Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

[budm]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Do you see any waveform at the GATE? And this done using force on BL_ON pin?

[tom66]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Do you see any waveform at the GATE? And this done using force on BL_ON pin?

I haven't checked the gate, because it's covered up by the thermal paste on the MOSFETs (no idea why...) INV ON is at 3.2V from the main board and BRI is at 4.6V.

[Scenic]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

As for the confusion about how to measure the transformers, that's easy to do when telling us how to check a different transformer to the one on our boards.
The link in post #22 and the image in post #30 (and the entire talk following these posts) are for/about a "4015A" transformer used on Darfon inverters, while the ones on our inverters are 6800M's

@tom66: like I said.. I've got all that stuff here. If you need it, PM me. Shipping shouldn't be all that expensive (even with DHL), as it's within the EU.
To me they're just random PCBs collecting dust :P

[tom66]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Interesting thing I discovered. When first turned on, there is a little spike on all of the transformers' primaries... except two. These two are connected to the same fuse. Sure enough, the fuse appears open...

But it didn't appear open when I first tested it, so maybe it's a polyswitch or resettable fuse? It is a green colour which is typical for PTC fuses.

I'll see if I can borrow a fuse from another board. It's got a "P" on it. It's a 3A fuse, which I don't think I have in stock at the moment. I have some 4A axial fuses (250V T), but I'm not confident I can solder to those and to the board.

[tom66]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

@tom66: like I said.. I've got all that stuff here. If you need it, PM me. Shipping shouldn't be all that expensive (even with DHL), as it's within the EU.
To me they're just random PCBs collecting dust :P

Thanks Scenic. I'll probably throw in the towel soon, after I check this fuse in closer detail.

[shepp]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

im sorry but there is no confusion, the transformers are still wound the same, they are from darfon 6800m's are they not? the actual ohm measurement will be differant but the way to test is still the same? if 1 out of the 8(or how ever meny there are) are differant to the rest then this would be a dud, process of elimination

Scenic your picture shows Darfon 6800M which are wound the same as 4015A, the only differance would be the actual resistance reading for that model as mentioned previously, but you dont even need the correct readings from the internet because it is very unlikely that the majority of the transformers would be duff only 1 or 2 might be but again process of elimination, i was only trying to assist people in the correct way to test the transformers so there was no confusion with void and useless readings

[budm]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Tom, you can use 1/4w 1 or 2 Ohm resistor as a fuse for now just to test the circuits. Then you measure the DC drop on the resistor to calculate the current draw. By the way, that is just surface maounted fuse.

[tom66]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

im sorry but there is no confusion, the transformers are still wound the same, they are from darfon 6800m's are they not? the actual ohm measurement will be differant but the way to test is still the same? if 1 out of the 8(or how ever meny there are) are differant to the rest then this would be a dud, process of elimination

Scenic your picture shows Darfon 6800M which are wound the same as 4015A, the only differance would be the actual resistance reading for that model as mentioned previously, but you dont even need the correct readings from the internet because it is very unlikely that the majority of the transformers would be duff only 1 or 2 might be but again process of elimination, i was only trying to assist people in the correct way to test the transformers so there was no confusion with void and useless readings

All transformers are wound the same. The fuse I've located is probably the problem. (There isn't a short after the fuse.)

[tom66]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Tom, you can use 1/4w 1 or 2 Ohm resistor as a fuse for now just to test the circuits. Then you measure the DC drop on the resistor to calculate the current draw. By the way, that is just surface maounted fuse.

Yeah... I tried it the cheapskate way.

First I checked how the PSU handled short circuits. It just cut out, good. (I believe this is actually an EU requirement - related to 240VA - but don't quote me on it.)

Next, I bravely soldered two wires and bridged the fuse.

Result. No smoke. It works! Screen lit up, good picture and most importantly the screen isn't cracked (I was worried it might be, because I couldn't tell with it off.)

Even the sound works... as I had suspected, previous user had muted the TV accidentally. The input trick didn't work because trying input brings up a dialog box asking the user to select an input - pressing input doesn't automatically switch between them.

The speakers on this TV are actually really nice - a three-way unit. And they do sound pretty good. Hey, when I go to university, I'm bringing one of my LCDs along with me ... now to decide the biggest size I can fit in the cramped dorm rooms.

Need to get a fuse, fit it, and reassemble the TV. I kept the screws this time in a labelled zip lock bag . I'll probably use a through hole fuse and some hot glue. I have some 3.15A radial fuses somewhere... I'm tempted to use one of those.

I'm just baffled how this fuse could have tested okay out of circuit, but fail in circuit. The only explanation I can think of is it is a resettable fuse (most resettable fuses fail by a decrease in tripping current as they age), but I see no reason for a manufacturer to use one. A short on the inverter wouldn't clear, unlike for example a short on a USB port, which is why a motherboard manufacturer might use one.

Thanks everyone for their help.

[budm]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Great!
Some TV the speakers can be set to OFF in the audio setup menu.

[Jasgriff]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Nice one Tom. Another one fixed hey!

Some good learnings from this one too.

[tom66]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

I used a 250V 3.15AH(T) fuse from a previous repair (managed to blow the primary fuse by letting the PSU primary touch the case... go figure.) I hot glued it onto the shield of the inverter (including the pins to stop shorts), so it shouldn't be difficult to remove or replace.

One can never have too many ongoing projects...

Two of them work (ready to sell), one of them sort of works (just needs to be screwed together after a cold joint is fixed) and one of them awaits a new PSU which will be installed after the other two are gone. Then I will focus on some bigger LCD or plasma to fix. Since the LG 42PC1D has gone, I've not had a particularly difficult problem with any TV... just the odd bad cap or blown fuse, or for the 17PW15/20 PSUs (Vestel) I just swap 'em out, not worth repairing as about 20 different things on them can fail.

I also fixed the PS2 (Just a dirty laser. Nice Nichicon caps all over the PSU.)

The Goodmans (left) uses an AU Optronics (AUO) LCD panel, which is fairly decent for a cheap TV. Motion performance is okay (a little bit of blurring, but not bad), colour and black levels are good too. The Hanspree (right) uses a Chungwha panel... motion leaves a nice blurry trail and backlight leakage is awful. Colour is okay, same as the Goodmans. Also, there are slight uniformity issues, but it's not very noticeable unless the screen is dark and you're near 30/150 degrees.

Both TVs are currently undergoing an overnight burn-in test.

[Jasgriff]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Nice,

Tell you what we need to see is a pic of Budm's repairs in waiting / fixed. He must have a massive pile of them!

I also need to fix that samsung 37" tv I have here and get it our of the way.

[tom66]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

Well, both passed the overnight test with no problems... so on to the next project!

[shepp]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

well done tom

[vinceroger69]

Re: Hanspree "Unknown Model" 32" LCD: No picture or sound, power LED

yes well done so reading through this thread the problems with this set was bad caps and a blown fuse? wish that lg i have was a easy fix as this.