Magnavox 42MF531D/37

[Fud]

Couple of years ago with help from you guys i got this tv fixed with a few bucks in caps that were blown and visually it was obvious.

This time after all this time and leaving it on constanty i shut it off for a while came home and tried to switch it on and the green light light would not come on even at all like it wasn't even plugged in, black sreen no sound etc.So i took it apart and started looking with a magnifying glass and couldn't really see anything cept what looked sort of burnt that i circlcled on the bottom of the board near the middle. So i'm going to check the rectifyer i think it's called but don't know if i have it labed - and + right and don't know how many volts it should read in DC

On the top are the four caps i replaced a couple years ago from Digikey and worked perfect and a higher voltage. The fuse has about 1 ohm about the same when i just touch the leads. the part circled in blue i can't tell where to check it on the bottom or what the reading should be when unplugged from the power i think thats where it sort of looks smudged on the bottom.

At first I was going to get a new board and they are selling for $180...forget that.

I was going by a post from a year ago with the same marks i put in but got confused by the working since i'm no expert.

Attached is a pic of my meter and hope that is good enough for a kind of cheap one.I'll desolder the aligator clips on it.

Any help would be appreciated or is taking the board to a tv shop and have them test it be better?

Thanks

[Dgtech]

Re: Magnavox 42MF531D/37

This time the repair isnt as front and center as before. First , I'd check the power coming off of this board on the top left connector. If you dont have power there, I'd check to see if you have power on both sides of the fuse.

[Fud]

Re: Magnavox 42MF531D/37

This time the repair isnt as front and center as before. First , I'd check the power coming off of this board on the top left connector. If you dont have power there, I'd check to see if you have power on both sides of the fuse.

I'm not sure where to check at the connector, there are 22 pins on the bottom of the board. The top left according to the pic right?

[Dgtech]

Re: Magnavox 42MF531D/37

Check the power from ground to both sides of the fuse.

Most likely, the component circled in blue is the pulse width modulator (PWM). These are known to go bad as well. First though, you'd have to find out if the proper power was going to it in order for it to work properly. Take readings of ground to each pin on this chip and record what you get.

When you get a chance, post the info of that chip. There's writing on the top of it.

[Fud]

Re: Magnavox 42MF531D/37

I don't see any writing on the top of it it's just black except beside it which is 7061, the part i'm confused about is when you say a lead to ground like as in the chassis when it's plugged in? I may be in over my head here.

[Dgtech]

Re: Magnavox 42MF531D/37

I was going to use that part location number to look up that part however I can't seem to locate a service manual for your set. The actual number would be located on the top of the chip (the visual side). It is very small print and it's not always white. You may need a magnifying glass to find this.

Sometimes I get ahead of myself and I talk technician talk. I assumed that you knew how to use a volt/ohm meter. Getting the info I asked for on the chip would let me know which pin to check for the proper voltage. This further would let us know how far the voltage is getting in this supply. If you say there is no light at all from the front LED (red or amber or whatever) this would mean that you have no stanby power from your supply.

In trying to find the problem, I try to divide the board into sections. Most of these switch mode power supplies are very similar in nature. I take the following as a very basic method of troubleshooting the power supply board. If you dont have voltage at stage C (regulators to the output connector), check stage B (midpoint fuse or PWM chip). If you dont have it there, check stage A (input fuse to main large capacitor).

Doing this, a person would have to know how to check voltages safely and know what voltages to check for (AC vs DC) at different stages. If this is for you but you don't know how to use the meter, do a little research on youtube about this.

If you still think it's over your head, check online board suppliers for this board. They will charge you an arm, a leg, and a partial toe knuckle.

[Dgtech]

Re: Magnavox 42MF531D/37

Well I found it in a different manual for a different set that uses the same power supply board. This info comes from the service manual of the 37mf321d TV.

The part 7061 corresponds to : IC TEA1507P/N1

By the datasheet below (see attachment) , pin #1 should be VCC - 20VDC.

