LG 50PQ6000 unstable 5v standby

**Baileybum1234** · 11-25-2012, 05:30 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by ben7

Most DVM's [that I know of] don't measure capacitance above 10uF.

What is the reading of the diodes, when you took D351 out?

P.S. We are both on different paths (me and tom66), feels awkward, doesn't it?

0.22v one way and 0v the other on both diodes in the component. (Diode removed from board and tested with DVM on diode test)

To be honest I dont the two paths its all amazing help I have had more ideas/suggestions this evening that the last 4 weeks of doing it on my tod.

**tom66** · 11-25-2012, 05:35 PM

Re: LG 50PQ6000 unstable 5v standby

Have you tested D352? Looks like it's got really hot. If it were leaky, it might stop the PSU from reaching full 5V.

**Baileybum1234** · 11-25-2012, 05:38 PM

Re: LG 50PQ6000 unstable 5v standby

Ok I will test D352 tomorrow after work I really need to get my head down I have a fair bit of driving to do tomorrow with an early start.

Thanks for your help this evening guys its been great and looking forward to tomorrow evening now.

**ben7** · 11-25-2012, 06:34 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by Baileybum1234

0.22v one way and 0v the other on both diodes in the component. (Diode removed from board and tested with DVM on diode test)

To be honest I dont the two paths its all amazing help I have had more ideas/suggestions this evening that the last 4 weeks of doing it on my tod.

This is so strange.

Are you finding that BOTH diodes measure 0.22 in the forward direction (plus probe on diode anode, and minus probe on cathode), and BOTH read 0 in the reverse direction?

Or, is your meter one of those cheapo meters? I've never heard of a diode being shorted in one direction. Are you sure your meter isn't saying 'OL'?

**Baileybum1234** · 11-26-2012, 01:17 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by ben7

This is so strange.

Are you finding that BOTH diodes measure 0.22 in the forward direction (plus probe on diode anode, and minus probe on cathode), and BOTH read 0 in the reverse direction?

Or, is your meter one of those cheapo meters? I've never heard of a diode being shorted in one direction. Are you sure your meter isn't saying 'OL'?

Hi ben,

Sorry was getting late for me last night.

Right the cathode is the middle pin on the IC and with the red probe on the middle pin and the black on either of the outer pins I get .0L

Witht the black probe on the cathode and the red probe on either of the outer pins I get 0.215v.

**Baileybum1234** · 11-26-2012, 01:22 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by tom66

Have you tested D352? Looks like it's got really hot. If it were leaky, it might stop the PSU from reaching full 5V.

D352 id 0.00v in both directions on diode test. Im guessing this is bad?

**tom66** · 11-26-2012, 01:43 PM

Re: LG 50PQ6000 unstable 5v standby

Yep! There's your fault... It looks like it got very hot, probably run at above its maximum current due to poor design.

**Baileybum1234** · 11-26-2012, 01:53 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by tom66

Yep! There's your fault... It looks like it got very hot, probably run at above its maximum current due to poor design.

Ok reality check.

Would it of killed anything else on its way out do you think? annnnddddd where would I find one.

Thanks for your help and ben7's I was going mad round and round in circules before I came on here.

**tom66** · 11-26-2012, 01:57 PM

Re: LG 50PQ6000 unstable 5v standby

I doubt it. Usually when a diode fails (short almost always), the power supply goes right into protection mode, hence the low 5V... and it may explain the 12V measuring 0V, as it -might- be on the 12V rail.

There is a part # on the diode. You may have to remove it to read it. Then you can find a replacement.

**Baileybum1234** · 11-26-2012, 02:14 PM

Re: LG 50PQ6000 unstable 5v standby

Well done tom66 good fault finding skilles there mate.

Its a VSB3200 M944A. Is it supposed to be regulating the input to the regulator?

**tom66** · 11-26-2012, 02:21 PM

Re: LG 50PQ6000 unstable 5v standby

I don't know what that diode does but it's bloody hard to get hold of.

It's a 200V, 3A schottky diode. Special type of low-loss diode.

**tom66** · 11-26-2012, 02:25 PM

Re: LG 50PQ6000 unstable 5v standby

Highest I can find is 150V.
http://uk.farnell.com/stmicroelectro...-3a/dp/1702811

This may be an "install it, see if it works, and if it fails, source the 200V one" job. I doubt that diode sees 200V transients on the 12V output. Probably 3-4x that in reverse at most. But I didn't design this PSU, so I don't know.

**Baileybum1234** · 11-26-2012, 03:20 PM

Re: LG 50PQ6000 unstable 5v standby

Blimey a rare one?

I think I might have the TV fixing bug. Have yet to see if this is the fix but I really enjoyed working around the board and learnt alot.

**ben7** · 11-26-2012, 03:37 PM

Re: LG 50PQ6000 unstable 5v standby

Good job folks!

LOL, I knew something was wrong, you said zero volts, instead of OL. As far as I know, a diode cant go shorted in one direction xD

Glad you kept pushing through, as there are people who come here wanting help, and they just loose interest, or think it is too hard.

-Ben

**Baileybum1234** · 11-26-2012, 03:41 PM

Re: LG 50PQ6000 unstable 5v standby

Its a fast acting diode with low voltage drop between anode & cathode often used in reverse protection and/or voltage clamping well goto love the net.

**Baileybum1234** · 11-26-2012, 03:43 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by ben7

Good job folks!

LOL, I knew something was wrong, you said zero volts, instead of OL. As far as I know, a diode cant go shorted in one direction xD

Glad you kept pushing through, as there are people who come here wanting help, and they just loose interest, or think it is too hard.

-Ben

I have been there many times with this

. I guess its the fact im interested in electronics that keeps me going. I just really appreciated the fact I could bounce ideas of some people who are obviously into it too it can help sooo mutch.

**Baileybum1234** · 11-26-2012, 03:45 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by ben7

Good job folks!

LOL, I knew something was wrong, you said zero volts, instead of OL. As far as I know, a diode cant go shorted in one direction xD

Glad you kept pushing through, as there are people who come here wanting help, and they just loose interest, or think it is too hard.

-Ben

Thanks for your input ben it really was appreciated also

**Baileybum1234** · 11-26-2012, 04:25 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by tom66

Highest I can find is 150V.
http://uk.farnell.com/stmicroelectro...-3a/dp/1702811

This may be an "install it, see if it works, and if it fails, source the 200V one" job. I doubt that diode sees 200V transients on the 12V output. Probably 3-4x that in reverse at most. But I didn't design this PSU, so I don't know.

20 quid minimum order hummmmmmmm what else do I need

**tom66** · 11-26-2012, 04:37 PM

Re: LG 50PQ6000 unstable 5v standby

0.39 ohm resistor (just in case) and capacitors.

There is a Farnell trade counter here in Leeds. It has a £5 minimum order. If I'm going up there soon, I could get you the items.

**Baileybum1234** · 11-26-2012, 04:40 PM

Re: LG 50PQ6000 unstable 5v standby

Originally posted by tom66

0.39 ohm resistor (just in case) and capacitors.

There is a Farnell trade counter here in Leeds. It has a £5 minimum order. If I'm going up there soon, I could get you the items.

thanks for the very kind offer Tom but I dont think I could wait that long.

Any one ever used this place?

http://www.donberg.co.uk/

LG 50PQ6000 unstable 5v standby

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