Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/check

[LeviathanEnt]

Greetings Everyone, Thanks so much for the wonderful insight I've found here so far. I've found quite a bit of information on this topic, however mostly centered around replacement caps and diodes.

Problem: For years this TV has had a problem powering up. Sometimes the power light would go green but no picture, requiring me to plug and unplug it till it worked. More recently I started hearing a whining noise (which later turned into chirping) when it would power up. Then a new problem started, turning on for a short time and then turning off after a few secs/mins. Upon powering back on the power light would flash repeatedly very fast, then either power off or power on. Now after a couple weeks of that, it simply went off. Leaving me with only the chirping noise. And no reaction from the power button.

I have read through the following 3 posts I found here:

https://www.badcaps.net/forum/showthread.php?t=11962
https://www.badcaps.net/forum/showthread.php?t=17378
https://www.badcaps.net/forum/showthread.php?t=30171

And the service manual:
http://www.tgohome.com/ServiceManual...&Search=Submit

I have replaced the following caps:
C921,952,953,955,956

I have tested the following diodes successfully with the following readings:
ZD901:0.544/OL
ZD902:0.540/OL
D925:0.481/OL
D907:0.498/OL
D912:Reads 0 in circuit due to resistors as stated in threads above, I tested it out of circuit previously and it gave a reading similar to those above although I don't remember the exact reading.

Still get chirping when connecting power to the power supply. (outside of LCD)
Voltage across C907: 167V

Note: I can read schematic symbols and have a general understanding of components. I have a DMM and a regulated soldering station and can use it fairly well.

Thanks again for all the help I have already found here and thanks in advance for what may come.

[mmartell]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

Did you replace caps with high quality ones or from Radioshack ?

[LeviathanEnt]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

Indeed the 3 - 1000 uF 35v caps came from the Shack (all that's open today). The others came out of my parts box. As for the others being higher quality, not sure. I did upgrade the 2200uF 15v to a 35v, otherwise nothing. And I understand you probably meant a better brand not a higher voltage.

For what it's worth, C955 was the only cap that seemed to have any visual abnormality, that is a bit of a peaked top.

Thanks for the quick response.

[tom66]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

I'm afraid that the capacitors you just installed could well have been worse than the originals, even if one were failed! General purpose "rat shack" capacitors are NOT suitable for switchmode PSU.

[LeviathanEnt]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

Fair enough. I can put an order in with Digikey or whomever for higher quality parts. Just figured I'd throw some parts at it over the weekend. Most of the caps came out of other salvaged known good power supplies and I happened to be passing the Shack, so I grabbed the 3 I didn't have.

Though it seems most of the people discussing these issues had some obvious visible problems; burns, leaking/puffy caps. And several people had the chirping continue after replacing these items, some of which were solved by diodes, which seem to be good.

So perhaps there is something else to look at? A few more voltages to verify or something? I'm not too good at deciphering the schematics as a whole, so I really don't know where to test for 12 and 24v or whatever it should be.

PS: Is the Radio Shack stuff "not suitable for a switchmode PSU" because of the tolerance or the ESR? Or just the build quality or all of the above?

[LeviathanEnt]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

So I guess the consensus would be to get new stuff from digikey or otherwise. I don't think I actually saw a consistent list of components to replace, Certainly, the caps I mentioned but some people talk about replacing all the caps on the board, some even beyond just the "can" style (electrolytic?). Not to mention the Mosfet and diodes. I don't mind buying new stuff, I just would like to get enough to hopefully be in the clear and get the right parts. Also when ordering, do any parts that match the specs on the components work or do I need to be more specific than capacitance and voltage?

Or I could buy a kit like this from eBay, but he mentions less parts for the chirp:

Repair kit #1 contain: 6pcs Nichicon high quality capacitors and 3 zener Diodes. fix chirping sound.
Repair kit will come with Locations of each components. PC BOARD # 715T2454-1 and 2

Symptoms; DEAD POWER SUPPLY. SOME OF YOU ALREADY REPLACE CAPACITORS BUT HAS Chirping sound. you need Kit #1.

Symptoms; DEAD POWER SUPPLY. If F901 fuse open and Q901 bad. you need repair kit #2.

Repair kit #2 contain:
1; 7 capacitors
2; 3 zener Diodes
3; 1 mosfet
4; 1 ic
5; 1 resistor
6; 1 fuse 6.3 amp.

http://www.ebay.com/itm/715T2484-2-P.../200948803931?

Or here's a complete refurbished power supply for about $100, though this is a 715T2484-1 and I have a 715T2484-4 (looks the same, different revision, prolly just as bad?):

http://www.ebay.com/itm/PHILIPS-37PF...item19e7864249

Thanks again for the quick responses.

[multimeter]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

sounds like bad startup cap to me with the chirping?,id replace that one,and output caps with panasonic fm series.and see how you go from there

[tvrepairguy]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

Its the ZD906...its the chirping sound. Spray and air can upside down on it. It will change the temp of the diode and the chirping will go up and down. This tells you that the diode is the one thats bad....spray rhe others and nothing happens....good. just fixed mine today and its up and running again ....took me a year to figure it out.

[tvrepairguy]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

I believe the part i used to replace th diode is NTE4892

[tvrepairguy]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

Start spraying one by one the diodes labled ZD followed by 3 numbers. The chirping will change when sprayed with the co2 from the aircan and will reveal the problem diode

[tvrepairguy]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

nte4982.....sorry

[orgwood]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

nte4982.....sorry

I have fixed 2 42" flat screen TVs so far - one LCD & one Plasma and trying to work on my son's version of this set Philips. I bought a cap kit with 2 zener diodes but the chirping continues...it's faster with the boards/cables unplugged. The area to the right of the big center transformer looks discolored especially around ZD908. I can't find a link to the schematic for this PS so I'm in the dark about values, etc. Any help would be appreciated.

Dave

[orgwood]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

I found the schematic and with budm and his help I was able to buy replacements for the FETs and the small IC and get this working. If anyone needs any help with theirs, please send me a message or post here and I think we can work you through your problem.

[orgwood]

Re: Magnavox 37" LCD 37MF337B/37 PS: 715T2484-4 Chirping after cap/diode replace/chec

https://www.badcaps.net/forum/showth...t=17379&page=3
Here's the link to the Philips SMPS thread since they basically are the same.