Herbalizer - Loss of temp regulation

[caphair]

Friend asked me to check this out for him. Says that the temp doesn’t regulate and just keeps increasing. Confirmed with melting plastic under the heating element.

Does power on and let’s you adjust the temp etc but just keeps increasing regardless.

Right away I noticed the front two legs of triac QX1 204S8E were lifted off the board (barely connected looked like solder maybe desoldered by heat)

If I measure from T1 to T2 I get 21 Mohms and from T1 to Gate I get .700 kohms. In diode mode from T1 to G I measure .323 both directions. Does that mean it’s good or bad?

No clue about these, wondering if someone has seen it before and/or could guide me where to look for a possible repair.

[momaka]

Re: Herbalizer - Loss of temp regulation

Can't see any damage to the legs of QX1. But since you do have a low resistance between T1 and T2 (21) Ohms on this Triac, I suggest to remove it from the board and check it again. If you still get that low resistance, it's bad.

It's not uncommon for cheaper devices like that to burn their TRIACs. Sometimes it's due to the TRIAC being undersized for the load, and other times it's just a "random" occurrence. In any case, if it does come down to a replacement, see if you can find a slightly higher rated part. That should hopefully prevent this from happening in the future.

Also, is there a relay anywhere installed between the heater and the TRIAC? At least I couldn't see on.
If not, I'd say this is quite poor design, because then the heater can remain on when the TRIAC is shorted, and that can certainly be a fire hazard. On better-designed devices, the relay is simply used for connecting and disconnecting power to the heater, and the TRIAC only does the line voltage/pulse modulation to give variable power output at the heater (and hence temperature regulation.)

No clue about these...

Same... which is quite ironic, given the text under the LCD on this PCB:
https://www.badcaps.net/forum/attach...9&d=1603122954

[caphair]

Re: Herbalizer - Loss of temp regulation

It’s not 21 ohms but M ohms and those readings were done with the triac off the board.

I’m wondering if the heating element itself is bad, maybe the internal thermocouple? Or whatever is used to let the mcu know the temp to regulate it?

[redwire]

Re: Herbalizer - Loss of temp regulation

What's it using for the one (or two?) temperature sensors? I assume thermistors. You can measure their resistance and the voltage across J6, J7 when plugged in.

I would measure voltage at the opto-coupler U10 LED and see if the controller is commanding the heater to be on. Careful mains is on the other side of the opto. That big X-cap can also bite.

There's very little solder on the JST connectors on the PCB, not enough paste was used on the pcb.

Everything looks melted so I'm not sure how repairable this is.

[caphair]

Re: Herbalizer - Loss of temp regulation

What's it using for the one (or two?) temperature sensors? I assume thermistors. You can measure their resistance and the voltage across J6, J7 when plugged in.

I would measure voltage at the opto-coupler U10 LED and see if the controller is commanding the heater to be on. Careful mains is on the other side of the opto. That big X-cap can also bite.

There's very little solder on the JST connectors on the PCB, not enough paste was used on the pcb.

Everything looks melted so I'm not sure how repairable this is.

It gets very hot quick and the plastic starts to smoke. Does the heater need to be plugged in while making these measurements?

Nothing plugs into J6 only J7 and and fan connector in between.

Is mains on the side of the opto with QX1?

[momaka]

Re: Herbalizer - Loss of temp regulation

It’s not 21 ohms but M ohms and those readings were done with the triac off the board.

Ah Ok, sorry about the misunderstanding.

In that case, I second redwire's advice. See which component gives feedback for the temperature back to the board and make sure it is working properly and has good contact to the main board.

[caphair]

Re: Herbalizer - Loss of temp regulation

Forgot to mention that the display will show the temp is way above the desired setting. Not sure if that helps eliminate some things to check for?

[momaka]

Re: Herbalizer - Loss of temp regulation

Forgot to mention that the display will show the temp is way above the desired setting. Not sure if that helps eliminate some things to check for?

It does.
That means whatever is reading the temperature may actually be working fine.

In that case, I suggest to check the Gate drive circuitry directly connected to QX1. So that would be R61, R62, C28, U10, R63, Q4, and whatever other components you trace connecting between U10 and the MCU that drives U10/QX1.

[stj]

Re: Herbalizer - Loss of temp regulation

is this a weed burner or something??

[CapLeaker]

Re: Herbalizer - Loss of temp regulation

stj prefers 12 gauge

[redwire]

Re: Herbalizer - Loss of temp regulation

It looks like Herbalizer went out of business fall 2018. $599 price point and 290–445°F
That high temperature is beyond thermistors, so they must be RTD's as the PCB silkscreen says. If the temp sensor is very low resistance then this is the case.

I think it's using phase-control for proportional heat control and from the zillion IC's on this it might even not use the MCU for most of the heater control. Have to know the IC numbers for U9, U5, U16 etc.

The display shows a high temperature above the setpoint, yet the heater is on?

The thing should have a safety thermal cutoff and UL/CSA/Intertek approvals.

[caphair]

Re: Herbalizer - Loss of temp regulation

It looks like Herbalizer went out of business fall 2018. $599 price point and 290–445°F
That high temperature is beyond thermistors, so they must be RTD's as the PCB silkscreen says. If the temp sensor is very low resistance then this is the case.

I think it's using phase-control for proportional heat control and from the zillion IC's on this it might even not use the MCU for most of the heater control. Have to know the IC numbers for U9, U5, U16 etc.

The display shows a high temperature above the setpoint, yet the heater is on?

The thing should have a safety thermal cutoff and UL/CSA/Intertek approvals.

While testing some things it almost caught on fire and now the display doesn't work and some plastic under the heater is melted beyond repair. I think for safety reasons I'm abandoning this repair, doesn't seem worth it. My house still smells like burnt plastic.

Yes the display would show the set temp but there would be bars showing it's well past that point towards the red region.

Appreciate everyone's input

[petehall347]

Re: Herbalizer - Loss of temp regulation

send it back .tell them you want your money back because its dangerous