Sanyo FVF5044 No Power. Voltage Drop on 2 pins


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Sanyo FVF5044 No Power. Voltage Drop on 2 pins

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JeffAvery
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Oct 21, 2017, 4:25 PM

Post #1 of 7 (1788 views)
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Sanyo FVF5044 No Power. Voltage Drop on 2 pins	Can't Post

Hello,

Thanks in advance for any assist on this. This TV was given to my parents and they asked if I could fix it. I am no electronics engineer by any means, but I had some vocational classes in high school (mid 80s ha, ha).

The symptoms are no power at all, I don't see any reaction when plugging in and powering on. I have no details on the history, I don't know if it was a gradual problem or sudden.

The TV is a Sanyo Model FVF5044 LED 50" (picture below of model)

The power supply checked out fine. I shorted the standby and power on/off pins and have the correct voltage on every pin (they are labeled on the back of the power supply). Figuring the power supply was fine after this, I mounted it back in, and started to check the main board. When I started checking voltages there, two pins marked 24v were only measuring 12 volts (pictures below)

I started to second guess if I'd measured properly, so I pulled the power supply again, and verified pins from the power supply were in fact measuring 24 volts. So, I mounted the board on to the TV again, didn't plug anything in, and the voltage dropped back to 12 volts. I don't have enough experience to know if this can be normal or not. Everything else on the power supply looks fine as far as that tells anyway. Physically, no visible problems. Once the power supply is grounded to the TV (bolted back in place) the voltage measures 12 volts. Take it off, the voltage measures 24 volts.

TV Model Information:
https://jeffavery.com/tv/model.jpg

Where the power supply pins connect to the Main Board Back:
https://jeffavery.com/tv/MainBordBack.JPG

Where the power supply pins connect to the main board front:
https://jeffavery.com/tv/MainBoard2.JPG

Full picture of the main board front:
https://jeffavery.com/tv/MainBoard.JPG

Where the power supply pins come from the power supply to the main board (back of power supply):
https://jeffavery.com/tv/PowerSupply.jpg

Where the power supply pins come from the power supply to the main board (front of power supply):
https://jeffavery.com/tv/PowerSupply3.jpg

Power supply model:
https://jeffavery.com/tv/PowerSupplyModel.JPG

Full picture of the power supply front:
https://jeffavery.com/tv/PowerSupply2.jpg

jts1957
Veteran

Oct 21, 2017, 7:01 PM

Post #2 of 7 (1781 views)
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Re: [JeffAvery] Sanyo FVF5044 No Power. Voltage Drop on 2 pins [In reply to]	Can't Post

Does the 12V & 5V supplies act the same? Are you using chassis/frame/panel as the reference for the black meter lead?
Try using the gnd pins of the plug that has the 24V.

How does ON/OFF (PWON) behave?

-------------------------
Location: Far, Far Away

JeffAvery
New User

Oct 21, 2017, 8:41 PM

Post #3 of 7 (1776 views)
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Re: [jts1957] Sanyo FVF5044 No Power. Voltage Drop on 2 pins [In reply to]	Can't Post

Hi jts1957,

Thank you for the quick reply! The other voltages (12, 5 and standby) all supply the same voltage from the power supply to the main board. So, no difference in voltages in them, just the two 24v supplies.

For ground I was using the gnd on the boards themselves, I just tried again with the chassis, just to do it another way, but the results were the same. So ground pins and chassis for ground, the voltages drop on those two +24v pins from 24v to 11.983v (pretty consistent too, right at 11.98 every time)

This is the first TV I've worked on, so I'm not 100% sure what you mean by the on/off pwon behavior.

For the SB (stand by) and ON/Off pins, I short them to get the remaining pins to supply voltage for the test. The stand by (5vsb) is at 5v normally when the board is energized, and at the main board it's 5v. Not sure if that answers what you're looking for? Thanks again for the assist.

Jeff

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jts1957
Veteran

Oct 21, 2017, 9:03 PM

Post #4 of 7 (1774 views)
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Re: [JeffAvery] Sanyo FVF5044 No Power. Voltage Drop on 2 pins [In reply to]	Can't Post

A particular plug has 4 pins: 24V/24V/GND/GND- Have you tried measuring across plug?
You are jumpering directly. You are using a 1K or so resistor?

-------------------------
Location: Far, Far Away

JeffAvery
New User

Oct 21, 2017, 9:32 PM

Post #5 of 7 (1772 views)
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Re: [jts1957] Sanyo FVF5044 No Power. Voltage Drop on 2 pins [In reply to]	Can't Post

Hello,

I'm not sure what that measurement would be exactly, 'across the plug'. If I measure from the +24 to the gnd on the same plug, it's putting out 24v on both pins on either ground. Is that what you mean?

I'm not using any resistors in any of my measurements, should I be?

I'm just shorting the stand by (sb) and on/off pins. Once I do that, I get voltages on all pins. Without doing that, I only get voltage on stand by, the rest are no voltage. I THINK that's the way it's supposed to be?

Other than that, I'm not sure what measuring across the plug would be, sorry for the noob :) Thanks again!
Jeff

jts1957
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Oct 21, 2017, 10:13 PM

Post #6 of 7 (1769 views)
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Re: [JeffAvery] Sanyo FVF5044 No Power. Voltage Drop on 2 pins [In reply to]	Can't Post

I'm saying that sometimes they will use a supply that has an isolated ground from the rest of the unit.

Shorting 5VSB to whatever, you should use a resistor for isolation.

-------------------------
Location: Far, Far Away

JeffAvery
New User

Oct 22, 2017, 5:58 PM

Post #7 of 7 (1764 views)
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Re: [jts1957] Sanyo FVF5044 No Power. Voltage Drop on 2 pins [In reply to]	Can't Post

Hi again,

Sorry for the delay. I'm going to close this post, due to user error. I'm too embarrassed to say what it was, but after I got off work last night I wanted to do a quick video to show you all I was doing...well, that's when the realization of user error came in. Thank you very much for all the assistance on this, it was helpful!
Jeff

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