Memorex MLT3221 - No Power

[kobkobk]

Re: Memorex MLT3221 - No Power

more test:
operation the p/s out of the tv,connect 220AC
at con. 3, between pin stb to 5vsb solder 1k resistor-got 5v,12v,22v at output
at con.4-5V with 1k resistor connect to pin BK-ON
results;got high voltage for 1or2sec,the red led blinking,12v supply for 2 sec to ic8 pin 13,15.at con 3 no change 5v,12v,22v are on
be continue

[Dgtech]

Re: Memorex MLT3221 - No Power

Post a picture of your board as well.

[mattmarkgo]

Re: Memorex MLT3221 - No Power

I'm looking around for IC2 but I cannot find it on your picture. Please specify. Also, I recently got a similar set working after I found the transformer above the main cap to be bad. It was arching intermittently. Whenever the set would fail, the LED on the bottom left hand side would come on. I had to replace the whole board cause there were no replacement transformers to be found for this board. Good luck.

thank you Dgtech for you effort to answer my question...........

[mattmarkgo]

Re: Memorex MLT3221 - No Power

[QUOTE=mattmarkgo;196624]thank you Dgtech!!!!!

[kobkobk]

Re: Memorex MLT3221 - No Power

hi
it is the seem power supply used on 32'' Telefunken tv there is no problem for the pic but...

thanks

[kobkobk]

Re: Memorex MLT3221 - No Power

thanks all friends i am working when you slipping. i am on the other said of the world
i put back the p/s and connected to tv
at stby got 5vdc and red light at front
try to power on:got back light for 2sec and off. no back light,5v,12v,22v are on the red led at p/s is on,at the front blue light on
for my understanding the ic D78F9222CX test the high voltage and if fault he cut off the vcc to ic SG3525AN then the high voltage cut offi also try to connect directly to ic SG3525AN at pin 13 12v [vcc] the back light on but weak
i can't fund the reason for this cut off
need your help or suggestion
thanks

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

Is the DC voltage across the big cap 160v or 400v? I also tried to feed 12v to pin 13 of the SG3525AN and got a dim screen. It turned out that I only had 160v across the big cap. Finally, when I got it to it's proper 400v (when set is on) the screen came up to full brightness.

[graywebdesign]

Re: Memorex MLT3221 - No Power

matmarkgo

when you described the voltages on IC2, I assumed you ment the low voltage controller( because you only showed 6 pins). In the picture that you posted, you actually have IC1 circled.

pin 1 of IC2 does go directly to HOT ground, so that is not a problem.

i am having a little diffuculty visualizing what is happening when you turn your set on. when you say the red light on the front of the set goes off. do you STILL have ALL of the correct voltages on CON3? (STB,5vstb,5v,12,24v) And you never see it change to blue? Does the backlight try to come on, even briefly?

[Dgtech]

Re: Memorex MLT3221 - No Power

Both of you should replace the power board. There's not going to be an easy fix to this problem.

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign
thanks for your fast replay
yes at power on i got 400vdc at the big cap
12v at pin 13,no change at big cap also 400vdc even the ic D78F9222CX stop
the 12v for the high volt.i also try to check the feedback input at this ic controller for that i need the service menu.
again thanks for the help

[graywebdesign]

Re: Memorex MLT3221 - No Power

Dgtech

You are probably right !!!

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

from what you are describing, it sounds like MOST of your power supply is probably working OK. to verify this, turn on the TV (whih blue light on the front) and shine a strong flashlight onto the screen to see if you can see either a menu or a picture of some sort (it will be hard to see-so look carefully).

If you do get something, your stb,5vstb,5v,12v,and 24v should be OK.

The 400vdc on the big cap also sounds OK and I believe that this is the required input voltage to the input of the 2 inverter switching mosfets Q16 abd Q17. If you can, check that these two transistors are OK as well as EC17 and EC18 (not bulging). Also, check fuse F2 (right next to the big cap) as this protects the above mentioned components.

