N/C, or tied to a power rail?

Trying to think what machine we have the schematics for... LC II I guess, from @max1zzz's work if not original.

 

[tashtari]

Are the unused pins N/C, or tied to a power rail?

Trying to think what machine we have the schematics for... LC II I guess, from @max1zzz's work if not original.

@max1zzz established here that the !ENBL2 pin on the LC II goes nowhere, and @Fizzbinn established later in the same thread that the IIvx works to boot from a DCD, so at least on those machines, it isn't tied to a power rail.

 

[twelvetone12]

Do the connectors resist heat? I have a reflow oven if you need a hand, but I think I'm on the wrong side of the ocean!

 

[Phipli]

In addition, to put the socket on one side and the 2x10 header on the other seems like it would require both parts to be surface-mount.

When assembling complex things on both sides, a trick is to use different melt temperature solders on each side. So, use a 200°C solder to put the first side parts on, then turn down your hot air/iron and use a 150°C solder for the components on the second side. No chance of remelting the solder on the first side.

Truth be told though, I haven't needed to do this ever yet because I tend to only have small components on the second side and if I hand solder them and don't take too long it's fine.

Do the connectors resist heat? I have a reflow oven if you need a hand, but I think I'm on the wrong side of the ocean!

Yeah, they do melt if you put too much heat into them. I try to use a lower temperature solder paste and be quick about it with hot air. I have one tube of solder paste that's like, 130°C or something. I use that for ROM sockets, given ROMs don't put out much solder anyway.

 

[tashtari]

Trying to lay out a PCB for this, I realized the flaw in my plan. The SEL signal on the floppy connector is unique in that it doesn't come from the SWIM, it comes from somewhere else that varies by machine. SEL isn't necessary for an HD20/DCD device, but it is necessary for a floppy drive, so without it, the utility of this adapter is limited to the LCII/IIvx/IIvi, which might be too narrow to really be interesting.

This would still be doable if it was paired with a ribbon cable with three connectors so SEL (and the voltage lines apart from 5V) could be passed through, though... hmm. If we're doing things that way, only the !ENBL2 pin on the PLCC socket really needs to be soldered to the board, plus however many pins are necessary to ensure that it's solidly attached, that might make for somewhat easier assembly.

I don't know, is the idea of adding a secondary drive connector this way interesting to anyone?

 

[Chopsticks]

you Could just add large enough to easily solder pads on the 2x10 pin connector side of the pcb. Then if someone only wants to use HD20/DCD they don’t need to worry about it but if they want floppy support then can solder the extra connections?

 

[tashtari]

So I made two different boards for this.

The first has a single 2x10 connector that gets all its signals from the SWIM chip underneath but (1) can't get SEL or 12V, so it's only good for connecting a TashTwenty or Floppy Emu in HD20 mode, and (2) requires soldering a bunch of pins on the PLCC socket, which is, as I found out, difficult.

The second has two 2x10 connectors, the first of which passes all signals through to the second except for !ENBL, which comes from the PLCC socket underneath so it gets the secondary !ENBL, thus making the connector good for an HD20 or a second floppy drive of any type, as well as requiring the soldering of only one pin on the PLCC socket - however, it requires that you either have a three-position 20-wire ribbon cable or forego having a primary floppy drive.

I soldered one of the second boards together (my soldering skills weren't good enough for the first) and tried it out on my LC II and it just barely didn't fit, there was a capacitor slightly too close to the SWIM chip. I still think this is a worthwhile avenue to explore but unfortunately I don't think I have any other suitable Macs to try it on - my collection isn't quite on par with those of some people around here. =)

Does anyone with a potentially suitable Mac want the board and parts to give this a try? You need (1) a Mac with a discrete SWIM chip in PLCC-44 form, not a DIP, not one with the SWIM integrated into an ASIC, and (2) the soldering skills to handle soldering a PLCC-44 socket to a small board. Your reward shall (hopefully) be a Mac newly able to handle a second floppy drive. =) Let me know!

(I'd post a picture of the boards but apparently the forum's object storage is down...)

 

[tashtari]

There we go.