Sceptre X405BV-FHD3 No power Won't turn on

[p1668]

I have a Sceptre X405BV-FHD3HF01001 or Sceptre X405BV-FHD3 that is not powering on. There is no standby indicator on the front of the TV.

Someone gave me the TV and he did not tell me what happened to it other than a good luck fixing it.

I opened the back cover to check for bulging capacitors on the power supply board and I didn't see any that are bad.

After reading on the forum, I used my DMM and started taking different measurements and found that there was no 5V standby power. With that, I found a Schottky Barrier Rectifiers MBR5200 diode (D10) that was shorted on the board. I then ordered the exact replacement and replaced it. At the same time, I replaced all the capacitors on the board with Panasonic capacitors, except for the big 150uF 450v capacitor.

With that, I am now getting 5V standby only when the main board is not connected to the power supply board. The TV still does not power on and still no standby indicator on the front of the TV. When the main board is plugged in, the 5V standby drops to 1.450V.

Here are some measurements below.

With Main Board plugged in
GND - -0.1mV
GND - -0.1mV
+5V - 0.5mV
+5V - 0.5mV
PS-ON - 1.001V
+5VSB - 1.450V
+5V - 0.06mV
+5V - 0.06mV
GND - 0mV
GND - 0mV
GND - 0mV
+12V - 3.4V
+12V - 3.4V

Big Cap - 165vDC

With Main Board unplugged
GND - 0mV
GND - 0mV
+5V - 0mV
+5V - 0mV
PS-ON - 0.1mV
+5VSB - 5.25V
+5V - 0mV
+5V - 0mV
GND - 0mV
GND - 0mV
GND - 0mV
+12V - 0mV
+12V - 0mV

I am lost at this point as to what to do next. Can please give me advice as to what to check or replace next.

[retiredcaps]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Either the 5v standby is failing under load on the power supply board or there is a short on the main board between the 5v standby rail and ground.

You can follow tom66's suggestion for testing the PSU.

https://www.badcaps.net/forum/showpo...81&postcount=4

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Which one is the 5V standby cap?
How do I identify which or where is the short?

[TVRepairNoobie]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Maybe check on fuse F1, at top left corner.
https://www.badcaps.net/forum/attach...9&d=1439441655

[budm]

Re: Sceptre X405BV-FHD3 No power Won't turn on

His main fuse is fine otherwise he will not have 165VDC on the main filter cap.
Did you replace caps C63, 64, and 67?
With the cables back in place, check the resistance (no power to the board) between GND and +5SB +5, +12V, +24.
You can also disconnect the cable and then use 47 Ohm 1W resistor as a dummy load to draw about 0.10A from the 5VSB to see if it can handle that, if it can then add another 47 Ohms in parallel to see if it can also handle 0.20A, then add two more 47 Ohms in parallel for about 0.4AO load.
BTW, where is the location of D10?

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

I tested the fuse and the fuse is good.
Yes, C63, C64, and C67 have been replaced.

With the board back in the TV and all cables plugged in, without power to the board.
These are the measurements.

+5v - 36.4Ω
+5vSB - 8.96kΩ
+12v - 0.935kΩ

I couldn't find where +24v is.

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Diode D10 is next to C62 and above the blue C37

[budm]

Re: Sceptre X405BV-FHD3 No power Won't turn on

'+5v - 36.4Ω' That is not normal!

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

'+5v - 36.4Ω' That is not normal!

Can you please explain why?

+24v - 14.63kΩ; taken from the switch for +24v

[budm]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Because it is very low resisatance, it should in the K Ohms range like the 5VSB.
That switched +5V also goes to the main board, right?
Please up load the pictures that show the whole back side of the TV so we can see how they are all connected.

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Because it is very low resisatance, it should in the K Ohms range like the 5VSB.

Ok. Does it mean there's a short somewhere or something else on the PS board that is bad or does that mean the main board is bad?
Thanks for you help, I am a rookie here.

[budm]

Re: Sceptre X405BV-FHD3 No power Won't turn on

If you disconnect the cable and check the resistance of switched +5V again, it will probably shows high resistance (it may show low resistance when the filter caps are first charged by the meter.
You can also check the switched 5V pins on the main board without cable connected to see if it will show low resistance.

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Pictures of the back of the TV

[budm]

Re: Sceptre X405BV-FHD3 No power Won't turn on

What you also do is to leave the cable that has the switched +5V connected and then disconnect other cables that are connected to the main board to see if the switched +5V will still show low resistance.

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

With just the PS board, no cables plug in
+5v - 57.7Ω

With just the main board, no cables plug in
+5v - 0.613kΩ

With just the cable PS board <-> main board
+5v - 36.7Ω

[budm]

Re: Sceptre X405BV-FHD3 No power Won't turn on

'With just the main board, no cables plug in
+5v - 0.613kΩ' so this is the reading on the main board pin?

And '+5v - 57.7Ω' on the power supply pin without cable connected? Then we need to check around that area of the output of the switched +5V section.
I see 47 Ohms resistor R115, is one end of it connected to the switched +5V connector pin?
It looks like it is, that is a big dummy load resistor, why would they want to waste 100mA of current or 1/2W of power.
So that is not the problem, it looks like the power supply cannot handle the load.

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

'With just the main board, no cables plug in
+5v - 0.613kΩ' so this is the reading on the main board pin?

Yes

And '+5v - 57.7Ω' on the power supply pin without cable connected? Then we need to check around that area of the output of the switched +5V section.

I see 47 Ohms resistor R115, is one end of it connected to the switched +5V connector pin?
It looks like it is, that is a big dummy load resistor, why would they want to waste 100mA of current or 1/2W of power.
So that is not the problem, it looks like the power supply cannot handle the load.

One end is connected to R89 and those two +5V next to the PS-ON.
The other end is connected to ground.
Where can I check around the output of the switched area?

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Which other components can I check?

[budm]

Re: Sceptre X405BV-FHD3 No power Won't turn on

Since there is only one transformer and circuit that supplies all the Voltages (5vstby, switched 5V, 12V, and 24V, and when the Voltages drops down, they all drops together per your readings in post one.
I would suggest you to disconnect the 24V wires first to see if the Voltage is still dropping, then the 12V and see again, then the +5 and see if the 5VSTBY will stay at 5V.
I think the problem is in the power supply board.

[p1668]

Re: Sceptre X405BV-FHD3 No power Won't turn on

How do I disconnect each wire and where are they located on the board?

Do I desolder each leg of the transformer one at a time and check the voltages?