Greetings fellow nerds.
So a major problem came up as i was making my latest videos and that was that my hot
plate stirrer broke.
Piece of shit.
Some part of it burned out and belched out smoke and afterward the hot plate was stuck
with the heater element on.
This is a major failure because without temperature control this could easily overheat and start
melting.
So let's crack this thing open and see if we can fix it.
I've already taken apart the major screws and connections to save time.
Now the good thing about a piece of shit like this is that because it's a piece of shit
the design is simple enough that even a relative amateur like me can figure it out.
Here we have the temperature probe leads that measure the hot plate temperature.
These relatively thicker wires are the heater element leads. Up here is the magnetic stirrer
motor.
We have what seems to be an isolated power supply module.
This blue cube thingie is probably a transformer and has an associated bridge rectifier and
capacitors to form another basic power supply.
The two black cubes in the center are relays.
This array of six transistors is likely part of the motor speed controller since this is
clearly a brushless motor.
And that big integrated circuit is likely some microcontroller for controlling and displaying
the temperature and motor speed.
Now why there are two power supply circuits and why one is hanging loose like this isn't
something I can't explain,
maybe some professional electrical engineer can comment.
Now as for what's actually broken, it's actually on the underside of the board.
Now the two white pads cover up voltage regulators but the broken part is that device in the
middle that i've uncovered and bent up.
You can see where it blew out and belched smoke onto the circuit board.
The part number is hard to read but it's a BTA225 from NXP semiconductor.
I checked the website and this is a high current triac.
Triacs are generally used to switch AC currents especially for things like lights and heaters.
This makes perfect sense that the heater would be stuck on if the triac shorted out. So i'm
going to have to replace that.
Now in addition to the power supply and the heater,
the triac is directly connected to another device back on the top side of the board.
Let me show you.
This tiny white chip over here is an opto-triac.
It's what switches the main triac on and off.
The opto-triac also isolates the control signal from the high voltage of the main triac.
This is important for safety so the high voltage doesn't accidentally shock the user through
the control knobs.
I'm going to replace this chip as well since i'm worried whatever current pulse destroyed
the main triac also might have damaged the opto-triac.
Alternatively maybe the opto-triac is what actually failed and the main triac blew out
in response.
Since it's just a dollar and sixty cents and i can order it along with the main triac,
I might as well replace it.
So the replacement parts finally came in so let's get to fixing.
First, we have to remove the broken parts. I'm going to start by desoldering the main
triac.
I'm holding it with a pair of pliers since the part can get very hot during desoldering.
You actual electrical engineers are probably laughing your asses off at my desoldering
technique at this point.
Okay there we go, one burnt out triac.
I might as well clean the board with a bit of methanol.
Wow, these black marks aren't just the smoke stains, the triac got hot enough to actually
burn the board.
I hope the copper traces aren't damaged.
Okay, now to remove the opto-triac.
Crap, I ripped out the part but some of the pins are still stuck in the board.
No matter, i can desolder the pins but it just takes longer.
Okay that's done. Now for the replacement parts.
I'm going to start with the opto-triac.
I bought 3 since with my relative lack of skill i'm likely to destroy one or two during
my repairs.
Also i want to have spares in case this failure mode happens again in the future.
After all if it happened once it's very likely to happen again.
Let me pop it in there.
I know this would have been tremendously easier if i removed all the solder from the holes
first but I'm an amateur.
I'll leave the professional work to you actual professional electrical engineers.
I'm going to add in some fresh solder to ensure the connections are good.
Okay that's in, now we replace the main triac.
Since this is a double sided board and there are traces for the main triac on both sides
I'll need to apply solder to both sides.
Whoops, crap, don't want to short out the triac.
Gotta desolder that.
I think I can almost hear you actual electrical engineers snickering at my epic fails.
Okay now for the other side.
And there we go.
Okay I definitely will not be adding soldering skills or electrical engineering to my resume.
Anyway let me reassemble the hot plate and test it.
Okay here we are, let me plug it in.
Okay looks good.
Before it was stuck on and would start heating as soon it was plugged in.
The fact that it's off when it's supposed to be is a good sign.
Okay let me actually turn it on.
Looks like it's working, the temperature is rising and i can feel the heat coming off
the plate.
Now let's see if it maintains a set temperature.
Seems to be hovering around the set temperature rather than shooting past it.
This test passes.
Looks like this hotplate stirrer can be put back into service.
And I still have my spares for next time this expensive piece of shit breaks.
Thanks for watching.
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