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Electronics => Beginners => Topic started by: jpyeron on July 26, 2019, 04:20:45 pm

Title: Trouble reverse engineering PCB to schematic - capacitor to nowhere?
Post by: jpyeron on July 26, 2019, 04:20:45 pm
I am reverse engineering a commercial (constant current) LED ceiling panel, to make an open source replacement / improvement.

The PCB has two capacitors on the PCB near the wires. They are 10.3uF.

The board contains two circuits of LEDs 3k white, 5k white. The capacitors are only on one of the circuits. I have been unable to probe out where the other pad goes. Any thoughts on where to go next

Title: Re: Trouble reverse engineering PCB to schematic - capacitor to nowhere?
Post by: KL27x on July 28, 2019, 04:20:54 am
Doh. Better check IP address to see if this is Treez opening a fake account.
Title: Re: Trouble reverse engineering PCB to schematic - capacitor to nowhere?
Post by: jpyeron on July 28, 2019, 05:44:02 am
I am not trez, I am easy to google if you care/need
Title: Re: Trouble reverse engineering PCB to schematic - capacitor to nowhere?
Post by: Nusa on July 28, 2019, 06:50:37 am
See what the voltage is across the capacitors when the panel is in operation. That'll at least tell you that it's not open-circuit. Which is an idea you shouldn't discard until proven otherwise.

Beyond that, you haven't given us enough information. Your schematic of something you can't explain is probably less useful than some pictures of actual traces and components on the board. How is the light used with the two circuits? Both on always? Each one independently? One always on before the other?
Title: Re: Trouble reverse engineering PCB to schematic - capacitor to nowhere?
Post by: jpyeron on July 28, 2019, 07:02:40 pm
The solder mask is a bit difficult to see through, my apologies.

Here is a key photo:

[attach=1]

Here is a a video of the whole boards (1 with the capacitor still on, the other with them removed):

https://youtu.be/gSdic5ZpIjU (https://youtu.be/gSdic5ZpIjU)

Here are photos of the the power supply shipped with the unit - it is being replaced.

[attach=2] [attach=3] [attach=4]

Sorry, I omitted the readings across the component. I get a transient spike of +/- 0.007v at power up on the circuit, then it stabilizes to 0v. I am powering it directly with a constant current bench supply.

As to the function, at the end of the second board it uses a common +, power supply (should) allocate 0-100% on one set and 100-0% on the other - so yes they can both be on at the same time.

The commercial specs are (if you want to google the product):
Tunable White LED Panel Light - 2x2 - 4,300 Lumens - 40W Dimmable Light Fixture
Part Number: LPD-TWR22-40
CRI   80 CRI
Current Draw   0.33A (330mA)
Efficacy   108 lm/w
Intensity   4300 Lumen
Total Power Consumption   40 Watts
Title: Re: Trouble reverse engineering PCB to schematic - capacitor to nowhere?
Post by: jpyeron on July 29, 2019, 03:31:16 am
The LED strips are driven by a NCE6005AS (http://ncepower.com/Upload/MOSFET/NCE6005ASdatasheet-11020756927.pdf).
Which get its input from 2 knock off r1210n531 (https://www.e-devices.ricoh.co.jp/en/products/power/dcdc/r1210/r1210nxx1-ea.pdf)

This pretty much ensures it is PWM based dimming.
Title: Re: Trouble reverse engineering PCB to schematic - capacitor to nowhere?
Post by: jpyeron on July 31, 2019, 01:15:05 pm
Is there any other information I can provide?