Sharp LC 60LE655U 2 long flashes + 2 short flashes

[carsearch07]

Hi guys,
I need some help in next steps to troubleshoot a PSU board.
I'm trying to save the board from becoming E-waste and hoping to learn a few things in the attempt.
This is my own TV and I just have basic electronics knowledge.

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TV : Sharp LC 60LE655U
Symptom : After a lightning strike with TV in standby, the TV does not turn on.
When switched on from mains, the LED light flashes :2 long followed by 2 short (repeats)
Per the manual of a similar Sharp TV (LC60LE640U), this indicates : Power Supply error 2 (*2) UR +13V error
I kept the TV unplugged for a while and also tried to reset using CH- and VOL+ while plugging in TV. No change.

Power supply unit : DPS-167CP A
Pictures at http://www.shopjimmy.com/sharp-runtk...-led-board.htm

With board connected to the TV, the main board momentarily sends a voltage on PS_ON and then immediately after that LED flashes begin.
I assume it tried to turn on the PSU, found an error and stopped trying to turn it on.

With the board on bench:-
Output from Bridge Rectifier BD7001 = 171 V (across output pins)
No visible sign of swollen capacitors, burn marks or leaks.

POWER SUPPLY BOARD PD connector pinout:
PD-1-2 = PNL12V
PD-3-4-9-10-11-12 = GND
PD-5-6-7-8 = UR13.2V ----> 0 V even when PS-ON is supplied
PD-13 = AC_DET ------>3.3 V when PS-ON is supplied using 1k resistor from BU5V
PD-14 = PS_ON
PD-15 = BU5V ----> 5V present
PD-16 = PNL-POW (Panel Power signal (input ))
PD-17 = PWM1
PD-18-20 = N.C.
PD-19 = DIMMER
PD-21 = OFL
PD-22 = ERROR
PD-23 = PWM2
PD-24 = STB

Without supplying PS-ON, BU5V is 5V and all other pins are at 0 V.

When I supply PS-ON using 1k resistor from BU5V
1. PS-ON = 4.6 V
2. Large capacitors 7800A/B have voltage = 412V (without PS-ON , cap voltage = 170V)
3. AC_DET = 3.3 V
4. All other pins = 0 V

Resistance across fusible resistor R7601 (in-circuit) = 0.1 ohm
----
Please let me know what else I can do to find the problems with this board.
Also, please point out any mistakes in my analysis so far.
Thanks

[budm]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Please give the Voltage readings with all boards connected:
POWER SUPPLY BOARD PD connector pinout:
PD-1-2 = PNL12V
PD-3-4-9-10-11-12 = GND
PD-5-6-7-8 = UR13.2V
PD-13 = AC_DET
PD-14 = PS_ON
PD-15 = BU5V ----> 5V present
PD-16 = PNL-POW (Panel Power signal (input ))
PD-17 = PWM1
PD-18-20 = N.C.
PD-19 = DIMMER
PD-21 = OFL
PD-22 = ERROR
PD-23 = PWM2
PD-24 = STB

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

With the boards connected, the steady state of all pins is 0 V except for BU5V which is 5V.

PS_ON momentarily gives 3.08 V before going to 0 V as mentioned in my first post. During this time, AC_DET has 3.3V

[budm]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

The AC_DET should be at steady state of >3VDC the minute you plug the TV into the outlet and should not change state at all wheter the TV is ON or OFF, it is the signal generated by the power supply board to tell the main board if the incoming AC is within the operating range or not, if it is not then it will not allow the TV to come on. So I want to make sure first that the AC_DET is OK or not.

[R_J]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Sounds like pfc circuit IS working but T7601 is not running, Check the resistance of R7601
Or with the power supply forced on do you get any secondary voltages on the caps IE: C7206, 7205, C7207. If you don't get any voltages then T7601 circuit is not working

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Thanks budm.
I double-checked AC_DET. It stays at 0 V if PS_ON is not supplied. I guess that means a problem generating AC_DET on the PSU board? Any suggestions on how to narrow down the problem or any other tests to confirm that the AC_DET circuit is a problem?

