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

[Paul Berger (Canada)]

(06-29-2017 09:35 PM)Titi Wrote:  

(06-29-2017 08:18 PM)Paul Berger (Canada) Wrote:  One thing I would check would be the reference voltage at pin 7 of U3, if it is wrong the output from the +5V logic supply will be wrong. The theory section starting on page 2-4 explains in some detail how this 5V regulator works.

I find +5.04v here ! U3-pin 3 : 13.92v (with jumper W1)

Ok well the +5V logic supply is a little bit on the high side, but even so the power light should come on. Comparator U3D is the control of of the 5V logic regulator, when I measure the inputs to it pin 8 is about 150mV less than pin 9 this would be due to the offset voltage for that comparator, the measurements that you quote suggest that there is an offset voltage of nearly 700mV and that is way too much, but still like I said previously, the power LED should still come on. Pin U3-6 should be higher than U3-7 which should result in pin1 being low, which in turn pulls down pins 1,2,14, and 15 of U9 74LS365, a hex tri-state non-inverting buffer. Pins 1 and 15 enable the outputs and 2 and 14 are inputs to two of the buffers Since this is a non-inverting buffer the outputs 3 and 13 (tied together) should also be low and that should turn on the power LED as well as enable some other parts of the printer.


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.

Paul.

Paul.