Dynex Dx-19E220A12 No standby led/wont power on

[jsmoke]

I have acquired a few broken tv's to gain some knowledge on how to troubleshoot them. So this one I was told it would shut off, but when I tested it it powered up fine and ran an hour great but I then turned the power off only to find the red led went out quickly and i have not been able to get it turn on again after unplugging many times.

So far I have tested a few things but have come up with nothing as my knowledge is weak because I am just learning. So far this is what I got and i am not sure what to do yet so any help would be greatly appreciated.

Thanks
jsmoke

Main In- 113.2 vac
Main fuse- 0.03 ohms
Big Cap @C506- 107v in correct polarity, 116v in reverse polarity
Bridge Rectifier @D501 AC Side~112.4, DC Side-106v in correct polarity, 116v in reverse
Cap @CV14-12.1v

HP03 Connector

BON-0.0V
PWM-0.1V
STB-5.0V
5V_1-5.0V
PON-5.4V
GND
GND
7V-8.6V
12V-12.1V
GND
GND
12V-12.1V
12V-12.1V

[budm]

Re: Dynex Dx-19E220A12 No standby led/wont power on

"Big Cap @C506- 107v in correct polarity, 116v in reverse polarity" Are you measuring right at the two legs of the cap? Do not use the chassis groind as a ground ref point when you measure the voltage on the primary (hot side) of the circuit, the ground ref point for the primary circuit will be the negative leg of that C506. The voltage on the at cap should be around 160~170vdc (120v x 1.414).
The secondary (cold) circuit ground ref point is the chassis ground.

HP03 Connector

BON-0.0V (this is the Backlights ON/OFF signal (from main board), >3V = Backlights ON)
PWM-0.1V (Backlights Dimming control, from main board)
STB-5.0V
5V_1-5.0V
PON-5.4V
GND
GND
7V-8.6V
12V-12.1V
GND
GND
12V-12.1V
12V-12.1V
So it looks like your main board is not working.
We will need good clear of the WHOLE main board, the pictures looks like it get cut out. I can see some LDO regulators that need to be checked out.

[jsmoke]

Re: Dynex Dx-19E220A12 No standby led/wont power on

I can confirm I am testing the cap at it's leg's. Seems to be low as sometimes when I have measured it it has only been around 96v. I am not good at taking pictures but will post these for now and hope to get some better ones with daylight tomorrow.

[jsmoke]

Re: Dynex Dx-19E220A12 No standby led/wont power on

Also here is the chip that is attached to the heat sink in the bottom left corner of the board.

[budm]

Re: Dynex Dx-19E220A12 No standby led/wont power on

That the stereo power amplifiers that drive the speaker.
I think we need to find out why you are not getting 160~170VDC on that large cap. Does that cap look like it has any corrosion on the holes where the legs exit? Do you have at least cap meter. Also I hoe your meter is OK.
This TV uses LED backlights so it does not draw that much power to cause the voltage on that cap to drop down to 96V.

[jsmoke]

Re: Dynex Dx-19E220A12 No standby led/wont power on

. The voltage on the at cap should be around 160~170vdc (120v x 1.414).

May I ask where the 120v x 1.414 comes in? As I would like to know how to tell what voltage should be because I didn't know if that voltage was correct or not.

My meter seems to be fine as is gives me correct voltages for many other things, haven't tested on dc that high tho. I do not have a cap meter yet but plan on getting one in a few weeks. Doesn't seem to be any corrosion near that cap but did touch it up anyways.

Also there is a little board on the top left of the power supply board, would I be correct at saying this is the inverter board?

[tom66]

Re: Dynex Dx-19E220A12 No standby led/wont power on

120V is the nominal "heating" voltage of mains electricity in the US and some other countries.

Thing is, if you take the average of a sine wave, you will find it is zero. So surely, the average power is zero? Of course, it isn't -- otherwise, nothing on AC would work.

So RMS is used, basically it states that a wave with an amplitude of sqrt(2) (about 1.4142) has an RMS voltage of 1V. So, for an RMS voltage of 120V, the amplitude of the wave is 1.4142 times that, or about 170V. The capacitor and bridge rectifier are, in simple terms, converting the AC to high voltage DC which the rest of the power supply uses.

120Vrms means that 120V AC has exactly the same heating power as 120V DC. If you put each through identical heaters, both would heat up equally.

[jsmoke]

Re: Dynex Dx-19E220A12 No standby led/wont power on

120V is the nominal "heating" voltage of mains electricity in the US and some other countries.

Thing is, if you take the average of a sine wave, you will find it is zero. So surely, the average power is zero? Of course, it isn't -- otherwise, nothing on AC would work.

So RMS is used, basically it states that a wave with an amplitude of sqrt(2) (about 1.4142) has an RMS voltage of 1V. So, for an RMS voltage of 120V, the amplitude of the wave is 1.4142 times that, or about 170V. The capacitor and bridge rectifier are, in simple terms, converting the AC to high voltage DC which the rest of the power supply uses.

120Vrms means that 120V AC has exactly the same heating power as 120V DC. If you put each through identical heaters, both would heat up equally.

Thanks tom66 that clears it up for me, guess it is a constant if only working on 120v. What would it be where you live then 230v?

[tom66]

Re: Dynex Dx-19E220A12 No standby led/wont power on

About 230 * sqrt(2) or 325V.

[budm]

Re: Dynex Dx-19E220A12 No standby led/wont power on

The capacitor will be charged up to the peak of the sine wave (minus Vf drop of the rectifier diodes) 120vRMS peak voltage is = 120 x1.414, peak to peak voltage is 120 x 2.82.

[jsmoke]

Re: Dynex Dx-19E220A12 No standby led/wont power on

Just a quick update, I ended up changing the cap @C506 with closest I could find that I had lying around( 100uf 250v instead of 150uf 200v) and now get 149v at the cap and bridge rectifier.I also get the same voltage in both polarity's now.

Can anyone recommend a replacement cap from digikey.ca to replace the 150uf 200v?

[tom66]

Re: Dynex Dx-19E220A12 No standby led/wont power on

This should do fine, if it fits.
http://www.digikey.com/product-detai...520-ND/1086745

[jsmoke]

Re: Dynex Dx-19E220A12 No standby led/wont power on

This should do fine, if it fits.
http://www.digikey.com/product-detai...520-ND/1086745

Yes that should fit fine. Will update once I get Order in. Thanks