Dynex DX-L40-10A Won't turn on.

[budm]

Re: Dynex DX-L40-10A Won't turn on.

Post 49:"There's a big resistor on the PS board that has over 15V on one side but 0V on the other. What's the wattage on that resistor?" If that resistor has 0.02 Ohms you will definitely will not be reading 0V on the other end.
It shows 0V because one end is connected to the circuit ground, and did you measure the resistance with the TV is still plugged into the AC outlet?
It is a bleeder resistor for he 16VDC supply.

[CapLeaker]

Re: Dynex DX-L40-10A Won't turn on.

He really does need a new meter.
Also my post 50 I mentioned to take one leg out or take the potential identified part out of circuit and measure it again.

[budm]

Re: Dynex DX-L40-10A Won't turn on.

Here's the results of the forced on state.

GND 0
GND 0
STB 2.8
5V S 4.84
5V S 4.84
12V slow drop to 0.01
12V slow drop to 0.01
GND 0
BR1 slow drop to 0.01
SW slow drop to 0.01
GND 0
GND 0
5V_M slow drop to 0.01
5V_M slow drop to 0.01

The 12v starts out around 7.9 and then drops. The 5v_m starts out around 4.8 and drops

This is the first time it's been powered on in days and this time plugging it in with the resistors in there were a lot of speaker pops which at the same time resulted in the readings for the dropping voltages to spike up and fall with each pop.
I wasn't able to reproduce this effect.

I would disconnect the cable to the inverter board and see if the 5VM, 12V, 16V, 24V will stay on.
The 5VM, 12V, 16V, and 24V power supplies (produced by the transformer T831) are switched on by the STB (PS-ON).
So it is either the main power supply kicks into shutdown due to over load or the PFC Voltage drops down.

[budm]

Re: Dynex DX-L40-10A Won't turn on.

He really does need a new meter.
Also my post 50 I mentioned to take one leg out or take the potential identified part out of circuit and measure it again.

I know I am getting frustrated.

[budm]

Re: Dynex DX-L40-10A Won't turn on.

These boards have the same layout as OP.
http://www.shopjimmy.com/catalogsearch/result/?q=122904

[CapLeaker]

Re: Dynex DX-L40-10A Won't turn on.

I know I am getting frustrated.

I hear ya!

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

Update

I know it's been a long time since I was working on this but I'm still wanting to narrow down which board needs replacement. Since my last post I've picked up a Fluke 27/FM, had to get the military spec to match my veteran status, and haven't taken any more readings past the first set of readings with and without the 1k resistors on the PS board.

The one thing I wanted to ask about the resistor placement was should I have the second one plugged into the second 5vS plug or the other set of 5vM? I had it plugged into the 5vM. The only difference the resistors made was it gave me a reading of 4.81 on the 5vS pins.

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

Do you have anything to check capacitance with? May be worth a try looking at that big blue cap C842. Resistors you can check with the power supply disconnected and your DMM in Ohm mode. If any thing gives you something weird, it is always wise to lift a leg or take the component out of circuit and check it with the DMM.
And we still need to see how much DC voltage is on the big black filter cap.

I don't think my meter can measure capacitance.

I checked that resistor I thought was bad and it's reading 1k like it's banding identifies.

I rechecked VDC on the filter cap and it's reading 336 VDC on one side and -71 on the other using incoming power plug ground and still reads 411 across the pins.

I checked C842 and put that in the pic as well.

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

Here's the back of the PS board. The pic I uploaded isn't turned to the side.

[R_J]

Re: Dynex DX-L40-10A Won't turn on.

When ever you check voltages in the primary (hot side) you need to use hot ground, in this case the large capacitor, negative leg. So measure the voltage on C810 ACROSS it not from chassis ground.
to turn on the power supply board, the cable between the power supply and main needs to be disconnected, Then connect a 1k resistor between 5V_S and STB, this should turn ON the power supply. Check if you get 12V

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

When ever you check voltages in the primary (hot side) you need to use hot ground, in this case the large capacitor, negative leg. So measure the voltage on C810 ACROSS it not from chassis ground.
to turn on the power supply board, the cable between the power supply and main needs to be disconnected, Then connect a 1k resistor between 5V_S and STB, this should turn ON the power supply. Check if you get 12V

V across is 404VDC

With the resistor in I'm still not getting more than 2V on the 12V pins and it's dropping voltage. I see it spike when I hear the speakers pop and then back to the dropping voltage.

[R_J]

Re: Dynex DX-L40-10A Won't turn on.

How can you here the speakers pop with the cable between the main board and power supply disconnected? only the AC cord should be connected to the power supply

[nomoresonys]

Re: Dynex DX-L40-10A Won't turn on.

Check all the diodes on the power supply, with tv UNPLUGGED from power, it's just an easy step to rule them out, sometimes it's a bad voltage regulating diode.

[nomoresonys]

Re: Dynex DX-L40-10A Won't turn on.

Check VD836 and 837, and the rest, if any read funny lift a leg and recheck.

[nomoresonys]

Re: Dynex DX-L40-10A Won't turn on.

Your back after 5 years SO you must be serious about fixing this tv. Well look at your documentation that came with your fluke, it will tell you if you have capacitance reading ability, you just need to do the work. It could be a lot of things, including a bad diode or bad capacitor as mentioned by Splitcrete etc.

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

How can you here the speakers pop with the cable between the main board and power supply disconnected? only the AC cord should be connected to the power supply

I don't know if that's whats making the pop noise but there is an audible sound when the voltage spikes.

[R_J]

Re: Dynex DX-L40-10A Won't turn on.

Can you check the voltage across the main filter cap without the resistor, (power supply in standby) that voltage should be 160vdc.
When the power supply is ON, the pfc boost circuit boosts that voltage but 404vdc seems a bit high, although not common the main filter could be bad.
Something else to check is when you do connect the resistor to turn on the power supply, do you here the relay click.

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

Check all the diodes on the power supply, with tv UNPLUGGED from power, it's just an easy step to rule them out, sometimes it's a bad voltage regulating diode.

I'm rechecking all the diodes after rereading the fluke manual. I had forgotten how hard it was to decipher some military manuals. I do believe there is at least one bad one. So far on the top of the board vd903 & vd904 are bad. My manual says a good diode will read between .400 to .600 and not make a beep when the probes check reverse polarity. Those 2 read out to .150ish and beep when I check the other direction.

Can you check the voltage across the main filter cap without the resistor, (power supply in standby) that voltage should be 160vdc.
When the power supply is ON, the pfc boost circuit boosts that voltage but 404vdc seems a bit high, although not common the main filter could be bad.
Something else to check is when you do connect the resistor to turn on the power supply, do you here the relay click.

I get 4.6vdc across the filter cap without the resistor.
Yes I hear the relay click with the resistor inserted.

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

vd836, vd837, vd905 and vd815 on the bottom of the board all give me bad readings like the 2 on the top.

[Funda]

Re: Dynex DX-L40-10A Won't turn on.

I found a replacement board here.

https://www.shopjimmy.com/dynex-1229...er-supply.htm#

I also found what looks to be a newer version here.

https://www.ebay.com/c/1500625215

Could I use the newer version?