Insignia NS-LCD019-09 issue: Power light turns blue for 3 seconds, the flashes red before going solid read again

[cajoeg]

Hello, I'm new to the group and to trying to repair a LCD TV. During the past few years, I've been collecting/repairing/restoring vintage personal computers (Commodore, Apple II, Atari, TRS-80, Texas Instruments, and Timex Sinclair). This has been my retirement hobby. Now I've gotten interested in trying to repair a LCD TV that I have and used regularly when working on vintage computers.

The LCD I'm working on is a Insignia NS-LCD019. I've downloaded the service manual that I could find, but it must be a different revision since not too many items in the service manual match the TV that I have even though the model numbers match, and the schematics are even worse. I've also searched the internet for videos, documentation, etc. to help me in identifying troubleshooting techniques and potential problems with this particular TV model. Thanks to this forum, I've downloaded a few PDF's to go through as well. Unfortunately, I'm at a blend spot for me.

The issue with my Insignia NS-LCD019-09 is that the power on light on the front of the TV turns blue for 3 seconds when powered on, then it flashes red 5 times before going solid read again. One other thing I did notice today is that the screen appears to be receiving some form of a signal because it very briefly flashes a very pale gray before going black.

At the advice of one repair sight, I purchased a new main board and installed it. It made no difference. But there was no guarantee that it was going to anyways. So I started looking closer at the components for anything that didn't look right such as swollen/leaking capacitors, burn marks on the PCB or components, loose wires, bad traces, poor solder connections. I found nothing. I also tried to see if it had sound but no video, but the set doesn't respond in any way since the power can't stay on.

Today I started to test the power board by checking the voltage coming form the power board to the main board. The voltages (+12 and +5) checked out correctly from the power board connector to the main board. I decided to see if there was any continuity at the GBU408 bridge rectifier. The odd thing is that there is brief continuity between the (-) and (+) legs for about one second, then it stops. I don't know if this is normal or not since I'm still learning the basics of electronics.

Below is an image for a GBU408 bridge rectifier for reference:


Does anyone have a recommendation as to what to check next? I know the TV has low value, but I like how it has so many video connection options since the computers I tend to work on have a wide array of video connection requirements. I actually did buy an identical replacement from ebay that works, but I'm not fond of swapping boards in the event that a problem on one board has killed the other. Plus, I like to learn things.

Thank you!

Joe

[nomoresonys]

Check the dc voltage of the on/off pin of CN902, ground on chassis, pos. probe on the on/off pin, take note of voltage with tv off/standby, leave probe where it is turn tv on with power button, take note of voltage, what do you get? Here's a little testing and some good advice: https://www.youtube.com/watch?v=_E2V2cHU24I

[nomoresonys]

Testing bridge rectifier, keep in mind the first test he does using diode mode is done with tv unplugged from power: https://www.youtube.com/watch?v=zK8oNhFaRdM

[cajoeg]

Thank you for the prompt reply! I did retest the bridge rectifier (I actually forgot that I learned how to test a while back). It's fine.

Now, since I'm still learning, please see the attached photo and let me know which pin inside the connector on the top should I connect to with the positive probe. The pink wire pin on top, or the white one below it? I tried to see if either was ground via continuity test, but got nothing.



Thank you!

Joe

[nomoresonys]

That's the wrong one, it's CN902, the same connector you would be testing for your 5 and 12 volt, which you already tested for 5 and 12, now just test the on/off pin as described.

[cajoeg]

D'oh! I double checked the letter, but not the number.

Below is a photo of the connector I did the testing on directly with the other end connected to the power board. The top two wires are +12v (black & white), the next two are GND (gray & purple), the next three are +5 (blue, green, yellow), the next two are GND (orange.& red), the next one is NF (brown), the next one after that is not connected, and the last wire is on/off (black).

During the testing of the on/off, I got no reading with the TV in standby mode, and no reading for when the power button was pressed as well. I did this multiple times, and even tested the +12 & +5 lines as well (they are good). I got nothing each time I tested\ the on/off.

[nomoresonys]

Not the correct method, do it like he does in the video in post #3, everything connected and probe on the connector contacting the metal part.

[nomoresonys]

We are trying to see if the mainboard is sending on off signal to powerboard, can't do that with mainboard unhooked.

