Minimax NT Control Board Failure?

[Wolfhound89]

Almost five years ago I replaced the thermistor in my Minimax NT pool/spa heater. It had been working fine. Once again I was getting the HI code on the display. I was not at all surprised given the arctic conditions we had here in Texas.
I knew what to replace so I order up the part and replaced it. After replacing the part and leaving all the panels open everything was working fine. Heater fired up fan ran good. After about 10 minutes I shut everything down and put the panels back on. Now I am not getting any power to the Minimax. The orange/white connector on the back of the control board is not showing 24v. So, I am thinking that maybe an internal to the heater protection device was tripped. Is this possible?

Also, another observation is that after this no power to the heater occurred when I switch the pump back to pool via the automation the main pump shuts off. Don't know if this is connected but a data point to share.

Thank you.

 

[Wolfhound89]

With the absence of the 24V could that be an indication of the control board failing?

 

[swamprat69]

The orange and white are the secondary ( 24v side) of the transformer. Are you getting power to the primary winding of the transformer? Are both the primary and secondary windings of the transformer showing continuity?

 

[Wolfhound89]

I will have to get back into the schematic and look into where to measure those at.

Thanks.

 

[Wolfhound89]

Continuity check results.

Primary / Secondary windings

Black to Red/White - continuity
Red to Black/White - continuity

24V side

Orange to White - no continuity

Thank you.

 

[swamprat69]

That orange to white open ( no continuity ) indicates that the secondary winding of the transformer is open. One side of the 24 volt circuit is grounded as indicated by the "GND" terminal on the ignition control. In many cases the transformer secondary is protected by a glass fuse (if so, check to see if the fuse is blown). While a transformer secondary can fail from age, stress or defects it is more likely that there is a direct short to ground in the circuit or an overload such as a gas valve solenoid that is stuck open. You can replace the transformer matching the VA rating listed on it and if there is no fuse on the secondary of the 24 volt circuit, put an inline glass fuse holder and fuse inline with the 24 volt circuit (orange wire) with the fuse sized to the transformer VA divided by the secondary voltage (24) example: ( 50VA / 24 volts = 2 Amp glass fuse ). It is easier to replace fuses than transformers. Check the back of the circuit board for any brown, black or burnt traces. Check the safeties and wiring for any shorts to ground. See if the heater will fire up and run. If it doesn't and blows the fuse at some point, note exactly where in the sequence of operation the fuse blows and the heater stops.