Dynex dx-22ld150a11 flashes white once to blank

[koppit]

It's the same make and model as this post, it does a white flash then goes to black (not two seconds), then you wait a few seconds and it does another white flash and goes to black. I'm getting nothing on the screen period, audio works fine, dvd player works fine.

Capacitors pass visual inspection. Fuse appears OK.

Not sure what the resistance values of the primary transformer should be..or if I should even be looking at it. It's the white one in picture 2 of the above post (this picture), labelled as a TDK part, with this text on it:

29LEC-T121 01 E206162
TDK X 1014 SRW-SBI4.1

I can't seem to find a value for it on google. In this picture it shows the pinout as 1,3,5,6,7,8,9,10,12 - they read 1-1.2 ohms when I test them on the lowest ohm rating on my multimeter.

I tested the resistance of the secondary transformer (this one) and got the following results:

1-2: 963 ohms
3-4: 975 ohms

Thanks in advance!!

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

Checked voltages on the rear of the power board;

https://www.badcaps.net/forum/attach...3&d=1341430417

all of the 12v's check out OK, the DIM and BL_ON come in at 3.2 . LAMP_ERR has no voltage, 5VSB shows 4.8v and the AC_OFF_DET shows .2v

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

Maybe it's not the power board, but the board that sends information to the screen?

[budm]

Re: Dynex dx-22ld150a11 flashes white once to blank

You say the screen flashes, if you look at the back, can you still see the glow on the back side? What I am trying to find out if the backlights turn off or if the T-CON board turns off.

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

Hey Bud, thanks for the reply. Looks as though the backlight goes off completely. From the back I see two flashes, one when you turn it on, then another about 5 seconds later.

[budm]

Re: Dynex dx-22ld150a11 flashes white once to blank

Can you monitor the BL_ON PIN to see if that voltage is steady or if it comes and goes when the backlights were flashing on-off, we need to find out if the main board is telling the backlights to go on-off or if the fault is at the inverter circuits.

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

The voltage when powered on goes up to 3.2, then drops to nothing, then a few seconds later goes back up to 3.2 and holds steady at 3.2v. Are you thinking this could be two separate components? No image and no backlight? On previous screens I've still seen the image, even if the backlight doesn't work ... this time no such luck.

[budm]

Re: Dynex dx-22ld150a11 flashes white once to blank

The image should be there if the main board and the T-CON are good, failed backlights circuits will not cause the main board not to display image, backlights are just the light source. So you may have two problems. If the BL_ON and the 12v are present but the backlights still not on, then you have problems in the inverter circuits. I see two surface mounted MOSFETs that drive the inverter transformer. Need to get the P/N to see the pinouts.

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

OK, I think these are the ones you're looking for: On the inverter board with all of the external connections, there are three mosfets, two close to each other at the top right of the third picture?

They appear to have an (A) logo with D452A on it, underneath that BA0K35

The third one near the cable connector says UTC L01117AL and 50A01NBC2

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

OK so I tried to test these with my DMM, EQUUS #4320. From what I've read, I have to arm the mosfet by holding the negative probe to the middle drain, and positive to the gate (left). Then switch out the positive and move it to the source (right). I get inconsistent readings when on the diode setting - what is 'normal', or do I need a better DMM to test these?

Also, do I need to remove it from the circuit? Would a 9V mosfet tester from ebay be a good investment?

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

After further investigation .. they are "AO D452 n-channel FET" (thanks to https://www.badcaps.net/forum/showthread.php?t=16807) but can't find the datasheet or a suitable replacement if necessary. Hope someone can help!!

[retiredcaps]

Re: Dynex dx-22ld150a11 flashes white once to blank

Your multimeter manual will tell you what readings are "normal" for a diode test. Most fets will fail, from what I have seen, as a dead short.

As for a replacement, if needed,

http://www.ebay.com/itm/120920841855

[koppit]

Re: Dynex dx-22ld150a11 flashes white once to blank

Unfortunately I don't have a manual for that DMM, I've had it for too long. I'll keep googling to see what I can find, and thanks for finding a replacement! I had spoken to digikey but they didn't have any in stock, and they quoted an alternative that also wasn't in stock... go figure.
Worst case scenario is the entire board is $30.. Guess that's not too bad, considering.
Cheers!