Memorex MLT3221 - No Power

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign
1 thanks for your help
2 the 2 cap 10u 400v was replaced again-no help
3 at pin 11,14 there is 12v ptp the fq=1:4x1000000=250mhz
4 Q16 drian there 30v ptp at Q17 drian more then 100v ptp
5 TEST- at pin 11,14 i solder 2 diodes zener 5.1v to GND ,the pulse was cut to 6v ptp,the results -the back light was dim. it is light 2sec ,off,then again for 2 sec then off.
at this test i see even if the output for the ccfl is low voltage it is react the seem.
any thought?

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk


I was expecting the frequency of the pulses on pins 11 an 14 of IC8 to be about 30 Khz.
12v peak to peak sounds ok because that is it's supply voltage.

It turns out that pin 11 of IC8 already has a diode to ground on it (D24). Pin 14 of IC8 also has a diode to ground on it (D23). It is interesting that your 2 zener diodes caused the CCFLs to oscillate from dim to off, dim to off,... every two seconds.

As far as the 100v ptp on Q17 drain and the 30v ptp on Q16 drain, I am not sure if (or how far from normal) these are.

I have the exact same power board that you do (IPOS 150 Rev 1.8 2006.11.25).

I am going to put it back in my Memorex MLT3221 LCD TV and start looking at all the wavforms on IC8, Q16, and Q17 with my ocilloscope and report to you what I am finding. Then we can compare measurements to find out what is different and then get yours to work the same as mine (and get your TV operational again!)

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

With my TV running normally, I took a photo on my scope of the output pulses on IC8. The upper waveform is output A (pin 11) and the lower waveform is output B (pin 14).

The scope is set up on 5 microseconds/division and the verticals are set up for 5v/division each.

As you can see, both A and B are about 12v DC (above COLD ground).

They are also 180 degrees out of phase with each other and each has about a 50% duty cycle.

Because one full cycle of A takes 15 microseconds, I calculate that these pulses have a frequency of 66.6kHz

I did't take any measurements across Q16 and Q17 because that would require putting my scope return lead onto the HOT side without an isolation transformer(I don't have one).

The conclusion that I have come to so far is that we need to get your IC8 to be putting out the same waveforms before we can even begin to continue to Q16 and Q17.

I have not yet looked at any of the other pins on IC8 because I need to get a DIPCLIP to do it safely.

So, in the meantime, if you want to look at all of the other signals on IC8, go ahead (you may be able to spot something abnormal and fix it). I will still look at all the other signals on my IC8 and report to what I have on a TV that is working normally.

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

The photo didn't upload on the previous post. Here it is.

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign hi
yes it is the seem at my HP scop as you can see at the pic,i hope i am not mistaken on my calculation the volt button is 2v per square and the time 2usec[micro] per square.
i also checked with frequency counter i get+-60.0khz you can see at the pic
this 2 measures was test at pin 14 of ic8.do not forgot i have only 1.5sec to make all my test measures,and the frequency is change i also see it at the HP scop.
if you operating your p/s can you make few measures for me?with volt meter to the gnd
1 all the pins at ic8
2 at d25,d16,d15,d19
thanks!!!!!! for your help

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

Your waveform on IC8 pin 14 looks good to me. Also your frequency of 60kHz looks good.

I took some measurements of IC8 while my TV was running normally. I thought it would be more accurate to make the measurements with my scope, rather than with just a voltmeter. Here is what I have:

Pin1 +5v DC with a very small wave riding on it (similar to output A and B)

Pin2 +4v

Pin3 and Pin4 didn't measure because don't think they are used

Pin5 sawtooth waveform 0v to +3v same frequency as output A and B

Pin6 +4v

Pin7 almost identicle to pin5

Pin8 +7v

Pin9 +6v

Pin10 0v

Pin11 same waveform as we have

Pin 12 0v (ground)

Pin13 +12v

Pin14 same waveform as we have

Pin15 +12v

Pin16 +5v

I could not measure D25,D16,D15,D19 because they are on the back side and I have my power board mounted in the TV with the CCFLs connected.

Also, on connector 4, Pin4 (white wire) has +5v and Pin1 (yellow wire) has +3v.

I think at this point, it would be a good thing to determine on which side of T6 the problem lies. I belive the best way to test this is to hook up your scope exactly the same way that I had mine hooked up (channel 1 onto IC8 pin 11 and channel 2 onto IC8 pin 14) Set scope on alt or chop to see both waveforms. set trigger on positive slope of output A ( pin11)

Then turn set on, let it shut off after 1.5 seconds and apply +12v to pin 13 of IC8. (the same as you did last time).

