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Old 04-23-2015, 06:02 PM   #41
sambul83
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Default Re: Westinghouse L2410NM No Power, No LED

It doesn't look like there're many helpers around. No problem, I'll continue the thread in a hope it can help others in the future.

Since rectifiers under right heatsink shown 0 Ohms btw G and S pins on-board, I kept testing them:

Voltages from the ground:

DS4 G - 5.9V, D - 22.1V, S - 5.9V
DS5 G - 5.9V, D - 0V, S - 5.9V
DS7 G - 5.9V, D - 10.7V, S - 5.9V

Not sure if these values are suitable given 5V, 14.5V and 24V power supply output? I suspect display resolution changes may require changing voltages, since the LCD goes black in btw different resolutions. Suspicious of DS5 D=0V...

I removed the right heatsink and all 3 parts to test off board. It wasn't easy by any means given lack of experience, multiple joints, and no way to reach rectifier screws. The best way probably is to add some solder to each joint, and then carefully remove all solder with cooper wick. Then try removing pins one by one by heating and pressing from bottom out with a screwdriver. I came to this through trial and error, lifted a couple of pads with solder vacuum in the process. Cooper wick absorbs solder much better if there is no pin sticking from the hole. Your iron quality and size makes all the difference. If someone tries this, prevent rectifiers overheating by hooking each to heavy locking plyers. Does lifting these pads make the board DOA?

Once removed, measured rectifiers resistance off board was:

DS4: G-S OL / OL, G-D 1.5 mOhms / OL, D-S OL / 1.5mOhms
DS5: G-S OL / OL, G-D 130 kOhms / OL, D-S OL / 130 kOhms
DS7: G-S 310 kOhms / 300 kOhms, G-D 300 kOhms / 40 kOhms, D-S 40 kOhms / 300 kOhms

Models:
DS4 456 SP10150
DS5 STPS20H100CT GKON7 VW CHN 702
DS7 STPS2045CT CC120V MAR 701

Do the above readings ring the bell - asking mostly myself for now?

More parts info:

The chip to the right of rectifiers looks like voltage regulator marked 4419 BA6515, more info here, but it doesn't feel relevant for me. This seems to be the right part.

I found some issues with very small caps on the board:

CS2 and both non-numbered caps connected in parallel to DS5 G pin measured OL on-board, it looks like they're open. One such cap was lifted with pad and removed. Can someone suggest suitable replacements or at least target part values? Also, what these lines of solder are for all around the board - are these extra cooling surfaces above pads, or to add some capacitance to pads?

I still want to think the board is salvageable since its harder now to find the same replacement. By any means it was great learning experience trying to fix my own electronics from ground zero, and learn in the process what to do, how and why. I will definitely fix the monitor.
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Last edited by sambul83; 04-23-2015 at 07:04 PM..
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Old 04-23-2015, 07:09 PM   #42
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Default Re: Westinghouse L2410NM No Power, No LED

The power supply board has PFC Voltage booster circuit, so if you only getting 180VDC, then the PFC is not working, the Voltage on the main filter cap should be more than 360VDC (measured between the two legs of the cap).
The Diode you measured as shorted are not shorted, they are dual diode with common Cathode in the middle pin, the two outside pins are Anode and are tied together by the traces on the board to form parallel diode connections to handle the load current.
Your power supply is working but not at full potential due to the PFC is not working.
I will have to trace the bottom side of the board and also locate the PFC Controller IC to test the Voltages, the PFC diode D2 should also be tested.
You have already looked at this pictures and see the notes of what to check?
http://www.badcaps.net/forum/attachm...0&d=1429619326
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Last edited by budm; 04-23-2015 at 07:19 PM..
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Old 04-23-2015, 07:43 PM   #43
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Default Re: Westinghouse L2410NM No Power, No LED

PFC controller at the bottom is TEA 1552T 2060R209, datasheet here. Also c656ld ez622 (turned around it reads 229z3 079597) that might be junction diode?

