Westinghouse L2410NM No Power, No LED

[jetadm123]

Re: Westinghouse L2410NM No Power, No LED

Okay, I'm a little confused. In post #15 you stated that your readings across S-G for Q2 and Q1 were 13 and 17 ohms.

In post #19, you're stating that S-D for Q2 and Q1 are 13 and 17.

Which one is it? And is it in ohms or kohms?

[PlainBill]

Re: Westinghouse L2410NM No Power, No LED

At this point you have a blown fuse and an unknown cause. The FET resistances were normal for in-circuit tests. (7K ohm does not sound like a short). I would hook a smallish (40 watt) light bulb across the blown fuse and apply power. If the light bulb glows brightly, you have a chance to determine what is drawing excessive current. If it glows dimly, Id replace the fuse, or use a larger light bulb as a substitute.

PlainBill

[kaboom]

Re: Westinghouse L2410NM No Power, No LED

Forget google. All you need to know is that they are dual common cathode TO-220 case rectifiers. It's easier to think of them as two single diodes (which they are) internally connected as follows:

center pin- common cathode
each outside pin- anode (diodes 1 and 2)

Depending on other components in the circuit, you'll probably have erroneous readings if checking in circuit. But removed from the board, you'll have the following Vf's on diode check mode:

*Black lead on center pin or tab*
Red lead to either outside pin: 225mV to 275mV for Schottkys and ~565mV to 610mV for others, be it fast recovery, ultrafast, or normal recovery. If both outer legs aren't within 5%, replace diode, as both sections are not balanced.

*Red lead on center pin or tab*
Black lead to either outside pin: Overrange indicator- "OL," ".1," "INF," infinity. Actually, it indicates that the Vf of the DUT is greater than the meter range on diode check, typically 2V. But that's the indication you want.

Make sure you use diode check, not resistance. You may use continuity check to weed out dead shorts, but not for junction testing.


"The diode at position D2 shows 432 in one direction, and open or "1" with the leads reversed and the multimeter at the diode test setting.
The diode at position D3 (lower, middle section of board) shows 575 in one direction, and open or "1" with the leads reversed and the multimeter at the diode test setting."

Looks like they're OK.

The NTC is a Negative Temperature Coefficient resistor. Its purpose is to limit the charging current of the cap when the unit is first plugged in or upon turn-on. A high resistance initially, then drops with I2R heating, to the point of disappearing from the ckt. It is in series with the AC line. Was that big cap also replaced? There shouldn't be glue on it if so... Depending on how/when the booster operates, you may have 340-380V all the time or only the rectified peak value of 120V AC (~170V DC) in 'standby' or 'off,' with the higher voltage under full power. And if you suspect those FETs, pull both of 'em and clip a 40W light bulb across the cap. Plug it in and bulb should light. Neither the booster nor main switcher will operate in that case. Rectified line voltage will just feed from the rectifier, through the filter chokes, through the booster choke and diode, into the cap & bulb.

I made a mistake regarding U4 on the back of the board. It is U2 that controls the PFC booster and U4 is the PWM proper. Hopefully, when the thing blew up, drain-to-gate leakage/breakdown from the FETs didn't backfeed into those ICs and destroy them.

I'd also replace the two FETs. You could rig up a test ckt to test them externally, but you'd have to take them from the board anyway. Resolder that AC inlet- is that a crack or insufficient solder on the one pin?

Once you get it all together, bring it up on a dim bulb tester, not a variac. The former will give an indication, but more importantly, current limiting if there's still a fault. The latter will not.

Tip: If your meter is set to the 20K scale, and you read 13.47, that's 13.47K ohms- not 13.47 ohms. Can cause grief and confusion!

-Paul

[ben3843100]

Re: Westinghouse L2410NM No Power, No LED

Normally, you would measure the resistance of S and D, S and G, D and G. Take a resistance reading across D and G.

Resistance across S and G looks like it's almost shorted. You may need to do two things:

1) you will to need reverse your meter probes and remeasure the resistance across S and G for Q1 and Q2. If you get the same results, I would suspect a possible short. Step 2 below will verify it.

2) since Q1 and Q2 are "in circuit", other components could be affecting your readings. If so, it may require that you remove the mosfets from the board to get more accurate readings.

I placed my multimeter on the OHMs 20k setting, placed the black lead on the source pin, and recorded the following measurements. I can remove the MOSFETs if you think it's necessary for further testing.

MOSFETS:
Q2 (left)
S-D - 13.68
S-G - open
D-G - open
Reversed leads:
S-G - 7.7

Q1 (right)
S-D - 17.3
S-G - open
D-G - open
Reversed leads:
S-G - 7.7

Board Resistors:
R12 (left, top) 0.4 OHMS - multimeter on 200 setting
R31 (right, top) 0.4 OHMS - multimeter on 200 setting
Ra1 (smaller resistor below and between R12 and R31) 508 OHMS - multimeter on 2000 setting.

Transistor?:
TR1 ("NTC") 0.01 - multimeter on 20k OHMs setting.

