Memorex MLT3221 - No Power

[Bakke]

Re: Memorex MLT3221 - No Power

So did you just replace the old diode in the heat sink?

[Bakke]

Re: Memorex MLT3221 - No Power

Excuse me my diode is a Her303 will it be okay to put a 304 in it. It is a IPOs 150 H. it says on the heat sink D120-0000-ipos150 H. and on the diode j710 Her 303

[momaka]

Re: Memorex MLT3221 - No Power

Excuse me my diode is a Her303 will it be okay to put a 304 in it.

If you meant Her 304, then yes, you can use that as a replacement.
Her 304 is essentially the same diode as Her 303 but with a higher voltage rating.

[Dgtech]

Re: Memorex MLT3221 - No Power

If your diode was shorted, then yes replace it with the 304. However, without you neither describing the nature of the failure or why you think it is the diode, I cant tell you for sure if it will fix the problem.

[Gagne1023]

Re: Memorex MLT3221 - No Power

I have had the same problem with the same tv. These posts were very helpful since I could just go straight to D10 and check it and that was my problem. I now have 5v across the connection and the tv will turn on. The LCD screen however will not. There is a little red LED light in the back that is on but I'm not sure what this indicates... Any ideas????

[Dgtech]

Re: Memorex MLT3221 - No Power

This power supply board has different revisions to it. Please post a picture of your board with the model number and rev number.

[Gagne1023]

Re: Memorex MLT3221 - No Power

IPOS 150
REV:1.8
2006.11.25
200-P00-HM150H

Thse are the specs on the supply board. The Rev number is there... not sure which is the model number. Also i should mention that i could only find one fuse on this Tv.

[Dgtech]

Re: Memorex MLT3221 - No Power

Well, there are two fuses on this board - F1 and F2.

F1 = Main power fuse (120VAC here so be carefull)
F2 = Small green component right next to the largest capacitor on this board.

Also, the two caps near the two transformers need to be checked. These might be 10uF, 450V caps. I just changed a pair in a Polaroid. The bad ones measured 4 nanofarads.

[Gagne1023]

Re: Memorex MLT3221 - No Power

I checked the fuses on the board and found where F2 was bad. It took awhile to get a replacement but once I got it and stuck it in there, powered it on and the screen flashed for a quick second then went black again... After rechecking F2 it had blown again... So any ideas on why it's blowing the fuse.... Also since I was ordering a fuse I went ahead and just replaced those two Caps that u had mentioned

[Dgtech]

Re: Memorex MLT3221 - No Power

The good news is that this blown fuse directs you to where the problem is. I have a TV with this same board that is showing me a whole different problem altogether and I dont know where to start. I dont know if it's the power board or the other board.

OK about your problem - There are a good two handfull of parts that would cause that fuse to blow. The main fuse (F1) would blow if anything before and including the bridge rectifier were shorted. So I think you're ok up to that point. F2, on the other hand, I think that is separating the hot side from the lower voltage side. Your problem is somewhere in the middle. Just curious, is that red power board LED still on? The board I mentioned above is failing somewhat the same way. Check here and compare my problem with yours.

https://www.badcaps.net/forum/showth...t=13573&page=2

[Gagne1023]

Re: Memorex MLT3221 - No Power

I can't tell you for sure because my LED is off also but I think it's because of that D10 diode... The HER 303.... I found were a 47 ohm resistor was reading 4 ohms. I switched that out and now no more fuse getting blown. The tv turns on now but the picture is really dim. I managed to put the tv in sun light and play with the menu so I could adjust all the picture settings and none of them changed the display... Any ideas on wats wrong... There is no lamp like on other LCD TVs so I didnt know if it could be fixed or if it needs a new LCD screen

[Dgtech]

Re: Memorex MLT3221 - No Power

Post a picture of the screen now. Is it dim on one side or the other, top or the bottom? If all over, you might have somthing still on the power board wrong. Carefully, what is the voltages off of the two mosfets near the two electrolytics?

[Gagne1023]

Re: Memorex MLT3221 - No Power

The LCD is to dark to take a picture of it, the tv just looks off. When I put sun light on it, all you can see is a glare. But I measured the MOSFETs and was getting a 0v reading, which led me back to the fuse(F2). I thought I had corrected it but I guess not because it was blown. I checked the resisitor I replaced earlier (R55) and it had shorted again. Also I I found two 62 ohm resistors had shorted (R27,28). I replaced them all and they all shorted again. Any ideas?

[Dgtech]

Re: Memorex MLT3221 - No Power

Resistors don't usually short out. When reading the resistors, you must have done so in circuit. To properly read resistors, you have to do so out of circuit, or simply lift one lead if possible. You are reading through another shorted component. It sounds like you are right there at the problem, you just have to find it. I'm gonna look at a board I have in my shop to try to help more. It's not the same rev power board but it will have similar components.

[Dgtech]

Re: Memorex MLT3221 - No Power

I'm going to give you a list of components to check. First, though, I want to make sure the main fuse did not blow.

Check the voltage across the main cap (largest).

If this is ok, (I think about 300 or so) then check:

Q4
Q6
D5
D6
D7

Check all of these for shorts. All should be taken out of circuit to check properly. Diodes are going to show a short in one direction, reverse the leads an it should not show a short.

Also... once you get the heatsink off to check the components connected to it, check the caps under it for shorts.

[Gagne1023]

Re: Memorex MLT3221 - No Power

Thanks for all your info you have been a huge help. Sorry you gotta work wit me a lil bit I'm still in school learning the trait and this TV has been great practice so thanks again. Ok so now with the board, the main cap only read about 160. I went ahead and pulled D6 and D7 and they were both fine... I wanted to wait to see if maybe the main cap was the problem before I pulled the rest of the components. So does 160 sound right or should I still pull the other components?

[Dgtech]

Re: Memorex MLT3221 - No Power

That sounds right, sorry for the mixup. Yes continue to check the other components.

[Gagne1023]

Re: Memorex MLT3221 - No Power

Ok I'm stuck again.... All the components you list checked out fine...even the bridge on the other side of the heat sink...also the caps underneath the sink were fine too. Anymore ideas?

[Dgtech]

Re: Memorex MLT3221 - No Power

Here are eight components to check for shorts. I put a red box around them.

[sguthrie@cisaz.com]

Re: Memorex MLT3221 - No Power

I have an issue with my MLT3221 and don't know if I should post it to this thread or start a new one.
Issue is that suddenly the screen went black and there was a smell of cooking bacon (strange I know but that is what it smelled like).
There is still power and when powered on the Memorex logo is displayed and there but the screen goes black. I have tried a full reset and have tried different input sources but no luck.
I have tried using the menu on the remote but the screen seems completely dead, apart from at start up when the logo displays.
I have substituted in my Vizio TV until I either get the Memorex fixed or buy a new one.
I have worked with electronics for many years and designed an built prototype guidance system computer boards using microprocessors and discrete components.
Since the TV is out of warrantee by a year I thought I might try to find out what is wrong before throwing it away and buying a new one.

So should I start a new thread? Or continue on this one?
I searched for MLT3221 and this was the only thread I found.

What do you think?

Thanks in advance