WLX-838 USB 10 port charger...

[SolomonMan]

Guys/Gals,
I have one of these...10 Port Chargers...The name is not on the top of the unit but the board Silk Screening says otherwise.

http://www.wanlongxin1.com/index.php...&product_id=42

Long story but it was sent to me DOA. Told me to keep it and refunded my money.

I have had it on the shelf to troubleshoot for quite some time and decided to get an order together to Mouser/Digikey/Arrow for a few other projects and thought now would be a good time to troubleshoot.

Anyways I have never troubleshooted a USB Charger...do not see a ground mentioned on the board...Its sloppy/dirty on the back...

I have included three pics and there is a number on the board.

WLX-838 Pcb:2017-03-22F Rev 2.0.

I tested the switch, fuse, the small transformer, and the bridge rectifier. They tested as they should. At least to my novice eyes.

I am going to get my ESR meter/meter and check the caps but I decided to test for shorts/opens in the large transformer next. (ESR across the room). I have included the back (image) test points and there is continuity in the gray squares but the red square no continuity (open)...Is this a Bad Tranformer/Inverter and if so how do I identify a replacement?

Anyone have a schematic?

Thanks again everyone.
Chris

[R_J]

Re: WLX-838 USB 10 port charger...

This is how the transformer is configured, Red=primary, Yellow=feedback, Blue= secondary.
I am guessing your secondary winding is open. remove the transformer and check for a broken wire on the secondary. If there are no numbers on the transformer. it would be a guess as to what would work, many variables on smps transformer
The unit sells for $9.59, I doubt you can find a transformer for that price.
Looks like you have had this for a year

[SolomonMan]

Re: WLX-838 USB 10 port charger...

R_J,
Time for some schooling...So the feedback loop is what is regulating the output at a fixed value?

I believe you are correct on the Secondary...I will try and get some time this week to de-solder it out.

Was hoping I could find a decent one from mouser/etc. and add it to the order possibly reducing the cost factor somewhat as I am ordering other parts...I believe I paid like 13 or 14 for it...but like you said its been a year or so...

Thanks
Chris

[R_J]

Re: WLX-838 USB 10 port charger...

I made a mistake in post #2. I have the primary and feedback lines reversed. when I looked at the top of board photo I saw D1 and thought it was a diode, but I see now it is the primary FET.

The feedback winding supplies the VDD voltage to keep IC1 working. IC1 will likely have a small startup cell to give it a kick start, It will internally produce a small vcc voltage but after the first cycle, the feedback winding & D3 will produce the higher VDD voltage and feed it VDD pin to maintain the operation. Regulation is done via the secondary voltage, with TL31 being a voltage reference ic, Part of this voltage controls the led side of the optocoupler, the photocell side of the optocoupler controls the duty cycle of IC1 to regulate the voltage.

[SolomonMan]

Re: WLX-838 USB 10 port charger...

R_J,
Again thanks for the help!

I misled by my image/posts...

Actually it appear the problem based from your colored diagram... the primary is the issue.

I got home and moved my desolder station around (previously it was under my desk) to the new shelves I built last weekend and decided to desolder is quick.

My newest image shows the problem of a broken wire. If I touch the wires/touch the one closest to transformer to other wire I get continuity as expected.

Is this wire repairable or should I get a new transformer and if so...does the continuity now help identify the transformer...I do not see any markings...

Thanks again.
Chris

[R_J]

Re: WLX-838 USB 10 port charger...

I had to change my diagram as I had the primary and feedback windings reversed. That broken connection is on the feedback winding, not the primary
Yes you can repair the wire, just clean any varnish off the wire coming from the transformer and solder a thin wire to it, then wrap the wire around the pin and solder it.
That broken wire would result in the IC1 not being able to maintain the VDD voltage, once it is fixed the circuit should work. That small electrolytic next to D3 is the VDD filter, it will likely have about 15~20 volts across the cap

[SolomonMan]

Re: WLX-838 USB 10 port charger...

I had to change my diagram as I had the primary and feedback windings reversed. That broken connection is on the feedback winding, not the primary
Yes you can repair the wire, just clean any varnish off the wire coming from the transformer and solder a thin wire to it, then wrap the wire around the pin and solder it.
That broken wire would result in the IC1 not being able to maintain the VDD voltage, once it is fixed the circuit should work. That small electrolytic next to D3 is the VDD filter, it will likely have about 15~20 volts across the cap

R_J,

Again thanks for the help!!

I will have to look for some thin wire in the morning (none in my office currently) and try to get things squared away tomorrow...I will let you know the outcome.

One thing though...when you said..."Regulation is done via the secondary voltage, with TL31 being a voltage reference ic, Part of this voltage controls the led side of the optocoupler, the photocell side of the optocoupler controls the duty cycle of IC1 to regulate the voltage."...the photocell side of the optocoupler controls the duty cycle of the IC1...can you dumb that down for me...I kinda read that as the optcoupler is more or less a simple timer of sorts...?

Thanks so much,
Chris

[R_J]

Re: WLX-838 USB 10 port charger...

If you have something like an old ac cord, use one strand of the copper wire to repair it, there is very little current in that winding and the wire is so short anything will work.
IC1 is a OB2263, have a look at the data sheet and you will get a better idea of how it works. it has a schematic that is close to this power supply

[SolomonMan]

Re: WLX-838 USB 10 port charger...

R_J,
Thanks so much for your help!

This morning after getting the older kids on the bus I decided to head out to the garage and see what bits of wiring I could find...An old wire used for a jumper temporarily for a automotive project was my target...Took a strand of its internal wire and got out my kit and went to town.

Included are my pic of the final result including a USB tester reading. The USB tester looks like it needs a serious cleaning inside but it appears to be sealed.

Its putting out in the image about 5.2 volt and about .33 amps...I changed to a couple other devices and based on charge of the device the amperage fluctuates...saw about a amp on another device (Most devices were close to charge).

I will read the OB2263 datasheet over my breakfast.

Again thanks for the help,
Chris

[sam_sam_sam]

Re: WLX-838 USB 10 port charger...

One more item not headed to the landfill
Good job repairing it