Is this high-voltage transformer OK?

[costinvint]

Hi, this is my first post here and I hope you can help me.

Im working on a 'Elo Entuitive 1725L-MSR'. The display turns on, but there is no backlight. I tested the lamps with another inverter and they work well. The inverter is getting 19V on the first and second pins, and 3.5V on the second when I turn it on -- this then goes back down to 0 after 1 second. The fuse is OK and I changed the bad capacitor on the inverter board.

Now I am looking at the transformers, and they are both open on the secondary side. There is no continuity between legs 1 and 3; or taps 'a' and 'b' in the picture. Leg 1 is continuous with tap 'a', and leg 3 is continuous with tap 'b'. There is no wire connected to tap 'a'; it dont even look like there was ever any solder here! Both transformers are identical. Could this be normal?

[retiredcaps]

Re: Is this high-voltage transformer OK?

I can't tell for sure, but the secondaries are the pins that connect to C14 and C19. Same for C15 and C20. I'm guessing they should be anywhere between 600 ohms and 1500 ohms?

If they read open on the 2000 ohms scale on a manual mulitmeter, then it suggests they are bad.

[Rtech]

Re: Is this high-voltage transformer OK?

Is this not one of those transformers where the secondary is actually between Leg 3,and one of the outside pins on the other end ??

[Rtech]

Re: Is this high-voltage transformer OK?

Have just looked at a Sampo similar inverter, and the secondary is from your leg 3 to the diagonally opposite pin.In this instance the transformer part code wasYST-1106 D,and was approx 210ohms.hope this helps.

[costinvint]

Re: Is this high-voltage transformer OK?

Ok, thank you for your help so far. The transformers are both stamped "YST-1709 0514". I took another picture showing the continuous legs. The ones with the question marks are not continuous with anything and the wire attached to them looks the same. Could this be the open secondary coil?

In any case, I think this is the faulty part. Can anyone suggest how to find replacements? I can get a similar inverter from ebay for like $12, but they are coming from China or Czech Republic and I rather not wait.

[PlainBill]

Re: Is this high-voltage transformer OK?

Ok, thank you for your help so far. The transformers are both stamped "YST-1709 0514". I took another picture showing the continuous legs. The ones with the question marks are not continuous with anything and the wire attached to them looks the same. Could this be the open secondary coil?

In any case, I think this is the faulty part. Can anyone suggest how to find replacements? I can get a similar inverter from ebay for like $12, but they are coming from China or Czech Republic and I rather not wait.

I would compare it to the other transformer. It certainly does appear to be an open secondary. A quick check on Google did not turn up any sources.

PlainBill

[costinvint]

Re: Is this high-voltage transformer OK?

Ok, I found it. I was being lazy and just checking for the beep -- I mistakenly thought that was good enough, but when I check the resistance the legs with the question marks are connected! One transformer reads 468 and the other 485; that must be the secondary winding. The other legs all read between 0.5 and 0.9 ohms.

So based on that , I now think these transformers are OK. What else could be wrong here?

[retiredcaps]

Re: Is this high-voltage transformer OK?

So based on that , I now think these transformers are OK. What else could be wrong here?

Check Q4, Q6, Q7, Q8, Q9, and Q10 for shorts.

Check F1 to see if it is open.

[Rtech]

Re: Is this high-voltage transformer OK?

One other fault that sometime occurs on these,is that the two inductors on the middle of the board are suceptible to 'dry joints',so that needs a quick check as well.

[costinvint]

Re: Is this high-voltage transformer OK?

F1 is OK. I think Q4 and Q6 are short, but im not sure how to test these, so I included all the resistance measurements in the pictures. I hope its OK to test these in-circuit.

[PlainBill]

Re: Is this high-voltage transformer OK?

Those numbers look good. The best advice I can give you at this point is to trace the BL_ON (or whatever it's called) signal. A picture of the bottom of the board and a picture of the top showing CON1 clearly would be a big help.

PlainBill

[retiredcaps]

Re: Is this high-voltage transformer OK?

F1 is OK. I think Q4 and Q6 are short, but im not sure how to test these, so I included all the resistance measurements in the pictures.

Can you list the part numbers for Q4 and Q6? I can't quite read them on the photos?

As a bonus, find and list the URL for them by searching for their datasheet.

[costinvint]

Re: Is this high-voltage transformer OK?

I hope these extra picture help; I took so many, I didnt know witch to include. As for the data sheets, im having a hard time finding them. I think Q4 reads "441 BE461S" or "441 BEA61S", and Q6 look like "4411 BE461S" or the last letter might be a "8", but I cant find the datasheet based on these. I took pictures of these ICs and I tried to enhance some to show the numbers better.