[retiredcaps]

Re: Magnavox 42MF531D/37

Couple of years ago with help from you guys i got this tv fixed with a few bucks in caps that were blown and visually it was obvious.

On the top are the four caps i replaced a couple years ago from Digikey and worked perfect and a higher voltage.

There is a good chance that the caps that you did not replace are possibly bad. The little caps play an important part and don't often bloat/bulge when they go bad. Of the 5 little caps, I see one is Capxon, a known poor quality brand cap.

Capacitors (C designation on the PCB board) die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

[Dgtech]

Re: Magnavox 42MF531D/37

Retiredcaps is up this late??? I'm going to bed. LOL

[Fud]

Re: Magnavox 42MF531D/37

Dgtech you were right, i couldn't see it at all with a magifying glass and overhead light until i shone a small flashlight across it then finally it was visible.
The part is a philips
TEA 1507p
6c0e801
Hn 6191.

And yes i didn't notice that one green capxon left on there because it didn't blow it's stack. But from what i heard about them they are not to be trusted in anyway ever.
Thanks for pointing that out retiredcaps. An ESR tester i kind of doubt radioshack has them but will check...every time i go in there they have nothing i need.

So that is a hint that the light switch has no light in the least points to a cap?

[retiredcaps]

Re: Magnavox 42MF531D/37

Thanks for pointing that out retiredcaps. An ESR tester i kind of doubt radioshack has them but will check...every time i go in there they have nothing i need.

If you plan to do more electronic repairs in the future, an ESR tester might be a good investment. If you are doing a "one time" repair, changing out 5 caps is way CHEAPER than buying an ESR tester.

So that is a hint that the light switch has no light in the least points to a cap?

In large TVs, there are typically 2 power supplies. One provides 5V standby. If that isn't working, the logic/main board will never turn on the TV.

There could a number of reasons why power LED is not lit. Dgtech's posts #6 and #7 are good starting points. At minimum, you will need a multimeter to measure the voltages. RadioShack does sell multimeters if need one.

[Fud]

Does this look suspect?

Found this after spotting it with a magnifying glass on the same board as above. I don't know if they are burn marks or just dirt and crud. I cropped the photo to show where it is as compared to the full photo.

[PlainBill]

Re: Does this look suspect?

Found this after spotting it with a magnifying glass on the same board as above. I don't know if they are burn marks or just dirt and crud. I cropped the photo to show where it is as compared to the full photo.

That looks like baked on flux.

PlainBill

[Fud]

Re: Magnavox 42MF531D/37

I looked up an old post https://www.badcaps.net/forum/showthread.php?t=11962 PlainBill and tested the two points the top right and the bottom middle of the same board and both parts showed up as 166 volts dc so i don't know if that id correct or not.So just rip out the old capxons and start there first? I'm no electronics guru by any means but sort of know what to do once figured out where the problem is. So far as far as i can tell the two transformers are working from that reading? I'm kind of lost when there are no specs online for it at all that i can find,

So the fuse is ok as well and now i'd reather not buy a new psu for 180 bucks around there what they are asking, well who would if it's just on tiny part that only costs a buck to replace right.

[PlainBill]

Re: Magnavox 42MF531D/37

I looked up an old post https://www.badcaps.net/forum/showthread.php?t=11962 PlainBill and tested the two points the top right and the bottom middle of the same board and both parts showed up as 166 volts dc so i don't know if that id correct or not.So just rip out the old capxons and start there first? I'm no electronics guru by any means but sort of know what to do once figured out where the problem is. So far as far as i can tell the two transformers are working from that reading? I'm kind of lost when there are no specs online for it at all that i can find,

So the fuse is ok as well and now i'd reather not buy a new psu for 180 bucks around there what they are asking, well who would if it's just on tiny part that only costs a buck to replace right.

Let's work this problem systematically. Randomly replacing parts is one way to fix something, but it's a very poor one.

166 volts is correct if your mains voltage is 120 VAC, typical in the USA and Canada.