Let me know how you make out and if you want to, we can keep working on your problem.

[mattmarkgo]

Re: Memorex MLT3221 - No Power

thank you guys for help!!!

[mattmarkgo]

Re: Memorex MLT3221 - No Power

i check con3 there are all ok...

[graywebdesign]

Re: Memorex MLT3221 - No Power

mattmarkgo

I would like for you to do the same test that I asked kobkobk to do. Shine a strong flashlight onto the screen and look for any activity like a menu. Because you said that you have stb=5v,5vstb,12v,and 24v (even though you have a dark screen),your low voltage controller IS WORKING. I don't know why your red light on the front of the tv goes out. For the moment we won't worry about it.

If you get activity on the screen, then we can proceed to find the problem with the high voltage inverter.

Let me know how you make out.

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign hi,
at power on i got picture for 1.5sec then black,no audio or voice.got output p/s 5v,12v,24v.blue light on at the front.i shine a strong flashlight onto the screen- there is noting at all.
i checked the 2 mosfets Q16 Q17 and the 2 x 10u cap at the first ,they are new.
at on ,at the derian of Q17 there is 400v and at Q16 the half 200v,and no change when the back light off.
any suggestion?
thanks for your help

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

If you put 12v back onto pin 13 of IC8, you said that you now have a back light, but it is dim. Try this again and carefully measure to see if you still have 400v on the drain of Q17 and 200v on the drain of Q16. If you do, then either IC8 is putting out pulses on pins 11 and 14 that are too narrow (less than 50% duty cycle) or Q16 and Q17 (with EC17 and EC18) are not generating a high enough voltage as input to the final CCFL step-up transformers. ( I'm sure this will be seen by the D78F9222CX and it will attempt to shut off the 12v to IC8 - which it can't do because you are giving IC8 12v). However, I,m sure it will complain by lighting up the red led on the power board. I have not yet figured out if it will try to shut down IC8 some other way.

If the pulses on IC8 are too narrow, we will try to figure out why next.

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign

i try 12v at pin13 got dim back light at the Q17 drain have 400v BUT,BUT at the output there is 2 parts DCT1 and DCT2 this 2 parts start to be burning,very hot. i think this 2 parts are protect over high voltage.so maybe my p/s making over high volt for the CCFL. if so i try download the oscillator control datasheet SG3525.
If you have any suggestion or any thought pls

thanks

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

It is very good that the DC voltage on Q17 drain is staying at 400v.

DCT1 and DCT2 appear to be there to protect the CCFLs from any voltage spikes greater than 3500v. Because they are getting hot, it looks like they are shunting the spikes to ground (or like you said, the inverter is simply generating too high of an output voltage to the CCFLs).

I didn't want you to burn anything out by forcing the 12v onto pin 13 of IC8, except only briefly to make some test.

Do you have access to an ocilloscope? One thing you could try would be to measure the duty cycle of the pulses on pin 11 and 14 of IC8. I believe that as the width of each pulse becomes greater than 50% duty cycle, then the output of the final step up transformers will rapidly become greater. When this happens, the microcontroller should stop IC8. But of course, by putting 12v on pin 13 of IC8, it can't.

Please don't burn out your board. If you do not have any to measure the pulses duty cycles, let me know and we will think of other tests we can do.

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

I had another thought. I know that you told me that EC17 and EC18 were new. However, because these two caps have an extensive history (on this forum) of being bad, maby you should recheck them. Probably, the best way would be to replace them with new ones. I could see how they might be causing the problem that you are having. I'm not sure, but I think part of their job is to absorb any voltage spikes from drain to source of Q17 and Q16 during switching. If either cap can't do this, then the spikes will be applied to the final output step-up transformers an jump from hundreds of volts to thousands of volts. (enough to jump the gaps in DCT1 and DC2 to ground).

So, try replacing EC17 and EC18 before going any further (even though they look ok).