Magnavox 42MF521D/37B

[junktv]

Re: Magnavox 42MF521D/37B

Took a break and put the rest of the caps in and it is still fluctuating.

[retiredcaps]

Re: Magnavox 42MF521D/37B

"May be I am wrong, but I see 4 bad caps (3 are grouped together, and one at the bottom right of the picture).

He replaced them in post #8 with an updated picture.

Since this board has PFC, what dc voltage do you get at the main DC filter cap when the TV is off and when TV is on?

Darn, I keep forgetting about the stupid PFC.

[budm]

Re: Magnavox 42MF521D/37B

"3 P10269-ND 100UF 25V FC
1 P11232-ND 47UF 35V FC" May be I am wrong, but I see 4 bad caps (3 are grouped together, and one at the bottom right of the picture).
Since this board has PFC, what dc voltage do you get at the main DC filter cap when the TV is off and when TV is on?

[junktv]

Re: Magnavox 42MF521D/37B

The first numbers where 20k ohm and second in diode mode.

To fill in the info on the chips they are.

6052 is a STTH8LD6FP voltage rectifier.

6076 is a STPS40H100CW schottky rectifier.

6071 is a MBRF10H100CT schottky rectifier.

7057 is a W26NM60 zener protected mosfet.

7062 is a W18NK80Z zener protected mosfet.

Forgot to label 6051 GBU8J bridge rectifier.

[retiredcaps]

Re: Magnavox 42MF521D/37B

6076
1-2 climbs & climbs to inf
1-3 0 & 000
2-3 climbs & 203
6071 same sink
1-2 climbs & climbs to inf
1-3 0 & 000
2-3 climbs & 276

1) Well nothing seems obviously shorted. I believe 6076 and 6071 pins 1-3 are supposed to be 0 and 000 if they are dual diodes.

2) If they are dual diodes, then test it like pins 1-2 like a regular diode and pins 2-3 like a regular diode. You should have 4 readings.

I could tell if they were diodes are not if they used pcb designations like D601 and D602 rather than meaningless 4 digit numbers.

3) If you have tested all the diodes and there are no shorts, then you could try replacing the other caps or try replacing the SMPS IC.

4) findchips.com shows no stock for the SMPS IC so you will have to purchase from ebay.

5) If you buy the SMPS IC from overseas, it is $4.40 total. If you buy from the USA, the cheapest one is $11.60.

6) There could be something else shorted on the board causing the fluctuation, but the most likely candidates are the diodes.

[junktv]

Re: Magnavox 42MF521D/37B

6059 is all over the place and climbing but was fine when i pulled it.
6075 755/0

Not sure if i should be using diode check so they will be the second set.
6076
1-2 climbs & climbs to inf
1-3 0 & 000
2-3 climbs & 203
6071 same sink
1-2 climbs & climbs to inf
1-3 0 & 000
2-3 climbs & 276

above 3081
7057
1-2 open & inf
1-3 open & 775
2-3 open & 482
7062 same sink
1-2 open & inf
1-3 open & 659
2-3 open & 470


I guess you mean the 2 pin deal on a heat sink labeled 6062 next to the large cap. It reads open and 443/0 with diode check.

I was testing the board on my kitchen counter not hooked to anything else when reading voltages. Btw i didn't replace the other small caps yet just the start cap/

[retiredcaps]

Re: Magnavox 42MF521D/37B

Another test to try is to disconnect all your boards and see if the startup cap voltage still fluctuates or not.

[retiredcaps]

Re: Magnavox 42MF521D/37B

Test IC above 5062 for shorts.

[retiredcaps]

Re: Magnavox 42MF521D/37B

Pins 1-2 does a short count up to about 20 @20k then shows open.

6062 near 3081 is reading 001 both ways in circuit and 520/0 out
6054 599/0
6055 606/0
6056 492/0
6066 516/0

The above all look okay.

1) Also test 6059, 6075.

2) See if 6076 and the other 3 pin IC on the same heatsink are shorted. Test pins 1-2, 1-3, and 2-3.

3) See if two ICs mounted on the heatsink above 3081 are shorted.

PS. If the photos are more clear and sharp, I could give the actual numbers.

[junktv]

Re: Magnavox 42MF521D/37B

Pins 1-2 does a short count up to about 20 @20k then shows open.

6062 near 3081 is reading 001 both ways in circuit and 520/0 out
6054 599/0
6055 606/0
6056 492/0
6066 516/0

[retiredcaps]

Re: Magnavox 42MF521D/37B

I replaced the cap and i'm getting the same readings.

That leaves 2 likely possibilites.

1) The SMPS itself is bad. What is the resistance between pin 1 and 2 on the SMPS?

2) There is something shorted on the power board causing the SMPS to fluctuate. Likely candidates for shorts might be diodes 6056, 6055, 6054, the diode above 3081, 6066, and others in that general area.

Use the diode check function to measure each. You should have two readings per diode. One should be between 0.3 and 0.8V and the other should show "out of range".

[junktv]

Re: Magnavox 42MF521D/37B

I replaced the cap and i'm getting the same readings.

[TechShui]

Re: Magnavox 42MF521D/37B

Have you checked the scaler board yet?

I've worked on Magnavox LCD TVs where BOTH the power and scaler boards were bad.

Specifically, the caps on the power board are a very common problem, and the IC that generates 12V on the scaler will sometimes blow, leaving a pinhead-sized hole on it.

[junktv]

Re: Magnavox 42MF521D/37B

Since I have to order them I figure I might aswell replace the rest while i'm at it.

3 P10269-ND 100UF 25V FC
1 P11232-ND 47UF 35V FC

There isn't an FC in 6.8uf 50v but there is a KG P936-ND and GA P14509-ND. I guess KG seems like it would be best since the GA has 5ma less ripple than the original capxon KM.
The 2.2 NP is a bi-polar with 25 ripple. It looks like digikey only has a nichicon VP UVP1H2R2MDD-ND instock with that spec or a panasonic SU P1197-ND with only a 18ma rating.

See anything wrong with using the P936-ND and UVP1H2R2MDD-ND?

Any other parts i should grab just in case while i'm at it?

[retiredcaps]

Re: Magnavox 42MF521D/37B

Both bounce from 1.4-11.

Replace the cap first as it is the easiest and retest/remeasure. Use something like Panasonic FC.

http://www.digikey.com/product-detai...0269-ND/266278

[junktv]

Re: Magnavox 42MF521D/37B

Both bounce from 1.4-11.

[retiredcaps]

Re: Magnavox 42MF521D/37B

Looks like pin 1 is VCC for a TEA1507P. So it's the 100uf 25v cap.

1) 11V DC is the required for the SMPS to start.

2) What is the DC voltage across the 100uF 25V cap?

3) What is the DC voltage of pin 1 (VCC) using pin 2 (GND) for ground?

4) Are any of the voltages fluctuating?

[junktv]

Re: Magnavox 42MF521D/37B

Looks like pin 1 is VCC for a TEA1507P. So it's the 100uf 25v cap.

Haven't said it yet but thanks to you guys taking time out of your day to help others.

[retiredcaps]

Re: Magnavox 42MF521D/37B

Find the datasheet for 7061 (likey your SMPS IC). Find which pin is VCC. See if the VCC has continuity to the positive leg of the capacitor. If yes, that is the startup cap.

OR measure the the DC voltage of SMPS IC VCC with respect to SMPC IC GND. Then measure the DC voltage across the cap that you think is the startup. Both DC voltages should be identical.

[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.