Not prime tuning error

You’ve probably figure this out a long time ago - but I know exactly what part is wrong with your unit because I fixed this same error in the middle of nowhere, depending on what subcomponent has failed, maybe you can too.

Here’s my little contribution:

During a misssion trip with the International Medical Alliance of Tennessee to the frontier region of the Haitian/Dominican Repbulic border our team encountered this exact error code/problem - on the first day of a planned week of surgery.  After passing the initial power-up software tests, it would fail the prime/tune procedure every time with multiple cartridges/tubing sets.  

Now, I’ve practiced electrical engineering for over a decade and am now a few months away from graduating medical school.  I didn’t expect to have to fix this equipment in the field and was limited to whatever the locals could provide for tools/equipment.  I’ve never layed eyes on this machine before, nor was I familiar with how it operates beforehand (I’m going into another surgical specialty).   So - keep that in mind with what I am about to say and how I describe it.  

How our machine was acting:  The prime software routine counts down to 0 seconds, and allows for priming of the tubing followed by pulling a slight vaccumm at the end of the cycle.  Symptomatically, after succsessfully priming the tubing, at around 22 secounds, our machine would begin to pull an extreme vaccuum - so much that it would collapse the IV line.  However, it apparently never sensed the vaccuum it was pulling.  It would reach 0 seconds and fail and give the “503” error code.  The machine has three main electromechanical “parts” that mate to the tubing cartridge:  the first two are a pair of black anodized, solenoids that are side-by-side and  dime-sized, one with a horizontal bar “-” and one angulated “/”.  They move freely and with little reisstance when de-energized (no power).  If you run the prime routine without a cartridge and push with a pencil on the middle solenoid during most of the cycle it clamps the tubing and offers a lot of resistance (which corresponds to the bypass/fluid short circuit tubing in the cartridge).  The other solenoid is open (little resistance) during most of the prime, but is clamped/high reistance briefly sometime between 22 and 0 seconds on the coutndown.  The final component is what I presume is a large Hall effect sensor:  It is magnetic, larger (about a silver-dollar coin sized) and attaches to a small magnet affixed to a circular diaphragm on the cartridge.  This sensor must be the pressure sensor for the feedback loop.  It has a lot more resistance than the two solenoids, even when de-energized, but still can be pressed in and returns freely so appears to not be corroded.

Don’t waste your time looking for documentation on-line, as nearly all the error codes in the manuals say something like “write the number down and call for repair”.  Useless information:  especially when your lucky to have power or running water, let alone a telephone or the internet!  After unsuccessful calls to the U.S. with a BME familiar with the unit, the Ophtho gave me the “green light” to do exploratory surgery.

The large Hall effect sensor connects to the main circuit board at connector J1 (labeled “Pressure”) with a 4-conductor (4-wire) ribbon cable.  The connector itself is a self-locking type you’d often find in automotive-like applications - they are easy enough to insert, but a PITA to remove.  This one requires that a small black tab be pressed while simultaneously removing it.  Be careful not to twist/damage the underlying circuit board.  I (carefully) powered the box with this the cable removed and ran the prime again and the unit behaved exactly the same, convincing me that this was indeed the source of the problem.

You can visually inspect the cable for defects, but the sensor itself is housed within a separate metal enclousre (EM shield? makes sense if it is indeed a Hall Effect sensor).  Pay particular attention to where the cable enters the housing, and push on the sensor from the outside to ensure that it isn’t pinching when the sensor travels back and forth.

I focused my attention on the cable-connector-circuit board connection as this is often where electronics of this era had failures.  Furthermore, our unti is a “world traveler” and has recently been in Kenya before returning to the US and now here (where I am currently) in the Carribean.  So I carefully cleaned the contacts on the J1 connector and re-attached the cable.

If you can’t be good, at least be lucky.  That’s my motto.  Our unit needed no further jungle-engineering and we completed three surgeries with it yeasterday and will continue with a bunch more today.  

I’d say you have a 50/50 chance that your unit also suffered from travel-related vibration/disconnection (easy fix) so paying particular attention to this could be very high-yield, too.  However, your unit could have instead a bad cable or actual connection (moderately difficult fix), or finally a bad sensor (difficult:  short of finding a scrap unit to swap this part out, I’m not sure what you can do in this case).

    Good Luck!