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FIXED: Problem was a rotted -5V contact on the power supply molex plug. Looked fine from the outside and measured continuity when a test lead was stuck in... Simple, but ran me around in circles for a bit.

I think I need a bit of help in troubleshooting my LC475. I'm scratching my head a bit over the schematic on page 13. A scope on pins 18 (or 19) of the DFAC chip shows that PWM is being generated when I trigger a notification. It reads a steady square wave under quiet conditions that then...

This should work: https://www.ebay.com/itm/296681016042

Rats. I'll have to put on the thinking cap and fabricate something.

I just ran into the same issue. An extra-tall IBM 128M simm leans way over the CPU and prevents installation of a heat sink. There are a couple of vendors who offer a standard-height 128M part at reasonable prices (~ 30-40 USD) and I'll probably go in that direction.

I believe it's a metric thread. Try Fastenal or McMaster-Carr.

I like the rails on your pre-heater. I bought an Aoyue unit last year that has only a set of short, narrow bars to hold the PCB making it a true PITA to use. Were those rails OEM or third-party?

@Tashtari - Just sitting down to solder together my phone net to DB9 kit and realized the orientation and offset (9 lines to 10 pin) at the IDC end of the cable is not specified. Can you clarify? Pin 1 of the IDC connector must be a no-connect, which just adds to the confusion.

There is at least one very good video that walks through the process of disassembling and cleaning 3.5" Sony drives. It's really quite simple if you take your time. I've probably done a dozen to this point with no problems or unintended damage.

Mac-sync-inator is a great gadget. I have perhaps a half-dozen passive adapters and the sync-inator was the only device that gave me a display from a newly acquired IIci.

My theory is simple corrosion from exposure to humidity. There may be exposed copper where the winding leads come through the cone. It does seem particular to SEs as none of my older or newer compact Macs ever had speaker issues.

I've never heard of anyone doing a re-cone on tiny speakers, but stranger things have happened. FWIW, all the dead speakers I've encountered had open voice coil windings.

I think I'll wait for regime change and try JLCPCB at that point.

If anyone is planning to have populated boards built I'd really like to have one of these. That much SMD soldering is outside of my comfort zone.

You mention it booting and reading diskettes. Can you write to the diskette?

Take a very close look at the entire power harness, starting from the solder joints on the analog board and ending at their compatriots on the motherboard. You may have a cold/cracked joint or oxidized contact somewhere along the line.

Heyco pliers are the appropriate tool for those who might have to do this more than once. I picked up a pair on eBay for ~ $50 USD.

FWIW, I replaced a dead SE speaker with an 8-ohm unit and it's been working fine. One can do extensive circuit analysis or one can simply take a leap. I suspect the duty cycle is too short to cause problems. YMMV.

I'm easily able to get reliable 44 MHz. operation from my Q650, but that seems to be the hard limit. Mac OS 7 is happy at faster speeds but A/UX locks solid at "loading device drivers". I have a feeling that A/UX puts far more stress on the machine.

Why not burn a new EPROM?