Diodes:
The diode at position D2 shows 432 in one direction, and open or "1" with the leads reversed and the multimeter at the diode test setting.
The diode at position D3 (lower, middle section of board) shows 575 in one direction, and open or "1" with the leads reversed and the multimeter at the diode test setting.[/COLOR]

Yes the diodes could be shorted. Set your multimeter to diode check.
1) Put red probe on one side and black on the other. Record reading.
2) Reverse the probes. Record reading.
One should measure between 0.4 to 0.7V and the other should be 0L or "1".

The diodes I mentioned at positions DS4, DS5, and DS7 have three legs, is there a different testing procedure for these? I tried googling to find a testing method for them, but I'm still not sure. They don't look the same as the diode at position D2.

• Check the rectifier in the output of the PFC- D2, I assume 4A/600V fast recovery. You have solid joints from the big cap all the way back to the line? I don't see any issues with the board traces, if that's what you're asking.
• Does the FET on the anode side of D2 have proper drive? Resolder back to U4 if in doubt. I have some fuses on order from DigiKey to replace the main fuse that's blown. This sounds like something I won't be able to test until I replace the main fuse at position FS1, correct?
• It's trying to start into a short, either D2 is shorted, that would explain your 5.4 volts on the cap, or one the secondary rectifiers is shorted. I'll replace the main fuse at FS1 when I receive my replacements, then recheck voltages at the main capacitor.

[retiredcaps]

Re: Westinghouse L2410NM No Power, No LED

It appears that DS4, DS5, and DS7 are diodes. Should I check these out as well? I'm not sure how to test those.

Yes the diodes could be shorted. Set your multimeter to diode check.

1) Put red probe on one side and black on the other. Record reading.
2) Reverse the probes. Record reading.

One should measure between 0.4 to 0.7V and the other should be 0L or "1".

[kaboom]

Re: Westinghouse L2410NM No Power, No LED

Check that NTC- if it's broken, you'll have no or intermitten line voltage into the front end of the PS. Check the rectifier in the output of the PFC- D2, I assume 4A/600V fast recovery. You have solid joints from the big cap all the way back to the line?

Does the FET on the anode side of D2 have proper drive? Resolder back to U4 if in doubt.

It's trying to start into a short, either D2 is shorted, that would explain your 5.4 volts on the cap, or one the secondary rectifiers is shorted.

-Paul

[jetadm123]

Re: Westinghouse L2410NM No Power, No LED

After reading up on how to test the power MOSFETS, I measured between the source pin and the gate and drain pins and received the following readings:

• On Q2 (left MOSFET) I received 1 for infinity between S and D, and 13.64 OHMs between S and G with my meter set at 20K.
• On Q1 (right MOSFET) I received 1 for infinity between S and D and 17.27 OHMs between S and G with my meter set at 20K.

It appears that DS4, DS5, and DS7 are diodes. Should I check these out as well? I'm not sure how to test those.

Normally, you would measure the resistance of S and D, S and G, D and G. Take a resistance reading across D and G.

Resistance across S and G looks like it's almost shorted. You may need to do two things:

1) you will to need reverse your meter probes and remeasure the resistance across S and G for Q1 and Q2. If you get the same results, I would suspect a possible short. Step 2 below will verify it.

2) since Q1 and Q2 are "in circuit", other components could be affecting your readings. If so, it may require that you remove the mosfets from the board to get more accurate readings.

[ben3843100]

Re: Westinghouse L2410NM No Power, No LED

Check the power mosfet for shorts. I can't quite see where it is on your picture, but it might be above D2?

After reading up on how to test the power MOSFETS, I measured between the source pin and the gate and drain pins and received the following readings:

• On Q2 (left MOSFET) I received 1 for infinity between S and D, and 13.64 OHMs between S and G with my meter set at 20K.
• On Q1 (right MOSFET) I received 1 for infinity between S and D and 17.27 OHMs between S and G with my meter set at 20K.

It appears that DS4, DS5, and DS7 are diodes. Should I check these out as well? I'm not sure how to test those.

[retiredcaps]

Re: Westinghouse L2410NM No Power, No LED

Check the power mosfet for shorts. I can't quite see where it is on your picture, but it might be above D2?

[jetadm123]

Re: Westinghouse L2410NM No Power, No LED

I would consider replacing the 4 caps on the inverter board, since they of poor quality and likely to fail.

[ben3843100]

Re: Westinghouse L2410NM No Power, No LED

Check the bridge rectifier too. It is the black 4 pin long component, just above the M$27 white serial bar code. Number the pins 1-4. With power off and lcd unplugged, measure the resistance between 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Any reading under 30 ohms suggest it may be shorted.
PS. Order more than one fuse in case it blows again.

• I rechecked the bridge rectifier (I had checked it earlier) and received a 1 for infinity between each pin using the method you suggested above.
  
• Since I'm ordering fuses, do you think I should order any other components from Digi-Key at this point?

[retiredcaps]

Re: Westinghouse L2410NM No Power, No LED

Check the bridge rectifier too. It is the black 4 pin long component, just above the M$27 white serial bar code.

Number the pins 1-4. With power off and lcd unplugged, measure the resistance between 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Any reading under 30 ohms suggest it may be shorted.

