replacement hp-t5054 replacement power board no power

[tmlfan]

picked up this tv a while ago, had no power but audio, pulled power board from tv to take measurements and such, plugged in several times to check measurements and then all of a sudden something failed/shorted and and basically ruined board

So basically i found and ordered a replacement power board, got it but was so busy at work it was a month before i could try it and now it is too late to return it, basically on the new board i dont get any voltages on the test points where the main board feeds power to the other boards, also tried across main caps and power transistor, both still 0V, doesn't make sense to me as it looks the the board was refurbished and a few of the caps seem to be upgraded from the parts store i bought it off of, checked fuses on main board also, they tested good, ill post pics of the board, hopefully they are clear enough to see

[dick_barton]

Re: replacement hp-t5054 replacement power board no power

Have you check the fuse marked in photo?

[Andrew F. Ali]

Re: replacement hp-t5054 replacement power board no power

Have you check the fuse marked in photo?

Re-check those fuses again. Is the ac chord OK? are you getting ac across the Bridge Rectifier?

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

Checked that fuse and it is still good, ac cord is still good also, when your powering these boards to test voltages is it fine to leave them out of tv and plug ac into board or should I put back in the tv first so the tv ground is attached to it

[budm]

Re: replacement hp-t5054 replacement power board no power

Can we see the straight shot pictures of the WHOLE board top and bottom side?
What is your country AC Voltage?

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

I am from Canada, (a.c. voltage), here is a pic of top and bottom of board

[budm]

Re: replacement hp-t5054 replacement power board no power

OK, the standby power supply section has its own little red rectangular which tested good per your reply, right next to that fuse is the main filter cap for the standby power supply. You need to find out if you do have about 160VDC between the two legs of that cap or not.
You will not have any DC on those two large filter caps for the main power supply until the board gets the PS-ON to turn on the power relays, but since you are not getting ANY DCV on the cold side so you need to fix the standby power supply section first. You can run the board by itself to troubleshoot the standby power supply section. You are 100% sure that you are not getting any standby Voltage, right?

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

Sorry for the late reply, I am getting 166v across that cap

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

Also double checked the voltage at PS-ON located here and it is measuring 0V located here on pic 4th pin from left

[jetadm123]

Re: replacement hp-t5054 replacement power board no power

PS-ON voltage will come from the mainboard. The 5V standby voltage is supplied by the power supply and is what is required by the mainboard to produce the PS-ON command. Since you have 0V from the standby power supply, as budm indicated, you'll have to repair that first.

[budm]

Re: replacement hp-t5054 replacement power board no power

https://www.badcaps.net/forum/attach...7&d=1510182086
Check or replace startup/running cap CB813.
Check the cold side Rectifier diode DB8?? to the right of that little green standby power transformer.
Check the 22 Ohms resistor RB820 which is close to pin 1 of the SMPS IC.
Check Zener diode ZB803, ZB804 to see if they are shorted or has very resistance in both direction or not.
Provide us the P/N of that standby SMPS ICB802 so we can verify the DCV of each pins of that IC with ref. to the primary side circuit GND. It looks like pin 4 is the VCC pin.
BTW: the part designator that has 'B' in it are for the Standby circuit. I.E. cBxxx, rBxxx, dBxxx.
The power supply board is SAMSUNG P/N BN44-00190A.
http://www.shopjimmy.com/samsung-bn4...wer-supply.htm
Oictures provided by shopjimmy.

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

Are you sure about RB820, only 2 resistors I see by pin 1 is RB829 and RB830

[budm]

Re: replacement hp-t5054 replacement power board no power

I just look at the pictures again, sorry it was typo, it is RB830, 22 Ohms.
Do not forget about the IC P/N.

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

ok heres my findings so far,

-CB813 rated for 47u/50v, measured 53u/20V plugged in

-ZB803/ZB804 measured 450k ohms both ways

-ICB802 p/n VIPer22a
KB3745

-RB830 22 ohm resistor measured 2.4 ohms

-DB864 diode on cold side OL one way/3.2K ohms other way

[budm]

Re: replacement hp-t5054 replacement power board no power

OK, I do not understand the reading of CB813, Are you saying that it shas 20VDC between the two pins of that cap when the board is plugged into the AC outlet?
Viper22 spec sheet attached.
We need to find out if we have enough Voltage at VDD pin 4 to run the IC or not. The startup threshold Voltage on VDD pin is 14.5V typ. so that VDD has to reach 14.5V when the power is first applied to the board, one the circuit is running and as long as it does not drop down to >8V which will put the IC into under Voltage shutdown mode, page 4/21.
The spec sheet has the explanation on how the IC operates.
You are working in the primary side of the circuit so the GND ref for the meter will be the negative leg of the main filter caps.

[Relayer]

Re: replacement hp-t5054 replacement power board no power

Hello tmlfan,

-ZB803/ZB804 measured 450k ohms both ways

Did you lift one leg of each diode when you made your measurements?
If not, you need to lift a leg on each to get a more accurate reading. You shouldn't be getting 450k both ways. Seems like other components are affecting your readings.
Regards,
Relayer

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

Rechecked DB864/ZB803/ZB804, unsoldered 1 leg from board, all tested fine, OL one way, high resistance the other way

Also got 20 VDC on pin 4 when board was plugged in

Was looking back at the measurements I took a few posts back,

-RB830 22 ohm resistor measured 2.4 ohms, should I be worried, don't these usually only have 10% tolerance

[budm]

Re: replacement hp-t5054 replacement power board no power

If the VDD is at 20V then the IC should be working. Are you 100% sure that you are not getting any DC out put on the cold side of this standby power supply? Otherwise replace the IC.
Looking at the picture of the resistor, I see Red, Red, Black, Silver = 22 Ohms 10% Tol.

[tmlfan]

Re: replacement hp-t5054 replacement power board no power

Checked half a dozen caps on the cold side of the board when plugged in, a couple of them had 1.3V across them and the rest were under 1V, so do you think the next thing to try is to replace ICB802

[budm]

Re: replacement hp-t5054 replacement power board no power

Yes.