One more thing I may not have made clear, I dont know if it makes a difference but, the backlight never turns on at all -- not even for a second.

[jetadm123]

Re: Is this high-voltage transformer OK?

I hope these extra picture help; I took so many, I didnt know witch to include. As for the data sheets, im having a hard time finding them. I think Q4 reads "441 BE461S" or "441 BEA61S", and Q6 look like "4411 BE461S" or the last letter might be a "8", but I cant find the datasheet based on these. I took pictures of these ICs and I tried to enhance some to show the numbers better.


One more thing I may not have made clear, I dont know if it makes a difference but, the backlight never turns on at all -- not even for a second.

Q6 is probably a AO4411. Q4 looks like one of it's 1's got cut off. If true, it's also a AO4411.

[costinvint]

Re: Is this high-voltage transformer OK?

Thank you. Here is an indirect link to that datasheet.

[costinvint]

Re: Is this high-voltage transformer OK?

Q6 and Q4 seem OK, if I am reading that datasheet correctly. I marked-up the photos to show continuity.

[PlainBill]

Re: Is this high-voltage transformer OK?

I hope these extra picture help; I took so many, I didnt know witch to include. As for the data sheets, im having a hard time finding them. I think Q4 reads "441 BE461S" or "441 BEA61S", and Q6 look like "4411 BE461S" or the last letter might be a "8", but I cant find the datasheet based on these. I took pictures of these ICs and I tried to enhance some to show the numbers better.


One more thing I may not have made clear, I dont know if it makes a difference but, the backlight never turns on at all -- not even for a second.

That's why I am going to suggest some additional troubleshooting. This particular design is a Royer oscillator. In a nutshell Q7, Q8, PT1, C12, L1, D3, Q4 form one oscillator. I'm sure you can identify the components that form the other. The FP5451A is the 'supervisor'; it controls the voltage to the oscillators, pulsing them on and off to adjust brightness.

If you look at CON1, you will notice that the two pins next to F1 provide power. The two pins at the opposite end are ground. The two in the middle control brightness and turn the inverter on and off.

One of the basis' of logical troubleshooting is if two identical circuits fail to function at the same time, the cause is most likely something common to them. In this case, the On/Off signal, the FP5451A, or the transistors which shift the level of the On/Off signal.

I would suggest starting by verifying the FP5451A is getting power, then tracing the signal from pins 3 and 4 of CON1 as they run through the maze of components. Hint: If you press the power button the On/Off should go high for several seconds, also the brightness control will change.

PlainBill

[costinvint]

Re: Is this high-voltage transformer OK?

I found the diagram for FP5451A. Leg 16 is reading 2.5V and leg 9 is reading 19.5V. This IC looks OK, right? Now I just have to trace

the maze of components

. What exactly will I be looking for when I do this?

[PlainBill]

Re: Is this high-voltage transformer OK?

I found the diagram for FP5451A. Leg 16 is reading 2.5V and leg 9 is reading 19.5V. This IC looks OK, right? Now I just have to trace . What exactly will I be looking for when I do this?

I don't know exactly; I've never gotten a handle on this part of the circuit.

I would start at Con1, pins 3 and 4. Both of them should change voltage (toggle) as you hit the power button. Usually after a few seconds the power LED will turn amber, at that point the voltages on 3 and 4 should drop. In the first post you say you got 19V on pins 1 and 2, and "3.5V on the second when I turn it on." Is that a typo - perhaps you meant 3.5V on the third? If that is the case, I would look at the back side of the board, pin 3 appears to be associated with Q1, Q3, and possibly Q15.

One thing that attracts my attention is the 2.2uF cap next to the FP5451A. This might be a red herring, but check the voltage across the cap, and where it connects. Ir it is in the power supply circuit and has 19V across it, don't worry. But if it's in a timing circuit, suspect it.

PlainBill

[costinvint]

Re: Is this high-voltage transformer OK?

That was a typo, I did mean 3.5v on the 3d pin. The first two are 19v.

Anyway, Im throwing in the hat. I cant trace threw all those little SMDs on the front and back of the board. I bought a similar board on ebay for $11.40 delivered. Its not the same one, I couldnt find that, but it has the same 6 input pins (1,2-VCC;3-ON/OFF;4-Bright;5,6-GND) and should do the trick.

I want to thank everyone for helping. I learned a lot, but now this is too much.