Magnavox L42FHD37YX7 Power Light No Picture No Sound

[rebelkustoms]

Hello Again guys, I have a Magnavox L42FHD37YX7, Got this one from the garbage, initial inspection it had a blown 5 amp fuse on the power supply. I replaced that and plugged the set it, the blue LED comes on and stays on. No response from power button and I cannot get a click from the relay. I have no picture and no sound. I would be grateful for any help. As per my last post, someone suggested I upload pictures of the boards with every post, I will do that gladly from now on, please tell me if you need any other pics or closeups.
THANKS!!!

[ReeceyBurger123]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

Checked the power devices on the Psu for S/C ?

[rebelkustoms]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

Checked the power devices on the Psu for S/C ?

Sorry, the fuse is as far as I got so far, where would be a good place to start?

[ReeceyBurger123]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

Well firstly do you know how to check for S/C or short circuits ?

[rebelkustoms]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

Well firstly do you know how to check for S/C or short circuits ?

not exactly sure, I am kind of a hobbyist here, my proficiency is in Pinball Machines, but I like doing this stuff too it is similar. So I know my way around the meter and I have a good Klein. I know how to test capacitors, resistance, diodes, voltages etc. Am I going point to point on the board looking for an open line?

[ReeceyBurger123]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

Right ok, set your meter to diode mode and touch the probes together. You should hear a beep or it will show 0 ohms. This is similar for testing components for S/C. As the fuse is blown something is definitely up.

Check youtube on how to test devices for short circuit, then begin test devices mounted on heatsinks.

[rebelkustoms]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

yea cool, a continuity test then. SO I should check the transistors etc, on the PS like that.

[ReeceyBurger123]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

Yes possibly some of them short causing the Psu not to come out of standby which could of blew the fuse.

[budm]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

It is RCA not Manavox.
http://www.shopjimmy.com/rca-275563-...pply-unit.htm#
RCA 275563 Power Supply Uni
Pictures provided by shojimmy.

Check the resistance between 'S' and 'D' pins of those 4 devices (power MOSFETs) mounted on the heatsinks.

[rebelkustoms]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

It is RCA not Manavox.
http://www.shopjimmy.com/rca-275563-...pply-unit.htm#
RCA 275563 Power Supply Uni
Pictures provided by shojimmy.

Check the resistance between 'S' and 'D' pins of those 4 devices (power MOSFETs) mounted on the heatsinks.

You are right Bud, so sorry i will fix that, I was working on a Magnavox all week last week and got them mixed up, when i typed the post title. As for the Mosfets,

1 pair reads 170 k ohms
2nd pair reads 7.5 M ohms

also wanted to show that Iwas looking around the board visually and I caught this little scorch on the backside of the board between these two resistors next to the fuse.

[budm]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

That looks like something from the chassis made contact with the AC HOT (Line) trace. Those resistors are high resistance high Voltage resistors for discharging the line filter caps.
BTW, check the resistance between the two legs of the main filter cap, it should show low resistance at first due to charging of the cap then the resistance should increase to higher value.

[rebelkustoms]

Re: Magnavox L42FHD37YX7 Power Light No Picture No Sound

Hey Bud,
so the way this thing is set up it doesn't look like anything could contact that pcb and short that, that side butts against a plastic door so who knows. Z

If the main filtering cap is the very large one on the board the 450 V 220 micro farad one. I tested it with the board disconnected , kinda hard to get a solid reading with it in series but it definitely starts at a higher resistance and drops. Starts up around 40 M ohms and counts down.