Samsung ue32h4510 turns on and off randomly (bad power board ?)

[CapLeaker]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

That problem was in this thread: https://www.badcaps.net/forum/showthread.php?t=47479

I hooked up my oscilloscope to the secondary and made sweep like very slow. When I heated the specific area (that didn't take very long), the voltage rail became unstable (so voltages would go up and down fast) then the PSU quit.

One more thing: the voltage on the main filter cap is staying put at 316V when the PSU shuts down?
.

Next, the PWM. If you follow the voltage from the main filter cap to the PWM on the backside of the board (goes through J809), there are a bunch of resistors it has to go through, maybe one is bad and the PWM loses VCC?

[Dannyx]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

That problem was in this thread: https://www.badcaps.net/forum/showthread.php?t=47479

I hooked up my oscilloscope to the secondary and made sweep like very slow. When I heated the specific area (that didn't take very long), the voltage rail became unstable (so voltages would go up and down fast) then the PSU quit.

One more thing: the voltage on the main filter cap is staying put at 316V when the PSU shuts down?
.

Next, the PWM. If you follow the voltage from the main filter cap to the PWM on the backside of the board (goes through J809), there are a bunch of resistors it has to go through, maybe one is bad and the PWM loses VCC?

Checked all of the resistors and they read OK. Both the 4704 ones (4.7 mega ohms) and the 243 ones. I might actually focus on that inductor again, as it's the only giveaway that something's wrong there, since it makes that random whizzing noise. I know that it's acceptable for coils to make a certain amount of noise (especially when caps start going bad and no longer filter), but this one definitely sounds off. Also, turning the backlight all the way down didn't change anything: TV still shut down when I touch the supply or flex the TV's chassis.

[Dannyx]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

New power board arrived today and it works perfectly. I'd still like to be able to fix the original one so I can at least sell it to gain some more money...it won't be easy now that I no longer have the tv to test it on, since it won't go unstable with no load on it.

[budm]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

I suspect something is bad in the primary drive circuit, there is one small startup/running electrolytic cap in the primary side that you can check the ESR, Voltage on it.
it can also be something in the secondary side that cause the power supply to be unstable. Also see the DCV on the main filter cap is fluctuating a lot or not too.

[Dannyx]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

I suspect something is bad in the primary drive circuit, there is one small startup/running electrolytic cap in the primary side that you can check the ESR, Voltage on it.
it can also be something in the secondary side that cause the power supply to be unstable. Also see the DCV on the main filter cap is fluctuating a lot or not too.

I actually REPLACED that cap and it wasn't that, so I still suspect the problem is in the secondary...haven't had time to mess around with it anymore - the Samsung power supply BN96-03058 in my other post is far more urgent, as it's been sitting for a week now due to lack of both parts and time (my shop is not to well stocked and we're pretty far from the nearest electronics shop) )

[CapLeaker]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

The only thing you can't test, are the backlights. Other than that, it doesn't matter of having the rest of the TV.

As mentioned before a few times now, we need to see if the voltage on the main filter cap and on the PWM stays stable.

[Dannyx]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

The only thing you can't test, are the backlights. Other than that, it doesn't matter of having the rest of the TV.

As mentioned before a few times now, we need to see if the voltage on the main filter cap and on the PWM stays stable.

Filter cap: yes, stable at around 316v even when the secondary starts having issues. PWM - sits at 108v with no LEDs connected (and at 87-88v WITH the LEDs attached), but starts randomly falling after a few minutes of runtime or when I move the board or the whole TV (also accompanied by the electrical noise which seems to be coming from that choke).

[budm]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

Sounds like you have bad solder joints on the board.

[Dannyx]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

Sounds like you have bad solder joints on the board.

That was my first instant guess, but after reflowing what I thought was most of the components, the problem was still there. I'll try that coil again, following CapLeaker's suggestion of pulling it out and thoroughly cleaning the holes first (even though I DID remove the coil once before soldering back in place, I didn't pay too much attention to removing every last bit of solder left in there, so I might still have a dodgy joint there).

[CapLeaker]

Re: Samsung ue32h4510 turns on and off randomly (bad power board ?)

While you are at it, do the same thing to DM861C.