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

[Paul Berger (Canada)]

(06-30-2017 05:02 PM)Titi Wrote:  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

Are you still using a setup similar what you had in you first pictures where you where using an external AA battery holder? The center pin of U2 should be ground and at the same potential as the "-" of the battery this might suggest you don't have a real good connection between the "-" of the battery and where you connected inside the printer so it is dropping a little voltage or maybe there is a slight offset in your meter, does it read 0 when you short the meter leads together? Attaching the "-" lead to a ground point inside the printer might bring the voltage on the center pin closer to zero.

Because there is an offset of about 0.68V it means that the other voltage readings are pobably a bit higher than they really are, but that does not change the results, the comparators in U3 work on the difference in voltages on the inputs and since the offset would affect all voltages the difference between them would not change, so I still think that U3 is defective.

For U3 what I am saying is LM339 and LM2901 are nearly identical so either one could be used to replace U3.

Paul.