Not sure how to check it now until the missing & open small caps are replaced, as shown on the above pic? Can I connect it to power outlet without these caps?

As to the PFC not working, 180V was measured at idle with PSB disconnected from other boards. I assume if it was twice lower than required, how then my monitor worked OK most of the time (until I started "professional repairs" ), only flickering 5-6 times then working normally again for 4 hours? Or that voltage affects only PS efficiency, but doesn't affect resulting output voltages?

For those interested how such power supplies (are supposed to) work, I found useful read: Switched-mode power supply.
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Old 04-23-2015, 09:08 PM   #44
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Default Re: Westinghouse L2410NM No Power, No LED

Without boosted voltage your inverter circuit will never work right since the Voltage will be lower. For example, you have 240V motor hook up to 120V, the motor may spin but when you put the load on the shaft it will stall.
The inverter circuit draws the most power from the power supply.
You should check the Voltage of the main cap when the unit is plug in and when power switch is activated to see if the PFC even try to start up.
Diode D2 just check in Diode mode with your meter.
TEA1552 is not PFC Controller IC, it is SMPS IC.

Last edited by budm; 04-23-2015 at 09:16 PM..
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Old 04-23-2015, 09:23 PM   #45
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Default Re: Westinghouse L2410NM No Power, No LED

Sorry U4 is SMPS IC, but the datasheet is correct? Also U2: L6561D ez622 Power Factor Corrector.

But will the PS even allow to switch on the monitor without these small open caps? If not, the readings won't be under load anyway - correct? What's the purpose of these tiny caps?

Also, if my theory is correct, switching LCD resolutions requires voltage change from PS? That voltage should be in a certain range to switch the resolution... it can't be just random voltage. Than I'm at loss how everything worked? But it was flickering beyond tolerable, so needed repair anyway.

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Old 04-23-2015, 10:20 PM   #46
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Default Re: Westinghouse L2410NM No Power, No LED

"But will the PS even allow to switch on the monitor without these small open caps?" What small caps?
Are you talking about C21, 22, 23 filter caps that show OL? did you completely discharge them before using the Ohm meter on them, any DC on the cap will cause the Ohm mode not to read correctly.
BTW, putting all new caps will not cause the stress otherwise all the new monitor will fail since they all have new caps installed, bad caps will cause stress and damages to the circuits due to AC ripple voltage being fed to the circuits that want to see clean DC voltages.

Check the DC Voltage between VCC PIN 8 and the GND pin 2 to see if you have at least 12V (trun on threshold).
You will be making Voltage measurement in the HOT DEADLY SIDE of the circuit, so do not touch anything.
BTW, did you check D2 as I asked?
What is you AC line voltage being fed to the board, 120VAC? The reason I ask is that you indicate you have 180VDC on the main cap which is higher than normal if the main is 120VAC, 120VAC x 1.414 = 169.68V, so you line voltage must be higher than 120V to get 180VDC on the cap.
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Old 04-23-2015, 10:33 PM   #47
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Default Re: Westinghouse L2410NM No Power, No LED

No, I mean CS2 and other 2 similar caps marked here measure OL in both directions (one tiny cap is missing in action). What are their values and where to get them? Does this area look "repairable" despite the damage?

As to C21,22,23, I measured now resistance on-board again upon discharge (as before), and all 3 show OL / 3.5 mOhm in reverse firm. D2 diode shows OL / 470 kOhm. I'll re-solder 3 diodes under right heatsink and measure V on the big cap under left heatsink tomorrow, if its safe to hook the PS to other boards without the tiny caps CS2 etc. As to other components near the big cap, are they all to be measured under load?

What I mean under "stress wear" - parts age together. Brand new parts are able of handling higher voltages without notable wear, while if one raises voltages on various older parts by replacing all caps, that accelerates their wear. Of course, very high failure rate within 6-month period after replacing caps reported in the longest thread re L2410 LCD where main effort was on replacing caps can be attributed to low skills level of repair "staff". I can see it looking at my own results.