PS. Order more than one fuse in case it blows again.

[ben3843100]

Re: Westinghouse L2410NM No Power, No LED

Did you measure the fuse? If not do so (power disconnected, meter on resistance, low ohms) It should read 1 ohm or less.
The fuse (you probably know this but just in case...) is the little black square by the power connector, you labelled it bel somethingerother (can't see crap tonight)

I actually didn't know that. Now that you mention it, I see it says "FS1" on the board next to it. I was wondering where FS1 was, since the other fuses are labeled FS2, 3, and 4. I measured across the leads on FS1 and received a 1 for infinity on my multimeter, so that seems to be the first issue I need to resolve. It appears to be a 3.15 amp, 250V fuse. It looks to be part number 507-1181-ND on the Digi-Key site @ .45 cents each.

[smason]

Re: Westinghouse L2410NM No Power, No LED

5.6v across the main cap is not good. From that, I'd say a bad bridge rectifier, or fuse.
Did you measure the fuse? If not do so (power disconnected, meter on resistance, low ohms) It should read 1 ohm or less.
The fuse (you probably know this but just in case...) is the little black square by the power connector, you labelled it bel somethingerother (can't see crap tonight)

[ben3843100]

Re: Westinghouse L2410NM No Power, No LED

Tough call to tell you where to test because the heatsinks are covering up most of the parts. I believe two of the low output voltages are from the two diodes mounted on the heatsink on the right with the label on it. The output of the each diode should be the middle lead. Try squeezing your red probe in to take a reading. With respect to ground, try measuring the voltages at both wiring harnesses of the power supply. I suspect that the power supply is not starting up, but we'll take it one step at a time.

I just got home and am continuing my testing. I can take the heat sinks off if required. I just carefully bent them open when I initially installed the new capacitors.

Next steps:

1. Check for mains voltage (like 120V or 240V DC) at the main filter capacitor at 1.4x the line voltage. With my multimeter set to Vdc and 600, I measure 5.6 volts across the leads to the large capacitor on the power supply board.
2. I suspect that the power supply is not starting up. When I plugged the board in after being unplugged overnight, I did hear multiple soft clicks in rapid succession coming from the power supply for the first 5-10 seconds.
3. From the label on the main power supply, it looks like this supply puts out 5V,14.5V and 24V. With respect to ground, try measuring the voltages at both wiring harnesses of the power supply. I measured each ribbon cable pin coming from the power supply and received the voltages shown in the attached pic. The only pin with any voltage was video board pin 5 @ 0.14V
4. I believe two of the low output voltages are from the two diodes mounted on the heatsink on the right with the label on it. The output of each diode should be the middle lead. Try squeezing your red probe in to take a reading. I placed the black lead of my multimeter on one of the power supply board mounting screws and the other to the center lead of each diode and received 0.0V on all three diodes. I initially received about .4 volts on the middle diode, but on the second and third trys I received 0.0V. After testing the diodes, I tested the ribbon cable plugs and all of them now show 0.0V. Residual power?.
5. I also measured the two diodes under the large heat sink on the left with no label and there is no voltage coming off the center leads of either of them.

[jetadm123]

Re: Westinghouse L2410NM No Power, No LED

From the label on the main power supply, it looks like this supply puts out 5V,14.5V and 24V. Have you tried measuring across the large 450V filter cap yet? Tough call to tell you where to test because the heatsinks are covering up most of the parts. I believe two of the low output voltages are from the two diodes mounted on the heatsink on the right with the label on it. The output of the each diode should be the middle lead. Try squeezing your red probe in to take a reading. With respect to ground, try measuring the voltages at both wiring harnesses of the power supply. I suspect that the power supply is not starting up, but we'll take it one step at a time.

[ben3843100]

Re: Westinghouse L2410NM No Power, No LED

Here are pics of the inverter and video boards in my L2410NM. There seems to be an editing time limit or I would have added these to my initial post above. I'll post the other voltage tests later tonight. That was a small piece of foil in on the first video board picture, btw. It fell on the board when I pulled the metal cage off of the back of the LCD panel.

-Ben

[smason]

Re: Westinghouse L2410NM No Power, No LED

There appears to be a big solder splash next to the yellow connectors in the last picture. That can't be a good sign.

PlainBill

Could be a chunk of foil tape from the disassembly process.

[PlainBill]

Re: Westinghouse L2410NM No Power, No LED

There appears to be a big solder splash next to the yellow connectors in the last picture. That can't be a good sign.

PlainBill

[retiredcaps]

Re: Westinghouse L2410NM No Power, No LED

Next steps:
[*]Check for mains voltage (like 120V or 240V DC) at the main filter capacitor at 1.4x the line voltage. (Do I set the meter to 600Vdc and measure between the two large cap wires?)
[*]Check for 3.3V, 5V, or 12V DC on the logic card. (Do I measure from a chassis ground to the exposed metal on each ribbon cable plug?

Excellent description, pics, and summary of the problem. If only more people would post like this, it would make getting help so much easier.

Report the voltages from above and we can suggest other tests points afterwards.