Need help DCLCD 19" LCD Monitor - I already replaced caps

[martini]

All:

I have two DCLCD 19" LCD monitors and one of them died a few months back. I was going to throw it out, but I decided to try to fix it. I did some research online and found that the capacitors are typically the problem, so that is why I am here.

The first thing I did was switch out the entire inverter board for the one in my monitor which already works. Once the working inverter board was put in, the broken monitor worked again - I therefore know the problem is on this board somewhere!.

The board is loaded with Elite caps which I guess can go bad.

I ordered 5 caps from digikey (all exact voltage, uf specs as the ones I replaced) in hope that it would be on of the 5 larger caps. I swapped them in with no luck. I then got determined and swapped the other caps between my working and broken board. The board which was originally working STILL works, and the broken one is STILL broken.



I swapped all of the caps with the red X's on it.

What else should I do? I'm out of time today, but maybe you guys can give me some guidance

I have more pictures if they are needed

thanks,
martini

[PlainBill]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

All:

I have two DCLCD 19" LCD monitors and one of them died a few months back. I was going to throw it out, but I decided to try to fix it. I did some research online and found that the capacitors are typically the problem, so that is why I am here.

The first thing I did was switch out the entire inverter board for the one in my monitor which already works. Once the working inverter board was put in, the broken monitor worked again - I therefore know the problem is on this board somewhere!.

The board is loaded with Elite caps which I guess can go bad.

I ordered 5 caps from digikey (all exact voltage, uf specs as the ones I replaced) in hope that it would be on of the 5 larger caps. I swapped them in with no luck. I then got determined and swapped the other caps between my working and broken board. The board which was originally working STILL works, and the broken one is STILL broken.

I swapped all of the caps with the red X's on it.

What else should I do? I'm out of time today, but maybe you guys can give me some guidance

I have more pictures if they are needed

thanks,
martini

You missed two (circled in red). Either can cause problems; the small one fails fairly often; the large one very rarely. You didn't specify the problem; 'broken' covers quite a range of problems. More information to us, the better results we can give. Not all problems are caused by bad caps.

The 5 caps on the upper left circled in lime green are associated with the audio amp. They seldom fail, and if they did the problem would be described as 'no sound' or 'buzzing'. The caps circled in blue are in the inverter section. Those circled in light green on the right are the main filter caps for the power supply.

PlainBill

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

You missed two (circled in red). Either can cause problems; the small cone fails fairly often; the large one very rarely. You didn't specify the problem; 'broken' covers quite a range of problems. More information to us, the better results we can give. Not all problems are caused by bad caps.

The 5 caps on the upper left circled in lime green are associated with the audio amp. They seldom fail, and if they did the problem would be described as 'no sound' or 'buzzing'. The caps circled in blue are in the inverter section. Those circled in light green on the right are the main filter caps for the power supply.

PlainBill

Can't belive I forgot to say the problem! The monitor turn on for one flash then turns off...flashlight test shows the image

I will swap the other caps and see

[weirdlookinguy]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Resolder every pin of the two transformers at the top of the board. Also a common fault with LCDs.

[PlainBill]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Can't belive I forgot to say the problem! The monitor turn on for one flash then turns off...flashlight test shows the image

I will swap the other caps and see

That problem COULD be caused by bad caps, but you've replaced all that could be responsible. As wierdlookingguy suggests, resolder the pins on the transformers.

Now that I look at it, this looks like the power supply / inverter for a monitor I repaired recently. Attach a picture of the bottom side of the power supply / inverter board while you have it out. Got it, that's the same board as the Sceptre Komodo IV I repaired. The quick flash sounds like shorted transistors. The picture will help point them out. If I'm right, this will be an expensive fix. Those transistors are about $.75 each!

PlainBill

[EGuevarae]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

... If I'm right, this will be an expensive fix. Those transistors are about $.75 each!

PlainBill

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I'm sure that dclcd and sceptere use the same parts...



Will post detailed pics tomorrow...thanks guys

[weirdlookinguy]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Make sure you resolder those joints before anything else... It's likely that there are more problems, but I've read up on cases where just resoldering the joints was all it took to fix the monitor. Won't take more than a minute, and you never know...

[PlainBill]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I'm sure that dclcd and sceptere use the same parts...



Will post detailed pics tomorrow...thanks guys

Agreed. But it's always nice to have pictures available.

And don't forget to resolder the transformers!!!

PlainBill

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

here are the photos - let me know what you think and ill start looking

[PlainBill]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

here are the photos - let me know what you think and ill start looking

I've circled the transistors in red. Even if only one of a pair is shorted, replace both. The transistors are Rohm 2SC4672; they are available from Digikey, their stock number 2SC4672T100QCT-ND. Also check and resolder all components in the area, especially the transformers and the gray rectangular caps.

PlainBill

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I've circled the transistors in red. Even if only one of a pair is shorted, replace both. The transistors are Rohm 2SC4672; they are available from Digikey, their stock number 2SC4672T100QCT-ND. Also check and resolder all components in the area, especially the transformers and the gray rectangular caps.

PlainBill

i will look into this - I swapped both transformers with no luck. When you say rectangular caps, do you mean the things next to the transformers on the topside of the board?

the transistors are small... hopefully i have a steady enough hand to solder them... chances are ill just swap them with my other monitor ... if i mess that up ill have two broken monitors!

haha

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

i just swapped the square capacitors.... one on the broken board seemed to have a crappy solder joint so i as hopeful that it would fix it.. however it didnt. i guess ill look at the transistors now

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

i just tried the transistors... i believe they are above my ability/tools. I have just been using my metcal soldering station and some braided copper solder remover. I don't think I can get the transistors off without damaging the board.

any tips?

[Bobdee]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Did you check for shorts as Plainbill asked you to do first
No point removing them if not shorted

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Did you check for shorts as Plainbill asked you to do first
No point removing them if not shorted

is there an easy way to test that with them on the board?

[Bobdee]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I think Plainbill meant you to check them with the low 200 ohms setting, looking for a 00.0 reading or close to that across the solder points, three readings each transistor, he should confirm this later when he comes online
Also Google chip quik

[PlainBill]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

I think Plainbill meant you to check them with the low 200 ohms setting, looking for a 00.0 reading or close to that across the solder points, three readings each transistor, he should confirm this later when he comes online
Also Google chip quik

Absolutely correct on both points.

PlainBill

[weirdlookinguy]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

Did you reflow the solder on the transformers yet? It will take thirty seconds and that's one more thing we can cross off the list.

[martini]

Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

sorry guys, haven't gotten back to this in a bit... i redid the transformers. I can check the transistors.

im looking for close to zero ohms across each combination of the transistor leads?


youd never believe it, but my projector died and it had a blown 470uf 25V elite cap in it... my life is filled with bad caps and transistors!