Insignia NS-37D20SNA14 no power.

[Spork Schivago]

Hello,

I have an Insignia NS-37D20SNA14 that isn't turning on. There's no standby light or anything. I check the fuse and it's bad, so I replace it. It was a 15A 250V round red plastic fuse, but I replaced it with a 15A 250V square red plastic fuse.

There's still no standby light. I check the caps with an ESR meter, they test good.

Then I lift a leg on the four general purpose plastic rectifiers. I tested them like you would a diode. Not sure if that's right or not. I thought they were diodes. They're Vishay 1N5407's. With a leg lifted though, the continuity is different for certain ones, which makes me wonder if they're bad. I solder them back into place and hook the power supply board up. Then I try powering it on.

I take the DMM and set it to VDC. I check the voltage on them, like I'd check a diode. Some don't have any voltage leaving at all. Not sure if that's proper or not. I used the ground coming in from the AC line as a ground source.

Would they be bad? They're the ones in DSC01948, in the top left. I also lifted the heat sinks and checked the components under there (MOSFETs and Diode arrays or whatever they're called) and they tested fine.

I tried checking to see if there was 12V on the connector where it's labeled 12V. I got nothing. I tried checking to see if there was 55V on the connector for the LED backlighting, nothing.

Thanks!

[dskall]

Re: Insignia NS-37D20SNA14 no power.

What's voltage on main cap

[dick_barton]

Re: Insignia NS-37D20SNA14 no power.

You do mean 1.5 Amp and not 15 Amp don't you! The diodes when lifted should really all read the same. I would replace them if they don't. They are general purpose 560V (800V peak) 3 Amp diodes.
Do you have any dc voltages on the white connectors?

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

You do mean 1.5 Amp and not 15 Amp don't you! The diodes when lifted should really all read the same. I would replace them if they don't. They are general purpose 560V (800V peak) 3 Amp diodes.
Do you have any dc voltages on the white connectors?

I thought 15AMP was insanely high, but when I read the fuse, it doesn't say 1.5AMP. It says:

T3, 15A 250V
382

Here's exactly what it looks like. Maybe it's rated current 3.15A?

The white connectors where the various wires hook up to? No, but I didn't check the PWM pin. So, how does the logic board turn the PSU on? I don't see a PS_ON. Does it involve the PWM pin somehow?

Here's the Vishay Diodes:

https://www.digikey.com/product-deta...GICT-ND/190144

Are they a good brand name or should I try purchasing a better one?

Thanks!

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

What's voltage on main cap

Which one is the main cap? That big one that's off by itself or those two big ones next to each other? How should I reference ground? Just black probe on the cathode side or should I reference chassis ground or something?

Thanks!

[dick_barton]

Re: Insignia NS-37D20SNA14 no power.

The boards are often poorly marked and I would be looking at 1.5A rather than 15A which would probably vaporise your components if there was a short. However looking up the board on google it's a T3.15A fuse.

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

The boards are often poorly marked and I would be looking at 1.5A rather than 15A which would probably vaporise your components if there was a short. However looking up the board on google it's a T3.15A fuse.

Thanks. Yeah, that's the conclusion I came to, a slow-burn T3.15A fuse. Just so happens the square one I put in had the same markings and shows as a slow-burn T3.15A fuse as well, so I think I'm good there.


I found two new 1N5400's in the basement. Too bad I couldn't use them, but I see they're rated for 50VDC, not 800VDC, like the 1N5407's. Looks like I'm going to have to order some 1N5407's.

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

What's voltage on main cap

For C625 (the 250V 47uF capacitor), with reference to the AC gnd, it's 0VDC. With reference to the capacitors gnd (the black probe on the cathode side), it's 0VDC.

I think I'm going to recap this PSU while I'm at it. Gonna start looking for new caps on digikey.

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

So I'm going through the caps. I see Mouser has a Nichicon 4.7uF 50v electrolytic cap ( http://www.mouser.com/ProductDetail/...wHjdTenA%3d%3d )

80mA for rated ripple current, 10,000 hours at 105c. Leakage current is 3uA. It's a ULD series. I think that would make a good choice for this TV, don't you? They're only 17 cents a pop....

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

These are the caps I ordered:

C510 -- http://www.mouser.com/ProductDetail/...wHjdTenA%3d%3d

C511 -- http://www.mouser.com/ProductDetail/...jtfSZwRA%3d%3d

C625 -- http://www.mouser.com/ProductDetail/...HFGGh%252bM%3d

C523, C524, C525 -- http://www.mouser.com/ProductDetail/...54ZssHrQ%3d%3d

C506, C507 -- http://www.mouser.com/ProductDetail/...2bSKyFA4BK8%3d

C521 -- http://www.mouser.com/ProductDetail/...52b7ehMA%3d%3d

C518, C519, C530 -- http://www.mouser.com/ProductDetail/...zZq52AGQ%3d%3d

D501, D502, D503, D504 -- http://www.mouser.com/ProductDetail/...RnVkhRo1AWo%3d


What do you guys think? Sorry for all the links, but this way, you guys can check out all the specs instead of me trying to figure out what specs you want to see and what ones you don't want to see.

C506 and C507 have a max ripple current rating of 860 mA. C625 has a max ripple current rating of 1,290 mA.

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

I've replaced the general purpose plastic rectifiers (diodes). Then I went and replaced the other diode I didn't notice earlier. Finally, I replaced all the caps. I checked every single one of the old ones for ESR and capacitance, they all fall within respective ranges.

One of the new caps I got has an ESR of something like 0.20, but the old cap has a lower ESR, like 0.02 ohm. Is this going to be a problem? In the first picture in Post #1, it's the far upper right one, the one that's all by itself.

Anyway, the television turns on now. So I'm wondering if I should attempt to gain access to the LED strips and resolder them. I believe this television has problems with the strips having been poorly soldered. I've never attempted anything like before and would like a good idea of what I'm looking at. Is it difficult, extremely hard, fairly easy, does it take a lot of time? I'd rather do the repair properly, rather than give it back just for it to break again.

I wonder why my DCA meter doesn't detect those general purpose plastic rectifiers as faulty. The DMM shows they do block electricity one way, but the resistance varies greatly when I measure it the other. The new ones all show around 6Mohms. Some of these old ones show around 6, around 4, and 0.2Mohms or something low like that.

Thanks guys!

[Spork Schivago]

Re: Insignia NS-37D20SNA14 no power.

I think I know why the DCA meter doesn't detect them as bad. With the bad ones, they're resistance is lower than the good ones, but it still blocks electricity the way it's supposed to block it. So, from the DCA's perspective, they measure good. If there weren't four them that were the same part #, I would have never of known they were bad.

I think from now on, I'm going to have to find the datasheet for the diodes / general purpose plastic rectifiers, and then use the DMM to verify that they're good.

I'm going to search the forums and see if I can find a thread where someone resoldered the LEDs on the LED strips, just to get an idea of what's involved and how to proceed on tearing the screen apart, without damaging it.

Thanks!