Wharfedale LTF37K1CB Picture problem

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

A digital meter can be acquired for around £6.99 from Maplins, or from other shops. It is pretty much necessary to use a digital meter for modern electronics which are sensitive to 0.1V drop.

Thanks Tom. Hmmmm £20 from maplins or £4 from ebay. Looks like I will wait a couple of days. Will post back once arrived and tested again.

ps. Thanks for all the help so far guys. I really appreciate it!!

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

Ok I'm back with more info and readings.

Got a digi multimeter, set to 200 DCV.

Have not had the telly on since I last wrote here.

Turned TV on and it stayed on, left it for over an hour and it was fine.

Voltages to the inverter are as follows for when it was running from start and just before I turned the TV off an hour later.
All voltages were taken while the TV was on and working

top white (marked VBR on the board) - steady 4.3v
bottom white (marked on/off on the board) - fluctuating between 3.7v & 3.8v
ALL 5 red wires (marked 24v on board) - steady 20.1v

After the hour I thought 'ok lets turn the set off for 15 mins', so proceeded to do so. Waited. Then turned back on.

Straight back to the way it was before no picture but have sound.
So I checked the voltages again with no picture.

top white (marked VBR on the board) - steady 4.4v
bottom white (marked on/off on the board) - steady 3.8
ALL 5 red wires (marked 24v on board) - fluctuating 24.7v & 24.8v

I hope this will help someone fathom my problem out.

[tom66]

Re: Wharfedale LTF37K1CB Picture problem

Only 20V on the inverter connections?

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

Yep. While it was running fine after 1st turning on but after turning off and then on again (then the screen lights went out again) it went up.

I thought that it was 20v because of power drain?

[tom66]

Re: Wharfedale LTF37K1CB Picture problem

20V is much too low. 23V to 26V range on the 24V line.

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

It is a weird one. its 20v when it was working fine and 24 when not.

So what do you think I should do? replace the 2 caps I pointed out were bulging slightly?

If so can you please give me some guidance to the best panasonic caps to get as there were so many to choose from on that site i posted earlier

[tom66]

Re: Wharfedale LTF37K1CB Picture problem

I'm thinking that the 20V is marginal -- the inverter's just about to operate on it and the TV works fine.

When it first tries to start up perhaps it momentarily drops below say 18V and the inverter then refuses to start up.

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

ok what I will do (will have to be tomorrow now as my sons about and cant do it with him about) is test it when it starts up and see what voltages it shows in each step of powering up.

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

Ok tested today.

When power off and not plugged in (obviously) 0v

When first plugged in without turning the TV on, light flashes (blue/red alternating) on front of tv & voltage shows 24.7, then light goes constant red (standby) and voltage then drops to 0v again.

Then TV turned on by button on side of TV and voltage goes straight up to 24.7v for a couple of seconds while the TV fires up then I get 20.1v as the inverter kicks in (blue led lights up and then goes out on inverter), lights up the back light and stays at 20.1v until the back light goes out and the voltage goes back to 24.7v

[tom66]

Re: Wharfedale LTF37K1CB Picture problem

So it would seem to me like 20.1V is really marginal and it can't normally run on that voltage but sometimes it can.

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

So we are looking at those caps on the power board then?

Can you recommend the right ones then please from the panasonic http://uk.mouser.com/Panasonic/Passi...z0wrk5Z1z0x3xj

Also I have a few service manuals in PDF if they are any help to you?

[multimeter]

Re: Wharfedale LTF37K1CB Picture problem

So we are looking at those caps on the power board then?

Can you recommend the right ones then please from the panasonic http://uk.mouser.com/Panasonic/Passi...z0wrk5Z1z0x3xj

Also I have a few service manuals in PDF if they are any help to you?

panasonic fm series,i use them in everything top quality and not bad price,you need to use low esr in power supplys.

the drop in voltage is pointing towards caps gone high esr,high esr=lower voltage output.

test output inverter pins to ground also,may just bring up a shorting rail that isnt cap related,you should have a high resistance reading in the KOHM range. unless the old caps are shorted,dosent normally happen like that though,they go high ESR.

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

panasonic fm series,i use them in everything top quality and not bad price,you need to use low esr in power supplys.

the drop in voltage is pointing towards caps gone high esr,high esr=lower voltage output.

test output inverter pins to ground also,may just bring up a shorting rail that isnt cap related,you should have a high resistance reading in the KOHM range. unless the old caps are shorted,dosent normally happen like that though,they go high ESR.

I'm so sorry to ask this but can you please explain exactly where to test and how (eg setting on multimeter), I'm still quite new to testing TV's (gimme a pc/games machine/mobile phone anyday).

