Thermostat Replacement on Roller Transport Processors

Hey all,

I've been in a pickle for a month now with a faulty thermostat on my Cap 40 processor and have been trying to figure out some solutions. I've reached out to Klaus at Thermophot but he has been sick as well as saying he is moving his warehouse so parts are unavailable for the time being.

Does anyone have any experience with swapping out thermostats? Aside from trying to find a direct replacement I have been looking at PID controllers as an alternative. Since the heating element on this unit is 3 lines in one it seems like it should be fairly straight forward but the issue comes from harvesting the thermo probe. I have not tried taking the original Jumo EMf-2 apart so I dont know if its even possible, let alone what type of connection it would be. Alternatively, since the probe seems custom fit for the processor, I could get around it by plugging the hole and running a different type into the bath.

Assuming the probe could be solved, it would just be swapping out the thermostat and relay with a PID controller, get the hot/neutral/ground sorted and good to go? I've no idea if the relay is running power to the circulators or motor just yet.

Is there an easier solution to this?

There's several listings on Ebay and others that have the Jumo thermostat you mentioned. $300+ new old stock.

gWaL said:

Assuming the probe could be solved, it would just be swapping out the thermostat and relay with a PID controller, get the hot/neutral/ground sorted and good to go?

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Yeah. If you can't find a snap-in replacement for the thermostat, which would be the very first thing to try, this would probably be the easiest solution. You may have to resort to having a probe lead run around the outside of the machine into the developer bath - not sure if that's mechanically feasible as I'm not familiar with this processor.

Does the original thermostat not switch anymore at all, or has it drifted off? Or does it work intermittently/erratically? I'd try opening it up to see if it can be mended; it's a long shot and my experiences trying to fix these types of thermostats aren't too good, but it's worth a try.

It turns on, heats, and cycles between a low temp and high temp but the difference between the two is roughly 1.5ºC now. The thermostat doesnt have a temperature scale so its a bit of guess work but its a consistent gap. So if I set it and watch the temp increase to a max of 35ºC then it go down to 33.5ºC before the heater turns back on.

Running a separate probe through the body and down into the dev bath seems possible, would probably just have to avoid running paper on that side. The PID controller is a bit nerve racking as the current thermo takes 240v and I am no electrical engineer.

That sounds like a fairly decent hysteresis for an old mechanical thermostat. I'd just leave it alone, personally.

That's good enough for RA-4