Rca l37wd12 lcd tv

[tom66]

Re: Rca l37wd12 lcd tv

Clear case of bad caps. Lelon make some of the worst!

[gelatinous]

Re: Rca l37wd12 lcd tv

Ok, I've replaced the lelon cap that was reading low (470uF 16V) with a BC COMP 1000uF 25V. Both caps are 85C caps.

I'm not sure what series the BC cap is because it's just what I had laying around.... my work did a big clean out of old stock and I snagged most of the parts they were getting rid of.

Anyways, with my scope I now measure a 200mVp-p ac ripple on the standby line instead of 4Vp-p, however still no joy from the mainboard. I need to troubleshoot it next, I guess the AC ripple made something unhappy.

Thanks for the help and guidance!

Nevermind, I think this may be the cap I used.
https://cdn.badcaps-static.com/pdfs/...90732faa08.pdf

[tom66]

Re: Rca l37wd12 lcd tv

Ok, I've replaced the lelon cap that was reading low (470uF 16V) with a BC COMP 1000uF 25V. Both caps are 85C caps.

I'm not sure what series the BC cap is because it's just what I had laying around.... my work did a big clean out of old stock and I snagged most of the parts they were getting rid of.

Anyways, with my scope I now measure a 200mVp-p ac ripple on the standby line instead of 4Vp-p, however still no joy from the mainboard. I need to troubleshoot it next, I guess the AC ripple made something unhappy.

Vishay/BC components don't make low ESR caps. The ripple from that PSU should be less than 10mVp-p.

You need to use a low ESR cap such as Panasonic FC, FM or FR series. They are available from Digi-key.

[gelatinous]

Re: Rca l37wd12 lcd tv

Vishay/BC components don't make low ESR caps. The ripple from that PSU should be less than 10mVp-p.

You need to use a low ESR cap such as Panasonic FC, FM or FR series. They are available from Digi-key.

will do, I need to place an order for parts for my PSX video converter anyways. I'll report back when I've swapped the component out again.

[budm]

Re: Rca l37wd12 lcd tv

Do not replace the cap with too high of the value, I.E. using 1000uF in place of 470uf, too much in rush current and it can damage rectifierS, resistor, transformer, or blow the fuse. 680uf may be, but not 1000uF.

[tom66]

Re: Rca l37wd12 lcd tv

Do not replace the cap with too high of the value, I.E. using 1000uF in place of 470uf, too much in rush current and it can damage rectifierS, resistor, transformer, or blow the fuse. 680uf may be, but not 1000uF.

It's not inrush so much (the 1.2 ohm source resistor will limit peak current), but changing the capacitance too much can destabilise the control loop, leading to -worse- ripple.

[budm]

Re: Rca l37wd12 lcd tv

But nothing to limit the Rectifier inrush current except the DC winding resistance and the power line impedance, if you put the DMM to measure inrush using Peak recording, you will see how much current it exposed to.
I use soft start circuits to limit inrush current in products I designed when deal with large caps charging in the first half cycle of the AC.
The current sensing circuits that detect the current of the Source resistor may fault triggered into shutdown also due to high in-rush.
I agree to disagree.

[gelatinous]

Re: Rca l37wd12 lcd tv

I have some low esr 470uF caps on order, I should have them on Tuesday. I just used the 1000uF because that's what I had laying around.

[tom66]

Re: Rca l37wd12 lcd tv

But nothing to limit the Rectifier inrush current except the DC winding resistance and the power line impedance, if you put the DMM to measure inrush using Peak recording, you will see how much current it exposed to.
I use soft start circuits to limit inrush current in products I designed when deal with large caps charging in the first half cycle of the AC.
The current sensing circuits that detect the current of the Source resistor may fault triggered into shutdown also due to high in-rush.
I agree to disagree.

That would apply certainly on the primary side. If you have too large of a capacitance, you risk blowing the fuse or tripping the breaker due to inrush. On the secondary side it is less likely to matter. It is quite possible that the current detection logic would detect excessive current (and it might lock out until reset), and that is why manufacturer's specifications must be used when replacing components.

[gelatinous]

Re: Rca l37wd12 lcd tv

Ok, I've replaced the cap with a 470uF 35V low ESR and measure ~50mVp-p ripple on the 5V standby supply (5.4V). Still no joy from the main board.