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Sounds like pfc circuit IS working but T7601 is not running, Check the resistance of R7601
Or with the power supply forced on do you get any secondary voltages on the caps IE: C7206, 7205, C7207. If you don't get any voltages then T7601 circuit is not working

Thanks R_J.
Resistance across fusible resistor R7601 (in-circuit) = 0.1 ohm

However, C7206, C7205, C7207 show 0 V with PS_ON supplied. I'm also not seeing any AC voltage across the primary of T7601

[R_J]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

You won't be able to measure the ac with your meter, its likely around 30-50 khz, The pfc voltage is supplied through that resistor to the mosfets in that circuit. I suspect the driver ic is not being turned on,
What is the number on that IC7601, I cant find a schematic for this power supply but there might be a similar one that uses this ic.
I think ac detect comes via R7001a,b,c&d (1meg each) to J7006, R7934 to Q3 and drives PC7902 opto. Check D7901 (across opto led) it is a zener and maybe got shorted.

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

You won't be able to measure the ac with your meter, its likely around 30-50 khz, The pfc voltage is supplied through that resistor to the mosfets in that circuit. I suspect the driver ic is not being turned on,
What is the number on that IC7601, I cant find a schematic for this power supply but there might be a similar one that uses this ic.
I think ac detect comes via R7001a,b,c&d (1meg each) to J7006, R7934 to Q3 and drives PC7902 opto. Check D7901 (across opto led) it is a zener and maybe got shorted.

IC7601 is labelled as SSC9522S SK343 03CU.

Trying to figure out if I can test the zener without desoldering. Would measuring the in-circuit voltage across it be sufficient?

[R_J]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Regarding the zener D7901, just check it in circuit, make sure its not shorted.
IC7601 requires vcc on pin 2 to work, it comes from around the standby ic7903 and feeds the ac_det ic and the ic7601
Also is there a number on that 5pin ic in that area? Is it "in1m101"

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Thanks R_J. Truly appreciate your input and the efforts you took to draw the circuit for me.

Regarding the zener D7901, just check it in circuit, make sure its not shorted.

D7901
Forward Bias resistance(FB) = 688 ohm (on 2K scale)
Reverse Bias resistance (RB) = 1465 ohm (on 2K scale)
Voltage across with PS_ON supplied = 0.6 V
Do these readings look ok?

For reference, I also took readings for 2 other zener diodes
D7913
FB = 783 ohm ; RB = 29.6k ohm ; V = 1.4 V (in both states of PS_ON)
D7907
FB = 800 ohm ; RB = Out of range > 2M ohm ; V = 15.2 V (off) and 15.9 V ( PS_ON supplied)

IC7601 requires vcc on pin 2 to work, it comes from around the standby ic7903 and feeds the ac_det ic and the ic7601

pin 2 of IC7601 = 14 V DC with PS_ON supplied; 0 V without PS_ON
On the AC detect trace (J7006 on bottom) = 10.5 V AC

Also is there a number on that 5pin ic in that area? Is it "in1m101"

Did you mean the IC that is just above C7916? That looks like a 6pin to me. The label says "S101 241A"

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Off-topic curiosity :
I noticed that the PCB has some red sections on top of some traces as well as under some Surface mounted devices. Is that some kind of insulation?

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

R_J,
I noticed that a small part of your yellow line trace is incorrect. You have it going up obliquely to the left but I was able to confirm that it goes downward (with a light behind the board) Picture attached.

[R_J]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

The red stuff is glue used to hold the smd's in place during soldering, on this board some locations are not installed, but they still but the glue.
I traced it the best I could using the picture, You have the board in front of you I don't
PC7904 seems to be the opto for the power on for the board, It controls the base of Q7902 which should have voltage on its collector (use J7055 to check) and when turned on supplies that voltage on its emitter and up to IC7601
So IC7601 IS being supplied its VCC, thats good, When you power on the board are you sure you not getting any voltages on the secondary supplies of T7601, like across C7204, C7205 or C7130?

