Magnavox 40MF430B/F7 Wont power on

[simcole]

Hi all,

I had a TV given to me recently and it was a Magnavox 40MF430B/F7

It has a blown main fuse (250v 8A) and a couple blown diodes. I'm ordering some replacement parts from Digi-key but I'm having trouble cross referencing some of my parts. ALL of the parts listed in the service manual aren't sold at digikey by part number. I'm having to put in what information I know and try to match it up. Some of this is VERY confusing.

Here is the service manual:

On page 71 I need 2 diodes. D1202 and D1203.

D1202# DIODE 1N5397BD NDL1001N5397
D1203# DIODE 1N5397BD NDL1001N5397

Closest thing I can find on digikey is this. Will this work?

My other big question is cross referencing this item: FCHS20A08


It's also on the page 71 on that manual as item D1721

D1721 DIODE SHOTTKY FCHS20A08 QDWZCHS20A08

Digikey sells this item that's close..

If y'all can help me find these comparable parts hopefully I can get this thing running.

[R_J]

Re: Magnavox 40MF430B/F7 Wont power on

The schematic shows them as 1n5406 General purp. 3A 600 v diode, digikey has them, or 1n5397 gen. purp. 1.5a 600v diode, they have them also,
whats wrong with the fchs20a08, is it shorted? being a shottky it will diode check at a lower reading on your meter compaired to a regular silicon diode, si checks around .7 and the shottky around .2 - .4

[simcole]

Re: Magnavox 40MF430B/F7 Wont power on

Thanks for the diode info. I'm confused on some of that stuff. The spec sheets not using the same terminology as digikey really makes it hard for me.

The fchs20a08 checks open on my diode test of my mm. I'm getting normal drop when I test from both anodes to the cathode. When I reverse the lead and put the black on anode and red on other anode I get tone. I also get tone if I move red to cathode, so I belive it's failed. I did not remove it from the board to test. None of the others test like this. This is my first schottky diode.. can someone agree with me here so I know I'm diagnosing this right.

I'm told a common problem with the main fuse popping on these boards is due to those type of diodes. We're you able to cross reference that part for me too? I appreciate the help.

[R_J]

Re: Magnavox 40MF430B/F7 Wont power on

Were D1202 d1203 Shorted? if they were, replace all 4 diodes in the bridge, D1201,1202,1203,1204.
To check the fchs20a08 the meter must be on DIODE test don't worry about the tone, with the black probe on the cathode and the red on either anode you shoud read about 180 (+ or - depending on meter) when you reverse the leads it should be higher, but because its in circuit the meter will charge the capacitor for that circuit and the meter reading will be off. leave the leads connected and see if the reading climbs up. Like I said, I dought that that diode is bad.

I would also check IC1201 pin 5 to 7-8 make sure there is no short between those pins, if there is then the ic is also shorted.

[simcole]

Re: Magnavox 40MF430B/F7 Wont power on

Were D1202 d1203 Shorted? if they were, replace all 4 diodes in the bridge, D1201,1202,1203,1204.
To check the fchs20a08 the meter must be on DIODE test don't worry about the tone, with the black probe on the cathode and the red on either anode you shoud read about 180 (+ or - depending on meter) when you reverse the leads it should be higher, but because its in circuit the meter will charge the capacitor for that circuit and the meter reading will be off. leave the leads connected and see if the reading climbs up. Like I said, I dought that that diode is bad.

I would also check IC1201 pin 5 to 7-8 make sure there is no short between those pins, if there is then the ic is also shorted.

The IC1201 tests good. It's not shorted out.

The diode 1208 was actually blown out on the side. In a service manual update it says that this is common and to just remove this diode and not replace it.

As for diodes 1202 and 1203 they show no signs of blowout. They just pass 100% of the voltage both directions.

Finally after testing the fchs20a08 using your method, I did get a .217 reading from either anode to the cathode. Once I reversed the leads it climbed up like you said. I thought the point of these type of diodes were that I COULDN'T pass the voltage that direction. That's why I thought it failed.


Edit: Page 29 of that manual applies to me. If the fuse blows out, use flow chart #2.
"Check the presence that the primary component is leaking or shor ted and service it if defective."
or
"Check the presence that the rectifying diode or circuit is shorted in each rectifying circuit of secondary side, and service it if defective."

What latin is this? Hence why I said I thought the rectifying diode might be bad.. it's the biggest heat sink on the board.

[whatusername]

Re: Magnavox 40MF430B/F7 Wont power on

Thread revival..
I have the same issue blown fuse saw the bulletin on diode 1208 will remove but just wanted to know how this issue was resolved

[whatusername]

Re: Magnavox 40MF430B/F7 Wont power on

Problem solved.. Ordered the repair kit from shop jimmy and installed 8 diodes and 1 ic and a fuse and the tv works.. if you do this repair make sure to leave the diode d1208 disconnected it comes with the kit but i didnt use it as per the bulletin