# Need Circuit board troubleshooting procedures on a computer monitor

#### Dodgydave

Joined Jun 22, 2012
9,936
Right, so you have NO AC mains input,,start looking for open circuits probably mov, filter, ..

#### Swofra

Joined May 19, 2020
16
Mov checks good, and everything else I could see between them checked good as far as I could tell. Not sure what you mean by filter. Just to be ensure I’ve used the right language, I get 122 volts to each of the bridge rectifier ac terminals from the main ac terminal. However when I put one lead on one of the bridge rectifier ac terminals and put the other lead on the other bridge rectifier ac terminal I get only mv between those two. Thanks!

#### Swofra

Joined May 19, 2020
16
when i test the output of the BR dc terminals, do I put leads on both bridge rectifier dc terminals (the 1st and 4th leads if you will)? And if so, what should I be getting?

#### Swofra

Joined May 19, 2020
16
replaced the fuse and i seem to be making progress. Now I am getting the BR DC terminals to output 159VDC and the big brown cap also is reading 159VDC, but when I test the soldered side points of the power connector CN701 I'm not getting any readings. What else could I check, and would there be any expectation for readings (or lack thereof) on the solder side. Thanks!

#### Swofra

Joined May 19, 2020
16
Anyone have thoughts on the above?

#### slackguy

Joined Feb 11, 2016
67
> "However, when I test the BR two inner contacts for incoming AC volts, I only get readings in the 2 millivote range, and the dc test of the outer two contacts (black probe on the negative, red on the positive) reads about .001"

https://www.repairfaq.org

The first thing you NEVER do is test voltage on a TV without a diagram. There are, say, 5 different grounds. What voltage it is depends on which ground you are biased to: and will fry components unless factory test points are not used.

It's very strange your trying to fix a TV board and haven't told us any of the symptoms of the TV.

The standard answer is "if you can, replace the board", btw.

I've repaired a few CRT, lost one (by not having a diagram btw), and another by apathy as to I knew I wasn't going to order the chip that was needed so fiddled and threw away. I have not repaired a LED TV yet (I got an Apple - lasts forever?) LED monitor/TV first came out in USA (Westinghouse) and are designed with a power supply on the outside of the TV because they are usually what fails. (power adapter). nice of them to think of us, much applause!

I assume you are working with a fresh new "power adapter" if you don't mind my reminding you? And I assume you have a functioning remote and aren't near any other remotes (bad remotes can prevent a TV from turning on, yes siree)

How did you determine the board is a problem? What are your symptoms?

#### slackguy

Joined Feb 11, 2016
67
E or electric field means 0 to hero. But V means "potential difference". If you see "100V" on a meter it means "of difference" not total (125V might be one side of the subtraction, or 100V is, you don't know which unless you have the circuit diagram). On AC setting it means RMS average, which even more remote a measure. But touching any higher V wire to a sensitive one, even though your using a meter: will zap it and possibly the meter too depending on it's quality. You have 3V chips and they are very sensitive to "shock", and a meter read to the wrong ground will produce that spike that "toasts chips on the board". But testing a circuit while it's on is INFAMOUSLY WRONG - that is, old TV (say, a nice General Electric) would give you test points and outcomes - without those you are just guessing unless you really analised every possible outcome of every transistor diode and ... forget that.

On the other hand, if you don't have a Westinghouse but some patent infringed chinese TV, and if the POWER SUPPLY is integrated (a seedy practice)?

Asus VK246H spec: General · Dimensions (WxDxH) 22.4 in x 9.1 in x 16.6 in · Display Type LCD monitor / TFT active matrix · Native Resolution Full HD (1080p) 1920 x 1080

Ok that's an old 1080p TFT, worth (cough) $50 used and$100 at most new. It's really not worth saving certainly not buying more than a power adapter for.

BTW when you shop for a new one

If you like picture quality and text quality get IPS or OLED or better (moderately ok contrast), TFT has poor contrast. The contrast ratings in ads are known frauds, you need to look into things further. Contrast is the big factor in quality. TFT may reduce "trails" (not all do) or higher frame rate (still low, and not all do): at the expense of contrast (without contrast, the picture quality is very poor). TFT have poor viewing angle. Most games push 3D so that the cards are pushing less than 60fps, so that higher frame rate is no good. Good OLED don't have much trailing compared to cheap TFT.

The old "legacy" CRT had far superior contrast (near perfect) and double refresh rate (gaming), no trailing, but they are heavy and no longer sold due to shipping weight I guess.

I had one of those ASUS returned it 1st day: still using my CRT for gaming, and IPS for "work like stuff"

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#### slackguy

Joined Feb 11, 2016
67
Let me re-emphasize ...

It's very strange your trying to fix a TV board and haven't told us any of the symptoms of the TV monitor.

The standard answer is "if you can, replace the board", btw. That board is unusual it looks very simple and single layer - like maybe it's a removable power module . If it is, then it should be cheap to obtain another one.

but you showed me a tan simple board, then a green layered ic board. are both inside the tv and separate? i don't see you mentioning what the photos are. really you take apart a LED these days your lucky if it's not damaged just taking it apart. they aren't made for maintenance anymore

> "I searched for the service manual online but did not have any luck". they have zero interest in anything but your upgrading. they will NOT give you a diagram unless your buying the company. (they always bug usa and programmers for GPL free stuff, going the other way you want a diagram? nothing is free going that way)

#### slackguy

Joined Feb 11, 2016
67
Let me re-emphasize ...

It's very strange your trying to fix a TV board and haven't told us any of the symptoms of the TV monitor.

You haven't said you have a new power adapter or can be sure remotes aren't causing a "no power" situation or even what the situation is. I can't even imagine why the others gave you advice to dig in without more info.

The standard answer is "if you can, replace the board", btw. That board is unusual it looks very simple and single layer - like maybe it's a

#### Swofra

Joined May 19, 2020
16
Thanks for the responses! To answer some of your questions, the pics are the top and bottom of a single board.
I originally posted that the board didn't power on, but that was way back in the first post
Asus VK246H monitor does not power on
I'd like to fix the monitor rather than buy a new one as I assume its just a couple of relatively cheap parts away from working and I like learning about things...and if I can learn more about electronics while trying to fix it while also avoid shelling out money to get a new board or monitor thats time well spent and a sense of accomplishment all rolled into one - all thanks to the great people on this site!

Look forward to any suggestions from you or anyone else on where to go from here.