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Power Supply Trouble Shooting

 
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AFryia




Joined: 09 Mar 2006
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Location: S.E. Michigan VPH-G70Q


PostLink    Posted: Sat Oct 22, 2016 2:53 pm    Post subject: Power Supply Trouble Shooting Reply with quote


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My Samsung plasma PN64E7000FFXZA does not power up and I'm hoping it is only the PS.

First thing I want to do is check voltages but I want to confirm one thing first.

Question: I have PS_ON and StdBy pins, do I short those together to turn the power supply on; or short PS_ON to ground?

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Curt Palme
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PostLink    Posted: Sat Oct 22, 2016 3:14 pm    Post subject: Reply with quote

Not sure, but can you measure the PS ON pin in standby mode and in 'on' mode to see if it changes? All those flat screen supplies are switching power supplies, so if there's a dead short on one of the outputs, it won't fire up. Often one of the Ysus or Zsus chips shorts out, and the set won't fire up. I'd disconnect those output driver boards first via the big white plugs to see if the set will power on. The odd Samsung power supply suffers from bad caps, but most that I've had were the main filter caps, that start to smoke and ooze out electrolyte.

If nothing else, you should get the standby 5 or 12 volt supply working when the set is in standby mode. that powers the IR receiver and a bit of the CPU board, whereas the 'on' signal then tells the SMPS to switch on fully. I'd be surprised if the standby supply is dead. It could be though if the main fuse inline with the AC power has blown. that then usually indicates a shorted switching transistor on a heat sink in the power supply, which is usually easy to find.
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AFryia




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PostLink    Posted: Sat Oct 22, 2016 3:44 pm    Post subject: Reply with quote

Curt,

The set will not power up at all. When I unplug and plug back in the standby light turns on for a brief second.

I completely disconnected the PS from all other boards. The StdBy pin measures 5.3 (which is in spec). The PS_ON pin measures 4.3V. Does this mean I put this pin to ground to turn on the PS?

The cheat sheet silk screen on the board does not give a spec for PS_ON. If I assume it is on the 5.3V side it is out of spec (5.04-5.56V) no?

I assume I need to power on the board to check the VS, VA,5.3V and 15V pins.

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PostLink    Posted: Sat Oct 22, 2016 3:52 pm    Post subject: Reply with quote

Ok, so your standby supply should be working. Try shorting the PS ON pin to ground to see if anything happens, or measure that pin to see if it falls to 0 volts when you push the power button.

Usually these circuits work on the old TTL logic principle.. anything under 2.3 volts or so is considered to be a '0', anything over 3.6 volts is considered a '1'. The logic may be set up in reverse though, so that 'on' needs to see a 0, or <2.3 volts.
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AFryia




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PostLink    Posted: Sat Oct 22, 2016 5:07 pm    Post subject: Reply with quote

I plugged the main board and its daughter board in, PS_ON is virtually zero (0.15), VS_ON = 0.15V, Stnby is still 5.22V. Pushing the On button does nothing.

I have some DC power, all the 5 and 15VDC pins are in spec. I get nothing on the VS, VA pins. I have 3.11V on the VS_CON pin, not sure what that is.

The daughter board has a slow blinking LED, It only has a number, no descriptor label.

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AFryia




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PostLink    Posted: Sun Oct 23, 2016 1:53 pm    Post subject: Reply with quote

AFryia wrote:

The daughter board has a slow blinking LED, It only has a number, no descriptor label.
OK a little research and the LED is apparently the heart beat on the Logic board. Slow blink indicates a problem with the Y-sustain or Y-main. But I don't have VS or VA voltages so it still could be a power supply.

So with the Y boards disconnected (no-load) I should see VS and VA voltage but I don't. I measure VS_ON at 0.15V (pull down) same as PS_ON so I assume the VA and VA should be on.

I'm still unsure because in one of the self help videos with a bad Y board you should still hear the power on audio tone. I assumed if I have all the low voltages the main and logic boards would work and I'd get the audio tone even without VS and VA.

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AFryia




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PostLink    Posted: Sun Oct 23, 2016 10:56 pm    Post subject: Reply with quote

Alright I know more about Plasma TV than I care to.

So I was able to jump the power supply and get the low voltage, VS and VA to turn on. When I plug in the Y (sustain) board in VA (55VDC) and VS (220VDC) are pulled down to near zero.

So what are the chances of a weak power supply vs. a shorted Y board?

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jts1957




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PostLink    Posted: Mon Oct 24, 2016 1:06 am    Post subject: Reply with quote

http://elektrotanya.com/samsung_pn64d7000ffxza_fast_track_guide.pdf/download.html
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PostLink    Posted: Tue Oct 25, 2016 2:05 am    Post subject: Reply with quote

Check the large chips and transistors on the Y sus and Zsus. Chances are the 130 or 200 volts has a dead short on it, and a dead short on either board is common. you'll measure a dead short from the main voltage supply line to chassis ground. Lift the connector from the offending board, and you'll get your 200 volts on the other board just fine.
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AFryia




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PostLink    Posted: Wed Oct 26, 2016 12:51 am    Post subject: Reply with quote

Curt,

I could not measure a short on any of the VS or VA pins to ground on the Y or X board with my Fluke.

Under the Y and X boards are dense foam pads that contact the solder traces. I assume that a secondary heat sink. Is it normal to have an oily film on the board where the pad contact? I don't see any bad caps and the film seems a dielectric.

The Y board had a lot of dry white film. I though maybe thermal grease baked on but it defied gravity more is at the top of the board and there aren't any sinks in that region. Maybe factory flux, the board was never cleaned properly after manufacturing?

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PostLink    Posted: Wed Oct 26, 2016 1:14 am    Post subject: Reply with quote

That's all normal. Is there a fuse on the Y or X boards? there usually is, inline with the main supply input.
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AFryia




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PostLink    Posted: Wed Oct 26, 2016 9:23 pm    Post subject: Reply with quote

No fuse on either X or Y board, just two on the power supply and they are good.

Well I ordered a X and Y board from Sears of all places. Had the best online price surprisingly.

I hope it is only the Y and I can return the X. Wish me luck.

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