@Vernon Barry posted:Add one more,
Variable channels with constant ON track power output, most likely a bad TVS which has shorted out (1.5KE51). These are in parallel to the MOSFETS so when they short, even if the MOSFET is off, you get the full voltage out bypassing the control by the MOSFETS.
FWIW- Zcontrollers have the same (1.5KE51) in the same arrangement in parallel to the variable control MOSFETS and have the same result- constant output regardless of handle position when that TVS fails shorted. Picture and details here https://ogrforum.com/...4#154167236021571964
My method is to use a side cutter to clip one end of the TVS diode leg and then check with a meter when you have one suspected shorted. This removes it from the circuit but still allows you to test the device with a meter. Again, the problem is, we have more than one device in parallel that might have failed- so disconnecting the cheapest and easiest one to replace (2 leg diode VS 3 leg MOSFET).
Thanks for the additional information and this could be a way to resolve the problem of replacing bad MOSFETs when the variable channels are used as fixed channels. If the two variable channels are always used as fixed channels, and a MOSFET goes bad, any issue of just jumping the TVS so now you are just getting full transformer voltage at the output of the TIU channel?
