Insignia NS-48D510NA15 No Standby

[neilc6]

This model suffers from bad backlights but my power supply is dead and no standby light and no standby voltage. Main fuse was good but found U807 (NCH, 650V, 8A) shorted and replaced it (subbed with 450V). Didn't fix it. Checked C822 and measures 100pF. Main filter cap is around 290V and drifting a few volts. Suspecting PFC IC may have been damaged. Only one set of wires to strips (10 rows of 6 LEDs) and reading about 60V on LED tester so not sure if there are bad LEDs as well. May or may not be related.

Power supply is HLL-4855WC (186132 according to Shopjimmy)

[R_J]

Re: Insignia NS-48D510NA15 No Standby

If U807 was shorted, Is R818 still ok? The circuit does seem to be working as the pfc circuit is sort of working.
I would then check the voltage on C819 (20v), C817 (16v) and C811 (16v) C819 47µf/50v would be my first suspect.
If one or all of those caps are bad, the vcc for the ic's will not be stable.
You might also want to check VD807, VD808 & VD812.

[neilc6]

Re: Insignia NS-48D510NA15 No Standby

If U807 was shorted, Is R818 still ok? The circuit does seem to be working as the pfc circuit is sort of working.
I would then check the voltage on C819 (20v), C817 (16v) and C811 (16v) C819 47µf/50v would be my first suspect.
If one or all of those caps are bad, the vcc for the ic's will not be stable.
You might also want to check VD807, VD808 & VD812.

R818 tests ok and not open. C819 bouncing between 0 and 50V. C817 is at 15V for a few seconds, drops out and cycle repeats. C811 cant find. I will pull off those two caps and test out of circuit tomorrow. The 3 diodes test fine.

I believe the 60 LEDs are one big string so expected voltage is around 160V with the LED tester. That is a lot of shorted out ones which likely took out the power supply.

[neilc6]

Re: Insignia NS-48D510NA15 No Standby

Tested C819 and C817 out of circuit and they are both good. I have ordered a new PS board. Appears to have two different strips for this model HD480DF-B37 or HD480DF-B32 with different lens spacing.

[R_J]

Re: Insignia NS-48D510NA15 No Standby

It is unlikely the led's took out the power supply, the led circut has ovp and ocp to shut it down. When you checked those cap voltages , did you check if there was any +12v or +14v on the XP805 plug? also was the main board connected?

[neilc6]

Re: Insignia NS-48D510NA15 No Standby

I opened up the panel to check the LED strips and they were all good. The black wire is positive and the white wire is negative and the tester measured 60V reverse biased. My tester is a little flakey and didn't give a reading when biased correctly. I did confirm the LEDs are all wired in series.

The connector voltages were checked with the main board plugged in. The capacitor voltages were checked on the bench with nothing plugged in.

[R_J]

Re: Insignia NS-48D510NA15 No Standby

But are you getting ANY voltage on the +12 or +14 volt output?
With the board on the bench (no main connected) it will just be in standby. so ic N834 will be soft/skip mode
I can only assume there is +14volts on XP805, so connect a 1K resistor retween the +14v and the STB pin. This will turn on the power supply.
Tha fact you were getting between 0~50v on C819 tells me you should also have the +14 volts on C856 (or xp805 pin 9,10).

C811 is a small elec. cap. between the a/c input and v802. It is the VCC cap for the PFC ic.

[neilc6]

Re: Insignia NS-48D510NA15 No Standby

I got a similar power supply HLL-4255WJ for Sharp LC-40N5000U and it had a shorted U807 FET and visible damage on R818 (blown). I replaced both and plugged it in and one leg of C822 blew as well as N834. Replaced those two and now power supply is working but searching N834 found this thread and dug up this old board in my junk pile.

Comparing boards, I found R808, R811 and R813 damaged on this board so replaced these 3 as well as N834 and still no standby. Found the schematic posted by RJ in another thread searching N834 so can see if I can track it down further. PFC voltage is a stable 155V.

[neilc6]

Re: Insignia NS-48D510NA15 No Standby

I compared my working board with the Insignia and the standby voltage is low
PFC = 159V (same for both)
20V (C819) 6.5V on the Insignia, 18.5V for the Sharp
VDD (C817) 8-10V unstable, 15V for the Sharp

Since the 20V is coming directly from the transformer not sure what is causing the low voltage. Checked R820, VD805, R821, R823, VD825 and C807.