On the picture of the top you had circled the SMPS controller in blue. On the picture of the bottom that IC is labeled 7061. You also labeled the mains filter cap. With power plugged in, measure the voltage between the - pin of the mains filter cap (2062) and the 8 pins of 7061. Report the readings, and the part number of 7061.

PlainBill

[Fud]

Re: Magnavox 42MF531D/37

Hi PlainBill sorry for the late reply, death in the family had me busy.

So i got the measurements for 7061 and had to have my wife read the meter because i didn't trust myself doing both at once with such tiny pins. I have them labeled in the pic in which order they were measured with the meter a 200v

1 165
2 -001
3 -001
4 -001
5 -013
6 -000
7 002
8 -000

I did them twice just to make sure and didn't turn down from 200v after measuring 1

The part num for 7061 is

The part is a philips
TEA 1507p
6c0e801
Hn 6191.

I don't know much about it but that much difference in voltage doesn't seem right.

[Dgtech]

Re: Magnavox 42MF531D/37

Ok, that's a little troubling. OK a lot troubling. From the datasheet attached above, pin 1 is VCC and max voltage intended for this for correct operation is 20VDC. Either something is really wrong with the board or maybe an error in measuring it. Pin 2 is Ground for this chip. When taking your measurement, use this ground (pin 2) - black lead. Red lead of meter to Pin 1 (VCC). It will be hard to get both on if you're not used to it.

If it really did have 165VDC on the chip that's supposed to have on 20VDC, it would have smoked.

[PlainBill]

Re: Magnavox 42MF531D/37

Hi PlainBill sorry for the late reply, death in the family had me busy.

So i got the measurements for 7061 and had to have my wife read the meter because i didn't trust myself doing both at once with such tiny pins. I have them labeled in the pic in which order they were measured with the meter a 200v

1 165
2 -001
3 -001
4 -001
5 -013
6 -000
7 002
8 -000

I did them twice just to make sure and didn't turn down from 200v after measuring 1

The part num for 7061 is

The part is a philips
TEA 1507p
6c0e801
Hn 6191.

I don't know much about it but that much difference in voltage doesn't seem right.

There are a number of problems; I'm a little surprised Dgtech didn't notice you totally missed the fact that the pin numbers are on the circuit board and they don't match what you assigned!!!

Next, even correcting the pinout, the readings don't make any sense, so let's start over. I've attached some information on the IC. The first is the schematic of a typical application, the second is the pinout. Measure the voltages again, but this time use pin 2 as ground (the real pin 2, not the one you used the first time).

For what it's worth, SMPS controllers that reduce the rectified mains voltage internally like this one does tend to have a high failure rate. They are available on eBay at somewhat reasonable prices, but don't order one yet.

PlainBill

[Fud]

Re: Magnavox 42MF531D/37

Aha no wonder I didn't see the spec sheet until a few hours ago. I had the board upside down so what i marked as 1 is actually pin 8 the drain which says max 250v which is the one that read 165v . Sorry for the confusion and didn't even see the tiny numbers on it so in my pic i marked them then a zig over to the left then across instead of following a horseshoe.

As in

5678
1234

How embarrassing. Lets see if i can straighten this out

8 165
7 -001
6 -001
5 -001
1 -013
2 -000
3 002
4 -000

As you can see i counted in a zig zag instead of around...doh.

[PlainBill]

Re: Magnavox 42MF531D/37

Aha no wonder I didn't see the spec sheet until a few hours ago. I had the board upside down so what i marked as 1 is actually pin 8 the drain which says max 250v which is the one that read 165v . Sorry for the confusion and didn't even see the tiny numbers on it so in my pic i marked them then a zig over to the left then across instead of following a horseshoe.

As in

5678
1234

How embarrassing. Lets see if i can straighten this out

8 165
7 -001
6 -001
5 -001
1 -013
2 -000
3 002
4 -000

As you can see i counted in a zig zag instead of around...doh.

Did you redo the measurements using pin 2 as ground, or did you simply reorder the readings? I ask this because -13 volts on pin 1 (Vcc) is very unusual.

PlainBill