Veltech LC-39GL12F - Intermittent Sound

[dick_barton]

For information only.

Picked up this set a few days ago with symptons no sound. Opened up the back to take some measurements and the sound returned. No amount of flexing and tapping the board would stop the sound.

Main Board T.MSD306.68A 12023

After running for about 4 hours the sound dropped out again and again no amount of tapping, flexing or cooling around the audio amp (R2A15122FP) would bring the sound back.

Out with the meter. Supply voltages on VD1 (Pins 13 & 14) and VD2 (Pins 37 & 38) were both present at 25V.

Checking the mute input (Pin 34) the voltage change on the pin when mute was selected on remote was 3.4V to 2.9V.

Followed the mute control line back to the two smd transistor (H1A & H2A) close to the audio amplifier "Power In" connector.

Resoldered the two smd transistors and problem now appears to be solved.

[ReeceyBurger123]

Re: Veltech LC-39GL12F - Intermittent Sound

Thanks for the post Paul

[dick_barton]

Re: Veltech LC-39GL12F - Intermittent Sound

Unfortunately, my sound problem has re-appeared and can drop out after the set has been on for many hours or refuse to come on at switch on.

Using an oscilloscope, I appear to be losing the signal input to audio IC. Applying an external signal to the chip gives me audio output so confirming the IC is still working.

The main processor on an identical board I have is an MSD306PT-LF-Z1 but I cannot find any information on it and think the audio codec is probably integrated on this chip.

Has anyone information on this IC since googling doesn’t seem to bring up any useful information.

I notice that many makers are using this main board (T. MSD306.68A 12023) and they all look identical having the same main board identification number but driving different make and size LCD panels.

My question is, are theses boards interchangeable into other maker’s sets using this main board if you exchange U10 supposing of course U10 is still working.

[dick_barton]

Re: Veltech LC-39GL12F - Intermittent Sound

Out of curiosity when I go into the service menu it says the checksum is correct so can I assume that this is not an EEPROM (SPI) fault and therefore I can only think that I must have an intermittent problem on the main board MSD306 IC?

[dick_barton]

Re: Veltech LC-39GL12F - Intermittent Sound

Reluctantly replaced the main board and fitted a Bush LC-39GL12F mainboard model T.306.68A 12023 Panel V390HJ1-L02
Set is now up and running. On screen menu looks identical to the Veltech menu.

[vinceroger69]

Re: Veltech LC-39GL12F - Intermittent Sound

Glad to here the set is now up and running mainboards in my opinion are hard to fault find at times and too be honest you can get some good bargains on them so i tend to just swop them unless its a easy fix ie eeprom or voltage regulator etc.

[dick_barton]

Re: Veltech LC-39GL12F - Intermittent Sound

The MSD306 main BGA IC was losing the audio output to the audio amplifier. Heating the chip did not help so finally gave up on it.

[vinceroger69]

Re: Veltech LC-39GL12F - Intermittent Sound

Well at least you gave it your best shot at repairing it sometimes a reflow does work so was worth a try, hows your new ir station now are you getting the hang of it? i did have the same model in my ebay list but un decided now.

[dick_barton]

Re: Veltech LC-39GL12F - Intermittent Sound

It does focus well on small devices and allows you to desolder without blowing off the very small smd's alongside and I'm happy with that.

I really only want it for repairing Tcon boards and not BGA chips.

I do believe that it comes down to knowing what temperature/time you need to apply heat for the various devices so the use of an external temperature meter is a neccessity.

Ecking767 replied quite positivly in my thread regarding the unit and I'm hoping he will come back and provide some more information on temperature and times.He appeared to be happy using it.

I must admit at the price it's not all singing and dancing but I have decided to keep it and will keep practising on old boards to try and get it right.


https://www.badcaps.net/forum/showth...ghlight=welder
Badcaps Veteran

[dick_barton]

Re: Veltech LC-39GL12F - Intermittent Sound

I've cannot for the life of me remember what the code was for access to the hidden menu. I normally make a note of it once I have it, but looks as though not this time.
The set is also badged as a Bush LC-39GL12F
Thanks

[dick_barton]

Re: Veltech LC-39GL12F - Intermittent Sound

Found the answer at last.

SOURCE, 2, 5, 8, 0, to enter service mode

[ducky29]

Re: Veltech LC-39GL12F - Intermittent Sound

As for the sound problem you should have done a firmware update.