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So... My IIGS was working just fine and I plugged a ADB cable I'd never used before into it and became distracted momentarily by something else. I soon, however, noticed a bad smell, and reached down to find that the ADB cable I'd plugged in was quite warm, almost hot to the touch. I shut the IIGS off and unplugged the new cable, and I tried one that I knew worked (and had just tested with my Performa 6200CD), but to my significant dismay, the ADB port no longer responded.
A quick Google search yielded some clues, including a forum that said I might be able to fix a fried ADB bus in a IIGS by replacing the chip that's connected directly to the ADB port. On my IIGS there's a little 8 pin chip that says, "Tokin D-16C" on top. More googling led me to the Tokin.com data sheet that tells me the D-16C is a "Dip Noise Filter". The only place I could find online that sells them was a fairly shady looking Chinese website that was charging quite a lot for shipping. When I put my nose up to this chip it does have that same bad smell I was smelling when I had the bad ADB cable plugged in, which makes me hope that it could be it. But I don't want to spend the money without more info.
So.. Anyone have any experience repairing a fried ADB port on a IIGS? Anyone know where I can find one of these chips or a reasonable substitute (if it is, in fact the burnt out culprit)?
https://www.mouser.com/ProductDetail/KEMET/D-16C?qs=%2Fha2pyFaduhERpGNwGEEEzpL5o1%252Bx74sRRXZgs%2F4JXk%3D
Not a common component now, because it is through-hole.
https://content.kemet.com/datasheets/TOK_DC101.pdf
You can likely find a suitable alternative, as it is just four small choke coils in sequence, in one package. I would guess that you burnt out one of the coils. Were you plugging devices into the ADB when the system, or the devices were powered on? That is much more likely to do this than a cable with broken connections.
Kemet p/n D-08C2A might be close-enough to cross, but it seems to be around 75 Ohms @1MHz veruss 48 Ohms @1Mhz an its bell curve is about the same, which means that it peaks higher and its dropoff is higher. I can't say if it is satisfactory, as I do not know why that specific choke was selected to use on the //gs ADB.
You could also use four individual minicoils with the same rating as the original Kemet part, instead.
What freight quote did you receive, and what price per unit? Note that most suppliers do not tend to handle [quantity==1], so, buying ten or twenty parts is likely the best option, reducing the per-unit freight cost; and possibly the per-unit cost as well. You can then sell 90% of them at a small markup, and cover your costs over time.
Don't forget to do a continuity check beteen the pins. The pin diagram is on page 11 of the PDF. You can also check resistance values across those connections to determine if any of them are wildly different. This can help you to identify which, if any of the minicoils, you burnt out. To be honest, it would be fortunate if any damage to the ADB was constrained to this component.
That's good to hear! Where were you able to find the part?
That's a lot of great info, thanks! I really hope I didn't fry the ADB on my IIGS, but I'll try replacing this component and we'll see. If I can find one for a reasonable price I'll post the results once I install it.
Today I stumbled upon a post talking about how to make homebrew coils to replace the Tokin (aka Kemet) part.
Here's the link: https://stason.org/TULARC/pc/apple2/faq/13-011-Recently-I-was-using-my-GS-and-smoke-started-coming-f.html
I was a little skeptical, but after installing the homebrew coils the ADB is working just fine on my IIGS. It's been running for a couple of hours now with no issues. Not sure how it'll work long-term, but my IIGS was always a bit of a beater anyways. I guess we'll see!
Hmmmm, I was just getting ready to use a passive S-video switch box as a keyboard and mouse A/B switch between my IIgs and IIci. After reading this thread, I guess that is a bad idea, eh?
I used to hotplug ADB stuff fairly often back in the day and never had any trouble. I'm not implying that I don't believe you guys or anything, but what exactly causes the coils to fry? That seems peculiar. Can I tie all the ground pins together inside the A/B switch to keep everything at the same ground potential and keep this kind of thing from happening?
The coils in my IIGS got fused I think because of a bad cable. And I've unplugged the ADB cable from my 6200CD when it was on before and that didn't fry anything. But I've read multiple articles stating that you can't hot swap ADB peripherals, and I'm just going to take their word for it. And I won't be taking any chances with my vintage ADB equipped Apple machines anymore.
Here's what I know:
It is not safe to hot-swap ADB devices. You can do it 100 times, but only that one time out of 100 fries it. The bus hardware was not designed to permit this, and there is not adequate circuit protection on it to ever consider it safe.
I have fried an ADB this way, and know the issue to be true; an since then, I always poer down both the system an the devices before shifting them.
I would expect vcc to be the issue, not earth. That said, I only state hat Appl state in their docs and what I have personally exprienced.
Hmmm, I wonder if I put an electrolytic cap across vcc and ground in the switch, if it would smooth things out enough to make it safe.
Edit: Hmmm, or maybe if there wasn't too much voltage drop, I could tie the VCCs together inside the switch with a couple of rectifier diodes. That would keep vcc and ground connected all the time, and the only thing getting switched would be the data line(s). Although without power interruption, I doubt the keyboard would reinitialize properly when switched to the other machine.