Re: Memorex MLT3221 - No Power
kobkobk
Congratulations !!!
YOU did a great job.
graywebdesign
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Last Activity: 01-31-2021, 03:01 PM
Joined: 10-31-2011
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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...Last edited by graywebdesign; 11-29-2011, 05:09 PM.Leave a comment:
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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...Last edited by graywebdesign; 11-29-2011, 03:21 PM.Leave a comment:
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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.Leave a comment:
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Re: Memorex MLT3221 - No Power
kobkobk
Here is the datasheet for IC7:
Click on "PDF" to get the actual datasheet.Leave a comment:
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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...Leave a comment:
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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...Leave a comment:
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Re: Memorex MLT3221 - No Power
kobkobk
The photo didn't upload on the previous post. Here it is....Leave a comment:
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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,...Leave a comment:
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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...Leave a comment:
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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...Leave a comment:
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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...Leave a comment:
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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...Leave a comment:
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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...Leave a comment:
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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...Leave a comment:
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Re: Memorex MLT3221 - No Power
Dgtech
You are probably right !!!Leave a comment:
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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...Leave a comment:
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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.Leave a comment:
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