Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

[rasscal]

Hi I have an Insignia LCD tv I picked up for a song. It doesn't work, and the person I bought it from said he went on vacation and when he came back it wasn't working anymore, so he suspects it got hit by a power surge.

When plugged in, the red standby LED comes on. When turned on, the led goes to blue, but no picture appears, and I couldn't get any sound from a device hooked up to it.

I opened it up, and there are no obvious bulging capacitors anywhere. I did find one component that looked a little suspect, marked "NR901" on the PSU board. One of the legs looks a little burnt up.

I found the Service manual for this TV from another thread, and this part is a NTC Thermistor (3ohms 5A +/-20%). I tested it at room temperature and it reads 3ohms, but I didn't try heating it up. I'm not sure if this is the problem or not.

I've also tested all the outputs on the PSU board while powered up, and they all measure within .4v of their markings, i.e.5v, 12v and 24v.

One thing I found is the ON/OFF and PWM pins are 0v whether or not the set is on or off. I took a 3.3k resistor and used it to jumper the 5v to the on/off pin on the PSU while the TV was on. The backlight came on and stayed lit.

So that leads me to suspect that the main board is not working. I'm looking into sourcing a replacement, but before I do that, can anybody suggest anything else I might have overlooked?

Service manual from this thread (post #21): https://www.badcaps.net/forum/showth...S-LCD37&page=2

[rasscal]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

I'm guessing the NTC thermistor isn't the problem if the PSU is turning on, I thinking the mainboard has the issue.

I'd like to troubleshoot it, any ideas what parts commonly go? Voltage regulators? Or should I just go and buy a replacement board. I really don't want to order one and find out the problem is somewhere else.

[munirutech]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

The on/off is it the one going to the inverter board that is 0v?

[budm]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

"One thing I found is the ON/OFF and PWM pins are 0v whether or not the set is on or off. I took a 3.3k resistor and used it to jumper the 5v to the on/off pin on the PSU while the TV was on. The backlight came on and stayed lit.
So that leads me to suspect that the main board is not workin"
Yes, you do have main board problem. You can start by checking the voltage regulator ICs, I never have luck fixing Insignia main board down to component level yet.

[rasscal]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

The on/off is it the one going to the inverter board that is 0v?

Yes, it's the one that just passes straight through the PSU board and is next to the pin marked "DIM" which I presume is the backlight brightness control. That one is 0V as well.

[budm]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

One is BL_ON (>2V = ON, <1V = OFF) , and one is for backlights dimming control.

[rasscal]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

I guess my next step is to start checking voltage regulators. Luckily for me, I have the schematic, so I at least have an idea which components to check first. I'll let you know if I figure anything out.

While I'm at that, does anybody know what issues a bad T-CON board might cause? Could it prevent the backlight from turning on? Just want to rule out that possibility.

[rasscal]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

One is BL_ON (>2V = ON, <1V = OFF) , and one is for backlights dimming control.

At first I was confused which pin was which, but the fact that there was a matching pair of pins labeled "ON/OFF" and "DIM" on both headers tipped me off that these must be the backlight on/off and control. I checked the service manual, and I confirmed this was the case, before I tried the resistor to turn on the backlight.

On this particular PSU, the pin labeled "PS" turns it on.

Incidentally, I found that if I turned on the TV with the resistor already in place, the backlight would flash on, then off in half a second. When I turned on the TV first and then (very carefully) inserted the resistor between the 5V and ON/OFF pins, the backlight turned on and stayed on.

[budm]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

"ON/OFF" = Backlights ON/OFF CONTROL pin
"DIM' = Backlights Dimming control pin.
PS = Power supply ON/OFF control pin.
PS is activated first, a slight delayed time later, the ON/OFF, Dim signals are sent out by the main board.

[rasscal]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

I checked all the regulators and they all appear to be working, even the one underneath the shield (took me a while to desolder those 8 metal tabs).

I just realized that when I turn off the set, the led flashes red 15 times before it goes solid. Does that have any significance? Under that metal shield there's a Zoran ZR39770 chip, which seems to be used in a lot of sets. Anybody know if this might be a diagnostic code?

[rasscal]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

Well, another night of troubleshooting and I have come up empty handed.

I checked two circuits, the BL_ON signal, which comes directly from the main processor (ZR39770 in this case), and the PANEL_ON signal which turns on the power to the TCON. Nether one is turning on, which in turn is not turning either the backlight or powering the TCON board.

I have already verified the backlight is fine by jumpering the BL_ON signal. I haven't had the guts to try jumpering the PANEL_ON (all those tiny little pins!) but I'm at a loss as to why the main processor is not doing it's job.

Unfortunately I haven't been able to find much information on this ZR39770 (or any of it's siblings), and it runs everything in this TV. It almost appears as if it's not booting properly. I'm starting to suspect it may be a bad eeprom or corrupt firmware image.

I guess that means I'll be in the market for a new mainboard. At least in the process of tracing out all the circuits, I discovered that the 32" variant of this TV (the ns-lcd32-09) is slightly different in that it sends 5V power to the TCON instead of 12V on the 37" (ns-lcd37-09. From looking at pictures on shopjimmy and ebay I can tell from the presence of various components in the corner near the TCON connector which boards are for 32" and which are for 37".

It appears the same goes for the VIZIO variants of this board, as well.

Thanks for all your help.

[rasscal]

Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) - Mainboard (CBPF8Z5KQ1) postmortem

I've come to the conclusion that it is the ZR39770 main processor that is dead, perhaps due to overheating. It appears the heatsink might have shifted and there looks to be some discolouration from heat.

What do you guys think?

If I find a replacement should think about installing a cooling fan?

Attached is a picture of the part of the board that is normally under the shield cover. The main processor is the one in the center.

[rasscal]

Fixed! Sort of... Re: Insignia NS-LCD37-09 (E378AZNKW1BCNN) no picture or sound

Well, I now have a working TV, although it is no longer an Insignia. Having determined that the mainboard was bad, I looked online for a replacement, but it seems all of them are more than I am willing to pay.

Since I had the full schematics and the datasheet for the Panel, I quickly realized that I could use the mainboard from any TV that had used a panel with the same resolution and voltage.

So I ebayed the cheapest 720p mainboard I could find, and with a lot of soldering wires, I now have a working 37" TV for about $35 in parts.

In addition to the different mainboard connectors (I used connectors from another donor RCA TV) I had to wire up a switch for the 5V line. The original mainboard had a mosfet to switch on and off the 5v power, but the RCA mainboard expects the power supply to turn on/off the 5V using the PSON signal.

I didn't have any spare mosfets lying around, and I couldn't find out how much current the mainboard needed on the 5V line, so I just ended up using a small 12V relay I had lying around, which uses about 30mA to activate the the coil. I also included a flyback diode. Right now it's switched on directly from the 12v line, but I think I will add a transistor as well, just to better isolate the 12V line.

While I was at it, I also wired up different coloured LED's to indicate the status of the various voltages, red for 5Vsb, yellow for 12V, orange for 24V, blue for backlight on, and green for 5V (after the relay is switched on. If this TV ever develops issues again, I can tell from just looking at these lights if it's a P/S issue or not.

Of course, the tv now needs an RCA remote, instead of the one that came with the TV, but any programmable remote can handle that. Also, the connectors on the mainboard don't match up with the cutout on the back of the TV. Right now I only have access to the 4 HDMI connectors.