40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

[wa11y]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Just measured AC across the large filter cap and it 'sitting' at 25VAC, it spikes up to 30V regularly but never gets under 24-25VAC.. Is that normal?

[tom66]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

I've often thought the AC voltage reading across the cap doesn't mean much, I would only look at DC for now.

[selldoor]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Just measured AC across the large filter cap and it 'sitting' at 25VAC, it spikes up to 30V regularly but never gets under 24-25VAC.. Is that normal?

Hahaha - i dont know - I was hoping Tom would make something of the result..Perhaps Budm will see this and chime in later.

Does the DCV fluctuate say over a 10 second period.

[selldoor]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

see here https://www.badcaps.net/forum/showpo...1&postcount=13

Depends on the result from the DC test.

[tom66]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Whilst it may work well with a Fluke, as that is ac coupled, it will not work with most cheap meters as the AC measurement is dc coupled.

[wa11y]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

The DCV doesnt fluctuate at all, the SMPS really seems to be supplying all the needed voltages, with the resistor in im getting a solid +5, +12 and +24., but since my backlight doesnt light up is that likely to be the main cause? or the inverter board? And is there any way I can tell or test say the individual 'globes' of the backlight if I have a laptop inverter handy or similar? or has it all been done now? Time to throw it in the bin??


Well I have an ancient fluke 8020a at my disposal but i dont think its any better at reading AC than my cheaper meter at anything other than 50/60hz...


Its a sad thing to throw these things out its such a waste

[tom66]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Have you checked BLON yet?

[wa11y]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

I jumpered pin 1 to 2 with CON2, but now I look at the 'service manual' I linked on the first page of posts, it says there that CON2

1 ON/OFF Power switch
2 STB5V Stand by 5V

and that

CON8 (THAT ACTUALLY COMES FROM THE MAINBOARD TO THE INVERTER BOARD)

1 ON/OFF Inverter switch
2 ADJ Adjust backlight


Do I have to jump Pin1 & 2 on CON2 as well as send 5v down the ON/OFF of pin1 of CON8??? Im confused now.

edit: I just also realised I think at the beginning I wasnt clear at all, the standby light is constantly ON, and flashes OFF [for a split second] every ~33seconds, & not the other way around.... MIL didnt think it did this before so not sure if that means anything and it very well could have done it before and she never noticed or doesnt remember.

[tom66]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Pin 2 to ON/OFF inverter switch if you get good 24V.

[selldoor]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Hi Tom I think he may need more guidance.
I think you are saying "yes" he needs to jumper pin2 to pin1 on con 2 to get the board powered up and then if that is producing 24v on the 24vpins then he should then
add the jumper from pin2 on con2 to pin 1 on Con8. ( Does that need a 500/1kohm resistor in )

[tom66]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Yes, that's what I mean. I recommend a resistor for safety reasons... most boards are fine without... but some can be poorly designed.

[budm]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

"Just measured AC across the large filter cap and it 'sitting' at 25VAC, it spikes up to 30V regularly but never gets under 24-25VAC.. Is that normal?" Unless you are using good True R.M.S meter like Fluke 87, it should have AC less than 5~3% of the DC reading on the filter (you are basically looking at AC ripple on the filter cap, I.E. dc =100VDC, AC shoould be less than 5VAC).
"Whilst it may work well with a Fluke, as that is ac coupled, it will not work with most cheap meters as the AC measurement is dc coupled." That is correct, for now he can disregard the reading.
If the Inverter board uses PWM for Dimming, he may have to ifnd out if he has any AC signal on this DIm pin, otherwise it will do 2-second to black when he force on the Inverter.

[wa11y]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Cool well we have back lights now!!

However (not sure if its an issue at all) but the power supply is making a constant very fast ticking/clicking/zapping noise , I measured across the big filter cap with my meter and I can see that the the zapping seems to be because of extremely fast voltage fluctuations, just like what was happening before but HEAPS faster (I can only see the fluctuations by looking at the analogue bar as there way too fast) ..

