Low Voltage from a Voltage regulator IC Advice

[steved271]

Hi folks, Hope this isnt a silly question.... I am new here and Relatively new to diagnosing faults...

My scenario is I have an old Plasma TV/Monitor that i have had sat here for a couple of years gathering dust.... so decided to see if i could use my brain and diagnose the fault.... The symptoms were that when powered the standby light comes on and stays on.... Nothing happens when i press the button.... I have downloaded the board schematics and found that the voltages from the power board come to the Pixelboard/Main board Ok... I then thought ok it isnt coming off standby so trace the standby circuit.... I find that all my voltages are correct except 1.... I have 3 Regulators IC1 is 5v in and 3.3v out, reads correct, IC 2 is 5v in and 2.5v out, reads correct, My 3rd IC is 5v in and 1.25v Out.... Now the specs i am getting from the data sheet for the part no is RT9164-18CLR which i found here http://www.cheertech.com.tw/RichTek%20C ... 164-15.pdf This leads me to believe that the 18CLR should be outputting 1.8v .....

My question finally is if this voltage is so low, can this cause problems further down the line IE. not enough power to send signal back to CPU or a low voltage shutdown error?

Sorry again if this is all basic to you guys... Just trying to get my head around it all and using junk to do so...

Regards


Steve

[nicholasdark]

Hi Steve,
Welcome to the forum and the world of diagnosing other peoples circuits hehe.

Firstly, one word of caution, I'm guessing you are taking care around the mains areas of the TV, but also not that some plasma and LCD TV's generate voltages in th kV range, these voltages didn't quite go out with the CRT screens as people often like to think. The newer screens tend to use LED backlights which run at relatively low voltages, however ear plasma and LCD screens used CCFL (Cold Cathode Fluorescent) tubes for their backlights. Given that they are cold cathode, they need to be run in the kV range.

As for your question, I've taken a quick look at the datasheet and it appears that it should be outputting 1.8V. If the output is around 1.25V then this may well be causing issues with electronics further down the line. The question is, is this cause or effect? In other words is it a faulty regulator that is outputting 1.25 instead of 1.8 or is something further down the line damaged. If it's the latter then I would suggest that it's pulling more current than the regulator can supply therefore the regulator is dropping it's output voltage to compensate.

Does the regulator get got at all?

Kind regards
Nick

[mykal]

hi steve
sounds like a defective electrolytic cap
check all the electrolytic caps by touching the tops if they are domed shaped -replace
i have seen this problem in many,many plasma and lcd tv

[piratepaul]

Hi, ( I cant down load the spec) I would trace from the button in... The button will trip a flipflop I s'pose check the flipflop... the button will change output to logic high or low depending on the spec.