If you now get the exact same waveforms that I had in my photo, then IC8 and it's associated components should be OK and the problem lies further down stream or in the microcontroller chip IC7. Please keep in mind that the 2 waveforms MUST be 180 dregrees out of phase with each other (Q17 and Q16 can not be on at the same time!).

Since you told me that DCT1 and DCT2 were getting hot the last time, don't leave the +12v on IC8 too long.

Please do this test and post a photo of your of your scope results (if you can).

If the your results are the same as mine, Q17,Q16,and their caps along with the 2 final output transformers SHOULD be lighting the CCFLs at their normal level.

By the way, when you gave me the peak to peak voltage readings across Q17 and Q16, how were you actually able to make the measurements? (hi-voltage probes and an isolation transformer between the TV or scope ?)

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign hi,

this is my measure at ic8:
pin1 go up to 3.5v then down to 1.5v
pin2 go up to 3.5v
pin3 got pules -Img00013 this pules came after CCFL off and it is constant
pin 4 not used
pin5-pin16 the seem your measures
pin 11,14 img11,12,10
on connector 6 pin 1,4 are the seem
for your ask at the measurements Q17,Q16.first of all i working on float place,it means i disconnect the GND electricity from my HP scope.I do not touch any thing connect to GND earth. I am very very careful i also use circuit break, it is cut the electricity if more then 3MA go to the earth. PLS BE CARE
can i ask you pls to measure IC7 pins

thank you for your help

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

Thank you for your explaination of how your HP scope frame is isolated from your probe return connector. I have a TEK scope and have never tried to set up mine the same way.

Your waveforms of the pulses on IC8 pin 11 and pin 14 look VERY GOOD ! They actually look identical to mine while my set is running normally.

At this point, I think it really does not matter what what the other pulses or voltage levels are on IC8 or even IC7. These two pulses are all that is needed on the gates of Q17 and Q16 (along with 400v DC) to start them switching at 60 kHz and feeding this into the input of the final step up transformers to generate approx 3000 vAC to run the CCFLs. I'm not sure if the CCFLs need an initial "strike" voltage first, however.

By forcing +12v DC onto pin 13 of IC8, I believe we are now running IC8 in "unregulated mode", meaning IC7 is no longer actually doing anything we need.

Are DCT1 and DCT2 still getting hot? It would be very helpful if you had some way to SAFELY measure the actual AC voltage going to the CCFLs. If it is reasonable, maby you could try removing DCT1 and DCT2 and see if the lamps come up to full brightness.

If the lamps still remain dim, double check the peak to peak voltages you had the last time across Q17 and Q16. Bacuse of the way you measured them (HP scope ground lead isolated from scope frame) I think they sound reasonable for driving the primaries of the 2 final step-up transformers. It is possible that one of these transformers might have say, some shorted turns, and that is why the lamps are running dim.

It is als a possibility that the lamps them selves may have a problem. That is what I thought was wrong with my set when it had only a dim screen when I forced +12v DC onto IC8 pin 13. So, I am hopeing that yours are OK also.

As far as taking measurements on IC7, I can give you so insights on this chip. It is actually a full blown microcomputer. I spent 7 years at RCA as an engineer writing software for these chips using Assembly Language and debugging in Machine Language. Without some very specialized and expensive equipment, it would be virtually impossible to "reverse engineer" the stored program to figure out what it is actually doing. Even looking at it's input and output ports would have verry little meaning.

I know many of the other users of this form are actually TV repair shops and must repair the set to established standard before they they are allowed to return the repaired set to their customers. I, on the other hand, "got my set out of the trash heap" and therefore have nothing to loose if I should burn it out or even run it with IC7 bypassed and therefore no AC regulation. However, being an engineer and knowing the consequences, I would never leave the set unattended or even plugged in unless I had an eye on it.

I don't know how much "risk" you are willing to take with your set, but please be carefull with whatever you do with your set.

Anyway, let me how you are making out and we will keep working on the problem.

By the way, you took some GREAT scope photos!

