Using a Multimeter - How?
So my heat bed is failing with a MINTEMP BED error. Prusa support recommended testing the thermistor with a multimeter. This link has SOME specifics:
https://help.prusa3d.com/article/mvzxcjkvtx-troubleshooting-multimeter-usage
I realize I'm a bit of an idiot so I'll ask: what exactly am I suppose to be doing here?
For example: the intro paragraph talks about testing PSU output but then very first image is showing the heatbed thermistor disconnected from the motherboard. I'm no expert, but if I disconnect this wire from the mobo to test, what am I testing?
Sorry to be such as noob, but I'd really like to do this right.
Based on the URL above, would this be correct?
1. Disconnect the heattbed thermistor wire (black with green end) from the mobo. Test the metal insert in the jumper connector per the first image. Really? Without power, what is the point of this test?
2. [With no power or with power?] Test the solder points on the bed where the heater wires are screwed in (see left image under Heat Bed).
3. Disconnect the heatbed wires from the motherboard[?] or from them bed itself and test them (with or without power). (see right image under Heat Bed)
4. Something should show [3.5 Ω - 4.0 Ω] for the heat bed (per the table in that document.) What test should show this?
It sure does sound like all the above should be done WITHOUT power since the article then talks about doing a test with the power ON.
The article is confusing because then it ends with a totally separate paragraph talking about doing a test WITHOUT power.
I'm sure the pros on this forum will find the above completely hilarious... 🙂
Thanks!
Dave
Re: Using a Multimeter - How?
I suggest you look up how to do resistance and continuity testing with a multimeter.
Re: Using a Multimeter - How?
Not exactly a helpful answer. Thanks anyway.
In the meantime, for those that are in the same boat I am and don't want to watch hours of extremely exciting electrical engineering videos on Youtube, when I test the heatbed wires (red and black from the motherboard) solder spots, I am seeing a reading of 3.7 - which seems to put it in proper range based on the article.
What should I test next to determine if its in fact a bad thermistor? I don't get any reading when I test the thermistor metal leads (but I am also not sure I *should* get a reading from this since its disconnected from the mobo.
Re: Using a Multimeter - How?
I got it - at least I believe I do...
HOW TO TEST IF YOUR THERMISTOR (AND/OR WIRE) IS BAD
Step 1 - disconnect power! You do not need/want it for this test.
Step 2 - Using a multimeter, test the red and black heating wires connected to the bed (if only to ensure you are able to test). I get a reading of 3.7 on my meter.
Step 3 - disconnect BOTH the thermistor wires from the motherboard (one wire is for the heatbed and one for the hotend)
Step 4 - test the metal leads in the HOTEND wire to ensure your multimeter is getting a reading (I get a reading)
Step 5 - repeat this test on the HEATBED wire (I do NOT get a reading).
So, for us noobies, does the above conclusively show a problem with the heatbed thermistor and/or thermistor wire?
-Dave
Re: Using a Multimeter - How?
Not exactly a helpful answer. Thanks anyway.
In the meantime, for those that are in the same boat I am and don't want to watch hours of extremely exciting electrical engineering videos on Youtube, when I test the heatbed wires (red and black from the motherboard) solder spots, I am seeing a reading of 3.7 - which seems to put it in proper range based on the article.
What should I test next to determine if its in fact a bad thermistor? I don't get any reading when I test the thermistor metal leads (but I am also not sure I *should* get a reading from this since its disconnected from the mobo.
It's "teaching a person to fish". Once you know how to use a multimeter to do conductivity and resistance testing, then the Prusa page is dead simple to understand. It's also pretty easy to learn.
However, if someone tries to help you, but has to try and explain all the fundamentals, then there's a high chance of a stuffup due to miscommunication, and a high chance of time wasting.
As for your final post, if you're not seeing any resistance calue, and it fails conductivity, then yes, it suggests a problem with the heatbed thermistor and/or wire.
Re: Using a Multimeter - How?
Not exactly a helpful answer. Thanks anyway.
