Zyxel P-320W with bad component

[imp]

Good morning,

I´m trying to fix a Zyxel P-320W wireless router for a friend, his description of the fault is that the wireless connection is very wacky. I´ve done a total recap since all the capacitor was of a bad brand (Jun Fu if I remember it right) but this didn´t solve the problem. However, I found one component inside which seems broken. It´s shorted between two of the pins and measures no voltage on the output. The input is 0,7V. On a identical circuit on the PCB I measure 0,8V and 1,5V between ground and pin 1 respectively 2.

Please see attached pictures. Anyone that can suggest what replacement component to order? There are MANY different transistors to choose from and this is not my speciality

[rogfanther]

Re: Zyxel P-320W with bad component

You should remove and measure it out of the board, but a 2SB1202 or 2SB1203 could be used.

The wireless don´t work, works with weak signal, or works-stop-reappear-disappear, cycling ?

[Behemot]

Re: Zyxel P-320W with bad component

Is there some solution for tha last symptom? Appeared on mine P660HW-T3, mainly under Linux to say, but I just scraped it later as cheap crap (which it is). Now got old SMC broadband and old Well Wi-Fi router with damaged modem as AP, both almost rock stable

[rogfanther]

Re: Zyxel P-320W with bad component

With the brands we service here, mostly it is caused by overheating of the wireless controller, bad caps, and when it just gets weak and stays weak, the RF amplifiers ( LP 5510, SST 12LP14, etc ) . This weak problem with burnt amplifier appears a lot in the D-Link DWL-2100AP, for example.

One simple thing that I have observed is also the channel. Due to driver bugs or other reason, machine would not like if router is in a particular channel. Change the channel to some common ones ( 6, usually ) , and it works with no problem.

Also, the psus many times are also guilty. Have seen many devices that ask for 1A, but when older ask for more, and the psu could barely deliver that 1A. Swap the psu for a good 2A one, and thing starts working . ( until other problems surface, but that is other history ). Even when new : the original psu for the DSL-2640B states 1A. Same in the device. But the psu can deliver more than that ( about to 1.5A ) . And the device also uses more than that 1A. So, when swapping the psu for another 1A model, the thing just reboots continuously. Even if the psu is good and works ok in another model.

[Behemot]

Re: Zyxel P-320W with bad component

I swapped caps for better and higher capacity, also did something for cooling, voltage was good (simple soft low-frequency transformer so the voltage would drop with higher load). Messed with channel too, but it just continued. The signal was strong, it just disappeared after wome time and reappeared again.

It was worse with higher load/number of connections. So I guess they just used crappy underrated components. Common problem, this router was not so cheap when new, but later as they dropped prices you could see what price point it really belonged to…

I guess that just most routers under 50 USD are craps and you have to be carrefoul as you can still find lot of craps even at like 70 USD price point.

[rogfanther]

Re: Zyxel P-320W with bad component

Absolutely right. Did it use a Ralink RT3050 / 3051 / 3052 chipset ? For what an opinion is worth, they are just crap . A Deer / L&C psu would deserve a gold award when compared with this chipset.

In all the brands I have seen with it ( D-Link, Tenda, Belkin, Linksys, some chinese no-name crap, etc ) , it is consistent in its behaviour : just dies. We have customers that told us that from 10 devices sold, 9 returned with problems. Wireless would die, or ethernet would die, or the whole thing would just light the power led and die.

Many times, they would wait just to be far from us to die. Example : in the beginning , when we had not give up in them yet, we replaced the flash chip in one of them, upgraded the chip, then wrapped the thing in a towel and stuck it inside a drawer. Connected to the network, and let if working, downloading linux isos and pinging a bunch of sites the whole weekend. No problem, all work ok. Let it cool, used it in the open whole Monday, no problem. Send it to customer on Tuesday. Thing worked on Wednesday, started giving problems on Thursday.

This happened with a lot of devices, so we know it wasn´t due to it being cooked in our "drawer test". Sometimes, a customer who bought one from us would return in a week or two, take home a new one, just to return again with same problems. Some people have exchanged 3 or 4 devices until either it works, they desist, or we exchange it to another model ( not Ralink based ) to them.

[Behemot]

Re: Zyxel P-320W with bad component

Man, no idea. But when it's not chip, than it's something else. Just recently got a thread here bout TP-Link where either voltage regulator died, or the chip got shorted and regulator was in protection mode, not sure. That thing got 4 different voltages inside IIRC…

[rogfanther]

Re: Zyxel P-320W with bad component

Yeah, designers use some strange tricks. But as most of the makers make little modification to the design circuits, once one brand/model is understood, most of the repairing knowledge can be ported to other models based in the same chip.... Of course, with the value of the devices themselves being always lower, customers usually don´t want them fixed..

[imp]

Re: Zyxel P-320W with bad component

You should remove and measure it out of the board, but a 2SB1202 or 2SB1203 could be used.

The wireless don´t work, works with weak signal, or works-stop-reappear-disappear, cycling ?

More like works-stop-power cycle-works for a while. But I´m not 100% sure.

I´ve measured the transistor out-of-circuit now and it´s completely dead, no contact whatsoever between pin 1 and 3.

I´ll try to locate a new one, let´s see how it goes

[imp]

Re: Zyxel P-320W with bad component

Found one at Digikey

[momaka]

Re: Zyxel P-320W with bad component

If it is working fine for a short period of time but then power-cycles, I doubt that transistor is the cause of the problem - if it was shorted, the router likely wouldn't work at all. I'm more inclined to think that the small caps around it are the cause of the problem. What brand and series are they? If they are not from a well-known Japanese brand, I think it would be a good idea to change those as well.

[imp]

Re: Zyxel P-320W with bad component

They are all Ruby's, changed them a while ago from Jun-Fu.

I´m also a bit confused whether this transistor actually causing the problem but that´s the only broken component I´ve found so far. Let´s see what happens after I replaced it.