Element ELEFW40C won't turn on.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

Here's a good video that goes into the differential probes.

https://youtu.be/RDLWQFgJ1uU

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

I got the replacement board today and it works fine.

I went through and recorded all the values on the good board for the transistors on the non-power supply part of the board. I'm going to switch out the good board with the bad board and see if the values are all the same. I'm hoping I find a bad transistor, then I can repair the broken board and maybe sell it to get some money back.

[vinceroger69]

Re: Element ELEFW40C won't turn on.

Glad a replacement board has got the set working and yes its a good idea hopefully you can find the issue.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

Okay, so like I said, I took measurements of all the transistors on the working board. Then I went and checked on the bad board.

There's one on the good board that has all 0.0000VDC on all three pins. I don't think it's active yet. But on the bad board, one of those pins doesn't read 0.0000VDC at all. It's in the millivolts range, but keeps climbing and climbing and climbing. Last I checked, it was around 80mv.

Then, there's one on the good board that has 5.17V on the input and the output is 30mv, but on the bad board, it's got the 5.17V (or around there), but only 8mv on the output. Would that be a bad transistor? I'll go check the rest of them.

[martino]

Re: Element ELEFW40C won't turn on.

Would love to see the eeprom from the good board swapped onto the bad board for a sec to see results.

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

Would love to see the eeprom from the good board swapped onto the bad board for a sec to see results.

I'm sorry, I ended up just giving the TV back. I got tired of having it around, but I still have the bad board. If you'd like, I can pull that eeprom and try dumping it, now that I have a CH341A spi / eeprom reader / writer.

[Agent24]

Re: Element ELEFW40C won't turn on.

So, I'm watching the video. I notice something that strikes me a bit odd. He doesn't have a square wave, but it's fairly close to one. When I put a square wave on my scope, I only see the top and bottom horizontal bars, I don't see the vertical bars. Is this normal for some scopes or does mine need some work?

It is normal for a CRO. They will show up on a DSO though, which is what he has.

I have a waveform generator. All the signals show on the scope, except one. That signal is all messed up. That means there's either something wrong with my scope or something wrong with the waveform generator. I'm leaning towards the waveform generator, because it's really old but the other signals work just fine. Maybe I should recap that as well and see if it fixes anything.

That depends, what is the signal that seems odd? Perhaps you are just not measuring it correctly.

Once I get the isolation transformer, it should matter what I plug into it, am I correct? I can plug either the scope into it or the device under test. I just need one to be not sharing the same ground with the other. If I had a scope that had isolated inputs, I should still purchase an isolation transformer though, right?

Typically you want to put the DUT on the isolation transformer. NOT the scope. In some very rare cases it would be desirable to 'float' the scope, but it's dangerous.
It will add some safety (for you) to use an isolation transformer anyway, if you have isolated inputs or not.

Finally, I still don't understand why when I tried probing the transformer it caused sparks on my oscilloscope. I understand an isolation transformer will prevent this, but I don't understand why it happened to begin with. Could someone try explaining what went wrong?

I thought you were probing a crystal?

[Spork Schivago]

Re: Element ELEFW40C won't turn on.

It is normal for a CRO. They will show up on a DSO though, which is what he has.


That depends, what is the signal that seems odd? Perhaps you are just not measuring it correctly.


Typically you want to put the DUT on the isolation transformer. NOT the scope. In some very rare cases it would be desirable to 'float' the scope, but it's dangerous.
It will add some safety (for you) to use an isolation transformer anyway, if you have isolated inputs or not.

I thought you were probing a crystal?

This time, I was probing a crystal, but the first time I tried using my scope, maybe a year or so ago, I tried using it on this worklight. I put the probe on the transformer, expecting to see a waveform, but I did something horribly wrong and sparks flew. I was lucky I didn't get hurt. After that, until now, I was afraid to use the thing! I just never had time to sit down and research it, but I feel a lot more confident now in my abilities.

I'll pull out the signal generator tomorrow and see what signal it is. I want to say the triangle wave.