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

The red stuff is glue used to hold the smd's in place during soldering, on this board some locations are not installed, but they still but the glue.
I traced it the best I could using the picture, You have the board in front of you I don't
PC7904 seems to be the opto for the power on for the board, It controls the base of Q7902 which should have voltage on its collector (use J7055 to check) and when turned on supplies that voltage on its emitter and up to IC7601
So IC7601 IS being supplied its VCC, thats good, When you power on the board are you sure you not getting any voltages on the secondary supplies of T7601, like across C7204, C7205 or C7130?

Voltage across PC7904 is 1.02 VDC on the secondary side and 0.8 V DC on the primary.

With the power supply off, Q7902 has
Base = 15.9 V DC with respect to BD (-)
Emitter and Collector = 0 V
With PS_ON,
Base reduces to 15.5 V
Collector = 14.9 V
Emitter = 14.2 V
(I may have mixed up the terminals for C and E)

I have double checked that there is no voltage across C7204,C7205 and C7130.

Is there a way to see if the big transformer T7601 is generating any voltage? As you pointed out earlier, the AC signal doesn't show on my meter. I don't have one but would an oscilloscope be the way to go?

Many thanks for your help and advice.

[R_J]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

When IC7601 is working, it's operating at around 30khz, most multimeters won't see that, Yes a scope will but one would need to use an isolation transformer also when connecting the scope ground to the hot side of the ps.
Here is the pdf of that ic, where it says external power supply is where your 14 volts is applied when powered on.

Just to confirm, the voltage across the main caps C7800a/b is 160v, and when power is turned on it goes to around 400v correct?
Is this voltage also on Q7601 Drain, and is there any voltage on Q7602 drain when powered on?
I guess there could be somthing preventing it from working associated with pc7601 opto, there might be something not alowing that circuit to function if there is an error somwhere else. Maybe the power supply board does need to see a valid ac_det line.
Using cold ground, what is the voltage on PC7902 pins 3-4, (cold side)

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Just to confirm, the voltage across the main caps C7800a/b is 160v, and when power is turned on it goes to around 400v correct?

Yes, confirmed. 167 V goes to 412 V

Is this voltage also on Q7601 Drain, and is there any voltage on Q7602 drain when powered on?

I'm not sure which terminals of the FETs are gate,drain or source. Is the middle one always the gate? I can't see the FET label unless I desolder the heat sink first.
Q7601
Middle terminal = 412 V
Both other terminals = 0 V

Q7602
All terminals = 0 V

I guess there could be somthing preventing it from working associated with pc7601 opto, there might be something not alowing that circuit to function if there is an error somwhere else. Maybe the power supply board does need to see a valid ac_det line.
Using cold ground, what is the voltage on PC7902 pins 3-4, (cold side)

The voltage on PC7902
pin 3 to ground = 4.52 V DC
pin 4 to ground = 4.95 V DC
pin 4 to pin 3 = 0.31 V (I would have expected this to be the difference of the above 2 voltages i.e. 0.43 V )
There is also an AC component to the voltages because of the on-off action which I think is making the voltage difference look incorrect.

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Off-topic curiosity:
I spotted a couple of things on the board ( Picture attached)
1. Why does the trace split into 2 sections with a thin empty line between the 2 sections? Any advantage over one solid trace?

2. There is a chevron-shaped hole under each FET between the pins and the heat sink boundary. What's the purpose of these holes?

[R_J]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

pfc circuit is working fine, thats ic7801, Q7601 has good pfc voltage on drain, Source is the other rivited pin (left) gate is the regular trace pin (right)
PC7902 could be pulsing as it is the ac detect opto.

The open chevron is just an air gap to isolate the drain & source pins better. likely to prevent any arcing which might occur due to high voltage pulses.
I don't really know 100% but the wide trace will be to handle the higher current the thin trace provides feedback for the circuit, maybe taping off the large trace closer to FB7805 caused issues so they went this way.

[carsearch07]

Re: Sharp LC 60LE655U 2 long flashes + 2 short flashes

Thanks R_J.
Anything further I can check?

I noticed that the gate of Q7801 is more than 600 VDC! My meter only goes to 600 V DC and it's shows OL in that range between the gate and hot ground. I'm surprised at such a high voltage especially since the largest capacitors on the board are at 400V and also in parallel with each other