Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

[Joesev414]

Hello everyone,

Before getting to the problem, I am not an electrical engineer by any means but I really want to learn component level testing/trouble shooting and I do my best to pick things up quickly, that being said...

I have a Magnavox 50ME314V/F7 (the Model of the boards are "BA4GU5G0201 2". The power board beeps when it is plugged in and when the CPU board ribbon cable is plugged in.

I have replaced the 2 components with the red stars in the attached photo "PB TOP - Full". But it still beeps when powered and connected to the CPU board.

I am not sure which diode is emitting the beeping sound (I assume the beep happens when a diode gets stuck open or there is a short). I also can not find any schematic or service manual for this model tv. I do have a DMM and would be happy to post any test results that you guys think would be helpful to help me diagnose this issue.

I am attaching photos of the Power board (PB) and the CPU Board (CPU).

Thank you all for any help or insights you can provide, I really appreciate the help and the ability to learn something I have been interested in for a while.

[dick_barton]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

A good starting point will be that you have quite a number of links with names on the power supply board. Eg AMP+13, P-ON_H2, P-ON_21, Protect3, OVP3, etc.
Can you list them all and give the voltage read at each point.

[dick_barton]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

Your power supply looks similar to that shown on page 40 of the attached pdf. Compare the schematic again the part numbers on the board and if they match up then the circuit does give expected voltages.

[dick_barton]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

Why did you replace the two components. What did you find wrong with them?

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

Why did you replace the two components. What did you find wrong with them?

I will work on getting those voltage readings a little later today. I replaced those two components because the capacitor's top was domed (and having dealt with blown capacitors in the past I assumed it blew) and I replaced the mosfet because when I tested it with my DMM it failed. (I used a simple go/no go test to test the mosfet. I know it's not a 100% accurate way to test a mosfet)

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

A good starting point will be that you have quite a number of links with names on the power supply board. Eg AMP+13, P-ON_H2, P-ON_21, Protect3, OVP3, etc.
Can you list them all and give the voltage read at each point.

Okay I have a stupid question, how do I test the links? Can you please explain to me how to go about testing them? (Where do I connect the test leads? Does the board need to have power supplied to it when testing the links? Etc.)

Sorry for my ignorance and what I assume is an extremely basic question, and thank you for your help!

[dick_barton]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

Turn the set on and with your meter set to DC volts place the black meter probe on chassis use your red meter probe to measure the voltages on the links. That is push you red probe onto the wire link to make the measurement.

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

Turn the set on and with your meter set to DC volts place the black meter probe on chassis use your red meter probe to measure the voltages on the links. That is push you red probe onto the wire link to make the measurement.

Awesome, thank you for explaining how to take those readings! I really appreciate it! 🙂 I will take and post those readings ASAP.

[kc8adu]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

probably shorted secondary diodes or protection zener.
very common.

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

A good starting point will be that you have quite a number of links with names on the power supply board. Eg AMP+13, P-ON_H2, P-ON_21, Protect3, OVP3, etc.
Can you list them all and give the voltage read at each point.

Sorry it took so long, but I took DCV measurements of each jumper.

Attached is a pdf of the spreadsheet I made that lists the jumper's ID, the jumper's Label, my DMM's reading in DC V, and the ground jumper I used when testing each jumper (I connected the board to power and connected my black test lead to the ground jumper labeled in the spreadsheet and the red test lead to the labeled jumper)

Please let me know if I did this wrong or tested the jumper using the wrong ground jumper. Also let me know if there is any other information that can be useful in determining which of these components has gone bad. Thank you again for all your guys help!!

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

probably shorted secondary diodes or protection zener.
very common.

Which components are those??

[dick_barton]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

It looks as though the initial standby voltage All+3.3V is missing and this needs to be resolved first. At this point a schematic would help.

If you disconnect the power supply from the main board does the ALL+3.3V read correctly.

Other threads talk about a short circuit capacitor on the mainboard C3637 which would be worth checking.

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

It looks as though the initial standby voltage All+3.3V is missing and this needs to be resolved first. At this point a schematic would help.

If you disconnect the power supply from the main board does the ALL+3.3V read correctly.

Other threads talk about a short circuit capacitor on the mainboard C3637 which would be worth checking.

YES, a schematic for this exact model power board and main board would be AMAZING!!and if anyone can find one I would be eternally grateful!!

So I am still trying to figure out all the components to test in the All +3.3V circuit. The PDF you attached earlier in the thread, has a Power board schematic that is close, but not the exact model and therefore in the trouble shooting section when it is showing all the components to test in that ALL +3.3V circuit, there are some components that are not on the board. That being said, the with the components I could find on this power board (some of the diodes listed in the trouble shooting section of that PDF, it says to test their voltage with power being supplied to the board. How do I test the voltage being sent to the diode properly so I don't short out/overload the diode?)