With this coming weekend being a long weekend I hope to go through some of the linear regulators and determine which are running or not running, as well as look up some of the IC's.

I'm also going to look into getting an ESR meter....

[tom66]

Re: Rca l37wd12 lcd tv

Ok, I've replaced the cap with a 470uF 35V low ESR and measure ~50mVp-p ripple on the 5V standby supply (5.4V). Still no joy from the main board.

With this coming weekend being a long weekend I hope to go through some of the linear regulators and determine which are running or not running, as well as look up some of the IC's.

I'm also going to look into getting an ESR meter....

What cap did you use? Seems odd that it still doesn't work. Does ripple increase under load much?

[gelatinous]

Re: Rca l37wd12 lcd tv

This is the cap that I used:
http://www.digikey.ca/scripts/DkSear...ords=P12415-ND

I haven't loaded it down yet, I'll try it tonight and take some more screenshots

[tom66]

Re: Rca l37wd12 lcd tv

Those look perfect. It's possible the extreme ripple has damaged some regulator somewhere.

[budm]

Re: Rca l37wd12 lcd tv

And how is the 22uf 200v cap on the primary side. The relay still does not click on, like I indicate before, you can bypass the relay so the main board will get the voltages from the main power supply, and if the TV still does not work, then more troublshooting of the main board will be needed.

[gelatinous]

Re: Rca l37wd12 lcd tv

And how is the 22uf 200v cap on the primary side. The relay still does not click on, like I indicate before, you can bypass the relay so the main board will get the voltages from the main power supply, and if the TV still does not work, then more troubleshooting of the main board will be needed.

I typed the wrong value for the 22uF it's actually a 47uF and measured 44.8uF.

I have tried bypassing the relay to no avail, there's a 3.3V supply PS_ON I think that the SMPS has to see before it turns on, so while 120VAC is getting to the SMPS without that PS_ON signal from the main board the outputs will not come up. I don't have a bench supply that is in working order at the moment or I would try and supply it externally.

[budm]

Re: Rca l37wd12 lcd tv

That is strange because my l26wd12 version power supply does not have PS_ON because it is being done by the power relay to supply the main AC to turn on the power supply, the main baord will then supply the backlights on signale to the inverter board.
Can we see the closed up pictures of the main power supply and the main board.

[gelatinous]

Re: Rca l37wd12 lcd tv

I could be wrong, I was going off of the interconnect diagram that was posted in another thread. I'll have another look and see.

[gelatinous]

Re: Rca l37wd12 lcd tv

That is strange because my l26wd12 version power supply does not have PS_ON because it is being done by the power relay to supply the main AC to turn on the power supply, the main baord will then supply the backlights on signale to the inverter board.
Can we see the closed up pictures of the main power supply and the main board.

I will try and take some pictures tonight. The lighting at my place isn't very good but I'll see what I can do.

[datenavis]

Re: Rca l37wd12 lcd tv

I am also having the same exact issue with the same exact TV.

All the caps on my 1W board tested fine and I see no bulged or leaking caps anywere.

My TV would also work if left on but then one day the buttons stopped responding so i unplugged it and plugged it back in, it would turn on each time but wouldn't always respond to buttons on tv or remote.

My boss gave this TV to me and It was working when I took it from the office. After a 15 min drive it has yet to turn back on. When I plug it in, I hear a little electrical charge but no CLICK like it used to. Solid red light on front.

gelatinous any more work been done on yours?

[gelatinous]

Re: Rca l37wd12 lcd tv

I am also having the same exact issue with the same exact TV.

All the caps on my 1W board tested fine and I see no bulged or leaking caps anywere.

My TV would also work if left on but then one day the buttons stopped responding so i unplugged it and plugged it back in, it would turn on each time but wouldn't always respond to buttons on tv or remote.

My boss gave this TV to me and It was working when I took it from the office. After a 15 min drive it has yet to turn back on. When I plug it in, I hear a little electrical charge but no CLICK like it used to. Solid red light on front.

gelatinous any more work been done on yours?

Sorry I haven't had a chance to do anymore work on it yet. I've been busy with other projects and teaching a friend how to drive.

I will try and get some pictures of the power supply and main board either tonight or tomorrow.

My TV currently does nothing if I bypass the 1W board with some seizer clips, I don't measure any voltage out of the supply at all.