Solenoid, GPU Plug - losing volts

[Bryan]

I have a 24v M20K model that was in avionics today for a firmware upgrade.  When they hooked me up to the GPU to supply power, my bus voltage was well below what it needed to be on the GPU at 27-28v.  They tested it with the relay open and found several volts dropped just across the relay.  With a load, the GPU was unable to keep the voltage up across the relay.

What could cause this and how do I get it fixed?

Looking at the IPC for my model, 25-2026, it shows a part number: 6041H202A (Solenoid - 24V) for item #26.  Is this what is going bad?  I would think a solenoid would either work or it wouldn't.

[ArtVandelay]

A solenoid could be closing but have a high resistance from corrosion or arcing, which causes the voltage drop.

 

[Yetti]

Never gets used.  Corrosion on the contact.  maybe plug and unplug GPU several times. Did they check the GPU voltage?

[Bryan]

Yes, we checked the voltage on the plug side of the solenoid and then on the other side. Voltage drop, it seems, inside the solenoid probably what @teejayevans suggested. 

[Yetti]

There are also the GPU pins on the plane side that are pretty well coated with a layer of yuck.     You could always take the moment to pull it all apart and make all the connections shiny bright.  Bad ground to the airframe could also be causing issues. Electrons flow from Negative to Positive.