Yes, the power card is what turns the tms on/off so it could cause this (I have yet to see this scenario)
I have replaced many tms for this code. I have not needed to replace a power card for code 26 but I'm still young...

you can test them with a multimeter with diode test function:

pos lead c1 - neg lead c2e1 open
c1 - b1/g1 open
c2e1 - b1/g1 open
c2e1 - b2/g2 open
c2e1 - c1 >1ohm
c2e1 - e2 open
e2 - c2e1 >1ohm
e2 - b2/g2 open