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

[Paul Berger (Canada)]

(06-30-2017 05:10 AM)Titi Wrote:  

(06-30-2017 01:06 AM)Paul Berger (Canada) Wrote:  The voltage on U3-3 is ok. It is connected to the print head voltage which is variable depending on the intensity setting, I believe that with the board out of the printer it would be the equivalent of the lightest setting, I measure about the same voltage with the intensity turned all the was down.

I measure with the board in... I find +17.4v with hightest setting.
My other tests about U3 (pin #)

1 : 5.42
2 : 6.45
3 : 13.89 (Vh)
4 : 5.09
5 : 4.75
6 : 6.42
7 : 5.05
14: 17.26
C7+ : 4.50 (Vbs)
U2 :5.07 (Vp) / 0.68 / 13.91

OK so the measurements above would suggest that the - input of U3D (8), which is connected to Vp, is more positive than the + (9) which is connected to reference voltage this should cause the output from U3D to be zero but that does not appear to be the case. Pins 1 and 2 of U3 should also be low according to your measurements. My best guess would be that the U3 is defective. Since the output of U3D is high this should mean that Q2 is turned off and the voltage at the base of Q1 should be less that Vh so that Q1 is at least partially turned on this would also account for the rise in output voltage (Vp) when you change the intensity setting which caused Vh to rise. 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.

Paul.