Sharp LC 60LE655U 2 long flashes + 2 short flashes

[carsearch07]

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

Thanks attainteddragon and R_J.

The diode tested fine after I lifted one leg. It was indeed a IN4148.

I still think the problem is in that general area of the board. The opto PC7904 has 0.6V on its diode side which means a very small current is flowing through it.
If the opto diode current increases,
--> the transistor side of the opto would see a drop in resistance,
--> the Q7902 transistor would turn on
--> Vcc would reach IC7601
and thus the UR13.2 voltage would rise to its expected level.

To test, I momentarily shunted the opto transistor with a 11k resistor and got a voltage on UR13.2 ( I have 11 test LEDs in series on the UR pin that lit up)

Does this analysis make sense? What can I test next?

[R_J]

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

Ok, by doing this test, check the voltage on ic7601 vcc, also check the pfc voltage on the large caps, is it at around 400v and stable?
Also check the three led+ voltages, are they ok?
Then shut it down and make sure none of the ic's etc are getting abnormally hot.
You could have a bad optcoupler?
Check the voltages on Q7305

[carsearch07]

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

R_J, sorry for the delay. I've been looking at this closely.

Here's my theory on what is happening:-
1. When PS_ON is supplied, UR is rising to above 14.4 V momentarily which is above the 13.2 V expected for UR.
2. Due to this voltage, the gate voltage on SCR Q7305 is high enough to turn the SCR on and it latches ON. This diverts current away from the opto PC7904 and acts as protection circuit.

So the crux of the problem is that UR is getting a higher voltage than expected. This points to higher voltage or switching frequency on the primary of the main transformer T7601. I still need to dig deeper to figure out what controls the transformer input.

I like this theory because it is more likely that the lightning power surge damaged something on the PRIMARY (hot) side.

----
When I tried the test of shunting the output of PC7904, the transformer created a loud hum which seemed abnormal so I didn't keep the shunt in place to avoid damage. I couldn't make the voltage measurements you requested.

[carsearch07]

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

Does anyone know anything about an IC labelled S101 241A ?
It is part of the AC-DET circuit on the hot side of the board.
I could not find any info on it at all.

Attaching a picture of the label in case I'm reading it wrong.

[dick_barton]

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

It may be an S101 (IN1S101-T6G) Brown out Supervisor IC for Delta Power Supplies