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign hi,

i start in the end i got your point i am also don 't care ,one of my friend give it to me.so i am playing to my fun.and i think no one dig very deeply like you and me.
i agree with you,i also think IC8,Q16,Q17,CCFL are good,so at this evening i start to check the controller IC7.this ''IC7'' get the stby command,send command to IC8 to start ,get the feedback from the high voltage,and he send the command to shutdown the high voltage if some thing wrong.

so i start to disconnect the feedback one by one pin 1,2 ,3,4 after disconnect pin 4 the high voltage stay on and the CCFL on.it is work for Several mints.
i must read about this controller.any information will be help,
be continue tomorrow evening
thank for your help

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

Here is the datasheet for IC7:



Click on "PDF" to get the actual datasheet.

[kobkobk]

Re: Memorex MLT3221 - No Power

wowwwwwwwww

this is piece of controller..... 300 pages and he got memory flash in-said
i think something happened to the memory flash,i need to get the firmware,and i most programer to read this controller,this ic is the last chance to fix this p/s .
thanks

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

DON'T GIVE UP !!!

You are porbably the ONLY guy on this forum who can fix this problem at this level !!!

Don't worry, I'll help you for as long as you want me to.

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

As an afterthought.

If you determine that you need to reprogram IC7 or replace the chip, I don't think that you will be able to find any downloadable flash file from anywhere. After all, none of us on this forum can get either a service manual or even a schematic for this power supply.

When I first got my TV, it was totally dead (not even STB voltage), I didn't even bother to fix the power supply. I bascially pulled the connector off of CON3 and fed the main board +5v,+12v,and+24v from other switching supplies that I had laying around. Other than no back light, the set worked beautifully. I was actually just going to mount the supplies on the back of the set and run it like that.

Then I looked at the inverter circuit on the power supply board. I removed the jumpers that would have normally fed +12v to IC8 and +5v to IC7. Using 2 other small "brick" switchers, I feed each it's new +12v and +5v.

To my surprise, the back lights now came on, but not at full brightness.

So I now had the set running with almost nothing actually working on the power supply board.

I was ALMOST ready to also "do away" with the inverter circuit on the board and design a much simpler replacement that did not use a microcontroller at all. I still think that the microcontroller IC7 is "overkill" for this application.

But, after reading the posts on this forum, I decided to check a few things, and sure enough, I found diode D10 shorted. I simply removed it (without replacing it) and the whole power supply came back to life. Even the back lights came up to full brightness.

The whole problem turned out to be that with D10 shorted, +5vstb was not being generated because IC2 (SMPS controller) was overloaded. IC1 (Power Factor Corrector) was not being turned on (I think it also needs STB on) and the DC voltage across the main big cap was only 167v DC. This low voltage is what was causing my CCFLs to not be up to full brightness.

After I removed the shorted D10, IC1 now started to operate and the voltage across the main cap was now 400v DC. (this is also at the drain of Q17). Now the CCFLs came up to full brightness.

Anyway, I just wanted to let you know that I would have figured out a way to substitute or design a different inverter circuit if I had to.

As I had mentioned in one of my earlier posts, no TV repair shop would have the freedom to do anything like that and most non-engineer type poeple should also NOT EVEN THINK of doing anything like this. But since you are ready to "tackle a microcontroller", you might actually enjoy the challange. Just please be carefull, especially not causing a fire.

Please keep me posted on how you are making out.

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

Please use this datasheet for IC7:



The previous one did not show the pin out for actual chip that we have. This datasheet does (20-pin plastic SDIP).

Also, it has been my experience that microcontrollers are very rugged and seldom fail. Often it is the signals that are inputted into it that are incorrect.

You said that when you pulled pin 4 of IC7, you got the back light for several minutes. Was it a full level or only dim?

I believe that pin 4 of IC7 is one of the Analog to Digital Converter inputs. It is possible that the 3000 VAC going to the CCFLs has a high resistance voltage divider to cold ground which feeds a very low "sense" voltage to this input pin. This is how the microcontroller can monitor the hi-voltage. The internal AtoD converter internally tests to see if it is with in allowable limits (both hi and low). If not, the program then turns off the transistor Q11 which then removes the +12V from IC8. (and then lights up diode D13 to all of our fustration!)

It is possible the the problem is NOT in the microcontroller itself, but rather in the circuit that is generating the "sense" voltage.

