Thanks for the suggestion - I checked out CR1 and it appears to work correctly (read the appropriate voltage drops and opens from the AC to the +/- pins) - I really think it has to be in U1 or one of Q1-4.
So I was just putting together a shopping list (I have to pretty much pass the store to get to work so I thought I'd drop in a grab the components regardless so they'll be on hand if needed).
The items I'm looking at are:
C3 & C4 - 15uF/35V Electrolytic Caps
U1 - LM3542N
Q1 & 2 - Fluke 272237
Q3 & 4 - 2N4403
CR 2 & 3 - TCR5315 (marked as a 2N4401 on the schematic)
In terms of replacements - I can do the following:
15uF/35V replaced with 22uF/35V (should be Ok to increase the capacitance, they don't have a 15uF electrolytic)
LM3542N replaced with a NTE1720 PWM regulator
Q3 & 4 replaced with 2N3906 PNP transistor
Q1 & 2 replaced with 2N3904 NPN transistor
The parts that I don't seem to have any information on are CR 2 & 3 - They are described as "Diode, SI, N-JFET, Current Reg, IF=5.3mA" so they must be using a JFET to protect the transistors.
I can't find anything about this part - 07910 looks like it is Teledyne Corp (Continental Devices) Hawthorne California but the closest I can come to a datasheet/more information is
this page:
Military/High-Rel : N
I(S) Nom.(A) Regulator Current : 5.2m
Z(T) Min (?) Dynamic Imped : 220k
V(L) Max. (V) limiting Voltage : 3.1
P(D) Max. (W) :
V(P) Max.(V)Peak Oper. Voltage : 50
Semiconductor Material : Silicon
Package Style : TO-18
Mounting Style : T
Any suggestions on what to use as a replacement that would be generally available? I can find several that will fit on Digikey but nothing that my local store seems to carry. I can't seem to find anything but maybe my SearchFu is just weak today...
TonyG