Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Yes, 12V (12,08V) come to the mainboard, but I couldn't find where do they exactly disappear. What would you suggest to look for in this case?

Tomorrow I'll post a picture of the printed side of the mainboard where 5V and 3.3V are present in certain test-points while in Standby. Again, in other TP they're absent.

Another remark: on the top lefthand corner of the MB there is a placement for external power supply (again these famous 12V) where this voltage is present in Standby mode.

Hmm. I think the PSU is good then. Can you post a very high resolution shot (2000x2000 max) of your main board? I am confused at where the 5V and 3.3V is generated from. Maybe it is from what looks to be an SMPS on the left hand side.

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Here is the printed side of the mainboard. The points marked in red have the nominal voltage in Standby mode. Other voltages are missing in this mode.

I'll take a shot of MB in max resolution, hoping to be as good as needed for you to find what you think the "cause of death" is.

Tom66, thanks again for your help, I do appreciate it

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

The pic:

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Hmm. I think the PSU is good then. Can you post a very high resolution shot (2000x2000 max) of your main board? I am confused at where the 5V and 3.3V is generated from. Maybe it is from what looks to be an SMPS on the left hand side.

Here is the Hi-Res of the MB. Hope it will do, 'cause my camera can't do better than this, sorry

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Diodes around the coils on the left hand side (presumably a SMPS) are looking good both in Standby mode and disconnected. I have a fear that it could be one of SMC ICs just next to them. In that case, there's nothing I could do. Lets hope I'm wrong. Maybe one of these SMD transistors has a current leak?

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

The big coils. Measure the voltage on both ends, while the power is plugged in. One end will measure some random value, maybe even 0. The other should measure 5V or 3.3V.

It is not difficult to repair SMD component faults yourself; all you need is a steady hand, solder wick and fine solder. The last two you can get for about £5 total.

Alas, the bottom of the board confirms my suspicions; the chip is a BGA. Nasty to fix if it goes wrong.

I was doing some searching and it seems your particular main board is also used in Polaroid TVs. The power supply seems to be working so it might be worth just replacing that board if you can find it.

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Hi Tom66,

I measured the voltage on both coils and yes, you're right about the voltage, but there's a catch: I get 3.3V (1st coil) and 5V (2nd coil) measured against positive power supply rail (+12V). If I measure it properly (against the ground), I get inverted values: -8.8V (1st coil) and -7V (2nd coil)! I'm a bit confused what is going on here?!

Just an hour ago I made it to power on once again, I didn't change a thing, the set responded to RC immediatelly after connected to mains. So, Tom66, you were right about ON/OFF pin - it does send 4.5V to the invertor, so the panel gets its backlight alrght, while ADJ pin had no voltage at all. On the other hand, the ON mode lasted a half of minute, so I didn't have time enough to find the source of 5V and 3.3V. Probably processor is not getting its supply voltage, therefore this malfunction. Yes, while working, processor gets pretty warm in just a few seconds, even working on idle. The EN25B64 (Serial Flash memory) has its 3.3V even in Standby mode.

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Alas, the bottom of the board confirms my suspicions; the chip is a BGA. Nasty to fix if it goes wrong.

I was doing some searching and it seems your particular main board is also used in Polaroid TVs. The power supply seems to be working so it might be worth just replacing that board if you can find it.

In fact, my first thought was to change the mainboard, but where (and how) to find it? I'm not bad myself in searches over the Net, but never managed to find anything about this MB; Can you give me any model or reference to search for? That would be great.

Other thought: since we don't live too far away from each other, I'd be glad to mail this MB for some hot air resoldering if you'd accept?

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

In fact, my first thought was to change the mainboard, but where (and how) to find it? I'm not bad myself in searches over the Net, but never managed to find anything about this MB; Can you give me any model or reference to search for? That would be great.

Other thought: since we don't live too far away from each other, I'd be glad to mail this MB for some hot air resoldering if you'd accept?

I'd give it a go, but I'm thinking it's a simple fault, and that the BGA isn't at fault in this case. It seems to be intermittent and BGA faults rarely are.

Voltages relative to 12V. Very odd. Can you check continuity between +12V and case of TV? It should be very high. It might be a positive ground case but I don't think I have ever seen a TV like that.

When the TV does power on, does it work properly? Do you get a picture? Or does it just leave standby?

I got a hit: http://www.shopjimmy.com/polaroid-3550c-main-unit.htm however although it looks similar, it's not identical.

Unfortunately you may be looking at a manufacturer specific part and this will be difficult if not impossible to source.

You best bet may be to sell the TV as-is to someone who knows what they are doing. (Not me!) A 24" LCD TV with a working screen but power problems sells for around £100 on eBay.

A question; approx what year did you buy the TV & when was it manufactured (if known)? Maybe similar TVs from this date would use the same board.

