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Old 01-03-2019, 10:41 PM   #41
jjanssen7
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

I wondered about that, but it won't consistently keep the VS up right now. It's easy enough to put a load on it and report back.
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Old 01-04-2019, 12:08 PM   #42
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

It may not keep the Vs up when connected to the Y & X boards due to excessive load on either Y or X board, (its not always a dead short). But the Vs will also likely drop or be unstable without any load, There is feedback to regulate the Vs supply. also the Va circuit takes a sample of the Vs voltage to adjust the Va voltage
There can also be over and under voltage protection circuits as well as over current protection. It looks like ICQ802 monitors Vs Voltage

Last edited by R_J; 01-04-2019 at 12:24 PM..
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Old 01-04-2019, 03:39 PM   #43
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Thanks for the info. I"m certain that I have to know if my power-supply is good before I move to main board or X/Y diagnosis. I'm thinking my next best step is to isolate the ps, load the VS with 120 watts worth of light-bulbs and see what voltages it produces and how stable they are. I'll report back later.
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Old 01-05-2019, 09:18 PM   #44
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

OK, I have loaded the VS down with 140 watts of light bulbs and it's back to cycling 5 times (attempting to bring VA an VS up) and then nothing. Unloaded the board stays on with VS at 230 and VA at 52-54 (but no higher).

Looks to me like something is bad on this PS. Any idea what I should check next?
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Old 01-06-2019, 03:57 AM   #45
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Are you using 120V light bulbs? Two in series?
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Old 01-06-2019, 09:06 AM   #46
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Make sure you are using two 120 volt (60 or 100 watt) incandescent lamps in series. 230v is high but likley due to being unloaded, the power supply is rated as: Vs 205v - 215v at 2.3 amps
Va 55v - 62v at 1.2 amp

What type of lamps are you using to load the Vs (140 watts) ???

Last edited by R_J; 01-06-2019 at 09:10 AM..
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Old 01-06-2019, 10:25 AM   #47
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

I am using a 75 watt and and 65 watt bulb wired in series. They are 120 volt bulbs.
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Old 01-06-2019, 10:51 AM   #48
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

That should work, They are connected between pin 1or2 Vs and 3 GND of CN802
They should light up and you should be able to measure 205 - 215 volts across it. If not I guess the power supply can't supply the current and is shutting down.
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Old 01-06-2019, 11:03 AM   #49
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

I'll double check what current it is trying to put out, but it's momentary and with a digital tester it only goes to 50-60v and both bulbs light up before cycling again. I have an older meter tester which might show a bit more swing on the "peak" and I can try that.
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Old 01-08-2019, 02:02 PM   #50
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

So I am getting somewhere with this board, but it's an odd one. Nick's hint at repairing the traces under the cold solder joints even though they look OK was a good one, now I can get my board to power on, and with stable voltages.

However.

After leaving it on the bench overnight, when I came back in the AM to test it. It would not start, back to cycling three times and then not attempting to start VS again. After cycling it a bunch of times I started to hear what a sort of "electrolytic" boiling/bad cap as it attempted to start. Bad main caps?

I shot just a tiny bit of hot air (10 seconds?) across the four main caps and it starts right up. No "hissing" coming from the main caps. Let it cool down, no start, just cycling. Warm it up ever so little, fires right up. I have repaired the pads under the caps, so I'm quite confidant they have a good connection to things.

This seems odd though. I can't remember ever needing to replace main caps on something as new/low hours as this. Even Samyoung ones like this. I just don't believe it's the main caps even though all the tests I know point to them being weak/faulty.

So my question is this: if there were bad solder joints under some of the main caps or other components, could this have prematurely weakened them? I have no idea on the history of this TV, but it is in like new shape with minimal (obvious) cold solder issues. It came to me through our liquidation stream.

I don't have anything large enough to test a 500v 120uf cap (there are four of them). They seem to be hard to source too (thru hole, lying on their side on the board).

Nick, others, any thoughts on what I'm seeing? Is it possible cold solder joints weakened the main caps?

Last edited by jjanssen7; 01-08-2019 at 02:54 PM..
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Old 01-09-2019, 01:16 AM   #51
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Quote:
Originally Posted by Truncatedhose View Post
Thank you for your help. I followed your steps and found that the VS does not drop if the YSUS ribbon is unplugged from the main board. So I guess the YSUS is defective. And I had already checked the power supply for bad connections and found only slightly suspicious connections and resoldering them changed nothing. I will look into a replacement YSUS and/or look into your service.
but mine is different, it drops like crazy when i unplug YSus (samsung PN43D490A1DXZA)
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Old 01-11-2019, 12:35 PM   #52
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

The pictures uploaded were very dark and did not clarify the situation.
I still maintain you have a cracked joint you missed. If you could take clear, well lit pictures of the joints from the through-hole transistors and diodes screwed in the heat-sinks, I will be able to visually see if you got it or missed it. Cold side only at this point, no need to picture the hot side.

