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Neat idea. @eric have you considered that as a feature before?

With asking prices for these adapters being kind of absurd, I figured it might be helpful to consider reverse engineering one. It seems like a couple of special purpose ICs, a ROM and a surprising amount of passives. I don't think I'm up for the challenge of reverse engineering it, but figured...

I had a similar issue post recap. esc, 4, 5, 6 and + would short the reset line when pressed. It turns out I shorted a trace right next to C24+ which was the issue. Maybe you did something similar near C15 or C26? I'd check that area first or by C116/C14 if you have the keyboard on the right...

Chassis, without a resistor. I'm still chasing down the problem. I found one open capacitor so far at C39 but replacing it didn't change the symptom.

I found a pad for C1 had come loose from all of the handling of the board. I reattached it and now get a chime, no video and then lose voltage (flup flup flup noises). The rectifier at CR20 seems okay, so maybe I have a bad cap somewhere else now. It's weird that the symptom keeps changing.

Wouldn’t -12V just be needed for audio and maybe serial? I’d be curious to know if it’s required for basic operation.

Update: Replacing Q7 changed the symptom to a vertical line (collapsed horizontal deflection). Q6 tested okay. Will test Q3 next.

Nearby resistors all tested okay. There is a 2N5485 (Q5) off of U2 pin 3 that shows resistance between source and gate in both directions. I'm not sure if this is because my meter isn't suited for it or if the transistor failed, but I've ordered some replacements to try.

Update: +12V, -12V and +5V are all testing okay at the floppy port. Next I'm going to try to check components downstream rom U2 on the analog board.

I discharged a 128K Mac without a bleeder resistor and manage to damage it. At first I got a chime but no raster at all. Per Macintosh Repair & Upgrade Secrets, I replaced the LAG chip on the logic board and got raster lines but a dark screen. I then replaced U2 on the analog board, but the...

I always wondered why many SCSI terminators are dual sided/gendered. Apparently it’s to help terminate further up the chain as needed but also works perfectly to terminate this drive using a typical 25-to-50 pin cable.

Not the backwards IDC-50?!

There is a pair of pins on the front side of the controller, but it’s 0V all the time. The manual for the Seagate drive itself refers to a diagnostic that uses a LED thats enabled by shorting some of the SCSI pins to ground. There’s nothing in the manual about a general activity LED. And...

The face plate has a LED diffuser but there’s no apparent header for it on the drive mechanism. For now I just connected a small green LED with a 100ohm resistor to +5V so at least it does something. Should it be possible to tap into the SCSI IO to make an activity LED?

I recently found a Mac Crate 40 MB external hard drive. It looks kind of weird, as if it were an accessory for an IBM instead of a Mac. The line of hard drives seems to have been launched in 1988 based on this ad in MacWorld from that year. The model I found is 40 MB and in fairly good...

Unfortunately, I wasn't able to easily clear the ground pins of a SE/30 RAM slot with the SP-440 alone. A hoof-style tip on the MX-500 worked fine to wet the whole joint, but the SDC-702 tip on the SP-440 would not, even with flux and/or fresh solder in the joint. All the other joints cleared...

I recently got a Metcal SP-440 Self-Contained Desolder System. Since there's so little info about this device online, I figured it'd be helpful to share my experience finding one, getting it working and some DIY recipes for hard-to-find consumables. Why the SP-440? Like many of you, I've been...

Exactly. It's like turning the opened Mac+TechStep into a dedicated RAM module tester. I used a IIsi to test 30-pin SIMMs and a LCIII to test 72-pin SIMMs since it's so easy to remove and install modules on those models.

BTW as a practical example of TechStep coming in handy, I used mine with one of the repro carts to test a mountain of 30-pin RAM SIMMs that had been sitting in a box. I was able to organize them all into sets of working and non-working by size within an hour or so.

There was a VHS tape ad!