MAGNAVOX no picture powers LED 47MF437B/37

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Pulled the diodes Test Results Below.

Diode 1 show 18 in both directions

Diode 2 shows 779 Red probe on output side.
455 Black probe on output side.

Output side being the one with the stripe.

Also some of the pad came up on the burned area when removing these Diodes.
Can I use a paperclip or some wire to bridge the two together?

And are there any stores that would carry these diodes?
I browsed Radio Shack website and couldn't find the "P6KE120A" diodes.

Thank You So Much For The Help!!!!!

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Pulled the diodes Test Results Below.

Diode 1 show 18 in both directions

Diode 2 shows 779 Red probe on output side.
455 Black probe on output side.

Diode 1 is definitely bad. Diode 2 is probably bad with those readings. I would play it safe and replace both.

Also some of the pad came up on the burned area when removing these Diodes.
Can I use a paperclip or some wire to bridge the two together?

Use an insulated wire. See

http://www.circuitrework.com/guides/6-1.shtml

And are there any stores that would carry these diodes?
I browsed Radio Shack website and couldn't find the "P6KE120A" diodes.

Get it from digikey. It costs around $2.75 USD for shipping and you get it in about 2 days. It is 60 cents at digikey. I would get 4 and have a couple of spares.

http://search.digikey.com/us/en/prod...ACT-ND/2770358

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Thank you for your help, Would a automotive wire 18 to 22 gauge work?
They have insulation on them and I have plenty of that available to me.
The website for the diodes looks like a decent site, I will order from there.
Thanx Again

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Thank you for your help, Would a automotive wire 18 to 22 gauge work?

I'm not a solder repair expert, but I believe it should work fine. Use your multimeter's continuity feature to "buzz" your work afterwards to ensure good electrical connection.

The website for the diodes looks like a decent site, I will order from there.

Many USA regulars here use digikey and I have never heard of a negative experince yet in 2 years of participation. For non USA members, expensive shipping costs force us to choose alternatives.

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Thank you, Will wait until I get my diodes installed and then will report back.

This Forum has so far proven to be very helpful.

Thank you to every one who replied.

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Hmm, I should have also asked you to check the two diodes just below the two ZD diodes. Check them the same way in circuit first and report your readings. These two diodes may be collateral damage victims?

[Mr Bill]

Re: MAGNAVOX no picture powers LED 47MF437B/37

He should still be able to add to his order. My experience with placing a digikey order over the weekend is they won't ship till monday evening. I usually get the ship email somewhere in the 9:30 pm eastern time.

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

The Diode in location "D925" measured "555" in one direction only, Infinite in the other.

The Diode in location "D907" measured "572" in one direction only, Infinite in the other.

The Diode in location "D912" measured "001" in both directions. Should I pull this one too and test it out of the board?

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

The Diode in location "D912" measured "001" in both directions. Should I pull this one too and test it out of the board?

D912 is bad if it tests 001 both ways. Yes, desolder and retest out of circuit.

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Thank you, I will do that tomorrow. Also should I be worrying about my transformer or is that thing bullet proof?

Thanx Again!

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Also should I be worrying about my transformer or is that thing bullet proof?

The big SMPS transformers rarely go bad. I see a Capxon cap by those fried diodes. They are terrible quality. If you can add to your order, I would replace all the Capxon caps with Panasonic FM equivalents.

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Hello, I am also a newbie to psu repair.

Just a reminder that when you install the new diodes, you must put them back in correct direction as the originals. A diode's job is to allow current flow in one direction.

[cashkennedy]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Use the 22 wire to brige the connection instead of the 18 guage, 18 is too thick, youll be soldering all day.

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Diode "D912" Test "584" in output side
Test "infinite" in other side.

That is taken out of the board.

Should I put that one back in?

Should I be worried about the test readings when it was in the board?

I will also look at getting the other capacitors. Might as well since I am doing all this.

Thank You !!

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Diode "D912" Test "584" in output side
Test "infinite" in other side.

That is taken out of the board.

That is a good diode. If you haven't desoldered all the bad components, the in circuit reading that you were getting for D912 may have been affected by the bad components.

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

When I put it back in the board, I get "001" in both directions again.

I had already removed the Diodes in the burned area.

What could the problem be?

[budm]

Re: MAGNAVOX no picture powers LED 47MF437B/37

It sounds like you have shorted load. I am still trying to figure what is connected to the Cathode side (the banded side of the Diode) of this D912.
So you replace the zd902 & zd904 which shown in the picture in the burnt area, but I cannot figure out where this D912 is located on the board.
The reason I ask is that these two Zener Diode are for the Snubber circuits to help protect the MOSFET (Q901 mounted on the heatsink) the drive the switching transformer.

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Sorry to be such a pain, It must be frustrating to have someone ask so many questions.

I really do appreciate all the help I am getting from everyone!!

[scatman0000]

Re: MAGNAVOX no picture powers LED 47MF437B/37

I haven't replaced the zd902 & zd904 yet. They should arrive here Tuesday or Wednesday.

Should I worry about the "Q901"?
Could it be damaged?

[retiredcaps]

Re: MAGNAVOX no picture powers LED 47MF437B/37

Should I worry about the "Q901"?
Could it be damaged?

Q901 and Q902 are easy to test. Do it in circuit first.

Number the pins 1, 2, and 3. Measure the resistance between 1-2, 1-3, and 2-3. Report your readings for both transistors.