Jobo CPE-2 - The heater dont turn off

[taulen]

Hello !

I just got myself a Jobo CPE-2 today, and most is in perfect working condition. But there is (of course) one small (?) problem...
The heater do not turn off, no matter what the dial is set to, at least it went from 15c to about 40c in 40minutes, even tho the temperature dial were set to the lowest possible setting, below 20c...
I guess this is either a problem with the rheostat in the temp dial OR the temperature sensor ?
Do any of you guys have had this problem ? What was the problem for you, if you solved it.

Also, where is the sensor placed ? Is it one of the two "cables" that are connected to the heating element ?
And, if it's the rheostat, is this something that would be able to buy, readily available part, or a third-party replacement part ?

Thanks for any tips or solutions ! =)

-
Jonny

 

[polyglot]

The potentiometer behind the knob MIGHT be the issue but that's unlikely. If it is, you can check by putting it somewhere in the middle and measuring the resistances between the three pins. They're a common off-the-shelf part.

More likely is that the temperature sensor is broken or disconnected; it will be a tiny bead on the end of some really thin wires, somewhere in the bath near the heater. On a CPP2 (with pump), the sensor is inside the pump housing.

It could also be the output transistor that switches the element has died shorted. Either way, you will need some electronic-debugging skills to find the fault. Schematics are readily available with some googling...

 

[anikin]

I had that problem with my cpa2. The capillary thermostat was dead. I looked around for a replacement, gave up and soldered up an electronic replacement made up of an op-amp, relay, pot and a sensor recycled from an old grill thermometer. It works fine for me, just the numbers on the dial don't match actual temperature - nothing that a sharpie could not fix.

You can contact cat-labs and see if they have a spare - this might be the easiest way to go now that JOBO is alive again


Sent from my iPad using Tapatalk HD

 

[CatLABS]

One of the two probes on the heating element is the temp sensor, the other is the heater protection fuse sensor (if you have 2 that means you have a CPE2+)
Corrosion on the temp sensor or a break otherwise, would cause the thermostat not to work properly.

We have spares in stock if you do not find the break or cannot repair it for some reason.

Let us know what you find.

 

[taulen]

Hm, thanks guys !
I have two "probes". But it doesnt say CPE2 plus on the front like I have seen on others. CatLABS do you know which is the temp sensor, or know where the temp sesnor ends up on the "main-board" so I can follow it ? If it's broken beyond repair, how much is it for a spare, if you want me to contact you, is this place to do so : http://www.catlabs.info/contact ? Thanks again ! =)

Edit:
One of the wires seems to end up at the potentiometer for controllig the temp, and the other wire ends up at the silver/shiny box that contains the "thermal overload protection" switch if this can help in locating which is the temp sensor. Both wires "SEEMS" to be okay, but I dont have my meter with me here so I cant check for sure right now.

Edit2:
After reading CatLABS post a bit closer, it seems that if one of the wires is for the fuse for the heater protection, than the other wire that not ends up at the heat overload switch is probably the temp sensor, might I be right in that ?

 

[taulen]

Sorry for the double post, this is the end of the wire that comes from the potentiometer, and ends up in the bath, near the heater-element. The other wire looks pretty much the same, but a rounder "tip" on the end...

It doesnt look much like a sensor Just a goey mess on the front, looks and feels like some glue. Is the sensor itself under the black covering plastic ? The wire is much more stiff the last 20cm or so.

 

[polyglot]

The temp sensor is a thermocouple, i.e. two different bits of metal stuck together. It looks like basically nothing - a couple little wires come together in a blob.

It will be the one that goes to the potentiometer. To see if it's OK, measure the continuity of the whole sensor-and-leads - it should be basically short-circuited, i.e. under 1 ohm. If the sensor shows an open circuit at the board end, it's broken. You will need to disconnect one lead from the board first so that you're not measuring other impedances in the board.

 

[taulen]

Hey, again thanks for the answers polyglot.
I just got around to test some stuff.
After taking a closer look, the two sensors, the "heater protection fuse sensor" and the "temp sensor", each only have one wire connected. One goes to the potentiometer and the other goes to the fuse protection unit.
So there is no way to measure the resistance between two wires on the temp sensor, since its only one. Strange.
On the potentiometer there are 4 wires connected in total, ground(green), black, white and the one from the temp sensor. If i turn the knob there is no change in resistance on either of the connector. And between black and white there is a short also no matter how I turn on the knob.
So I'm kind of lost on what to do next.
I don't understand how the one wire will be enough to measure the temp, and the potentiometer also seems to be dead...
Do you, or someone else here have some tips for me ? It would be much appreciated, that's for sure !

 

[anikin]

What you see is a mechanical capillary thermostat. There are no wires to measure resistance. The best way to get it working is to contact catlabs and get a replacement.

 

[taulen]

Okey, thank you anikin ! Sent catlabs an email, lets see if they still have a spare for me =)

 

[taulen]

I just wanted to let anyone know that I received a thermostat (that includes everything, from the "potentiometer" to the "wire" that is the temp-probe, its all in one "package") from CatLabs today, and it solved the problem.
So thank you to all that helped, and especially to CatLabs for great service and for making sure we still can get parts for our Jobo processors ! =)