Harman P61 burnt circuit board

[techguy802]

I haven't used my Harman P61-2 since last winter, but I recently came home and as soon as I opened the door I smelled a "burnt electronics" smell. I heard the room distribution fan on the pellet stove running even though it was set to off. No lights were on and nothing else was running except for that fan. I immediately unplugged it. Later in the day I tried plugging it back in and the blower came right back on so it has sat unplugged since.

Digging around online, I thought it might be a shorted triac for the distribution blower so I was getting ready to order a couple. I pulled the board tonight and found a pretty bad burnt spot. It looks like a resistor (or 2?) has cooked. I'm pretty handy with soldering and electronic repairs... anyone know how I would go about tracking down the specific resistors I need to attempt this repair? Thanks!

 

[zrock]

you will have to find a board where you can see the color of the one that is really burnt. You can order them online for cheap. Looking at the back of the board the trace looks pretty burnt and you may have to put a jumper wire in to make it work.

 

[Pelleting In NJ]

So, doing a little bit of reverse engineering from your pictures, that burnt resistor seems to be in the Gate drive circuit of the Room blower Triac (Q4 or Q3). I am guessing that when the Triac failed, it shorted internally and effectively connect all three of its terminals together, which would apply AC line voltage to the resistor, blowing it open.

Typically, the Triac and gate drive circuits are identical for each of the multiple Triac circuits used on a stove control board. And, looking at the PCB routing in the pictures, I suspect that R4 is also a gate drive resistor (for another Triac), and would be the same value as the blown resistor (R?), so orange-blue-brown would be 360 Ohm, probably a 1/4 W size. I would replace the (Q4 or? Q3) Triac, the 360 Ohm, and the gate drive optocoupler U3 (MOC3052), as it was also probably damaged by the Triac short.

https://www.digikey.com/en/products/detail/stackpole-electronics-inc/CF14JT360R/1741406

https://www.digikey.com/en/products/detail/liteon/MOC3052/3199529

 

[Pelleting In NJ]

I would also take an ohmeter and check the value of the resistor next to the blown one, to verify that it is still good (360 Ohm), and not damaged by the burning of the failed resistor.

 

[Pelleting In NJ]

Found a picture of your board...yes, that is a 360 Ohm resistor.
Send me a case of beer if this fixes your stove....😀

 

[techguy802]

Found a picture of your board...yes, that is a 360 Ohm resistor.
Send me a case of beer if this fixes your stove....😀

View attachment 315888

Wow, you went above and beyond! I really appreciate the time you took to look into this for me. I just ordered all the parts so I should be able to dive into it next week. I'll definitely keep you posted!

 

[techguy802]

I wanted to give an update as promised:

The resistors were 360 Ohm, but ended up being 1/2 watt instead of 1/4 watt size. I reordered from Amazon so I could get the replacements faster, but was in a hurry and ordered the correct 1/2 watt but wrong Ohm. 🤦‍♂️. This was frustrating and things got put on the back burner for a few weeks until I had the motivation to deal with it again.

I finally ordered the correct 1/2 watt 360 ohm resistors and worked on it last weekend. After removing the old resistors and starting to clean up the board, the damage was worse than I thought. Some of the traces started coming off the board with a gentle cleaning and that's when I knew to call it quits. I ordered a brand new OEM Harman board and should have it this week. Thanks again for the help and looking forward to having a working stove again!

 

[Pelleting In NJ]

OK, but you could have repaired the lifted traces with some short lengths of soldered-on bus wire.....
Then you will have a spare board.

 

[Kazo]

@zrock , sorry to highjack the thread
that's what I posted the other day

I'm new here, pellet stoves are the new 'beasts' to me, but have been in repair/service field (industrial electronics & automation) over 50 years.

Posting here as I want to help friend of a friend (on pro bono basis) , who presented me with controll board with burns and defective components.

I was able to find some (all?) defective components, but have a problem with the value of R10 resistor (desoldered on a side of board) which measures ~8.5kOhms, but the codes read 12(3 or 4) 1, 123 or 124 ohms (the 3rd band not descernable, except for a light color) , not common values. Resistor itself doesn't show any thermal stress, nor triac Q3 to which it's connected is defective.

Can someone, who did such a repair, has a board, verify the value for me please?

TIA,

by reading the thread I piggy-backing, I'm hoping you would be able to answer my question(?)

Thanks