HM502JX Samsung: missing Vbus signal

[linius]

Hello,

I have a HM502JX Samsung that doesn’t respond whatsoever and no Led blinking when I try to connect it.

I’ve done the following:
Measured where I receive power:

Sidenote: is the black IC just next to the mini usb connector some kind of mosfet ? I don’t find anything about this chip (S/N: 3426183 t056)
So I don’t get any power to my regulator because this 3426183 doesn’t allow any current to pass.
There is a VBUS pin 8 on the jm20329 chip that checks if 5V supply is connect via a resistance divider, see data sheet (provide by Arvika in another topic):
http://www.hxwtek.com/upload/jm20329_standardsch_lqfp48_1v0_for%20open.pdf
And I measured the Vbus pin, no voltage when 5V is present on connector.

I also measured the resistance and I have a 4.3 K between Vbus pin 8 and Gnd and 4M between Gnd and Vcc on the connector.

Now my question is:
Can someone point me to R2 and R3 (numbered like in the data sheet)? because I assume it’s a bad soldering…

[fzabkar]

See viewtopic.php?f=1&t=25581&p=174993

I suspect that the "t056" part is a choke which filters the +5V supply.

[fzabkar]

I suspect that the "t056" part is a choke which filters the +5V supply.

No, it's a PolyZen.

USB Peripheral Protection using PolyZen Devices:
http://www.circuitprotection.ru/upload/ ... PZ_USB.pdf

ZEN056V130A24GS, Raychem, PolyZen, 5.6V, 1.3A, marking t056:
http://www.farnell.com/datasheets/1500300.pdf
http://www.comtec80.com/files/polyzen.pdf

Attachments

[linius]

Thank you, fzabkar!

Again good lesson, never assume how a component works.

I will first test if its bad soldering because its a bit twisted on the board.
And then replace it.

I will let you know if it fixed.

[fzabkar]

If the PolyZen proves difficult to obtain, you might like to replace it with a polyswitch and 5V TVS diode. Alternatively, you could use a 2A fuse, or if you are certain that there are no other problems and that your PSU is good, then you could link Vin and Vout with a wire.

Good luck.

BTW, you can find polyswitches on old motherboards. They were/are used as current limiting devices on USB ports.