Also all the measurements I took were taken with the Power Board, powered and the main board NOT connected. Should I have taken all the readings WITH the main board connected?

[dick_barton]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

I believe the ALL3.3V supply is the standby supply so if it was not present with the power supply disconnected from the mainboard then that needs to be fixed first.

That being said, the with the components I could find on this power board (some of the diodes listed in the trouble shooting section of that PDF, it says to test their voltage with power being supplied to the board. How do I test the voltage being sent to the diode properly so I don't short out/overload the diode?)

If the diode is on the secondary side (COLD) of the power supply then use your red meter probe to test the diode with black meter probe on chassis.
If the diode is on the primary (HOT ie Live)side of the power supply then the black lead connect to the negative "-" leg of the large 400V capacitor (C605 in the schematic) and again use the red probe to test the diode voltage.

[lookimback]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

I had a the same problem a while back, same model. PSU was chirping. It turned out to be a short on the main board pulling the supply low. If you can figure out what pins are standby, PS_on, and BL_on, you can force the PSU and backlights on with the main board disconnected.

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

I had a the same problem a while back, same model. PSU was chirping. It turned out to be a short on the main board pulling the supply low. If you can figure out what pins are standby, PS_on, and BL_on, you can force the PSU and backlights on with the main board disconnected.

Are you referring to which pins on the ribbon cable connector that connects the PSU to the Main Board? and if that is the case, how would I force the the PSU and backlights on with the main board disconnected if I can find the related pins.

Also, where was the short on the main board? do you remember which component was causing the short?

Thank you

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

Other threads talk about a short circuit capacitor on the mainboard C3637 which would be worth checking.

I tested C3637 on the main board, with my DMM on the diode test settings and got a measurement of 245mV. (that was measured with no power connected to the Power Board)

With the power board connected and my DMM on DCV, the schematics you have earlier in this thread show C3637 @ 4.7V and I measured 1.75 (Fluctuating from 1.79 - 1.69) - I had the black test lead attached to one of the bolt holes that mount to the chassis and the red test lead on the same side it was on when I tested the component with no power. So it seems as though there is not enough power coming through to C3637 (Based on my simple understanding of electrical engineering.
Could that mean the capacitor (C3637) is bad or would it mean that a component upstream of C3637 is what went bad?

[lookimback]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

Are you referring to which pins on the ribbon cable connector that connects the PSU to the Main Board? and if that is the case, how would I force the the PSU and backlights on with the main board disconnected if I can find the related pins.

Also, where was the short on the main board? do you remember which component was causing the short?

Thank you

I wasn't able to find the short. I just replaced the main board. Unfortunately, I don't know what pins are what. Check them all for voltage, and the one that's 5v will be standby. Not sure how to identify PS_on and BL_on.

[budm]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

I tested C3637 on the main board, with my DMM on the diode test settings and got a measurement of 245mV. (that was measured with no power connected to the Power Board)

With the power board connected and my DMM on DCV, the schematics you have earlier in this thread show C3637 @ 4.7V and I measured 1.75 (Fluctuating from 1.79 - 1.69) - I had the black test lead attached to one of the bolt holes that mount to the chassis and the red test lead on the same side it was on when I tested the component with no power. So it seems as though there is not enough power coming through to C3637 (Based on my simple understanding of electrical engineering.
Could that mean the capacitor (C3637) is bad or would it mean that a component upstream of C3637 is what went bad?

How about in Ohm mode? measure in both directions by swapping the test probes. You use Ohm mode so you can see what the resistance your are seeing.
How about C3214 on the main board? See if it has one on your main board.
BTW, did you see this thread?
https://www.badcaps.net/forum/showth...ighlight=C3637

[Joesev414]

Re: Please Help! My Magnavox 50ME314V/F7 Beeping From Power Board

How about in Ohm mode? measure in both directions by swapping the test probes. You use Ohm mode so you can see what the resistance your are seeing.
How about C3214 on the main board? See if it has one on your main board.
BTW, did you see this thread?
https://www.badcaps.net/forum/showth...ighlight=C3637

So I tested C3214 in Ohm mode and measured in both directions, it measured 24 Ohm in both directions

I also tested C3637 in Ohm Mode and with the black lead on the left hand side, I got a reading of 1716 Ohm and when I tried to read it the other way, it went all the way up until the DMM read 1

I will also look at that other thread.