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Old 04-23-2015, 10:55 PM   #48
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Default Re: Westinghouse L2410NM No Power, No LED

"What I mean under "stress wear" - parts age together. Brand new parts are able of handling higher voltages without notable wear, while if one raises voltages on various older parts by replacing all caps, that accelerates their wear. Of course, very high failure rate within 6-month period after replacing caps reported in the longest thread re L2410 LCD where main effort was on replacing caps can be attributed to low skills level of repair "staff". I can see it looking at my own results."
I f that is the case, then 1000's of monitors and TV I repair would have come back to me by now. Wrong type of cap, general purpose caps are the problem, they have to be low ESR type.
The one by the rectifier diode is part of the R-C snubber to protect the diodes, the circuit will still function without the snubber but the diode will fail. The board looks very nasty with those soldering works. I do not know what the function of CS2 is, they are MLCC- Multi layer Ceramic Capacitors. no way to tell the value without the cap meter.
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Old 04-23-2015, 11:10 PM   #49
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Default Re: Westinghouse L2410NM No Power, No LED

I was looking on YouTube a guy detached similar heatsink with several diodes screwed to it in 2 min, and it looked like new. What I was doing wrong here? Do you think its still reparable, or better to try locate replacement board?
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Old 04-23-2015, 11:31 PM   #50
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Default Re: Westinghouse L2410NM No Power, No LED

It looks like the iron is not at least 40 WATTS or higher, 60W is preferred with wide tip for de-soldering this kind of works, and flux should be used and add solder to the joints
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Old 04-24-2015, 12:53 AM   #51
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Default Re: Westinghouse L2410NM No Power, No LED

I was trying to add flux, and it prevents cooper wick from absorbing the solder, so it just covers broader area and makes shorts, then more to cleanup. I'll try to get a better iron and set of tips, now only one narrow tip, may be that's why it takes much time to melt.

Mains are 120V now. D2 diode shows OL / 470 kOhm.

Hope you can suggest values of these 3 tiny caps, otherwise I can't repair this board. The problem is, when plenty of these monitors were failing, it was a large supply of power boards. Now I don't see any, and seldom price is twice higher.
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Old 04-24-2015, 07:37 AM   #52
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Default Re: Westinghouse L2410NM No Power, No LED

The circuit with CS2 MLCC cap is on a control line connecting UP1 L0651 817C Optocoupler through US1 431 shunt diode and CS16 / CS18 caps with power line to ribbon cable connectors to Main and Inverter boards (about 1/3 of all connectors). The circuit seems to control some voltages supplied from the main transformer through jumpers to the other boards. DS4, DS5 and DS7 rectifiers input & output is also controlled and directed through US4 4419 BA6515 4-pin mosfet and tiny caps to the same and other pins of the main and inverter board connectors.

The reason I removed DS4, DS5 and DS7 rectifiers to measure off board was one of them shown 0V output, and their in-circuit resistance readings were strange. But now I think it was the wrong move only leading to further board damage, as 0V was possibly due to open tiny cap. That prompts to measure resistance of all caps on board even the tiny ones before considering removing a group of components mounted on a heatsink, which may not be an easy task for a novice with primitive tools. If tiny caps gradually change resistance by charging from the Meter, they're probably good. As to larger caps easy to remove, consider pros and cons of replacing them if they show normal voltages and resistance in both directions, and don't look bulged. Repair shops likely change all caps since they provide warranty to consumers. But in home repairs that logic may not apply, as you always can open and fix the device again.

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Old 04-24-2015, 03:59 PM   #53
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Default Re: Westinghouse L2410NM No Power, No LED

Quote:
Originally Posted by budm View Post
Check the DC Voltage between VCC PIN 8 and the GND pin 2 to see if you have at least 12V (turn on threshold).
This PSB has TEA1552 controller. It measures 11.01-11.4V btw GND pin 10 and VCC pin 8.

