Magnavox 42MF521D/37B

[junktv]

Anyone have a service manual for one of these?

Trying to see if I can fix this for a friend of the family. Symptoms are a steady flashing power button after it is pushed with no picture or sound. Has the normal bad caps and seems the diodes check out.

I was able to find the spec sheet for the capxon gf caps so have 1 P12384-ND and 3 P12409-ND for replacements in the cart.

[tom66]

Re: Magnavox 42MF521D/37B

Both of those caps are suitable replacements.

If you have a digital multimeter, you can check if the PSU outputs are in spec - if the caps are bad, they will usually read low.

No luck finding a service manual on my favourite sites.

[junktv]

Re: Magnavox 42MF521D/37B

I looked also and this board isn't labeled for + and gnd.

[tom66]

Re: Magnavox 42MF521D/37B

I looked also and this board isn't labeled for + and gnd.

Can you post a pic of around the connector going to the main board, and going to the inverter?

[retiredcaps]

Re: Magnavox 42MF521D/37B

This power board probably has the same suspect diodes 6054, 6055, and 6056 as the Philips models.

[junktv]

Re: Magnavox 42MF521D/37B

This power board probably has the same suspect diodes 6054, 6055, and 6056 as the Philips models.

All diodes seem to read one way but some do climb. Those you listed are 500-600 and steady.
The frame does have a LG.Phillips sticker.

[junktv]

Re: Magnavox 42MF521D/37B

Just checking for a manual again incase someone has one that wasn't on last week.

I have the new caps in now just haven't tried it. To clarify post #6 i tested the diodes still in the board.

Tom66, I'll get some pics tomorrow before i try it.

Thanks

[junktv]

Re: Magnavox 42MF521D/37B

Well i tried it and at first the power button lit up and got bright staying on like it should when working fine but the screen never lit up. I turned it off and realised i forgot to plug in the left inverter. So i unplugged it, let it sit for a bit and plugged in the inverter to try again. This time it acted like it did originally where the power light blinks and won't shut off after being pressed.

Sorry for the bad pics, all i have is a cell camera.

[tom66]

Re: Magnavox 42MF521D/37B

Check you're getting a good +24V going to the inverters.

[selldoor]

Re: Magnavox 42MF521D/37B

As you say pics are not great however can you look near pin 11? on the big transformer
there is something doesnt look quite right as though it might be shorting/arcing.

[junktv]

Re: Magnavox 42MF521D/37B

Where do i check that? DC?

Here are pics of one of the inverters.

[junktv]

Re: Magnavox 42MF521D/37B

As you say pics are not great however can you look near pin 11? on the big transformer
there is something doesnt look quite right as though it might be shorting/arcing.

Yes 11/12 on both plugs are bridged. Looks like it is supposed to be there.

[tom66]

Re: Magnavox 42MF521D/37B

Where do i check that? DC?

Here are pics of one of the inverters.

DC 200V range. Test the red and black wires. It might be easier to test it at the inverter plug.

[junktv]

Re: Magnavox 42MF521D/37B

They were all bouncing from 15-23v except the out side red on wire on the left inverter. It was dead.

[tom66]

Re: Magnavox 42MF521D/37B

They were all bouncing from 15-23v except the out side red on wire on the left inverter.

This indicates a bad startup cap usually - on the primary, a small cap 10uF to 47uF.

[selldoor]

Re: Magnavox 42MF521D/37B

No didnt mean that - see attachments I meant the red circled bit in reflow2
In reflow I have marked in red something which looks a bit burnt - is it just the pic.? I have also ringed joints in pink on both that could probably do with
re touching but again it could just be the pic.

EDIT

If the back light doesnt come on at all have you tested the white block fuse on the inverter board.

[junktv]

Re: Magnavox 42MF521D/37B

That is flux that was on there and the pic. Some joints did have a bit too much solder and those pics are from before i capped it.

The fuse was the first thing i checked.

[junktv]

Re: Magnavox 42MF521D/37B

Following a test that Plainbill suggested in another thread on one of these i came up with a low voltage and fluctuating readings.

https://www.badcaps.net/forum/showpo...2&postcount=13

DC1 19-23v
DC2 20v

In the 2nd pic it shows the voltage for the inverters. Should i be getting any reading on the middle 2 pins?

I'm not sure what i should be getting on the pinout for the logic board or what is what. The wires alternate red/white/red/white etc so I didn't poke around there.

[selldoor]

Re: Magnavox 42MF521D/37B

Did you miss Tom's post where he said it could be the startup cap?

[junktv]

Re: Magnavox 42MF521D/37B

Woops


I'm guessing it would be near the ic chip and the big cap. There is a 6.8uf and a 100 uf and i'm not sure which it might be. I've actually been trying to scrounge up some from junk i have laying around to test but all i've come up with is new 2.2uf fc's i bought extra of.