DaveC wrote:
I'm trying to troubleshoot an error with an HP ink jet printer
(Photosmart 3210) that says "Ink System Failure". All other
components seem functional.

In the printer there is a small PCB with a few soldered
components
that appear to sense ink flow or pressure. It is in series with
the
pump output.

http://i48.tinypic.com/o8xz84.jpg

http://i49.tinypic.com/r76kib.jpg

How does this work? Are these 6 LEDs and photodiodes? Just
detecting
the presence of ink doesn't seem likely. Wouldn't movement or
pressure be what is detected?

What does this PCB do and how does it do it?

Thanks.

If you're talking about the tiny black rectangular parts numbered
R1-R6, they are resistors.