DYNEX DX55L-150A11 Randomly turns off

[dskall]

Re: DYNEX DX55L-150A11 Randomly turns off

I had low 357v on main cap. Replaced out of tolerance feedback resistors. Don't remember numbers but three in series on back of board. Brought it up to 391v.

[freakaftr8]

Re: DYNEX DX55L-150A11 Randomly turns off

That makes perfect sense low voltage on a main cap means low primary which means any spike in current that the secondary can't keep up with will cause a shutdown on a feedback circuit since the power supplies working in overdrive trying to regulate all voltages and keep a good voltage going to all secondary outputs

[dskall]

Re: DYNEX DX55L-150A11 Randomly turns off

I didn't post a confirmed fix because I hadn't run more than about an hour. But it was shutting off at that time around every 20min. I made both of the repairs at the same time. When I was testing voltages at ic it would shut down. Maybe the fix was the low voltage and not the ic. I have it running for several hours now with no shutdown. I have no good inputs to test with except to take it to living room and hook up. My wife getting tired of lifting them. Maybe I should help her. LOL

[freakaftr8]

Re: DYNEX DX55L-150A11 Randomly turns off

So sure enough. Power across the filter is 355vdc. Seems low. Those 3 power resistors are supposed to be .15 ohm. Well they are reading .28ohm. This would cause the low voltage on filter caps Right?

[dskall]

Re: DYNEX DX55L-150A11 Randomly turns off

I will pull my board and post where they are. They are smd resistors on back of board

[dskall]

Re: DYNEX DX55L-150A11 Randomly turns off

R804,5,6 Are the feedback resistors for N801 which is the pfc controller NCP1653A. In series about 1.9m

[budm]

Re: DYNEX DX55L-150A11 Randomly turns off

R804,5,6 Are the feedback resistors for N801 which is the pfc controller NCP1653A. In series about 1.9m

That is the typical failure when you have low Boosted PFC Voltage, common failure in SAMSUNG TV and causes the backlights to flash, but the sad part is that people on web said to cut the jumper wire to fix the problem when in actually it disable the LOW Boost Voltage shutdown circuit. The cause is the resistors in the PFC OUTPUT Voltage control feedback.

[budm]

Re: DYNEX DX55L-150A11 Randomly turns off

So sure enough. Power across the filter is 355vdc. Seems low. Those 3 power resistors are supposed to be .15 ohm. Well they are reading .28ohm. This would cause the low voltage on filter caps Right?

You have to subtract the probe leads resistance from the reading to get the resistance value when measuring in low Ohm.

[freakaftr8]

Re: DYNEX DX55L-150A11 Randomly turns off

ThatsThat's something I always forget. Dumb move on.my part. Ok well these three resistors two of them for the feedback is a 620k and one is a 680k. One of the 620K ohms were reading 590 k. Anything but a 680 k. Power at the filters are now 406v. No shut down yet. Hopefully we may be onto something. Dskall I believe the low PFC is truly the cause now. I'm leaving the TV on all night will know more in the morning

[Burningstariv]

Re: DYNEX DX55L-150A11 Randomly turns off

Waiting to hear back from your update freak, I'm already a noob when it comes to electronics and I'd hate to fix one part and have to do more. I dont even know if i know how to change a resistor.

[freakaftr8]

Re: DYNEX DX55L-150A11 Randomly turns off

Okay the update. It's still working. No shutdowns at all last night or this morning. I also powered it down after being on for hours and then power it back up.

I'm fairly confident now that this power supply has a problem with PFC feedback. When the voltage goes lower than acceptable the thermistor gets extremely hot. When this starts to happen the voltage goes low on the primary caps and the power supply struggles to keep the TV working. 391 - 407v seems optimal when this power supply is functioning in its on state. Any less than that I would look at the feedback resistors that dskall had pointed out

R804 R805 R806. in SERIES these should equal 1.95mohms

[Burningstariv]

Re: DYNEX DX55L-150A11 Randomly turns off

So I bought the pwm controller is this the same as the pfc you are talking about freak or is that another part. Also what resistors would you recommended if those 3 are bad also.

[freakaftr8]

Re: DYNEX DX55L-150A11 Randomly turns off

Well it depends on how you feel about your soldering skills if you want to pull and replace that pwm controller. It is kind of a chore considering their 16 pins. But I'm somewhat confident that maybe this controller is not bad to begin with. The resistors I am talking about if you look at the back side of the board. You're going to need to order two 620k And1 680k smd resistors. I believe the rated at 1 watt.


What I would do is place a voltmeter set to DC and check the leads of the main filter cap there are two of them you can check either one with the TV power on. Tell us what the voltage is reading off of that main filter cap period black lead to negative side red lead to positive side

[dskall]

Re: DYNEX DX55L-150A11 Randomly turns off

I just used regular 1/8 watt resistors. The current on feedback circuit should be quite low. I had thought maybe bad thermistor because it was getting hot. Haven't checked it after the repair.

[Burningstariv]

Re: DYNEX DX55L-150A11 Randomly turns off

I'm confident in my soldering skills. I plan on getting 1 of these

http://www.ebay.com/itm/25pcs-1-8-WA...-/182442959957

and 2 of these

http://www.digikey.com/product-detai...RCT-ND/2022737

I'll go ahead and check the main filter cap before I purchase any further parts including the ones above.

[dskall]

Re: DYNEX DX55L-150A11 Randomly turns off

So I bought the pwm controller is this the same as the pfc you are talking about freak or is that another part. Also what resistors would you recommended if those 3 are bad also.

Do you want to cancel order for controller as I don't think it is the problem.
Your digikey is for 620ohm should be 620kohm

[budm]

Re: DYNEX DX55L-150A11 Randomly turns off

BTW, to trim the output Voltage you can vary the resistance of the resistor that is connected in series to those 3 high Ohm resistors to GND, it will be much lower resistance usually around 20~50K Ohms range depend on the required feedback Voltage on that resistor to get 390VDC output, the DCV on that resistor is also very low since it is part of the Voltage divider circuit.

[freakaftr8]

Re: DYNEX DX55L-150A11 Randomly turns off

Well this is a confirmed fix. Budm and dskall are correct. I have replaces both "6203" resistors because of drifting values. This in turn brought the high voltage from 355 volt to 407 volt. No more shutdowns.

[cyberthief]

Re: DYNEX DX55L-150A11 Randomly turns off

I am completely new to all of this but I am not afraid to fry a TV that is already not working. I appreciate all the effort you guys have done and figuring out the same issue I am currently having with my TV. Could I bother one of you guys to identify in a picture which were the parts that were replaced for the fix. I would greatly appreciate it, thank you.

[dskall]

Re: DYNEX DX55L-150A11 Randomly turns off

What voltage do you get across your large capacitor on power supply?