I have 2 outputs on the inverter board (can be seen in the pictures I posted)

BTW the inverter is BRAND NEW! not a reclaimed one

I would also take it that I would be looking for Low ESR Caps then?
Would these be the ones I am after?
http://uk.mouser.com/Panasonic/Passi...yzh23sZ1z0yp75

[multimeter]

Re: Wharfedale LTF37K1CB Picture problem

I'm so sorry to ask this but can you please explain exactly where to test and how (eg setting on multimeter), I'm still quite new to testing TV's (gimme a pc/games machine/mobile phone anyday).

I have 2 outputs on the inverter board (can be seen in the pictures I posted)

BTW the inverter is BRAND NEW! not a reclaimed one

I would also take it that I would be looking for Low ESR Caps then?
Would these be the ones I am after?
http://uk.mouser.com/Panasonic/Passi...yzh23sZ1z0yp75

the link you gave are a step up from panasonic fm ,fr is better,and they will be fine too,you need the 105 degree temp ones for the power supply as there will be a lot of heat from surrounding heatsinks/poor ventilation etc.


your inverter is brand new so that should be fine.

you need to check the voltages coming out of the power supply,you documented that the voltages were around 20 odd volts,that would be on the low side to power your inverter board,the 20 odd volts will be coming from the power supply to the inverter which should be around 24volts going into your inverter.

to test for possible shorts on the power supply set your dmm to around 200 ohms,or auto ranging if you have the feature on your dmm,clipping your black probe to cold ground (chassis) you then put your red probe onto the output pins one at a time where it says i,e 24v 12v etc,(this is the readings from your power supply),you want to see a reading going into the k ohms range,this will indicate infinite resistance ,this is a good sign you dont have a short on that one rail,then move onto the next pin and so on.

if you find you get a reading say around 30ohm or 3ohm(not k ohm) this will indicate a short somewhere on the power supply and will need further investigation.

panasonic series low esr caps,fc-fm-fr,105 degree are all absolutley fine.

a cap with high ESR will cause a voltage drop and will not power what its supposed to power.

it seems your inverter isnt getting enough voltage from the power supply to keep itself switched on.

heat is also your freind in diagnosing cap problems,heat your caps with a hairdrier or heat gun and see if the inverter stays on,if it does,replace those caps.

surrounding outside temperature will often also cause the caps to either work or not,if its warm inside there is a good chance the caps will warm to,and that is what could be causing your intermittant problem

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

Hi Multimeter,

Thank you for your very detailed explanation. PERFECT!!!

Ok I done what was suggested but I don't think this little multimeter can take it lol

Set @ 200ohms, when I touch the 24v power inputs to the inverter the display just goes off.

I think it is down to what it can handle.

The specs are here: http://www.hobby-hour.com/electronic...multimeter.php

[multimeter]

Re: Wharfedale LTF37K1CB Picture problem

Hi Multimeter,

Thank you for your very detailed explanation. PERFECT!!!

Ok I done what was suggested but I don't think this little multimeter can take it lol

Set @ 200ohms, when I touch the 24v power inputs to the inverter the display just goes off.

I think it is down to what it can handle.

The specs are here: http://www.hobby-hour.com/electronic...multimeter.php

that is also a good sign if your meter goes"OL" OR "1" both meaning open circuit,if you get a reading however of "0.1" that would mean a short.

just to confirm,you did these tests on your power supply?black probe to cold ground and red probe to individual pins on the output inverter pins?

also what does your meter show when turned on and the probes not touching each other? should be "OL" OR "1" on resistance reading.

[multimeter]

Re: Wharfedale LTF37K1CB Picture problem

just read the spec on your meter,it will go to 200ohm- 2000 kohm,that is ideal.

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

Ok. This is weird.

I just done it again with the black touching the chassis, the I touched the red to each of the 5 power inputs to the inverter from the power supply.

While the TV backlight was still on all I got was a "1" on the display after a milli-second flurry of numbers but as soon as the backlight went off and I touch the red wires the display goes off. nothing displays.

Should I be unplugging the inverter and just testing the pins on the power board?

[multimeter]

Re: Wharfedale LTF37K1CB Picture problem

Ok. This is weird.

I just done it again with the black touching the chassis, the I touched the red to each of the 5 power inputs to the inverter from the power supply.

While the TV backlight was still on all I got was a "1" on the display after a milli-second flurry of numbers but as soon as the backlight went off and I touch the red wires the display goes off. nothing displays.

Should I be unplugging the inverter and just testing the pins on the power board?

yes remove inverter plug from power supply,set unplugged,then read your resistance readings from the power supply,sorry should have added that in my previous post

[Smokin House]

Re: Wharfedale LTF37K1CB Picture problem

Ok tested again. with no power to the TV and with the plug at the power supply to the inverter unplugged. All 5 red pins have no movement on the meter, it stays showing 1__._ (the _ indicates no number)