TAZ 5 Heated Bed Failing

I currently have a TAZ 5 with a heated bed and PEI surface. The bed is no longer heating. It was acting funny a few days before with one quadrant reading cooler than the rest of the bed and the Temp chart on the Cura controls appeared like it was dropping out. I was thinking it was just bad wiring but manipulating the wires no longer works. How can I check the Bed to see if it is the controller or the bed itself? This is in a maker space so I need to have this machine operational quickly to keep my folks happy.


Hi Corr

I am not sure if and how the controller checks the thermistor and thus you should check that one as well.
There are chances that the controller switches the heater off if the thermistor is gone.

As you are in a maker space I guess you have a multimeter at hand!?
with that you can check the continuity of the wires as well as the resistance of the heater sections and the thermistor.
You would need a needle for the wire checks in order to penetrate the insulation of the wires close to the heat bed.

With the multimeter in resistance mode and the the connectors disconnected from the controller first check if you can measure any resistance in the heat bed. Just from the connector. the heat bed (thicker white wires) should be in the low Ohms range and the thermistor should be around 100kOhms at room temperature.
In case one of the to is showing extreme high resistance this is the one were you have the pain to check if the wires are ok.
Here the needle gets handy. You stick it into the wire as close as possible to the heat bed and then measure that wire from the connector to the needle. if that is around 0 Ohms the wire is ok if not you probably found the culprit.

Repairing a broken wire is quick done if you have a soldering iron and some heat shrink at hand.
The Thermistor can be repaired / replaced as well. Here is only the calibration to be checked after replacing.
If the heat bed itself is burned… well… this to fix is not so easy… sorry

All the Best

A simple continuity check of the bed with a multimeter will tell you if its the bed or something else. It could also potentially be a duse in the rambo board, the 2 grain of rice sized ones or the big one.

I-T-W.com has the beds and the controllers available in refurbished if you want to get some spares on the

Ok, my readings are 1.8k ohms on the heated bed white wires and OL on the meter for the red thermistor wires. If I connect the red thermistor wires I do get a reading at the control panel however with a wiggle or two it seems to drop in and out. With it reading the bed will still not heat.

Sounds like you may have a fried thermistor.

That should be around 1.8 Ohms on the heat bed, and about 120K ohms on the thermistor.

If you are actually reading 1.8K then your heat bed is burned out.

Hi corr

the wiring of the thermistor seems to be… done :wink:
what worries me more it the 1.8k Ohms on the heat bed.
with that it can not get warm :open_mouth: just checked that the bed should do 8 - 10A at 24V which leads to 2 - 3 Ohms that the bed should have. The heater is supposed to do > 200W with 1.8k Ohms it only would do 0.32 W
This gets confirmed by not heating when the thermistor is reading.

I am afraid that your bed is gone :frowning:

All the Best
P.S. ups… kmanley was faster…

DOH. Did I say that? It is reading 1.8ohm. My bad.

Hi corr

THAT changes all :laughing:

This leaves you with a broken wire on the thermistor or a broken thermistor.
My best guess is that it is only a wire and can be fixed. :wink:

if the wiring on the TAZ is done similar to the mini, than chances are good that one of the wires broke were it is bend around the aluminum base. Easier might be to play a new thermistor with new wires :wink:
Check with your friends from maker space if they have one 100k thermistor some were in one of the bins.

As piercet mentioned check also the fuse on the controller. With a blown fuse everything stays cold :smiley:

All the Best

I checked the fuse on the controller and we are good.
I think a new thermistor is definitely needed.

Now prior to the bed not heating at all I was having complaints that the bed was showing irregular readings with a handheld temp sensor (granted this is not a medical grade device) that we have in the shop. The readings were of by 20 degrees or so in one quadrant, enough to think something was up. This seemed to be more obvious after the machine was run for a while. Other times you turn it on and all read the same. My PEI is bubbled up pretty good also. Is my best bet to order a replacement bed or try a thermistor fix and see if we have less failed prints?

So, I have a good thermistor on hand here and I don’t get any ohm readings on it when I use the meter. Do these need to be heated or something to show resistance?

Make sure the DVM meter you use is set and can read the 100K - 200 K range of the thermistor.

Got it figured out. Apparently when you zip tie your wires going to the heated bed very tightly to the aluminum bed plate the movement seems to cut through the wires. :unamused: Go figure. Thanks for the assistance.

If the readings were off by that much in only one section of the bed, you may also have a burned out bed coil. Also, bubbles in the pei are an insulator, parts will not stick to them. If they are large, you will want to re bed the pei sheet.