I won a local auction for an Apple Lisa!!!

[berskyboy]

I'm assuming the "-" prefix in these readings doesn't indicate negative voltage... if it does then let me know.

that denoted a measurement.  Sorry I wanted to separate  it.

But what about this value?:

C. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the lower end of R30 on the daughterboard (R30 is at the left edge/corner). The voltage should be near 4V.  Then while watching the voltage, turn on: the voltage should drop immediately to near 0. If the voltage remains high (around 4 VDC) then the soft-power circuit is suspect.

-no 0V, but I might not be putt the probe correctly

[berskyboy]

So I suspect that replacing Q1 & Q2 (and ensuring there are no solder bridges remaining) is likely to be sufficient to repair the fault that blows the fuse.

The original 2N6308 transistors are no longer made, so finding a substitute is the usual option, although one could look for old-stock originals on eBay etc.

A few posts back, you referenced a Newark/Element14 cart with BUX48A transistors in it. Did you find references that indicate this is a suitable substitute?

Does anyone else have a recommendation for a currently available 2N6308 substitute that works in this PSU?

This is what I found.

BUX48A
TRANS, BIPOLAR, NPN, 450V, 15A, TO-3

https://canada.newark.com/multicomp-pro/bux48a/trans-bipolar-npn-450v-15a-to/dp/23AJ5969

from AI or google:

Yes, the BUX48A can replace the 2N6308 in most high-voltage power supply, inverter, and switching applications. It matches the package type, exceeds all critical maximum voltage and current limits, and provides equivalent or better switching speeds. Solitron Devices, Inc. +3

https://solitrondevices.com/datasheets/2n6306_8-ds.pdf

[sigma7]

But what about this value?:

C. ..

-no 0V, but I might not be putt the probe correctly

The fact that E - H show the SG3524 attempting to run indicates the soft-power circuit is working, so I think it doesn't matter if either you weren't able to probe it or my predictions were incorrect.

This is what I found.

from AI or google:

Yes, the BUX48A can replace the 2N6308 in most high-voltage power supply

Neither AI nor google have any direct knowledge, they've only collected bits of information from elsewhere, and sometimes combine them incorrectly, so they can't be considered an authoritative or reliable source. eg. AI was previously telling you to replace a part that isn't there.

So I'm hoping there is a better source, if not, we will compare specifications in an attempt to confirm the suggestion is reasonable.