Replace/fix oven encoder with no visible pins

[D.Kruger]

Hi, I'm trying to fix a 25  oven's control board. The problem is that the rotary encoder that controls the timer misfires when rotated, making it hard to use.
I've fixed encoders before by cleaning their contacts or just replacing them, but the problem here is that it seems to be covered by a plastic case, and there are no visible pins to desolder, only 4 plastic pins that I cut hoping that would help release the plastic cover, but didn't help at all.
Any idea of how to disassemble or desolder it?
I attached some photos for clarification; the text in the case says DIEHL, which seems to be the company that built it. In the last photo, the encoder is located under the caps, in the bottom left of the board.
It seems that there are some traces going under it, so it might be an SMD component, but I find it a bit weird and unnecessary since it would be the only component on the board.

[Gyro]

My guess is that the encoder segments are implemented directly on the PCB as traces. The 'encoder' would then just be a plastic housing supporting the shaft and moving contacts. It should be possible to remove the housing by melting the plastic studs on the other side,. The problem then is retaining enough plastic to re-fix the housing after cleaning, adhesive (especially cyanoactylate) is likely to track underneath and contaminate the contacts. Sometimes countersinking the PCB holes will give enough space for re-heat staking.

It looks as if there are PCB holes around the edges for mounting a normal pinned encoder. This may be a solution if the PCB tracks have become too worn, and you can match up a suitable replacement.


Edit: Re-reading your post, I'm not sure why the housing won't come off. I think it is very unlikely to be any kind of SMD encoder.

[coromonadalix]

the encoder has 4 pins who are molten on the pcb to provider holding force ...

and yes i do think  you have the encoder traces on the pcb ... witch will complicate a substitution

[wraper]

Without bodging a standalone encoder, the only thing you can do with it is take it off, clean the contacts and PCB, maybe bend contacts a little bit, apply lubrication and put it back. I drilled small holes in the plastic housing instead of studs as there was nothing remaining to melt to attach it back and fixed it with tiny screws. Worked like new for years until I gave away that microwave oven.

[Gyro]

One other thought. There is a center hole in the PCB that locates the end of the shaft, this looks like a fairly loose fit. It may be that dripping a little of your favorite switch cleaner/lubricant through the hole and exercising the shaft may restore adequate performance. It's is a bit of a 'kill or cure' suggestion which will depend on a low degree of wear and debris on the PCB segments. It is nowhere near as good as getting the housing off and doing a proper inspection / clean / lubricate.

[D.Kruger]

Thanks for the help, guys! I think I'm going to try first cleaning it through the shaft's hole, and if it doesn't work, I will try to disassemble it. I still find it a bit weird that I couldn't release it after cutting the plastic pins; it feels like it might be glued to the board; do you think that could be the case?

[Gyro]

It could be that the heat staking of the pegs was forceful enough you push the plastic deep into the texture of the sides of the holes, but I've never come across pegs that held that well (as they appear to be from your description). I would expect any glue to be visible on the outside of the housing, something viscous to avoid it spreading inside and onto the segments. I suppose it's possible that there is some sort of glue film that was pre-applied to the plastic but that seems unlikely too and would probably still be visible at the join.

[D.Kruger]

Hi, I cleaned the encoder with some isopropyl through the shaft's hole. Now it works well when I keep a bit of pressure on it while rotating it. It's not perfect, but it's more than good enough for an over-20-year-old oven. Thanks everyone for the help.