magnavox 37mf321d/37 powering on problems

[fixerofthings]

Hello all, I've done some searching on the forum for some help, found one possible thread with a similar condition to what my particular tv is doing, but I don't think its 100% the same thing.

Anyway, here's what it does: No green LED power light glowing at all, remote will not function at all (it was working fine and new batteries installed just in case), but if you use the power button on the front of the tv it will try to power up. The backlight comes on fully once, then shuts off, tries to turn on again with 3 or 4 quick flashes, then nothing. It repeats this when pushing the power button again.

A little background on the tv....about a year ago the power board did fail and it was the usual capacitors that failed. I replaced them new/better quality ones and the tv was back up and working with no other issues. No other components on the power board were damaged at that time. This board does not have the zener diode on it that sometimes commonly fails, the board is version 2, not 3.

I recently replaced the LCD screen with an NOS one due to some physical damage that happened to the screen during a move. I did reuse the working Inverter board and TC board from the old screen as a precaution because I knew these were working fine. Everything was fine up until last Thursday when it started doing this new problem. BTW, this model has the Chungwa Claa370wa03 display in it, so I think it is an earlier model 37MF321D/37.

I have checked out the power supply board for damage and have found none. Tested the voltages on the board per the service manual and they all seem to be in spec. I visually checked the scaler board for damage, but found nothing. It looks to be like new, no charring or anything like that. The scaler board number is 313815868281 and was working fine up until recently. So I don't think this is my issue, but can't rule it out yet.

I'm leaning toward the IR board since the led is non functioning and the IR remote is not being seen by it. Also, it seems to be the first thing to "check" in the manual's flow chart.

Has anyone seen this IR board having similar issues, and is it as common as the PSU failures? The scaler boards seem to be a common failure as well, but only with the Lc370wx1-sl04 lcd unit. As I stated above, mine has the Chungwa Claa370wa03 lcd.

Opinions?

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

When you say "No green LED power light glowing at all" is this the standby light that is on at ALL times, or just when the TV is on?

You may have replaced the PS capacitors before, but how sure are you that they were of adequte quality, low enough ESR, and high enough ripple current? I ask because it sounds like a bad PS cap issue again.
But it may also be bad caps on an inverter or other board dragging down the main power supply.
You could take the IR input out of circuit, and then try using the on button to rule out the IR circuit.

Also, did you check the voltages with a scope or meter? High ripple on the voltage would indicate a exessive load from bad caps again, or defective component elsewhere. You could try pulling the backlight plug loose, and re-measuring voltages, to see if it stays on without that load.

That should get you started.

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

I checked voltages using a meter as I do not own a scope. The caps are not "ruptured", meaning no goo coming out of them. The green LED is not lit on either standby mode or "on" mode, totally inop.

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

Ok, but how is the LED supposed to operate is my question.

Did you try isolating either the IR circuit or the back-lights?

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

Also, bad caps most definately do NOT have to be leaking to be bad.
Just ask any experienced person on this forum if that is the case.
And most, if not all meters will not tell you if they are good, in or out of circuit.

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

Ok, but how is the LED supposed to operate is my question.

Did you try isolating either the IR circuit or the back-lights?

I have a spare backlight inverter board, known good as it worked fine with the old screen. I swapped it in and there was no change with the condition.

The green LED is supposed to dimly glow when in standby mode and brightly glow when the tv is powered up and on. It does neither at the moment.

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

You could take the IR input out of circuit, and then try using the on button to rule out the IR circuit.

The power on button is part of the IR board.

Also, the caps that I purchased were USA made Sprague brand caps of the exact same values as what the originals were marked at. Got them from mouser. I didn't "skimp" when it came time to replacing them. I highly doubt that the caps are bad on the board 6 months later, since all the voltage values on the output pins of the PSU meet the specs shown in the service manual and are not fluctuating.

The problem did not become a gradually worse thing this time, like it was when the caps failed before. This was a sudden failure without warning. The tv worked fine last wednesday night. I went to work thursday all day, came home and tried to turn the tv on that night and nothing. Started doing what it does at that point.

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

I found that Encompass, the site that sells factory replacement parts for Phillips and Magnavox lists the IR board, the power button (the actual button, not the electronic switch), the PSU board, and the Main/Scaler board as the top 4 in-demand components for this model tv. I think for the $2.60 they want for a NEW IR board, I'm going to take a chance and try that.

It just seems odd to me that the LED will not light, the IR won't recognize the remote control and the power button doesn't seem to do much of anything anymore, and no one seems to think that its the IR board, since all three are on that same board.

Also the factory troubleshooting flow chart says to start with this first, then the PSU, then the Scaler/Main board.

I realize and understand that the caps on the PSU are common for failure, but it is due to the poor quality originals that magnavox used. If they've been replaced with better quality components that meet the same uf and voltage specs, and they are not bulged or leaking, how could they fail in a different way than they did last time?

