Currently am a technician for a medical equipment company. I have been repairing a warmer recently over the last few months. Well, several of them. We are the retailer. The controller is a LOVE controller - the nurses just love the name haha.

Anyway - the warmers are supposed to hold 40deg C. They often will be sitting at 24deg C when I go in. I replace this controller, and the fault goes away.

Problem is, I cannot find anything wrong with this controller. Its simple, will bench test fine with a load. And also bench test with a load whilst I am heating the controller itself.

We are supporting this product for several more years. Unsure what can be done to resolve this. Any advice would be great. Oh. Item 13 is a 220/110 transformer.

Mod edit: rotate image, reduce file size - JohnInTX

 

Doesn't look like there is any temp adjustment. Have you tried replacing the probe? Or due you have the correct model probe installed?
I also see a thermocouple #8.
SG

 

Having been victim of nursing care in the past 5 years, are you sure what the nurses are doing?

 

Doesn't look like there is any temp adjustment. Have you tried replacing the probe? Or due you have the correct model probe installed?
I also see a thermocouple #8.
SG

Sorry I should have explained more.

There are several levels of programming in this controller, alarms etc, including the temp.

The temperature(s) I actually validate with calibration probes after maintenance or a service. The thermocouple is correct, and it works with a new controller when I replace that.

I currently have a controller that I pulled out of a warmer that was only reaching 24 deg C. Its controlling a small oven that I hooked up as if it was installed. And is holding the oven to 58 deg C. I have put the controller inside the oven at 58 deg C to see if it fails when it gets warm....

I guess we can keep replacing these controllers but would rather find what is going wrong

 

And is holding the oven to 58 deg C.

OK. So this test unit you have programmed for 58 C? Is there any kind of a default setting like 24C that the unit might revert back to in case of power loss or if something glitzes?
SG

 

Hmmm interesting thought. The last one did this straight after a service and electrical test. I played around with the settings, and it worked again. But the client called me back the next day and I replaced the controller.

 

You have two controllers in the schematic. Are the failures always in one section? What's the model number of the LOVE controllers?

 

Is this the TC amplifier:

I cannot read that part number. Presumably, it has cold junction compensation. Can you share that information?

 

The schematic is of the double cavity warmer I repair. It comes in several sizes, mostly though, the size is a single unit with one controller.

The double unit has two controllers. I am finding that no matter which model of warmer I am working on, that replacing the controller fixes the problem. The same controller is throughout the series of warmer.

The chip is HEF4051BT NXP Chip.

The statement about the unit going into a form of "limp" mode is really plausible given the experience I have had. Is this a possibility with this chip?

 

Is this a possibility with this chip?

No. It would have to do with the microprocessor and the programming.
SG

 

"I am finding that no matter which model of warmer I am working on, that replacing the controller fixes the problem. The same controller is throughout the series of warmer."
So, do you reuse the failed controllers, or just toss them? Have you contacted LOVE?

 

The HEF4051 is just an analog multiplexer. What are you using to amplify the thermocouple? The reason is that I use the MAX31856 digital thermocouple amplifier. It has a couple of fault modes that lock it. So in firmware, I always check those faults to clear them. Of course, replacing that board would fix the fault, and back at the factory, it might not be detected,

 

Currently am a technician for a medical equipment company. I have been repairing a warmer recently over the last few months. Well, several of them. We are the retailer. The controller is a LOVE controller - the nurses just love the name haha.

Anyway - the warmers are supposed to hold 40deg C. They often will be sitting at 24deg C when I go in. I replace this controller, and the fault goes away.

Problem is, I cannot find anything wrong with this controller. Its simple, will bench test fine with a load. And also bench test with a load whilst I am heating the controller itself.

We are supporting this product for several more years. Unsure what can be done to resolve this. Any advice would be great. Oh. Item 13 is a 220/110 transformer.

Mod edit: rotate image, reduce file size - JohnInTX

WE do not have a circuit schematic, we are only presented with a wiring diagram that provides no information at all about the temperature controller circuit. 24C seems to probably be the room temperature and not what the package is providing. So which part is the TS replacing? If it is the entire package shown in the wiring diagram then we can make guesses. If it is that little module shown in the photo we can only guess that it may be failed temperature sensors.
And the one time that I tried to apply for a service position for medical electrics they demanded a Masters degree in the subject before even accepting an application. I never went back, l aready had a BSEE and many years of experience.

 

Ha - this is NZ 24deg is most definately not room temp. Hey so we have changed to a new controller. This is now reduntant for me, no point chasing it.

I had no information about this unit than what I have given. The sensors are still ok as they stay installed for the replacement controller to utilise.

The LOVE controller, well, they said that Daisan (or whoever the company was) bought out a company run by hippies who named that particular design. And kept the name.

And it sounds like the people who were looking for an med elec needed to get their hands off themselves. Its not rocket science just requires several trades in one person.

 

In case there may ever be a need for a functional controller of the style that so many have failed, with no information there is always that beginners option of checking parts to see what has failed. Of course if they are tightly nit packages then a better choice may be to" recycle responsibly." Some things are a real challenge. First comes checking the power supply voltages of a working and non working unit, then possibly voltage checking other points.
One question is about the 24 degree display. Was that consistent among failed units? Andwas that near the room temperature? And could you try a substitute sensor on the bench in the shop? Of course, if that type has been abandoned then the effort is just for your education.