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

To answer your questions first:
This is not a positive ground chasis.
When the TV powers on, then it works without any problem, everything is there: picture, OSD, sound, backlight... Then, after half a minute or so it goes Standby just like that. Afterwards, no matter how hard I try, I can't power it on again. If I disconnect the mains and try ON button, it just might power on again, but not more often than once or twice per day. So, let's call it an "intermittent fault".
I have to agree about BGA - I have also applied some physical pressure on the heatsink and it never gave any positive result, so I guess that bad joints on BGA pins is ruled out?

Selling the set wouldn't really be an option, because I've seen some more of these with the same fault out there and it seems nobody is interested in.

This TV is a 1080P with USB port (with DivX and many other compressions reading capability, rich with codecs), HDMI, SCART, RCA, S-video ,coaxial and digital out... I was really happy with this TV, also SAMSUNG tuner used to receive even a bit weaker signals without problem. I'm gonna miss it, really. Yes, the set was bought for Christmas two years ago.

I have to admit that so far I haven't seen a MB that reminds of this one. It would be hard to find the replacement.

If you'd still give it a try, just let me know. I have to give up here, at least for now. I have to fix my wife's car. This summer things just seem to never stop getting broken.

Thanks for your prompt help, Tom66 and looking forward to hear from you again.

John

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

At the moment, I am really at a loss. Is there a way to turn it on without the remote control? (For example, on the side panel.)

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Is there a way to turn it on without the remote control? (For example, on the side panel.)

Yes, but not more often than with RC.

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Yes, but not more often than with RC.

So RC is probably good.

Can you get a pic of the connector which goes from IR to main board. Also one which goes from side buttons to main board. (They might be on the same connector.)

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

No doubt they both work good. There are two connectors, one for IC RC and other for top buttons.

If you take look of my previous photo (better resolution than this one), you'll find these connectors at the top of the MB. Blue connector (the third one from left to right) is for RC, and white one next to it (fourth from left to right) is for top buttons.

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

The only way forward is to really get a service manual, but I have no clue. In very rare cases, calling the company up and asking nicely can do this. I can find only a few references to Seeltech on the internet, which means it is almost certainly a rebadge of other TVs. For example Vestel makes a lot of TVs for the Goodmans, Matsui, Nikkai, AcousticSolutions, etc. brands - they are all the same. If I could get a service manual I would be able to help more. But right now I am just stuck.

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Yes, I know what you mean, Tom. In fact, on the user manual there's not a single word about helpdesk, nor any instruction if the set gets broken! There is just some name and address of (presumably) importer and/or wholesales distributor. Not a single telephone number. Well, I know: when I bought the TV I didn't ask questions about maintenance, I was really self-confident, but now what?! Never mind, I'll track it down and find some contact, I'll try to get that service manual and then we'll fix it (if only BGA is still alive and kickin').

Funny, but the part of MB with DVD connectors still has 5V even in Standby mode, but TV doesn't power on?!

Just in front of two coils we have mentioned earlier there are two SMD diodes (respectively) and there's 3.3V and 5V voltage in Stby mode. From there on it gets hardly possible to track the voltages due to a load of SMD components squeezed one against other on a very small surface. There's a couple of SMD transistors looking good, but who knows what happens when the current strikes?!

You're right, Tom: without a service manual or at least schematics it is almost impossible to fix this board.

I hope someone would see my MB and suggest from what other brand was it rebadged. That would help a lot. I can't imagine that Seeltech has made an original design here, and still the brand is untraceable?!

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

What do you think of bad (or damaged) eeprom dump? Can it cause such a problem? I am prone to believe so. Any advice?

Thanks again.

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

What do you think of bad (or damaged) eeprom dump? Can it cause such a problem? I am prone to believe so. Any advice?

Thanks again.

There is usually a small chip (EEPROM) in a socket which can be removed. (It is not surface mount.) *Carefully* use a screwdriver to wedge it out. Put it in a safe place. Some TVs will turn on without this, others won't. However, I'm inclined to believe this won't fix it as your problem is intermittent.

Reading and writing the EEPROM is not easy although I have done it before using a PICkit 2.

[joste]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Nope, everything is SMD and not a single socket and chip that can be removed. I guess this makes the whole operation hardly possible.

Simply, I got out of patience and if I don't find some "instant" solution (like exchange MB or something), I'll give it up.

I'll give a call to importer and wholesale distributor to hear their say. Maybe thay still can help a bit, who knows.

[tom66]

Re: Seeltech ST2468DHD 24" LCD HD TV Standby only - help needed!

Nope, everything is SMD and not a single socket and chip that can be removed. I guess this makes the whole operation hardly possible.

Simply, I got out of patience and if I don't find some "instant" solution (like exchange MB or something), I'll give it up.

I'll give a call to importer and wholesale distributor to hear their say. Maybe thay still can help a bit, who knows.

Good luck. Your best bet right now may be to extract the 24" LCD panel and CCFL tubes. The tubes sell for £3 - £8 each (there are usually 10-15 in a small set like yours) and the 24" LCD would sell for around £100, since it's 1080p. Then save up the money and buy a set which has an easy to get service manual.