Just a quick tip for the community here as this seems to be a common misconception for testing power supply boards: Samsung plasma power supply boards do not need a load to test for VA and VS voltage. I don't care what model it is, if it is a Samsung Plasma power supply when isolating your power supply if you short your VSON to 5v and PSON to ground your VS and VA lines will come right up assuming your power supply is functional.
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Old 01-11-2019, 12:47 PM   #53
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

From post #44
Quote:
Unloaded the board stays on with VS at 230 and VA at 52-54 (but no higher).
so the power supply must be ok.
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Old 01-11-2019, 03:36 PM   #54
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

I think Nick is on to something, with his note about cracked solder joints and trace repair. I also found that loading up this PS was crucial in getting to the bottom of things (see below). My apologies for the pictures, at the time I assumed they were good enough to identify the location of the burnt resistor Nick was talking about at that point.

To recap:

When I first received the TV, the PS board did not power up properly when jumpered. It would just cycle three times and then make no more attempts to start up. At that point I reflowed (but no trace repair) the cold solder joints under the heat sinks. That stabilized things, allowing the unloaded, jumpered board to power up to VS at 230 and VA at 52-54 (max).

However, the board would consistently fail under load.

Then, once Nick indicated that the traces themselves could be bad, I repaired the traces.

At that point, even under load I could get the VA/VS to go up to normal but noticed then when cold, the board would not start up on the first try. When cold (jumpered, connected to the light bulbs) it would take several attempts to power up (with the top main cap making a hissing sound on each attempt). If I allowed it to cycle a few times like this it would start and VS and VA come to normal.

Or, when cold (jumpered, connected to the light bulbs) If I heated up the topmost main cap for even 5 seconds it allowed the ps to power up from a cold condition perfectly. I've even isolated that cap with an "air dam" to ensure that's the only part being warmed.)

I've ordered replacement main caps, if only to rule them out. I will install them and report back, with pictures if that doesn't correct things.

Last edited by jjanssen7; 01-11-2019 at 03:43 PM..
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Old 02-01-2019, 11:37 AM   #55
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Any updates on this?
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Old 02-02-2019, 01:29 AM   #56
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Not really. I did replace the main caps (to rule them out). As expected, no significant change. I have re-soldered all the cold solder joints (especially on the secondary side) and repaired any of the pads that even looked marginal.

I've heard people find diodes or FETs that get leaky but haven't quite failed. Maybe the cold solder joints stressed some component that's near failure but tests OK?

At this point i really don't know how to narrow down the problem as the symptom is here/then gone (power cycling/hissing noise only when PS is stone-cold) Testing is a problem because any more than two or three power cycles (I have to unplug it after each one) and it starts normally. (BTW, heating even the new main caps very slightly still causes it to fire up first try from cold. How weird is that?)

As this is going to be my own TV for a while, my plan is to re-install the board in the TV and see how it reacts. I have no history on this unit so I'd at least like to see if it powers up and has a picture etc. before I invest more time into it.

I'm always open to more thoughts/questions... I wish I had a scope to capture the cold-start cycle but I guess I woulldn't know how to interpret what I'd see anyways.

-Jeff

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Old 02-11-2019, 03:58 AM   #57
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Still cracking away at this... I suspect that ICS801 may have some problem nearby or is faulty itself. Once I traced the problem back to that area of the board, I noticed that it may have a crack through the top (unfortunately right through the the markings). warming the caps even slightly that feed this IC and the TV starts quite normally. Can anyone identify this so I can find a datasheet and investigate further?

The top line is 25600
The bottom line is A09Y

The middle is ??33M. Possibly ?233M. (You may be able to see the fine crack through the "5" in the top line BTW.)

This IC is located "top-Middle" of the board.
Attached Images
File Type: jpg 20190211_010428.jpg (631.8 KB, 6 views)
File Type: jpg shopjimmy-bn44-00602a-bottom.jpg (996.3 KB, 1 views)
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Old 02-11-2019, 12:51 PM   #58
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Default Re: Samsung PN60F8500AFXZA, can't determine X or Y failure

Comparing this IC with the same IC on Samsung plasma PS's of similar years I see that I likely have all the info and this is a 25600 controller IC.

Top line 25600
Second line Logo(obscured) followed by 33M
Third line AO9Y

Picture attached to this post is of the IC on another parts board of a similar year plasma but not the same model.
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