legacy power master

Our club uses quite a few of the Legacy PowerMasters with no problems. Is the two loops that each PowerMaster is powering are the center rails completely isolated from one another?

@Terry Oursler 090218 posted:

My issue is with two power masters, i have three in use or better put want to use, one works as supposed to, two don't, one responds to cutting the power but only goes to half-power, the other does not seem to respond at all to commands from a Legacy command base they all worked as supposed to in the beginning as i bought the Legacy base and power masters in spring of 2021 power master #6-37146, i run a large layout and each power master was to control a large section or loop of rail, the two in question DO NOT cut power when a short occurs also i scoured the manual and followed all the resets multiple times, i see no issue inside, no burnt or separated connections, no burnt components, can anyone shed light on this??

Just like the ZW-C answer the other day, these symptoms of not working properly, jumping from off to partially on but not fully on, you power master may have been damaged by a derailment or voltage spike. You likely will NOT see burned components, FETs can fail shorted internally and NOT show visible signs that are obvious.

I recently got a legacy powermaster for testing and cracked it open to better understand the construction

https://www.digikey.com/en/pro...mi/FDP047N08/1853911

Point being, if one of the MOSFETS fails shorted, you get that partially working state where off is power off, but ON is 50% or half the waveform stuck on.

Testing for failed shorted FET(s).

Note, if you reverse the meter leads, + to S and - to D then you would be measuring the internal diode structure inside the FET. In other words, they should be open circuit normally in the off state D+ to S-, however, reverse polarity, the internal diode conducts. If it shows shorted both directions, then a good chance that is the cause.