magnavox 37mf321d/37 burned power supply

[whiz62]

Got this for TV for free and it is pretty rough so don't want to spend a lot on it. Looked up on ebay and shopjimmy prices for power supply are crazy.

looked up manual on elektro tanya and can't find diode location 6079 or location 3045 and it was burned so I have no idea what type smd it was. I looked on shopjimmy and blew up the pic to see if I could see markings on smd but at 3045 it is not readable. would like to scab on something to see if I can get it going.

Any help is greatly appreciated.

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

Here is picture of problem

[budm]

Re: magnavox 37mf321d/37 burned power supply

How about the pictures of the whole board? both sides of the board.
Also the pictures of the whole backside of the TV.

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

More pics. Have been unable to link to this site till this morning.

[lookimback]

Re: magnavox 37mf321d/37 burned power supply

Good closeups of the bottom are going to be necessary. Split it into 2 or 3 pics if you have to. I recall having one of these with a bad diode on the bottom, one of the glass ones. I didn't have burns though.

[budm]

Re: magnavox 37mf321d/37 burned power supply

Power supply SCH.

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

Thanks for the schematic Budm. It is the same one I found i think. It does not have components 6079 or 3045 in the index or the schematic that I can find. Am I missing something?

Lookimback, here are some other pics but probably aren't good enough.

Am also replacing bloated cap at 2074. symptoms were green led on front panel blinking all the time when plugged in.

[lookimback]

Re: magnavox 37mf321d/37 burned power supply

I was able to find a pic of the back of this board which isn't burned. maybe that will help.

[lookimback]

Re: magnavox 37mf321d/37 burned power supply

You have an entire diode (6079) which has burned off of this. Something shorted really bad. I can't tell if there was something at 3045 on the bottom.

[lookimback]

Re: magnavox 37mf321d/37 burned power supply

You're board is a revision so it's different from your schematic. I found the parts in the service manual. You can download the service manual here.

[budm]

Re: magnavox 37mf321d/37 burned power supply

That is the same manual that I extracted the power supply circuit from, so we need an update diagram for the OP power supply.
The pictures are not clear enough for me read the printing on the tag of the power supply.
SJ has good pictures of the board:
http://www.shopjimmy.com/philips-313...er-supply.htm#
It looks to be the same as your, but need the verification of what is printed on the barcode sticker.

I can see that the voltage output pin 1 and 2 of connector 9061 connector is fed to the Anode of D6079, the Cathode of D6079 is connected to the resistor R3045 (more likely to be low Ohms resistor), the other end of R3045 is connected to pin 3 of connector 9061.
So you need to check the resistance between pin 3 of connector 9061 against PIN 6 (6~8 are tied together) which are GND pin.

[lookimback]

Re: magnavox 37mf321d/37 burned power supply

I can make out the last 5 numbers, 68291. So it's this one. http://www.shopjimmy.com/philips-313...upply-unit.htm

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

THanks guys for all the help. Gotta go to work now. will update.

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

Thanks Budm & Lookimback. Just got home from work and good info from you two. The bar code sticker reads on top 3138 168 68291 and bottom of sticker reads p5p1170251786. Also do not get any resistance between pins 3 and 6 or 8. At least now I have somewhere to go, Thanks again!.

[budm]

Re: magnavox 37mf321d/37 burned power supply

Thanks Budm & Lookimback. Just got home from work and good info from you two. The bar code sticker reads on top 3138 168 68291 and bottom of sticker reads p5p1170251786. Also do not get any resistance between pins 3 and 6 or 8. At least now I have somewhere to go, Thanks again!.

Is that reading with all the boards connected to back to original? Something is drawing too much current through that resistor.
BTW, I look at the SCH of the power supply and see that pin 3 is the 24A (24V) output, the Diode and the resistor were added for some reason, but the circuit should work with the diode/resistor nit in place. You should check that diode also.

[lookimback]

Re: magnavox 37mf321d/37 burned power supply

I could be wrong, but the diode which is burned off the board looks to be connected to pin 1 or 2, which I think are both 16v output. 6, 7, 8, and 10 are ground. So maybe the 16v and 24v have both shorted to ground, or to each other?

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

Thanks again guys for the quick posting. This TV will have to wait till the weekend. I will plug everything back and recheck the pins asap and post findings.

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

Got home from work and checked resistance from pin three and 6 thru 8 and got 68.7K. Also looks like the blown diode is a 9.1v-500mw zener and the resistor is 2.2 ohm-5w from what I can find from internet search. Thanks.

[budm]

Re: magnavox 37mf321d/37 burned power supply

I believe the Zener and the resistor are used to clamp the 24VA power supply from going. too high, or if the +16V falls too low.
When the differential Voltage between +24A and the +16V is more than 9V, the Zener will conduct.
If everything is normal, the Zener is not on, 16V + 9V = 25V, so if 24V (the Voltage across the Zener will be only 8V (24V - 16V = 8V) goes higher than 25V the zener will be on.

[whiz62]

Re: magnavox 37mf321d/37 burned power supply

Got the zener and the resistor that were fried and have found another problem. Evidently I missed this shorted mosfet during my initial check of the board. It is a p45nf3LL which I can find nowhere except on ebay from china. Anyone know of an alternate? If not looks like I will have to wait till end of next month. Thanks.