Nah, I did not passed out, but will soon.
5:25 AM here...
You can bet your bottom dollar, I was desperate... Look at this contraption:
I'll post more details later after some good sleep, but here's the progress tonight:
Dodgy 4094 which controls LM339 to control low current ranges? Testing with LA on inputs and outputs.
So I removed 4094, installed collet sockets (it's not analog critical part anyway, don't want solder board too much)..
Then decided to replace RP200 (it was soldered by prev.owner, remember?)
Removed it..
And...WTF..
Missing pin on the bastard.. And yes, it's common pin for all 7 resistors in package to pullup LM339 output. No wonder JFETs were not working..
And since I did not have any MC14094 in DIP, but I really could not wait, used wrong sized DIP14-SMT adapter, desoldered 4094 from dead HP 33120A board, put some wiring, and...tada...:
Will it work? I gave some decoupling love too with pair of 1uF 16V X7Rs
Now my 3458A have 3 SMD components in it!
Bingo...
Was another issue tho, TR300 (yellow long thingy on A1 board near vishay resistors) is extremely sensitive, if I bend it just a little or touch it - ohms and current measurement go berserk and selftest failures all over it. I think bad contact inside of that thing.. So
ManateeMafia's burnt board could be a handy donor, I believe.
Did very rought CAL with 10V from Keithley 2400 and 10K from ESI DB52 (not even 4wire lol), passed without errors. So, almost done, perhaps?
Time to crash in bed now.