Memorex MLT3221 - No Power

[plnyberg]

Re: Memorex MLT3221 - No Power

DGtech, I have a lot of experience soldering/desoldering, but I am with you... I do not want to do more than needed. I am still ordering the other caps, but I am going to change the two 10uf caps first.

I put a flashlight up to the front of the screen and hit menu on my remote and I could see the menu. Should I try with a tv show? is there a difference in the menu and a picture from a tv channel or movie?

Which to fets are you speaking of? Q16 and 17? I made a few measurements in circuit with the tv on:

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

Q16 Center pin 134.4 vdc

Should I make some more measurements? Should I desolder them and test them out of circuit?

I was a little worried about them being bad and possibly blowing those two caps again.

[budm]

Re: Memorex MLT3221 - No Power

FYI:
http://s807.photobucket.com/albums/y...rex%20MLT3221/

[Dgtech]

Re: Memorex MLT3221 - No Power

I'm just curious about something, plnyberg.

Have you put a flashlight to the screen yet to see if there is a picture behind it? The voltages that you put in your original post all look ok. This would tell me that your only problem is the circuit driving the backlights. Unless you seriously want to pull those heatsinks for the heck of it and change all the caps underneath, I'd stick to the high voltage section first. It is common to change all the caps but not neccessary. Depending on your skill level of desoldering, this could be a nightmare. Retiredcaps is giving you good advice, however in this case, I might change the two caps (10uF @450V) and I'd check the two mosfets involved in that circuit as well.

[retiredcaps]

Re: Memorex MLT3221 - No Power

Unless someone here has already done it?

Even if someone has done it, it is NOT guaranteed to be correct since manufacturers routinely make revisions and even complete board changes while keeping the same model number. When I fix a monitor, I usually never look at a posted list of caps. It only takes 5 minutes to list the caps and get the dimensions.

With DIY, you are guaranteed to get the correct caps and you can add spares + other items if you wish.

[plnyberg]

Re: Memorex MLT3221 - No Power

Ok, thanks. I guess I will be doing a cap inventory on that board tomorrow Unless someone here has already done it?

Edit: I'm not trying to be lazy, just wondering if someone had already put a list together. I did a few searches and could not find one. If I can get a good list together I will post it here. It looks like the replacements for EC17&18 will be a little taller.

[retiredcaps]

Re: Memorex MLT3221 - No Power

I would like to order from this site since I am getting answers and help from this site

The gesture is appreciated since it helps support this forum, but the badcaps.net store is more focused towards motherboards so you are unlikely to find all the caps here.

Most members here like digikey.com. A DIY approach using digikey.com is about 1/2 the cost of an ebay "kit". Shipping from digikey.com, if you are in the USA, is a very reasonable $2.90 or so and you get the caps in about 2 days with first class mail.

[plnyberg]

Re: Memorex MLT3221 - No Power

You are right, I was just looking for a kit with all of the caps for that board.

Do I have to just order them separately? I only see one 10uF cap on the badcap.et store, but it is 400v rated. I would like to order from this site since I am getting answers and help from this site But the original caps are 450v, of course they were HEC which is probably why they failed.

So yes, I want to replace all of the caps on the board. Any suggestions of where I can find a kit with GOOD caps? Is there a kit I am not finding on the store here?

[retiredcaps]

Re: Memorex MLT3221 - No Power

I checked D10 and got .4v one way and the other way it climbed to 1.5v. I will take it out and retest.

Those readings indicate the diode is good even though the readings only climb to 1.5V.

Yes, those two caps are slightly domed, one more than the other. I will order them and replace.

Here is my standard answer for people who only think about replacing the obviously bad bloated caps.

https://www.badcaps.net/forum/showpo...84&postcount=3

[plnyberg]

Re: Memorex MLT3221 - No Power

Thank you for the quick response.

I checked D10 and got .4v one way and the other way it climbed to 1.5v. I will take it out and retest.

Yes, those two caps are slightly domed, one more than the other. I will order them and replace.

[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.

[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?

[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?

[mattmarkgo]

Re: Memorex MLT3221 - No Power

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

[graywebdesign]

Re: Memorex MLT3221 - No Power

kobkobk

Congratulations !!!

YOU did a great job.

[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

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.

[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

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.

[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

Here is the datasheet for IC7:



Click on "PDF" to get the actual datasheet.