HP-82183A... Problem with ASTEC 0950-0408 :(

[Titi]

So, about "U2 :5.07 (Vp) / 0.68 / 13.91", my measure is from "-" of battery.
I don't know if this test is correct (sorry, I'm really not an electronics )

If the U3 is dead : "I find subs quoted for U3 1826-0287 as LM339 or LM2901 both of which are comparators with the same pinout and very similar characteristics for this application I think either one would be suitable."

Then, how to confirm the default of U3 to be sure ?

Best regards & thank you Paul for your help !

Thierry