Dead As A Doornail. Sony KDL-40EX400

[budm]

Re: Dead As A Doornail. Sony KDL-40EX400

So you get 0 Volt on all the pins of the the connector of the power supply that goes to to the main board?
How about the pictures of the whole back side of the TV so we can see how all the boards are connected together?

[Michale32086]

Re: Dead As A Doornail. Sony KDL-40EX400

Well, I am glad to see it's not something simple and obvious.

I'll check those things...

[nomoresonys]

Re: Dead As A Doornail. Sony KDL-40EX400

found it, A quick background on what happens at startup on these supplies. AC power is applied, the mains filter cap charges to full voltage (1.4 x line voltage). A low current path (bleeder resistor or constant current source in the SMPS controller) charges the Vcc filter cap to (usually) about 16V. At that point the SMPS controller starts.

The SMPS controller turns on the main power FET briefly, sending a surge of current through the primary if the transformer, causing pulses of current through the secondaries and a tertiary winding which provides Vcc for the SMPS controller. This is followed by additional pulses until the secondary voltage reaches the design value - usually 5 volts.

There are a few things that can stop this start-up cycle. If the Vcc filter cap is open, Vcc decays to below 10 volts and the process stops before the tertiary winding can provide enough voltage. An excessive load on the secondary will have the same effect. That can be a reversed cap, bad diodes, short on one of the loads, etc.

I'd have to see the part numbers of U2 and U4, but it appears to me that U4 is most likely the SMPS controller, mainly because of it's proximity to the opto-isolator.

PlainBill. Nice explanation of start up, post #28 of bens thread, Thanks

[nomoresonys]

Re: Dead As A Doornail. Sony KDL-40EX400

theres a good post by plainbill, about the startup deal, I'll try to find it.

[CapLeaker]

Re: Dead As A Doornail. Sony KDL-40EX400

be extra careful with the wires.
Since the tv is dead as a nit, I wonder if the power supply has standby voltage or not?

[nomoresonys]

Re: Dead As A Doornail. Sony KDL-40EX400

you probably already know, safety first, be careful working with power supply, HIGH VOLTAGE, on primary side can be deadly.

[Michale32086]

Re: Dead As A Doornail. Sony KDL-40EX400

You have not much choice than to solder up some wires to the filter cap and measure it that way if you have to.

K, I'll give that a shot.. Thanx

[CapLeaker]

Re: Dead As A Doornail. Sony KDL-40EX400

You have not much choice than to solder up some wires to the filter cap and measure it that way if you have to.

[Michale32086]

Re: Dead As A Doornail. Sony KDL-40EX400

Is that the 120V AC input? Your meter was set to DC.
DC starts at the bridge rectifier!

rookie mistake...

Yea, 118v... So we're good..

It's like putting your boat in the water forgetting to put in the plug..

It's a mistake you only do once..

"We're not going to make the same mistake, I can tell you."
"No, no.. You are making all new mistakes."
-Jurassic Park II

[nomoresonys]

Re: Dead As A Doornail. Sony KDL-40EX400

Is that the 120V AC input? Your meter was set to DC.
DC starts at the bridge rectifier!

oops, that would explain it.

[CapLeaker]

Re: Dead As A Doornail. Sony KDL-40EX400

Is that the 120V AC input? Your meter was set to DC.
DC starts at the bridge rectifier!

[Michale32086]

Re: Dead As A Doornail. Sony KDL-40EX400

Yep, tried 3 different cords. All the same

[nomoresonys]

Re: Dead As A Doornail. Sony KDL-40EX400

thats strange, is your power cord good?

[Michale32086]

Re: Dead As A Doornail. Sony KDL-40EX400

Well, this is weird..

I don't get any voltages from the connector..

So I figured I would check the incoming voltage at the 2-pin power connector..

http://sjfm.us/temp/SonyKDL1.3gp

It's all over the place......

AND upside down

[Michale32086]

Re: Dead As A Doornail. Sony KDL-40EX400

did you check at the connectors?, you probably checked the fuse, if you have no stndby voltage, its a power supply issue.

DOH!! Yea, the connectors.. I should have remembered that...

Fuse is good..

I'll check the connectors. Thanx

[nomoresonys]

Re: Dead As A Doornail. Sony KDL-40EX400

did you check at the connectors?, you probably checked the fuse, if you have no stndby voltage, its a power supply issue.

[Michale32086]

Sony's are fast becoming the ThinkPads of TVs in my book...

Totally dead. No indication of power..

A check of Toms Service Manuals showed only manuals for how to configure the video. Nothing on the Power PCB...

Normally, my first stop would be on the large cap to check for power. But it's flush against the pcb and not accessible..

What's my next best option for checking voltages??