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It's more likely for reverse polarity protection. Except now it's failed and current is flowing in both directions.

Yeah, I'm guessing high is the default. The data sheet for the 1736A is a bit confusing because it shows the reset net label as active low, but it looks like according to other parts of the data sheet it's active high. It is strange that the 1736D setting isn't working, as it shouldn't be that...

The interrupt usually triggers the debugger if the system is booted, or during startup will typically give you a "Sad Mac" error which is normal. Typically there is a dedicated interrupt ⎉ button, but I think on the 540c does not have one, you have to press Command⌘ + Power to trigger the...

The Powerbook will technically run without that diode. I think that's just for reverse polarity protection.

Just out of curiosity, if you switch the reset polarity under Dev. Config, does it read? I can't find any clear documentation on whether that setting matters for reading.

I know my programmer does warn about the reset polarity when switching to the 1736D, as it's a feature that the 1736A does not have. You may want to double check you have this the right way around, because I think the default on the 1736D is active high rather than active low, while it looks...

You're using the XC1736A setting on an XC1736D? I think those have different programming voltages.

You can actually do it without target disk mode. You just need to interrupt the target Powerbook before it starts up, and as long as there aren't any SCSI ID conflicts it works, even on older Powerbooks that don't support target disk mode.

I've been thinking about designing one, like a diagnostic card to help with issues like a bad SWIM. Unfortunately I haven't found a bad SWIM to test with yet and haven't had enough money to order PCBs yet. The difficulty does depend on what you want to do with the ROM code itself. Disabling...

You can override the built in ROM or expand on it, or even add a ROM disk. Though I believe disabling the built in ROM requires changing a jumper on the logic board.

Here's the pinout from the female connector end:

So it boots without the power adapter if no SCSI device is plugged in correct? What does it do when it doesn't boot? A BlueSCSI shouldn't be able to draw enough power to cause that, and typically the battery should be able to provide enough power to blow the fuse. If you have an oscilloscope...

That's 4.5Ah. It's basically the capacity, so on paper with a constant 4.5 Ampere draw it should last an hour, or 4.5 hours at 1A.

The protocol is already known, but I don't know if anyone has ever gotten around to doing anything with it. It's nothing complex, someone just needs to throw something together for it.

You're seeing the full battery or charger voltage because the MOSFET isn't getting any voltage on the gate. At 0V it will just pass through the full voltage to the +5V. Normally you'll see around 2-4V on the gate, though it varies a bit. Here's a simplified simulation if you want to see how it...

Yes, it needs to be connected to both positive pins otherwise things like the 1.2V reference, negative voltage generator, and some signaling will not get power. You should then see the battery voltage on the blue highlighted pin in the earlier image.

It sounds like you may have a bad battery cover switch or bad connection somewhere. Power from the main battery is only making it to one of the two battery inputs on the 4-pin connector.

So it sounds like the comparator isn't turning on power to the rest of the hybrid, and for some reason the 1.2V reference isn't working either. On the comparator, check the V+ pin marked in yellow, it should be around the same voltage as the battery. The green mark is the same 1.2V...

The MOSFET at Q16 isn't being properly driven, or in very rare cases is bad. Check the highlighted points at each end: You can check that there is voltage making it from the hybrid to pin 1 on Q16. If there's no or very low voltage on both ends then there's likely a problem with the OpAmp...

On the original card the greyscale is disabled when an external monitor is connected. I would assume that's the same case here.