LA40 M81BD combo PSU inverter

[maxvalutech]

This old set picked up had four obviously bad caps on PSU. After replacement set clicks on then after a few seconds clicks off and this happens repetitively. PSU is putting out the 12 and 13 volts when turns on. The on/off voltage seems low at 1.85 but it goes to zero and works the main board which does its job. So I suspect the inverter side has a problem as no sign of backlight at all. Have not looked at balancer yet. Just seeking to see if someone on here has "been there done that" and can point to likely section or component on the inverter side. Only one post came up on search and is useful but do not have that particular component or any idea on what a test should read.

[budm]

Re: LA40 M81BD combo PSU inverter

Any good clear pictures of the board and around the connectors so we read the labels for each pins of the connectors?
So what are command signals did you look at beside the ON/OFF? There are more than one commands signals that the TV needs for it to come on and stays on.
Right now we blinded because we do not have the TV or the boards in front of use to look up.
BTW, where is the model number of this TV?

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

Thanks budm fraid my pics not that good only phone camera and small workspace. Based in Oz so model probably for this area. Connector pins run up PSU from 1 inboard to 23-24 at top and only turn on indicator is pin 1 on/off, 3 is stby 5.2, 4 to 6 gnd, 7 and 8 12v, 9 to 12 gnd, 13 to 16 are 5.4v but no other info, 17 and 18 gnd, 19 is 13v , 20 gnd, 21 and 22 are 13v, pins 2 23 24 nc. All the voltages come up and remain other than Pin 1 going to zero as expected. Will try get pics up now. Edit I think the 13v is for inverter reading other post.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

Pics I hope....

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

First I pass apology to budm as of course there is an inverter on/off control and it is on the small connector. Missed it as working in small space and not visible to me when set boards at waist level - only seen it when board pulled again. So I had checked that 12 volts were at cvv out and from the regulator U1809 and into U1802. So put board back and checked again to be sure - the on/off clicking started again but was staying on a bit longer then as I probed suddenly on came the Samsung chime followed by the screen and I got menus etc up. Attached DVD to HDMI and went well for an hour. This is an old set from 2007 so i hoped maybe some poor contacts or loose wiring in connector. But not to be when switched no restart. Forced backlight on with jumper and screen then showed thin continuous multi colored vertical lines. No sign of backlight otherwise but could only see 0.2 and 0.4 volts at its on/off while clicking. Looks like main board problem now.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

Just to clarify that as start is attempted the 5.4v on the inverter connection to the main board goes low but the on/off pin only goes from 0.02v to 0.04v so it seems the main isn't responding to this but is OK turning on all the other voltages on the other large connector.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

After 8 weeks away put this set up again for further testing. Switched it on and of course it started with no problems. But then on trying a restart no go and seemed to "hang" at just as backlight switch on due and before chimes just clicking off then on off as usual. Took the main board out for a look nothing obvious so set up an Eeprom pin 5/6 short but again no luck with that. Ran soldering iron over a few components still no go. Frustrated I held source and menu buttons down on ir board while pointing remote at standby and holding power on as well - set springs to life as I hear chimes and release all keys. All menus work in normal course and I can also get into service menu as set turns off and on normally now. I don't have original remote and to get to dtv it seems I need it as user manual confirms it is not available in source menu nor is it showing on plug and play even when asked therein do I want digital scan and I select yes. Overnight when set switched off at pp I have to restart it with the 2 buttons on set plus remote pwr on after which all normal again. Backlight voltage doesn't get turned on when clicking so perhaps it is an Eeprom problem?? Now I can't find anything in service menu to help me get dtv turned - tuner is set to auto and dtv has Australia selected. Can't find much on this nor a service manual. Any assistance welcomed.

[syaoran123]

Re: LA40 M81BD combo PSU inverter

Looks like you replaced only the 4 bulging caps. Replace ALL the filter caps (the surround caps. Also test the blue film capacitors to see if they are in spec.

