Mastech MS6514 thermometer

[jtu]

I have bought a relatively cheap thermometer. The intention was to use it for measuring electronics parts working temperatures occasionally.

I'm wondering about two things:
1. Sometimes it "goes crazy" for several seconds, showing nonsense on the screen.
2. It adapts to high temperatures (like measuring solder iron) very very slow. For example, I tried to measure temperature of my solder iron. It took ~10 minutes for it to reach temperature close to the soldering station reading.

Otherwise seem like a nice product for the price.

Any others experience? Is it by Mastech design or I might have a damaged item?

[jtu]

Anyone?

[doktor pyta]

There are some 'MS6514' videos on Youtube. Try to watch them carefully. Nevertheless I think You have faulty unit.

[PA0PBZ]

Can you test the thermocouple on another device?
I can't find anything about the measuring speed but the calibration procedure suggests that it is not really fast:

2. Calibration methods:
a) Put the thermometer into a thermotank with
the temperature of 25°C for 3 to 5 minutes.
b) Power on the thermometer to stabilize the
thermometer.

3 to 5 minutes for 25°

[jtu]

... Nevertheless I think You have faulty unit.

Seem that this is the correct answer. Device died with burning electronics smell, "magic smoke" as they say

[jtu]

Good idea, thanks!

You can take a look at the teardown pics including IC's here.

No question about what the obvious culprit is: Silicon Labs USB-UART chip CP2102. It makes sense, magic smoke occured on (a bit after) connecting the device to my Mac.

A bit better question is: why? I can not imagine my Mac giving out unstable voltages or current surges just out of the blue. Must be the device itself. As I complained initally in the OP, unit seemed faulty from the beginning. Now I'm thinking if the USB chip could be the root cause or just blew as a consequence of something else.

Of course, I'll try to find and replace the chip first. And try to reproduce the problem second. I have no experience with CP2102. I should dig into datasheets about which versions of the chip is used here (DCLOX4). But maybe somebody can advice on this? Mouser offers 3 chips in the QFN-28 package.

NB One thing bothers me a bit. The PCB seem to be the same for all MS651x models. See model descriptions here and here. I have bought ( or at least was buying...) the most advanced, MS6514 model. Why not all the components are deployed? For example, has U9 to do something with other way of power management for a simpler model?. Or, why no diodes on temperature inputs? Can it be so that it is some copunterfeit unit? From the engineering quality it certainly does not seem so...

[markce]

I also have a MS6514, and its nice, for the price.

I've replaced the thermocouples with better ones. What's provided with the meter are just starters, worst I've seen so far. Note the thermocouple connector on the MS6514 is very sensitive, clean and don't touch the contacts.

The meter uses an internal NTC to compensate for environment temperature, so needs time to stabilize. Helps to position the meter some time before taking a measurement.

[jtu]

I also have a MS6514, and its nice, for the price.

I've replaced the thermocouples with better ones.

What do you use for thermocouples? Something like this from China or did you go for higher level? I’d appreciate link or product name/code.

[jtu]

I replaced the USB chip finally. It took some time before I could because I ordered some stuff for SMD soldering and order just came in. I trained a bit on couple old PCB's and went to do it.

The old chip was fried and the PCB below it was fried, even plastic stand ~1cm from the chip was melted.

When I got it off and cleaned a bit all the unconnected PCB trace PIN connectors also went off. Fortunately the connected ones are not damaged. It was hard to solder the new chip in because it did not flow nicely because PCB is damaged. But after some tinkering I finally managed it. Measured all connections for non- or short contact.

Ok, it turns on now at least. Logic works nicely, but does not measure and battery low sign pops up more often than not.

When one thermocouple is attached it mostly shows -0 degrees, but from time to time it shows several seemingly random temperature measurments in a row for a second or two and goes back to -0. With both thermocouples attached it shows random numbers more often.

I know that it is already past economically reasonable repair, I'll look for a new thermometer / temperature logger. But I still am thinking about what could be the cause and how to debug it. Just for the sake of learning something new.

Let me know if any idea pops up into your mind reading this.

I did add few more pics to the gallery from today.

[jtu]

This should be moved to repair now, how do I do it here?