[kobkobk]

Re: Memorex MLT3221 - No Power

dear graywebdesign hi

first of all i wont to thank you for your help and your Support,you give me the drive to continue.i am usually don't Consult with any one more then 30 years.i don't know but this my lucky and my honor to discuss with propositional engineer.

back to work,i try to read and learn this controller and try to find out the firmware for the flash as you said no chances.
i follow from d15,d16,d19 they are testing the high voltage and any change from the parameters at the memory flash it is cut off the high voltage. at the IC7 there is 4 analog feedback s at pin1 pin2 pin3 pin4,all this 4 pins are disconnected.so for now i cut the feedback all the 4.also d25 but d25 send cut off Immediately to IC8 if there over high voltage .at this point the TV is working but any change it turn off the CCFL.
pin18 pin19, i connect 2.2k resistor to 5v constant.the TV is stable and working very good for 5 hours.
this TV will be in used at my garden at the summer time,i can Afford ,to stop hear and use the TV with out Protection.the Protection is for the CCFL,there is noting to worry there is the DCT1+DCT2 and they working good.
thanks for all,for any help you can mail me at private message

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

Congratulations !!!

YOU did a great job.

[mattmarkgo]

Re: Memorex MLT3221 - No Power

i have memorex mlt3221 sounds ok,backlight ok but no picture

[Dgtech]

Re: Memorex MLT3221 - No Power

Did you open it up yet? Do you plan to? Did you read earlier in the thread how other sets were fixed? Do you plan to post pictures to this thread anytime in the future?

[plnyberg]

Re: Memorex MLT3221 - No Power

If I need to start a new thread please let me know.

I have a Memorex 32 inch flatscreen tv, MLT3221
The power supply board is IPOS150 REV 1.8 20061125

1. TV was working fine

2. Power went out for a few hours

3. Power came back on. When I turned the TV on the sound worked, the red circle below the screen turned blue, but the screen was "black".

4. I shined my maglite on the screen while I had the menu on the tv up and I could see the menu options (brightness, contrast etc..). Adjusting brightness did nothing.

5. Opened the back up. Red LED above CON2 on power board flashes on and off at about 1 second interval while the TV is on. Is this a sign of a problem?


6. Voltage measurements
con4
Black wire - 0 vdc
empty slot
White wire - 4.86 vdc
empty slot
Yellow wire - 3.10 vdc

con3
Marked --- Measured
24 --- 23.98 vdc
Agnd --- 0 vdc
Gnd --- 0 vdc
Gnd --- 0 vdc
Gnd --- 0 vdc
12v --- 11.92 vdc
5v --- 5.11 vdc
5sb --- 5.10 vdc
STB --- 4.72 vdc

EC2 (large cap) 400 vdc with tv on (172.5 vdc with tv off but still plugged in)

F2 good - 342 vdc on each side with tv on

Q17 left pin (gate?) 123-125 vdc
center pin 342 vdc

Q16 Center pin 134.4 vdc

IC8 pin 13 0.203 vdc

I checked D10 in circuit with the power cord disconnected. It has resistance both ways. One way it starts low, builds up to about 23K ohms then starts falling; the other way it starts around 1 M ohm and rises until it is too high for my Fluke 77 III. I imagine that since I am making those measurements in circuit I am charging and discharging caps. Anyway, I do not "think" D10 is shorted. Should I still take it out and check it?

I read through all of the posts in this thread and tried to come up with a list of all of the points to check. If I missed anything or if I should check something else please let me know.

I will get my Tektronix TDS 350 out later today (it is boxed up right now).

7. What voltage drives the backlight(s)? I assume that the white wires and connector on the left side of the board feed the back light, but I do not know if my Fluke can handle the voltage so I have not tried.

8. I am tempted to jump 12 vdc onto pin 13 of IC8, but I would like to do some more testing first. I apologize if the pictures are not good enough, I have a very old digital camera, I tried my best.

9. Is there some way to "measure" the leads going to the backlight and get any useful information?

[retiredcaps]

Re: Memorex MLT3221 - No Power

I checked D10 in circuit with the power cord disconnected.

You can test in circuit.

Put your Fluke on diode test. Put your black probe on one leg, red on the other. Note reading. Reverse leads and note reading.

One way should read between 0.4 and 0.7V and the other OL.

If the readings show a short either way, then desolder and retest out of circuit.

7. What voltage drives the backlight(s)? I assume that the white wires and connector on the left side of the board feed the back light, but I do not know if my Fluke can handle the voltage so I have not tried.

The voltages to drive the backlights can easily be over 1000V AC. We usually NEVER ask people to measure these voltages even though the Fluke could probably survive albeit with some possibly burnt parts.

Those two brown caps above the word Proview look bloated to me.