Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

[cage]

Hi,

I've got a wall wart for a wrt54g that has no power output on the barrel connector when measured with my multimeter. I'm curious as to how I would troubleshoot this. Upon visual inspection I don't see anything obvious. Any tips would be most appreciated.

[stj]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

start by checking the cable isnt bad
and check the box-fuse in the corner where the red&black wires are.

if both are good, try replacing c4

[budm]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

Check that red rectangular fuse on the primary side.
Also check the resistance of both conductors of the output wires to the DC jack.

[stj]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

Check that red rectangular fuse on the primary side.
Also check the resistance of both conductors of the output wires to the DC jack.

i said that.

[cage]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

I noticed that you can pull the red box off that fuse. The fuse certainly looks like it's gone. The markings on that fuse say T1.0A250V.

I assume this is a part I can get off digikey easily? Not sure what exactly to search for.

Thanks for the tips.

[budm]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

i said that.

So?

Fuse is Time delayed 1A fuse 250V
Check the leg spacing:
http://www.digikey.com/product-detai...1176-ND/809320
http://www.digikey.com/product-detai...9CT-ND/3306889
http://www.digikey.com/product-detai...2BK-ND/2093104

[stj]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

you arent supposed to be able to open them!!!!


and dont just fit a new one - they usually blow for a reason.

[cage]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

The fuse had two tabs holding the cover on. In this case you could remove the cover.

So you suggest not replacing the fuse then? How do you expect it to work properly?

[stj]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

i dont, something ELSE made the fuse blow.
you have to find and fix the fault before you fit a new fuse.
unless you like replacing fuses!!!!

do you have a meter?

[cage]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

Yes, I have a multimeter.

[stj]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

o.k. make sure D4,D5,D6,D7 and the part bolted to the heatsink dont have any legs shorted together.

[cage]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

It seems D7,D5 and D4,D6 are shorted together by design.

Please see the attached bottom of the pcb. The bottom right is where D7 is located.

[CapLeaker]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

that is the bridge rectifier. it is not shorted by design, unless one or more of the diodes are shorted. If the diodes aren't shorted, see if the transistor that is bolted on to the heat sink is not shorted, like stj already mentioned. Test everything in diode mode.

[cage]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

Tested all those in diode mode and they are not shorted.

[CapLeaker]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

what about that small thee legged thingy and that big diode?

The voltage drop of these diodes should be in between 0.4 and 0.8 volts.

[budm]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

What do you read using Ohm mode on the Diodes and on the power MOSFET mounted on the heat sink?

[cage]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

In diode mode the smaller diodes (D4,D5,D6,D7) measure all read around 580. The larger diode reads 219. The three legged thing reads around 1850 and 833 on the different legs.

I'm not used to getting this in depth with troubleshooting and measuring values so I may not be doing this properly.

[stj]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

your doing o.k.

set your meter to read atleast 400v and meter the pins on cap C1
this is just to make sure it's not charged or the next thing will blow your meter.

if it's NOT got any noticable voltage, check if it looks shorted with resistance-setting.

[cage]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

Read the cap C1 with setting above 400v and got no reading.

Read the cap C1 in resistance setting and value never changed from 1.

[stj]

Re: Linksys AD12V/1A-SW Power Supply for Linksys WRT54G - No power output

that sounds strange.
normally when you do resistance on a cap the reading looks like a low value, then slowly rises as the cap charges.
i wonder if it's open-circuit.
does you meter have a setting for capacitance?