LCD Samsung LA32B350F1 - sound, no picture

[burntfingers]

Do I need to suspect one of the inverters?
Sound is there OK, but a perfect picture only appears for a second or less any time it is powered, on the standby touch button.

Sadly, the Manual does not have the diagram.
Manual suggests replacing the entire PS board [which, I guess, would not be cheap - customer wouldn't accept]**.

http://elektrotanya.com/?q=showresul...at2=schematics


** Are these LCD sets getting more into the disposable "dispensation" with such faults?

[retiredcaps]

Re: LCD Samsung LA32B350F1 - sound, no picture

Do I need to suspect one of the inverters?
Sound is there OK, but a perfect picture only appears for a second or less any time it is powered, on the standby touch button.

That would be a good guess at 2 seconds to black. See

http://lcdparts.net/TransformerDetai...ProductID=3944

for the secondary pins.

Measure both transformers and see if all 4 readings are within 3% of each other. Post your measurements.

$20 on ebay + free shipping if that is the problem.

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

Secondary readings are similar - on one, there is a slight difference [1003 Ohms instead of 1030].
Would the set run on half of the lamps if I removed the suspected inverter?

[randtek]

Re: LCD Samsung LA32B350F1 - sound, no picture

That minor diffrerence is probably insignificant. I would supply a single color test pattern and look carefully at the screen before it goes out. Do you see any areas that look slightly darker? It could be a bad CCFL (cold-cathode flourescent lamp)

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

That minor diffrerence is probably insignificant. I would supply a single color test pattern and look carefully at the screen before it goes out. Do you see any areas that look slightly darker? It could be a bad CCFL (cold-cathode flourescent lamp)

Thanks for the tip - I will try it next.
The normal TV picture looks OK, but I will feed a red signal and watch.

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

Yes, there is a band of about 15 centimeters on top of the screen, with gradually less light.
The very top edge is with the least light.
The rest has perfect red.

[randtek]

Re: LCD Samsung LA32B350F1 - sound, no picture

The very top lamp is out. If you are brave, you can try dsisassembling the panel and replacing the bulb. They are available from sources on the net. You could also look for a used panel.

[tom66]

Re: LCD Samsung LA32B350F1 - sound, no picture

It's not always the lamp. Sometimes the blue capacitors can fail open circuit. Try swapping the lamp connectors around: for example plug the topmost lamp into the socket below and vice versa - then see if the band is fixed (lamp failed) or if it moves (cap or transformer).

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

It's not always the lamp. Sometimes the blue capacitors can fail open circuit. Try swapping the lamp connectors around: for example plug the topmost lamp into the socket below and vice versa - then see if the band is fixed (lamp failed) or if it moves (cap or transformer).

Oh, that would be an easy one, I guess!
But I will check them tomorrow - I already checked them for shorts in-circuit and nothing strange to mention.
As for stripping the enclosure with the lamps, not the easiest jobs.
I know another friend who also has exactly this same model, and I guess this would be some sort of a stock fault that I will have to repair sometime again.
It would very nice to fix this one first.

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

Checked blue caps - 3pf 5kv - OK.
Swopped lamps, same result: top one not on.
Swopped inverters, top lamp now OK, third not on.
[Still on only for a second]
Conclusion: faulty inverter.

Must I replace both?

[tom66]

Re: LCD Samsung LA32B350F1 - sound, no picture

Are you sure about 3pF? That's very low. Typically it's 20-50pF.

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

Are you sure about 3pF? That's very low. Typically it's 20-50pF.

Actually 3pf, 6kvolts.
Check proof.

[PlainBill]

Re: LCD Samsung LA32B350F1 - sound, no picture

Checked blue caps - 3pf 5kv - OK.
Swopped lamps, same result: top one not on.
Swopped inverters, top lamp now OK, third not on.
[Still on only for a second]
Conclusion: faulty inverter.

Must I replace both?

No. the transformers, part number QGAH02107, are available for $20 on eBay. I suspect you did not measure the windings correctly. There are two secondaries on each transformer, it is almost certain one of them is open.

PlainBill

[tom66]

Re: LCD Samsung LA32B350F1 - sound, no picture

Interesting CCFLs. Never seen curved ones like that.

Anyhow, note how the faulty inverter output is very dim but it is lighting up slightly; this generally rules out a driver problem. Double check the secondaries as PlainBill suggests but also check the wiring and the orientation of the connector (it sometimes matters which is white and which is pink/blue/other.)

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

Thanks, guys.
Went back to measure transformer pins [in circuit], and they show:
Ti 801
1-2 = 1021 ohms
2-3 = 1023

Ti 802
1-2 = 993
2-3 = 1031

[Remember I swopped the transformers - originally the reading 993 was for the faulty lamp on top of screen; now lamp number 3 is the one not lighting]

[tom66]

Re: LCD Samsung LA32B350F1 - sound, no picture

993 is on the low side, and outside 3% tolerance compared to the average of 1025.3, so consider replacing it, but before you do that - check the primaries; should appear as a near dead short; check the FETs (should be open); check the fuses (if any.)

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

993 is on the low side, and outside 3% tolerance compared to the average of 1025.3, so consider replacing it, but before you do that - check the primaries; should appear as a near dead short; check the FETs (should be open); check the fuses (if any.)

I will do that, thank you.

[retiredcaps]

Re: LCD Samsung LA32B350F1 - sound, no picture

Ti 801
1-2 = 1021 ohms
2-3 = 1023

Ti 802
1-2 = 993
2-3 = 1031

In post #2, I included a link identifying the secondaries.

I don't know your numbering scheme above with 1-2 and 2-3, but if you use the link what are the resistance measurements for S1-S2 and S3-S4?

[burntfingers]

Re: LCD Samsung LA32B350F1 - sound, no picture

Final report:

Customer agreed with quotation and the power panel was replaced, fixing the problem.
Could not get one inverter from agent: had to get the whole board.

[aswan@vodamail.co.za]

Re: LCD Samsung LA32B350F1 - sound, no picture

Just for interest. I had the same experience with the same model. What I found to be the problem was one of the inverter transformers.
I did the flaslight test first and saw display and sound without backlight.
How I got to that was by swoping the 2 inverter transformers. The dark line moved from second top lamp to bottom lamp. Trying that is alot easier than changing lamps. My supplier did not have stock of the inverter transformer so I had to replace the complete board. As soon as they get stock I can replace the faulty inverter and have a working board on hand.

I must also mention that this seems to be a common fault on various screens and tvs. On for a second and then off. I want to thank the person that came up with the flashlight test.