In the meantime, for those that are in the same boat I am and don't want to watch hours of extremely exciting electrical engineering videos on Youtube, when I test the heatbed wires (red and black from the motherboard) solder spots, I am seeing a reading of 3.7 - which seems to put it in proper range based on the article.
What should I test next to determine if its in fact a bad thermistor? I don't get any reading when I test the thermistor metal leads (but I am also not sure I *should* get a reading from this since its disconnected from the mobo.
It's "teaching a person to fish". Once you know how to use a multimeter to do conductivity and resistance testing, then the Prusa page is dead simple to understand. It's also pretty easy to learn.
However, if someone tries to help you, but has to try and explain all the fundamentals, then there's a high chance of a stuffup due to miscommunication, and a high chance of time wasting.
As for your final post, if you're not seeing any resistance calue, and it fails conductivity, then yes, it suggests a problem with the heatbed thermistor and/or wire.
And if messing with a multimeter was going to be a regular occurrence in my life, I would agree with the fish sentiment. I, however, hope to never need to screw around with this again.
I could care less about the fundamentals of electrical theory and multimeters. Just tell me what to do, I'll do it, and I'll submit the results. Prusa wants me to test a bit before they replace anything, no problem, but I have zero interest in learning the details of this. I'll put forth the extra effort to help troubleshoot, but you bet I want to be told exactly what to do (if only to reduce the miscommunication you yourself mention). Sending me to Google to learn about resistance and continuity testing? Yeah, right. 😆 😆
I think you are confusing my original post with one that actually wants to know the ins and outs of this - I most certainly do NOT. I want to know how to test based on Prusa's request to better address what is wrong...
Finally, yes, thank you for answering my question that NO reading is indicative of a problem. I've sent this back up the line to Prusa's support - let's see what they have to say next.
Re: Using a Multimeter - How?
I suggest you contact the live chat. They will run through it with you step by step.
i3 Mk3 [aug 2018] upgrade>>> i3MK3/S+[Dec 2023]
Re: Using a Multimeter - How?
Yeah - no reply for the last couple days now so I'll try the live chat. I figured I'd help their work load and do it via email...
UPDATE: Check that, while on hold for live chat, I got an email they will be sending me a replacement. Thanks all!
Re: Using a Multimeter - How?
I am an EE could help you use your multimeter, but there are so many different models on the market that I can't get specific unless I see a picture of the multimeter you propose to use. With a good quality closeup picture, it's possible to give you "...for dummies" instructions that refer to specific settings of specific knobs, specific wires and wire connecting points, and how to interpret what you see displayed. ALL of those things vary depending on the model of multimeter you are using! And this guidance will of course only refer to the specific measurement you need to take.
Honestly, it's not terribly difficult to actually understand what is going on; I knew as much as you need to know about electricity for this job when I was in high school, before I took any college courses. If you will let yourself spend 10 or 20 minutes to understand the fundamentals of current, voltage, and resistance, you will be able to "fish" through future electrical problems with ease. And you'll know right away what your measurements mean. :geek:
Re: Using a Multimeter - How?
I am an EE could help you use your multimeter, but there are so many different models on the market that I can't get specific unless I see a picture of the multimeter you propose to use. With a good quality closeup picture, it's possible to give you "...for dummies" instructions that refer to specific settings of specific knobs, specific wires and wire connecting points, and how to interpret what you see displayed. ALL of those things vary depending on the model of multimeter you are using! And this guidance will of course only refer to the specific measurement you need to take.
Honestly, it's not terribly difficult to actually understand what is going on; I knew as much as you need to know about electricity for this job when I was in high school, before I took any college courses. If you will let yourself spend 10 or 20 minutes to understand the fundamentals of current, voltage, and resistance, you will be able to "fish" through future electrical problems with ease. And you'll know right away what your measurements mean. :geek:
Thanks - I was mainly just wanting general instructions around what state the wires and machine (power) should be in for these tests. In the end, removing the power cord and testing the thermistor wire once removed from the mobo was all that was needed. For the first time tester, I should have tried it on a wire I knew was good BEFORE testing the suspect wire. Once I did that, it raised my confidence I was doing it correctly *and* confirmed the wire was bad.
All good - the replacement is going out within 2 days from Prusa...