Anyone with experience repairing a bad MAIN board?

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

Micom (multicontroller) is a separate processor (it contains its own firmware), which controls the power supply of the DC / DC converters and the standby power of the entire board,
it also puts the motherboard into operation when the ON button is pressed or from the remote control.

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Sorry if i don't read entirely the discussion, i put my thoughts, my attention is towards 2 elements of this board, 1 is the microcontroller with a pencil mark on it, its firmware could be corrupted, it holds the standby software that is responsible of the state of the enabling signals that starts the smps dcdc stages, 2 is the dc dc that feeds the uC, probably a sot23 with 3,3v output near the uC..

I don't think the uC can be executing any program as I can't find any voltage across the board that can be fed to supply a uC, I can only see 8.7V

I agree that the dc-dc close to the uC could be bad, I will see if I can find the IC model and hopefully it has external (no BGA) pins

Thanks!

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Micom (multicontroller) is a separate processor (it contains its own firmware), which controls the power supply of the DC / DC converters and the standby power of the entire board.

So according to what you say this IC could be managing the whole sub powers of the main board? Where is this IC? Are you seeing it on this board?
Thanks a lot!

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

in the case of bad firmware i don't he can go far, does RT809 series have that support? i don't think

To be honest if we get to a point where I find that either I need to reprogram a flash memory or I need to replace a BGA IC, I would be giving up and buying a new main board. I already have one identified on ebay but I still want to give this try, this TV is for me and I am taking the challenge

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

It has a separate 3.3v power supply, somewhere next to it there should be its own 3.3v converter. And you need to find this voltage in general.

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

It has a separate 3.3v power supply, somewhere next to it there should be its own 3.3v converter. And you need to find this voltage in general.

Sorry Im getting a bit lost, Im not sure if you are talking about some capabilties in the main uC or a different IC, which I don't know where it's located on my board, that manages the power supplies
Could you please elaborate on this?

Thanks a lot

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

In post 21, I posted a photo.

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

In post 21, I posted a photo.

Oh sorry! I missed the attachment.
So you believe there's a datasheet for this so I can take measurements and compare? Or if not how can I test it?

Thanks

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

Check if there is voltage between pins 47 - 48, should be 3.3v.

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Check if there is voltage between pins 47 - 48, should be 3.3v.

Checked. Nothing-> 0v

Like I said before I haven't found any single voltage on this board other than 7.8V.

Also VSS in this IC is not connected to chassis ground, is this normal?

Thanks!

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

A high-quality photo with a high resolution of this area can be posted.

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Absolutely. This is the best detail picture I've been able to get with a "real" camera.
Thanks in advance for all your help!

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

Here there is a diagram from another model, but also with such a micom and how everything is implemented.

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

I forgot to ask, is there a short circuit between 47 and 48 pins?

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

I forgot to ask, is there a short circuit between 47 and 48 pins?

No, I checked and there's no continuity between VSS and VDD.

By the way I checked again and I DO have continuity between VSS (47 MIcom) and chassis ground, so this is not an issue

Thanks

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

Im about to quit on this board, a new one costs 25 EUR on ebay so this isn't probably worth at this point...

[edugimeno]

Re: Anyone with experience repairing a bad MAIN board?

What do you think of this part? Looks like coil on top is fried? I tried shrting with what I could (thin pliers end tip) but got no light on st-by-led and got a really little smoke line for under 1 second in that area...
Also the other coil (bottom) is not probably assembled but just wanted to point it out...

[Davi.p]

Re: Anyone with experience repairing a bad MAIN board?

edugimeno you have misunderstood almost the entire discussion, i repeat for the voltage regulator that feeds the uC=microcontroller=micom (that is another processor) : probably a sot23 package with 3,3v output near the uC..

[howardc64]

Re: Anyone with experience repairing a bad MAIN board?

There are very few components between MICOM VDD and 12v connection (providing 7.8v in standby mode) to the PSU. I used diode and ohm mode to figure out the circuit on my board. Looks like 7.8V is converted to 3.3v through a bank of resistors. Here is a pic of my board. Your board maybe different and have sot23 providing 3.3v per @Davi.p in post #38 (However, that sot23 could also be a reset monitor per schematic in post #33 p40, here is link to reset monitor datasheet )

VDD = 3.37v
B = 3.37v = VDD
GND is ground
V = 7.8v in standby = 12V connection from PSU
F? looks like a fuse

Anyway, the key is to trace from PSU connector to see where 7.8V trace go to. Look up component and try to understand where 3.3v conversion is done. Use diode mode and ohms mode to figure out what component is connected to what.

If you have a fuse (F?) like mine, maybe it is broken?

[lotas]

Re: Anyone with experience repairing a bad MAIN board?

Yes, this is a small choke L2320, voltage passes through it, which means that something is short. check with a multimeter on each side where this inductor is located for resistance relative to gnd.