I'm sorry, but I don't buy the idea that the PSU is bad again, especially since it puts out the correct values on the correct output pins without fluctuation.

It's either got to be in the IR board or something went wrong in the main board, but I'm not entirely convinced its the main board either, since there doesn't seem to be any kind of "overload" condition, where something has fried.

Every post I find on the internet with pictures of a failed main board, there is something fried on it. The main board in this one seems to appear as new and had no "fried" smell to it.......

I'm going to go with my gut instinct and try the IR board first, as one it logically makes sense because of what the tv is doing (or not doing in this case) and because the cost is negligible. I think I paid more for the new caps last year when those failed on the PSU!

[truep]

Re: magnavox 37mf321d/37 powering on problems

The power for the I/r board is generated on the main board from the 16V supply. check for 5V on the I/r board first. It should be on pin 5 of the connector on the I/r board. There should be 5V on pin 1, but that may not come on till it powers on.

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

Sorry truep,
I was unable to respond yesterday.
Yes I agree with all you have said, it seems you did right by the caps, and from all the info you gave you are right to go with the IR board.
-Lemur

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

I mean sorry Fixerofthings

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

Is there much on that IR board? such as an IC?
If not, I would be troubleshooting the board and not buying one.
If so, just get the board.
-Lemur

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

Is there much on that IR board? such as an IC?
If not, I would be troubleshooting the board and not buying one.
If so, just get the board.
-Lemur

There are two momentary switches that sit on either side of the main indicator LED, the IR sensor for the remote, the connector for the ribbon cable, and a few resistors that I can see. I did double check the ribbon cable that feeds this board, and that seems to check out ok, no breaks, shorts, etc.

For the cost of the board assembly, I think its easier to replace it than to try fixing it. Here's a link to the part in question, pics below as well: http://www.encompassparts.com/item/6...5866181/Cba_Ir

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

Boy it's hard to believe that board would cause those symptoms,
But I can't disagree with you, at that cost, even if it doesn't fix it, it's still worth the price of knowing that's not the problem!

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

Boy it's hard to believe that board would cause those symptoms,
But I can't disagree with you, at that cost, even if it doesn't fix it, it's still worth the price of knowing that's not the problem!

Like I said, it seems it one of the top 4 in demand parts for this model tv....this board, the power button itself, the PSU board, and the scaler board for the other model screen (which I don't have in mine)......

I'm going to give it a shot and see if it changes anything.

[whiz62]

Re: magnavox 37mf321d/37 powering on problems

my philips tv had about the same symptoms. got an IR board from ebay and same symptoms. It turned out to be the ribbon cable. now remote works and power led is working as it should. can't tell if yours has ribbbon cable connector or not. good luck

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

my philips tv had about the same symptoms. got an IR board from ebay and same symptoms. It turned out to be the ribbon cable. now remote works and power led is working as it should. can't tell if yours has ribbbon cable connector or not. good luck

I'll double check the cable, thanks for your input.

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

The IR board came in today, and............

same issue. Rechecked the cable again, etc. I'm at a loss and really don't want to spend any more on this TV. I may consider parting it out.

Any LOCALLY interested parties, let me know.

[ENERGYSAVINGS]

Re: magnavox 37mf321d/37 powering on problems

I wish I were local, I'd buy it from you. But you can sell the panel and the inverter boards, that should be worth some decent cash. The rest of the TV is suspect. I know you want to trust the PS, but I would not trust it at all. All the voltages are not there until the TV powers up.Caps are not the only thing that goes bad on the PS. And If the caps went bad before, what was feeding them got stressed.
Sorry it didn't work out out for you, but it's not a total loss. Some are.
Look on the bright side.

[fixerofthings]

Re: magnavox 37mf321d/37 powering on problems

Decided to give it another try at getting this beast working again. I was 99.9% sure that the PSU board was fine, but got a killer steal, I mean deal, on a reconditioned one. So after listening to another member on here that seemed to think that it still could be my PSU board that I repaired last year, I went for it.

Just replaced it, and...............nope. Same problem. So.....with that said, I did some searching and found a "tested known good, guaranteed" inverter board and a similar condition scaler/main board also, for next to nothing. These will be coming in next week, so my plan is to replace each of them one at a time and see what results I end up with after each component is replaced.

I'm keeping the old repaired PSU board around as a spare for now, and whichever of the other two boards I replace and there ends up with no change, I will keep that as a spare as well. Starting to believe that the issue is with the main/scaler board rather than the inverter board, but as I said, I will change them out one at a time and see what the end results are. Hopefully, the final results will be a working tv again.

I weighed out the cost of what I have into it all together, plus my time, and it is still cheaper than investing in a new tv at this point. Its a good thing this tv was given to me for free originally......I don't think I could be this patient with the thing if I purchased it new and had these issues with it, knowing what the high cost of it was back when it was new!