Panel Heater Power Board repair

[FIIIP]

Hello,

I have this power board that use chinese PN8024R regulator to output 12V, but instead outputting 12V it outputs like around 28v to 50V.
If anyone have any idea what could be wrong, please let me know. Here is the thread from another forum: https://forum.allaboutcircuits.com/t....208572/page-4

Thank you!

 

[mechtronics]

Hello,

I have this power board that use chinese PN8024R regulator to output 12V, but instead outputting 12V it outputs like around 28v to 50V.
If anyone have any idea what could be wrong, please let me know. Here is the thread from another forum: https://forum.allaboutcircuits.com/t....208572/page-4

Thank you!

did you check the bridge rectifier diodes? using DMM?

 

[FIIIP]

did you check the bridge rectifier diodes? using DMM?

Yes, they were fine, but I replaced them anyway

 

[mechtronics]

Yes, they were fine, but I replaced them anyway

what about all other components? capacitors? inductors? etc and how did you check them? did you physically desolder them and take them out and check them? and another thing to point out is a lot of switch mode power supplies use feedback so when a load is connected to it the output voltage stabalizes. under no load voltage will be higher than usual. under load voltage stabalizes. when you have something connected to the output use a digital multimeter to check what the voltage is when load connected to output.

 

[bertus]

Hello,

Did you have a look at the datasheet?

Bertus

 

[mechtronics]

what about all other components? capacitors? inductors? etc and how did you check them? did you physically desolder them and take them out and check them?

Hello,

Did you have a look at the datasheet?

Bertus

i checked that aswell.

 

[FIIIP]

what about all other components? capacitors? inductors? etc and how did you check them? did you physically desolder them and take them out and check them? and another thing to point out is a lot of switch mode power supplies use feedback so when a load is connected to it the output voltage stabalizes. under no load voltage will be higher than usual. under load voltage stabalizes. when you have something connected to the output use a digital multimeter to check what the voltage is when load connected to output.

Yes, I have desoldered all components, and checked them, here is the list.

@bertus Yes,I have checked it, I am not building their rtypical usage scenario with these components to see how it will behave.

 

[mechtronics]

Yes, I have desoldered all components, and checked them, here is the list.

@bertus Yes,I have checked it, I am not building their rtypical usage scenario with these components to see how it will behave.
View attachment 69925

when you had a load connected to the power supply what voltage reading across the load were you getting?

 

[FIIIP]

When I have control board connected, it burns AMS117 3.3V... and contorl board beeps repeadetly fast, but when i check after AMS117 its shorted... i replaced it a couple of times.. Control board works fine on 9V battery when connected(and AMS117 is new)...

 

[mechtronics]

When I have control board connected, it burns AMS117 3.3V... and contorl board beeps repeadetly fast, but when i check after AMS117 its shorted... i replaced it a couple of times.. Control board works fine on 9V battery when connected(and AMS117 is new)...

is there a feedback resistor to the comp pin 3 of the IC?

 

[FIIIP]

This outputs 15V... instead of 4.7uF/25V i put 10uF/50V because I dont have 4.7/25V, and instead capacitor 333, i put 2A223J green capacitor

 

[FIIIP]

is there a feedback resistor to the comp pin 3 of the IC?

Nope

 

[mechtronics]

This outputs 15V... instead of 4.7uF/25V i put 10uF/50V because I dont have 4.7/25V, and instead capacitor 333, i put 2A223J green capacitor

 

[FIIIP]

The two caps before the PN8024R are each 8.63uF(I guess this is together since they are connected in circuit), in circuit, for reading off the circuit, there is a table above I already sent

 

[mechtronics]

the capacitor on pin 3

The two caps before the PN8024R are each 8.63uF(I guess this is together since they are connected in circuit), in circuit, for reading off the circuit, there is a table above I already sent

what about cap connected to comp pin 3

 

[FIIIP]

The green one is 22uF i tried replacing them with 22nK100, but that didn't solved anything

 

[mechtronics]

The green one is 22uF i tried replacing them with 22nK100, but that didn't solved anything

i can see in the picture that you are missing an AC Neutral terminal where is that? you have AC Live and AC live out and AC neutral out.

 

[FIIIP]

What do you mean?

 

[FIIIP]

i can see in the picture that you are missing an AC Neutral terminal where is that? you have AC Live and AC live out and AC neutral out.

Oh, you mean on the board, it got desoldered when i was unpluging the wire, I soldered it back

 

[FIIIP]

This outputs 15V... instead of 4.7uF/25V i put 10uF/50V because I dont have 4.7/25V, and instead capacitor 333, i put 2A223J green capacitor

So, I replaced 2k resistor with 1k resistor, and now its outputting 12.3V...