LED PWM dimmers.

[Richard CSL]

I have 2 different moving heads with dimmer issues.

both heads dont seem to be producing pwm from the main processor, I have 5 volts dc constant, but no pwm signal.

I am going to guess the main chips are the issue and the heads are scrap at this point?

any suggestions appreciated.

[DrV]

Do the other functions work? Are the lights on full full or zero?

 

[KevinE]

can we see the schematic?

 

[DrV]

17 hours ago, KevinE said:

can we see the schematic?

 

Or even just a hint as to the type? More info = more useful help

[Richard CSL]

On 6/21/2024 at 8:55 PM, KevinE said:

can we see the schematic?

 

The manufacturer does not exist, I have tried to contact Made In China , but no response. almost impossible to get schematics these days.

I havre bought some cheap PWM dimming boards from Alibaba, when the signal from the processor is connected the led comes on at full power as the pwm appears to be full 5+ volts. also the units power supply at this point shuts down as there is too much current draw, so I am guessing the other components are for current limiting

[Richard CSL]

most of the chip and power transistors have the numbers removed / sanded off. this I presume is to prevent repair.

very annoying as this fixture may well have to be scrapped now.

[dmxlights]

A lot chines copies of light you will find that.

What all wire go to the main board in the mover its a chance that the main board has feedback from the led driver board and know what its doing also to this could be used to speed up and slow down fans in the mover. What make you think the led driver board needs to be replaced does it work at all with the original board.

Please post here the problems your having with the original board as someone may know where the fault is  can you also post a good photo of full board both sides and of any labels on it.

Edited July 17 by dmxlights

[indyld]

Some better info about the symptoms (not guesses about the problem), the diagnostic steps taken and the outcomes different parts of the system disconnected, plus good quality images of both sides of the boards (LED and controller), and perhaps we can be of more help. At the moment, there is nothing do work with.

Also forget the non-original boards at the moment, it is a distraction.

In one of the images with the MCU on it, there is an SOIC-8 that looks unhappy but it is hard to tell due to the quality.

Edited July 17 by indyld

[KevinE]

so you're saying you've scoped the pwm coming out of the microcontroller and it is stuck at 5V? I'm confused. If the signal is wrong, why did you fit a new led dimmer?

[Kazeja]

From a traditional dimmer point of view, some manufacturers use inverse logic for PWM. 

Positive logic would be 0v (off) to 5v PWM Inverse logic would be 5v(off) to 0 PWM. 

If your "Alibaba" cards use +ve logic and you're feeding an inverse logic signal into them then yes, a 5v (inverse OFF) signal will send the LED to full. 

K.

 

[timsabre]

On 7/18/2024 at 1:51 PM, Kazeja said:

From a traditional dimmer point of view, some manufacturers use inverse logic for PWM.

 

It's not so much "inverse logic" as whether the PWM is switching the ground side of the LED or the positive side. Usually, one side of the LED is connected to the positive power and the PWM switches the ground side (because this uses N-channel FETs which are cheaper and easier to control). When the FET is turned on the output goes to ground and the LED comes on.

[Kazeja]

Thank you for explaining much better what I was trying to say.

K.

[Richard CSL]

https://es.aliexpress.com/item/1005001836699671.html?spm=a2g0o.order_list.order_list_main.20.2286194dTAgzaZ&gatewayAdapt=glo2esp

I have found these hopefully this will solve the problem.

 

Edited August 20 by Richard CSL