[nomoresonys]

Any tv in this age range I always suspect capacitors first, electrolytics are usually the first caps to go bad. You can do what's called a dirty test, it isn't a full test but if it isn't at least passing the dirty test then you know it's probably a bad cap, demonstration there, notice he puts his meter on 20K ohms setting, at least test all of the electrolytics, no need to de-solder, test them in circuit: https://www.youtube.com/watch?v=NqvL7Cyemiw

[cajoeg]

I have strike two! Sorry, learning from ground zero. I do greatly appreciate your patience and guidance.

I did use the technique shown in the video by leaving the connectors attached. I did this three times. When the TV off, I had no reading. When I pressed the power button, it briefly read 1.27V and then that went away. The subsequent tests showed even lower reading in decreasing order down to 0.3V.

I'm going to remove the power board and take a look at it.

Thank you very much!

Joe

[cajoeg]

I took out the power board and checked it over. I found nothing obvious. I even checked some of the traces for the on/off wire connector back to the IC on the board. As a second test, I took out the main board and installed the replacement main board I had purchased that was sold as being tested and good. It also provides the same test results. Perhaps I need to replace that capacitors on the power board?

[nomoresonys]

Ok, that's not exactly what you would expect, the voltage on that pin when tv is working right would be 3.3 or 5 or so, not 1.2. Another test that works sometimes if a capacitor isn't too far gone is heat all the electrolytic caps with a hairdryer for a couple minutes, then try the tv, try it before it cools down. So what it can do is bring the esr down enough to make the tv work but only briefly, doesn't work if a cap is too far gone tho. Use only a hairdryer, a heat gun would be too much heat and more than likely ruin things.

[cajoeg]

Thank you! I'd rather just replace capacitors. I have plenty in stock, and it's fairly easy to do.

Just to make sure, we're both talking about the capacitors on the power board, correct?

Thanks again!

Joe

[nomoresonys]

Yes powerboard, that would eliminate those old caps from suspicion.

[cajoeg]

Thank you. I replaced two of them as of this morning. The other I had to order. I retested after replacing the two capacitors, and the TV still has the same issue. I'll keep going until I find the culprit(s).

Joe

[nomoresonys]

Is that the model with a bunch of electroltics on the mainboard? This is where that testing with 20k ohm setting could come in useful, easy method to test many caps quickly. The thing about buying replacement boards is most of them are just yanked out of similar aged tvs with the same old caps in them, unless someone recapped it.

[cajoeg]

Yes. Below is a image of the mainboard. I agree that the so-called "working" mainboard likely has the same age components.The seller stated that it came from a working unit with a broken screen, and that their technicians tested it. For $25 plus shipping, I had to take a chance.

I just now tested a few capacitors on the extra mainboard using that method, and they show that they are good. Interesting method! Unfortunately, I put the TV back together in anticipation of waiting for the new capacitors to arrive, I also am cleaning up my den from the recently acquired TRS-80 computers, and the anticipation of 3 Timex Sinclair 1000's I got for a great price, and one TRS-80 Model 100. So I'll have to wait before I open up the TV again to work on it.

Thank you!

Joe

[cajoeg]

Okay, back at it while the wife took the grandchildren to a park for a a few hours.

I replaced four capacitors on the power board. I attached a photo showing the four I replaced that have a blue dot on them (used MS Paint to apply dots in photo). Even though they tested good, I replaced them. There's a very large capacitor that tested good while still on the board. I reinstalled the board and tried to power up again. I didn't expect any change, and there isn't any. Still flashes the LED.

There's also two components that I don't know what they are. I circled them with a red circle. Are these some type of capacitors that I'm not used to seeing (in computers)?

I'll watch more of the aforementioned basic diagnostics video to learn how to test the bridge rectifiers properly. After that, I might even swap the power board from the good TV and see what happens. At least then I might be able to identify if the problem is on the power board or not. I still don't like that idea given the potential risk.



Joe

[nomoresonys]

Yes those are caps. I think I would test all those caps on the mainboard, go ahead and test them on both mainboards see if you find any differences.

[cajoeg]

Before I started testing the other capacitors, I saw this video on YouTube where the technique used to isolate the fault(s) on a TV gave me the idea to quickly check for a short:

https://www.youtube.com/watch?v=kallk3Kcbp0

I found a short at a resistor near the bridge rectifier. I got continuity on the resistor each time I checked it. Today, I removed the resistor and checked it again. It still has continuity. It's a 39 Ohm Resistor, 2W 5%. Of course I didn't have one in stock, so I ordered one. Here's a photo of the power board and the associated resistor:



I also removed the bridge rectifier for more accurate test results. It appears to be good. But I'll be replacing it as well just to give it a new part.

When I get the parts in, and soldered in place, I'll test the board again.

Joe