[attainteddragon]

Re: LA40 M81BD combo PSU inverter

if this is an la40r81bd you will have a corrupted eeprom.

if you short out pins 5 and 6 for a couple of seconds while booting, you can sometimes get it to reset. ic1803 in the middle underside of the main board.

you can also fit a blank in these and they will rewrite the data, but you need to change a couple of things in the menu. panel specs and such.

ic1803 is atmel 752 chip, 24c256bn

[syaoran123]

Re: LA40 M81BD combo PSU inverter

if this is an la40r81bd you will have a corrupted eeprom.

if you short out pins 5 and 6 for a couple of seconds while booting, you can sometimes get it to reset. ic1803 in the middle underside of the main board.

you can also fit a blank in these and they will rewrite the data, but you need to change a couple of things in the menu. panel specs and such.

ic1803 is atmel 752 chip, 24c256bn

He said he already tried resetting the eeprom and didt work. Plus intermittent faults are never caused by faulty eeproms.

[attainteddragon]

Re: LA40 M81BD combo PSU inverter

Took the main board out for a look nothing obvious so set up an Eeprom pin 5/6 short but again no luck with that.

my bad, missed that.

but then again, this only works sometimes and an eeprom replacement is commonly done on this model.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

Thanks guys your probably both right! Set was turned off at pp all night but started normally this morning and again just now. But my main problem is the set is no use as a tv until I can get digital channels installed. No info I can find on this. The original remote has buttons tv/dtv to select between source and d-menu to input commands. Universal remotes don't have those and hard to source an old or original one.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

Atainteddragon the m and r are much the same I think and in one review I saw it said the m was the upmarket one (mainly different frame for looks I think). The price new around $3300 back in 2007 so someone making some money then as these models certainly troublesome - cheapies today are about $300/400 here so I won't sling off at them.

[attainteddragon]

Re: LA40 M81BD combo PSU inverter

i'm lucky to get $200 for a 40" but i live on the outskirts.

i do have a couple of remotes around, but they all live with sets unfortunately.

had an la40b650 today that i had sitting around for ages. looked like gamma ic, changed it out, still bad. came across another t-con, still bad. ended up being a corroded panel pcb. a few destroyed caps, corroded traces and gave the same result as a bad as15 chip. oh well.

[syaoran123]

Re: LA40 M81BD combo PSU inverter

I have a spare original remote actually. If you want i can sell for $20 plus $10 postage. Cheap for an original remote.

The m and r are a substantially different class. The M has glossy finish and excellent picture quality that exceeds that of the LEDs sold today. The R is shit.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

I have the set going now with DVD player and the picture is very good. I had set top box connected then at start got an all pink cast over picture menus and all but it was stb at fault. I have another main board same number but entirely different inverter area with big heatsink - can't remember set model but was 2008 build and burnt out resistors was problem there. This set been switched on/off about 10 times today all ok but so frustrating. I do sell some sets but 40" $90 to battlers 32" $50/60 but then I get them for nothing. Be happy to take remote thanks as I think will revive this one so let me know details ( for direct credit transfer) to my gmail maxforvalu .

[syaoran123]

Re: LA40 M81BD combo PSU inverter

There is a way to scroll thru to DTV with the panel buttons according to the manual. Try that first.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

Yes have tried for that but only TV comes up. The user manual I have is very plain in stating dtv is not available via source but only by TV,/dtv button and to navigate then by d-menu button. There are 3 remotes advertised on eBay as suitable for this model - none have those buttons and one even says it doesn't have the d-menu button which indicates he at least is aware of the problem.

[dick_barton]

Re: LA40 M81BD combo PSU inverter

Try each button on the universal remote to switch between TV and DTV. I have a universal and very often one of the buttons will do the switch over. Often being the AV button.

[maxvalutech]

Re: LA40 M81BD combo PSU inverter

Thanks dick barton I had tried that with two remotes one a Samsung from much later model (has a 3D key) and a universal. Both remotes work all but the dtv bit. Of course I don't know the set history but it is 2007 make and later make of this model may well have a changed flash memory program.