dynex hdtv/emerson hdtv troubleshooting

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

I measured the cap again and it was 155 reading in volts...the pin 3 to pin 6 reading says 0L and looks to be ohms...I am using a fluke that sets the scale automatically and it doesnt
have a dial you can change the setting.

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

161.2 volts with the fluke meter? Ok,stick with the fluke I'd say
On the 13 pin connector,pin 3 is 5vstb? or pin 4,I cant read the print clear..
what do you read there? measure between pin 3(or 4) and pin 6(GND) with meter on 20 volt DC..

OK, we are trying to find out if you do have DC Voltage at the 5VSTB on the pin of that 13-pin connector or not, so I do not understand why you are using Ohm mode when testing the board that is being powered unless you want to damage the meter.
You use Ohm mode when the board is not plugged into the outlet.
So at this point you have 0V at the 5VSTB pin? Correct readings are important to us so we will not be doing wild goose chase.

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

Here is the spec sheet for the 5VSTBY SMPS IC.
We will be doing the DC Voltage test and the resistance test once we know for sure we do not have 5V at the 5VSTB pin.

[martino]

Re: dynex hdtv/emerson hdtv troubleshooting

maybe a pic of the fluke meter to make sure its on the right setting?

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

"OL" means over range. So are you getting OL or 0V? 0V then meas we will have to look at the STBY section. Right now you are getting the 160VDC for the main voltage to run the STBY power supply which will be the IC and the components around the IC that MARTINO had redlined.

0 volts..

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

OK, now we will be working in the primary side (deadly side), you will be measuring the DC Voltages using black probe on the pin 3 which is the Ground pin of the IC, then use the RED probe to measure the voltages on all the other pins, report the readings, I.E.

Pin 1 : xxx V
Pin 2: xxx V
Just make sure you do not let the probes slip on you.
See the spec. sheet so you will know the pinout of the IC STR-A6XXX series.

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

Pin 1 = 0 volts
pin 2 : 5.16
pin 4 : 0
pin 5: 2.24
pin 7: 167
pin 8: 167.3

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

OK, the IC is not driving the transformer since the VCC pin 5 only has 2.24VDC.
Unplug the power from the board and let it sit for about 15 minutes, then take the RESISTANCE reading between pin 3 (Black probe on this pin) and all other pins, report the readings and make sure if to tell us if the meter is showing in OHMS, K OHMS, or M OHMS.
BTW, the voltage reading is done with the power supply board by itself and no cables between the power supply board and the main board connected? If not, then try measuring the 5VSTB pin again without having the main board connected.
The problem can be bad IC, bad startup cap C528, main board is drawing too much current.

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

No it wasn't connected to the main board,just to the power supply.

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

pin 1: 1.9
pin 2: .215M
pin 4: 2.0
pin 5: 36.6k
pin 7: 1.9M
pin 8: 1.88M

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

I would expect Pin 5 VCC resistance should be higher than that, try removing the startup cap C528. I also need REALLY GOOD CLOSED UP AND WELL FOCUSED picture on the bottom side of the board around that IC, I need to find out what other components are connected to pin 5. You may have bad IC at this point.

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

i have to take the pic on the cell phone...hope you can see it good.is c 528 the big black cap I tested originally?...

[martino]

Re: dynex hdtv/emerson hdtv troubleshooting

No,the big black cap is the main filter cap,don't worry asbout that one
The one budm means is located right beside the IC you measured,if you look at the pic in post #16,it's right below the chip I circled,C528 is printed beside it....

food for thought:budm,do you think that because it's a power surge that killed it,that the zener diodes/resistors could be suspect? 2 different value zener diodes in series,followed by 2 resistors parallel sitting between Vcc and Pground? Voltage spike-zdoides pass current-resistors fry...
Just a thought as I'm sitting here with popcorn following this in a aid to learn from you

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

so are you thinking that it is probably this board that is bad? I did go out and buy an inexpensive soldering iron but I don't how good I will be micro soldering after over 20 years away from it..lol

[martino]

Re: dynex hdtv/emerson hdtv troubleshooting

Yes,the 5volt standby is missing,it's the life line of your TV.
When TV is off,the 5volt standby remains active,keeping part of the mainboard alive.
Mainboard is patiently waiting for the power on command from you.It then turns on the powerboard(12v,24v etc)needed for full operation.
We need to get the 5v standby back first,then we can test if the rest is operational.
Now a easy way out is to just replace the entire powerboard,but that is up to you.
Telling me you already bought an soldering iron tells me your interest in component level repair is high enough,also,it's probably cheaper this way as it might just be a cap and/or a diode etc..,you learn lots,its fun and the for ever fame from your better halve is priceless...(my wife thinks I'm einstein already,eventhough I constantly need help from the pro's here,lol)
Having said that,and not to be depressing,there is also a change the mainboard is defective due to the power surge.Therefore fixing the powerboard with a few bucks will keep cost low just in case...You're in excellent hands with budm here!!
***end of motivational speech***

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

thanks for that post,Martino...I'm just amazed how much of this I've forgotten though in the last 20 years,but with you guys helping me out I should be fine..

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

No,the big black cap is the main filter cap,don't worry asbout that one
The one budm means is located right beside the IC you measured,if you look at the pic in post #16,it's right below the chip I circled,C528 is printed beside it....

food for thought:budm,do you think that because it's a power surge that killed it,that the zener diodes/resistors could be suspect? 2 different value zener diodes in series,followed by 2 resistors parallel sitting between Vcc and Pground? Voltage spike-zdoides pass current-resistors fry...
Just a thought as I'm sitting here with popcorn following this in a aid to learn from you

That is why I request the bottom side of the board to see how that IC gets its VCC voltage from, and if it also has Zener diode in that section.

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

OK, see the picture attached, see if point 1 is connected to point 5 as marked, if it is, lift up one leg of that suspected Diode then power up the board to see you will have 5VSTBY.

[ddarn]

Re: dynex hdtv/emerson hdtv troubleshooting

sorry, my electricity has been out but now back on...the suspected diode is d509? You said lift it up..clip one of the legs to raise it up or melt the weld and raise it up?

[budm]

Re: dynex hdtv/emerson hdtv troubleshooting

Melt the solder and lift up one leg off the board.