Other components in PFC/Boost Converter in-circuit, no power:

R12 0 / 0 Ohms shot sound
Q2 1-3 OL / 20 kOhms, 1-2 890 kOhms / OL , 2-3 OL / 160 kOhms
C21 and C22 caps are charging and discharging when measured
Transformer L1 1-1 0/0, 1-2 OL/800kOhms, 1-3 OL/800kOhms
C1, C2,C3 OL / 800 kOhms

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Old 04-24-2015, 04:04 PM   #54
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Default Re: Westinghouse L2410NM No Power, No LED

I am talking about the PFC CONTROLLER IC U2 L6561, the smps IC is working because you are getting the output voltages.
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Old 04-24-2015, 04:53 PM   #55
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Default Re: Westinghouse L2410NM No Power, No LED

U2 gives 10.9V btw GND pin 6 and VCC pin 8.

I found shot resistor R12 @ 0.2 Ohms next to D2 - see above. It's color coded: green - gold - white - green - brown, which seems to mean 15.9 Ohms +- 0.5% as per The Resistor Guide.

All that probably means I shouldn't remove the right heatsink anyway, it was a bad move expected when no help is provided. Now pay, pay, pay...

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Old 04-24-2015, 04:57 PM   #56
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Default Re: Westinghouse L2410NM No Power, No LED

You are correct.

GND = GROUND, PIN 6

GD is the GATE drive.
So the Voltage barely is below the 12V (11V minimum) the required minimum Turn-on Threshold.
We need to locate the filter Electrolytics cap connected to the VCC pin of this PFC IC.

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Old 04-24-2015, 05:19 PM   #57
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Default Re: Westinghouse L2410NM No Power, No LED

It seems to be C21, and it tests 2 mOhms / 1.4 mOhms in-circuit off power, 10.9V powered. But again, if U2 voltage is below threshold, why CK1 voltage 180V exceeds the target 169V, and how this all is related to flickering issue?

And how the resistor can loose resistance & get short rather than burned & open? Or does it mean that the circuit is short - then why the monitor was working OK most of the time?
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Old 04-24-2015, 07:39 PM   #58
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Default Re: Westinghouse L2410NM No Power, No LED

"how this all is related to flickering issue?" How do expect the circuit to operate correctly at the lower voltage than it should be?

"And how the resistor can loose resistance & get short rather than burned & open? " What is the color code or the value as printed on the resistor? Are you sure it is not Fusible resistor or Source resistor which are <1 Ohm? I cannot see which resistor that is.
I think at this point it is time to buy new power supply board.
BTW, the resistor just above the D2 and to the right of the MOSFET is the Source resistor for that MOSFET.
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Old 04-24-2015, 08:10 PM   #59
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Default Re: Westinghouse L2410NM No Power, No LED

It may be, but... there's no such boards supply in North America, and its $70 from China, almost like a new monitor on sale now.

The resistor is rated 16 Ohms. This thread holds high diagnostics skills value regardless of the outcome, since both failure and success are normal outcomes in technology projects, and they change places all the time. Did you mean C21 cap affects lower voltage from U2 and needs replacement?

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Old 04-24-2015, 08:21 PM   #60
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Default Re: Westinghouse L2410NM No Power, No LED

15.9 Ohms is very high resistance for that Source resistor for that PFC MOSFET, it does not sound right. I have never seen PFC MOSFET circuit using that high of the resistance, the highest I have seen is 0.82 Ohms.

"It seems to be C21, and it tests 2 mOhms / 1.4 mOhms in-circuit off power," Is that resistance reading or ESR reading? Even for ESR, that is very low for 47~100uF cap for the VCC. 2mili-Ohms (0.002 Ohms!) that is way too low to be true for ESR.
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