I let the magic smoke out -- Blower Circuit Dead

[Phillip P]

While the main HeaterMeter was doing its thing outside, I was using the secondary inside to test some probes that I felt a bit off. (They were.) Had a nice rolling boil in a pot and a stray dot of water managed to hit the HM. I saw a small plume of smoke leave the HM in that familiar capacitor-being-fried kind of way and now the blower circuit doesn't work.

The Pi is fine. The HM seems fine. The only thing that doesn't work is the blower circuit.

I remembered a thread from a while back outlining blower circuit troubleshooting, but my google-foo is not up to the task.

If anyone can point me to that thread or have some troubleshooting advice, I would appreciate it.

 

[RalphTrimble]

The blower circuit is pretty simple really, the feedback circuit is about as large as the main portion....

I would try the blower in pulse mode (instead of voltage mode), as pulse mode does not require the feedback circuit.

Take a look at the schematic, should be pretty easy to fix....

I would suspect Q1 or Q3 got toasted..... or perhaps D2, my guess is Q1, as Q3 is a much more hearty device.

The only electrolytic cap in the circuit is C12, and there is the little .1uf cap at the end (C7). Maybe C12 died, but my money is still on Q1.....