Dell 2209W - no power at all - stripped down but can't see anything obvious

[Jasgriff]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Hi batz,

Are the big components around it easier to take out and put back in that taking the Ic off?

If you could take the chip out then you would test the vcc and gnd pins again to see if the measure low ohms like they did in circuit if the do then that means that the ic is shorted. You would then need to test the vcc and gnd pans on the board to see if they are showing low ohms which would mean that there is something else wrong too.

Its difficult to say if just replacing the chip will work as we really need to understand if its blown first. If so we wold have to look at what blew it or what has blown around it. If its not blown then there is definitely something else gong on.

Either way you either need to lift the leg or remove the chip to know what's going on.

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

OK, seems like the best plan is to remove the IC and test it.

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Sorry for the delay, I just got time to do this. I have removed the IC using the 'flood all the pins' technique, not too tricky.

The measurement on the IC between pin 4 and 6 is 6.4ohms.

The measurement on the board pads between pin 4 and 6 is 1Mohms - the same as when the probes are apart.

Do I go ahead and order a replacement IC? If so are there any specific ones recommended?

[budm]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Yes, get the new SMPS IC, same P/N that you have indicated in the earlier post LD7575?

[selldoor]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

This seems cheapest
http://www.ebay.co.uk/itm/5PC-NEW-LD...item3a6c2e73df

I and another badcaps member have bought transformers off this one without
problems
http://www.ebay.co.uk/itm/5PCS-PWM-C...item3a691edcdd

packs of five so room for error. It does take a couple of weeks for delivery
so if you are desperate to get it done then UK but its the same price for one
so no room for error. Remember as well as error we dont know if the item just
failed or if something else caused it to fail so its probably better to have spares on hand.
I have had a bit of a look to see if there are equivalents but none came up. CPC do have "similar"
items for less than £1 but I dont know enough to say if they would do.

[Jasgriff]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Do we not need to get batz to check for other faults in case fitting another chip leads to it being shorted again?

[budm]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

I believe he already checked the MOSFET that is driven by this SMPS IC already.

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

I am happy to check anything else before I order. I guess the link for 5 is the best bet but if we were confident it wouldn't blow again then this one is in the UK and just as cheap:

http://www.ebay.co.uk/itm/LD7575PS-L...ht_1042wt_1415

Is it OK?

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

@selldoor - can you post the CPC item details so someone can check it out? I'd be happy to set up an account with them as long as it was easy/cheap enough.

[Jasgriff]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Batz I only had a quick glance back through the thread hen I posted that question. If the mosfet is not shorted then its unlikely that it will blow again.

[selldoor]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Looked more into cpc and at data sheets - no good im afraid.
also checked RS electrical and Cricklewood Electronics. Both have lots of ics
but not this one.

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Thanks Selldoor.

I have bought 5 of the LD7575 chips from this vendor:

http://www.ebay.co.uk/itm/2807605999...84.m1439.l2648

Virtually the cheapest and it looked like the most professional of the cheap far east listings.

I'll post back when they arrive.

Thanks again everyone for contributing to helping me in this thread.

Ian

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Hello again all!

The five ICs arrived today and this evening I have carefully soldered one of them onto the PCB ... the screen is still dead ... argh!

I measured the resistance across pin 4 & 6 of one of the ICs that I didn't use and it measured around 406kohm. I measured across the same pins on the IC that I soldered on the board and it initially measures high like 1Mohm but then drops down to around the same figure of 401kohm. Is this perhaps because the power supplied from the ohmeter is charging some capacitor somewhere?

I can perhaps post some pictures tomorrow and measure some more voltages but for now it's getting late so I will wait for (hopefully) some helpful suggestions!

Thanks again
Ian

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Here are some pictures of my IC soldering!

Hope someone can come back on this thread with some suggestions of what I can do next.

Ian

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

By the way you can see on the pictures that I managed to damage the track to component C953.

I don't think the track is broken just the surface protection damaged when solder dropped on to it.

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Where have all the helpful people gone who posted earlier in the thread? I am reluctant to give up on this monitor but I am clueless to diagnose what might be wrong with it.

Even if someone could review my IC soldering attempt it would be better than silence ...

[retiredcaps]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Restart with all your voltages measurements again. With a new SMPS IC, we cannot take the previous readings as valid.

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Restart with all your voltages measurements again. With a new SMPS IC, we cannot take the previous readings as valid.

OK will do, busy weekend so will come back ASAP.

[Batz]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Hi all, sorry for the delay have been very busy home and work. I have done some testing and here are the results to as many of the previous voltage measurements as I could find.

First I tested the fuses and fuse resistors and they all seem fine (continuous)

These are all with the power supplied to only the main board, everything else disconnected.

AC Input voltage 243V
Big Capacitor = 330V
+24V marked on back of the board = approx 30mV
+5V marked on back of the board = varies from 0 to 6V cycling around
+20V marked on back of the board = approx 20mV
Between pin 4 & 6 on the IC I just replaced = 193V
Between pin 13 & 15 on the other IC (SG6901ASZ) = approx 0mV
Capacitor C957 = 193V
Capacitor C952 = 900V to 1800V rapidly cycling around (I had to test this a couple of times to make sure I wasn't misreading it!)
D850 = 1V (ditto, very strange reading on the multimeter, just shows '1 V' no decimal point values)
C862 = ~ 14mV
C963 = Cycling from 0V to 11V and round
C931 ~ 20mV

This bunch of tests took quite a while and at one point I somehow managed to blow the fuse in the multimeter again but luckily I bought a 10 pack! The board also noticably warmed up with the characteristic 'warm TV' smell. However this is not a bad 'something is burning/blown' smell though!

So things are obviously quite broken still!

Hope you guys can come back with some ideas, I should have some time at home tomorrow so if you need things testing I should be able to get them fairly quickly.

Thanks again for all the input so far.

Ian

[selldoor]

Re: Dell 2209W - no power at all - stripped down but can't see anything obvious

Hi its too late for me to get my head around this tonight hopefully colleagues across the pond will come up with something.
My only thought is that you have broken the meter - try taking the battery out - might reset it. Test it on things you know the voltage /resistance of.