Is it normal behaviour or should it (for the most part) be 'quiet' when working? I have myself heard SMPS's in PC's making 'zapping' sounds when there working normally but nothing like this before. Never heard this from a LCD monitor either. Im sure I could hear this noise with the back on if I were standing in front of the TV its not very quiet this time.

[selldoor]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Does the backlight flicker at all along with the ticking?

Looks like we are back to the Main board to see why there is no BLON Signal

[wa11y]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

No the backlight itself appears to be functioning perfectly the screen looks just as it should.


Well tom already said.

4.6V instead of 5.2V could indicate bad caps.

& now realising that the mainboard actually supplys the ON voltage for backlight please tell me would it still be possible to be the caps on the mainboard?? I mean unless there is a bad eeprom or failure of one of the SMD IC's or something it probably would be right?



OK now what I maybe should have mentioned up first..

The mainboard has NOTHING but "XUNDA" caps on it... & I actually did decide to replace ONE of the 'big' 470uf caps because the ESR was 'suspect' (according to me reading the chart on my meter but I dont really have much idea here since this is really my first time using this meter). But im now just thinking maybe I should be replacing all the caps on the mainboard and hope for the best??? ... I can always remove them afterwards to use again if it doesnt work so no loss there at least.. I actually wrote down all my original readings which in ordinary 'wally' fashion I lost almost immediately after putting them all back in.

I might remove every cap again and give it another go.. Ill post my results here in a hour or so maybe someone will see something I didnt, its about the least I can do right now.


Just need to say also thanks so much to selldoor yes I was confused before with what to do and you completely cleared that up, and thanks so much tom and everyone else for the help and bearing with me so far I do really appreciate it. Thx 'guys'

[selldoor]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Nice to get a bit of encouragement now and again. If you havent already ripped off all the caps - near the con 8 there are 2 switching transistors one has t1A on it - cant see the other. Maybe they are in the circuit to switch on the backlights.
Here is the datasheet.

[wa11y]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Both of those transistors have the same part numbers. The collector of Q4 goes directly to pin1 (on.off) on CON8... I tested between the base and collector, + base and emitter and got no reading on either of those transistors, are they really NPN transistors the numbers on them are t1a 86 (since its sideways im not sure it could really be 98, but I think it is 86)

Well I did already take the majority of the caps off so at least here is what i got on my meter (making sure to zero it after each test).

CA1 - 470uF 35V - 0.08R
CA2 - 470uF 35V - 0.07R
CA3 - 470uF 35V - 0.07R
CA5 - 470uF 35V - 0.09R
CA6 - 470uF 35V - 0.09R

CA9 - 470uF 16V - 0.09R
CA12 - 470uF 16V - 0.13R
CA23 - 470uF 16V - 0.14R

CA13 - 220uF 35V - 0.13R
CA15 - 220uF 35V - 0.13R
CA17 - 220uF 35V - 0.13R

[[CA7, CA8, CA18, CA19, CA22, CA25, CA26, CA27, CA28, CA29, CA32, CA35, CA38,]]
220uF 16V -- ALL 0.12 - 0.14

[selldoor]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

I dont know if the esr is good or not - I dont have an esr meter so never bother with it.
Perhaps detail the test you did on the switching transistors - they are fairly common so there may be others on your boards you can compare them with? or some on an old board you can borrow.

[wa11y]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

I had my meter in diode test mode, with the COM connected to the base, that's all I did on both tests.

I have tested a brand new low ESR 470uF 35v cap and its 0.04 on the meter.

[selldoor]

Re: 40" LCD Rank Arena (rebadge?) has standby, V+ seem OK, but wont turn on.

Both of those transistors have the same part numbers. The collector of Q4 goes directly to pin1 (on.off) on CON8... I tested between the base and collector, + base and emitter and got no reading on either of those transistors, are they really NPN transistors the numbers on them are t1a 86 (since its sideways im not sure it could really be 98, but I think it is 86)

Well I dont think that is correct - in diode mode you should have got some reading. - On resistance mode should read OL one way?
See here
http://www.allaboutcircuits.com/vol_3/chpt_4/3.html