Hisense 58r6e power board troubleshooting

[DoorOfTime]

Hi all, I browsed previous threads on Hisense TV's but had some questions I haven't been able to sort out myself. This TV has a red standby light that when powered on, flashes twice, returns to steady, and cycles a few times before returning to a steady solid red.

Poking around the power board (P/N rsag7.820.8349) I have the following voltages with everything disconnected:

Main board connector: 12V ~9.3, STB ~0, VAMP is transient; first measured ~18 and gradually dropping to sub-16V.
Bridge Rectifier: (+) to (-): 167VDC
Filter caps: 368VDC

I've tested every diode, mosfet and cap with a multimeter and didn't come up with any obvious shorts or burnouts. I did notice that 6/8 of the legs of the main transformer are common and test as ground when the circuit is on which seemed odd to me.

I've also noticed there's a faint but consistent "ticking" sound coming from somewhere near the main transformer or varistor portion of the board but haven't been able to pin down what it's coming from. When the board has been disconnected from mains power the ticking sound starts slow and gradually speeds up to steady state (I'd guess 5hz) over ~20 seconds.

I'd appreciate any advice on how to narrow down the likely culprit before I pull the trigger on a full new power board.

[williej]

Re: Hisense 58r6e power board troubleshooting

This should be the schematic.

[R_J]

Re: Hisense 58r6e power board troubleshooting

I suspect you have an issue with your backlights not the power supply, Also I suspect your meter is not giving you proper readings. The 12V and the Vamp are connected together by W841/W843. STB is the power on pin for the power supply, ) volts indicates the tv is off, this line needs to be 3~5v to turn on the power supply.
368v across the main filters indicates the pfc circuit is working ok.

Check the voltage across the plug going to the led's while turning on the tv, If it rises above 160v (200v) then drops down, It indicates an open led string.

I did notice that 6/8 of the legs of the main transformer are common and test as ground when the circuit is on which seemed odd to me.

You can not check resistance with power applied, you will damage your meter or the power supply.
You are checking the dc resistance of the transformer winding which has one end connected to ground

[DoorOfTime]

Re: Hisense 58r6e power board troubleshooting

Thanks both for the replies--having the schematic is definitely helpful!

It looks like the readings with the main board unloaded aren't reflective of when the circuit is loaded, which was my mistake. Re-reading with the LED cable and main board connected, there's a steady +12V, STB is measuring at 2.9V, though VAMP is still measuring ~19V (I confirmed that VAMP is connected to VD821 and +12V to VD820).

Check the voltage across the plug going to the led's while turning on the tv, If it rises above 160v (200v) then drops down, It indicates an open led string.

Sure enough the voltage is hitting ~200V then dropping down within a second or two. Cheap light strings burning up seem to be a hallmark of these Hisense TV's, so I'll get on testing those. Thanks!

You can not check resistance with power applied, you will damage your meter or the power supply.
You are checking the dc resistance of the transformer winding which has one end connected to ground

Sorry if that was unclear. I was measuring for shorts with the board disconnected and was surprised when 6 poles all ran to ground. I had the idea there were multiple windings which should be isolated from each other, which I still don't fully understand but realize is working as intended.

[R_J]

Re: Hisense 58r6e power board troubleshooting

The two windings (200v and 12v/16v) are seperate, but since the each have their center tap connected to ground, the dc resistance shows them all low resistance to ground.

[DoorOfTime]

Re: Hisense 58r6e power board troubleshooting

Sure enough, there was a single bad LED on the strips that took out the entire TV. Unfortunately, one of the flat ribbon cables snagged while setting the screen back down and crimped badly enough to tear out an ~2 pixel wide line up the entire screen

Thanks for the assist guys... God I wish they made these ribbons reparable!

[dskall]

Re: Hisense 58r6e power board troubleshooting

Here's your fix.
https://www.badcaps.net/forum/showthread.php?t=104059