Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
Thanks for that bit of info. Because it didn't blow on the test table I installed it back into the TV. I will pull it out again and continue testing in a few weeks.
briankb
Member
Last Activity: 07-02-2017, 08:36 PM
Joined: 11-25-2012
Location: Lake City, Florida
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
Thanks for that schematic! It looks just like my board. I replaced Q908 and the mosfet just above R927 in the photo. The fuse did not pop as far as I could tell, but I still need to pull the fuse and test it. It's a slow blow white ceramic fuse and I'm not sure if those show visual signs if blown.Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
thanks to this thread and wikipedia I understand what a bridge rectifier does and how it works. very cool. two men enter one man leaves :-)
[url]http://en.wikipedia.org/wiki/Diode_bridge[/url]Re: Magnavox 42MF437B/37 Blowing Fus...e_bridge[/url]Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
You were right I did test it like a diode, I did it again and it failed.
I will double check these tomorrow and check what other caps I need for a order.
Thanks for your considerable help!!!
Were all of these tests just from experience or is there a method to tracing these things down? Or do you just test all of these diode,mosfets, ect... until you find something fail?Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
There is a small one without a heat sink (I think) at Q908 (right of the 450v cap). I flipped the board over and tested what I think are pins 2-3 and I get a reading in both directions.
Isn't the 450v cap a lelon? What's the reason for not replacing it as well? Just curious so I can learn more about these things.Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
I removed the bridge rectifier and performed the test as shown in the video. My results were the same as the video so I assume this bridge rectifier is good.
What should I check next?Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
Thanks for explaining the D922 diode :-)
I'm about to pull the bridge rectifier and test it again.Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
W26 is what is in place now and it is bad. The W18 was a suggested part by rayrod earlier in this thread.
D922 looks like a mosfet it has 3 pins and same shape as the other two....Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
Thanks Mr Bill! I checked the FETs again and the left one is fine, all readings were above 1M ohm however the center most FET was bad. All of those readings were below 30.
mostfet readings:
1-2 = 1.5Ω
2-3 = 0Ω
1-3 = 1.4Ω
Also just to be clear on the bridge rectifier test I get a reading on 1-2 and 2-1, neither are OL. Same for 3-4 and 4-3.
1-2 (black-red) = .881v
1-2 (red-black) = .459v
3-4 (black-red) = .882v
3-4 (red-black)...Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
I tested the bridge rectifier and get a reading on 2-1 and 4-3 instead of OL, all other readings were as expected. Does that make sense?
Also I tried to test the mosfet's on the center heat sink but I'm not sure I did it correctly. The one near the center seems bad but I need to find another way to test them or just replace them both. To test the mosfet I put it in diode mode (my meter only puts out 1.5v so i used my solder stations power supply set to 3.5v to switch it on). I then tested in...Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
@selldoor - I tested the various diodes again after reading retiredcaps instructions. They are all good. I'm not sure which component is the bridge rectifier you suggest, but if you can help me identify it I will try to test it.
@rayrod81 - I looked at those closely with a mag and it does look like they were replaced once, the solder joints on the bottom show signs of flux. However the one closest to the center isn't a W18... it's a W26NM60 and the one to its left is blank. Perhaps the last...Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
Just below the fuse it does read "T5.0AH 250V EC TYPE". I found a 5HT 5-R online for $.30ea.
The component at D901 is a diode, as per the icon underneath and also it has only two leads. I tested it with my DMM as well as ZD902 & ZD904; they all gave a reading other than zero....Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
Thanks for the help so far!
@selldoor - I took another photo with more light and a close up on the fuse area....Leave a comment:
-
Re: Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
I tried a few of them, assuming the grey stripe on one end is negative. It's hit or miss but I'm replacing the batteries in my DMM and trying again.
Are mosfets the transistors on the heatsinks? I don't know how to test them, please enlighten me :-)Leave a comment:
-
Magnavox 42MF437B/37 Blowing Fuses after "Professional" Repair
[B]Background[/B] (feel free to skip this part): A few years ago my first HDTV, this 42" Magnavox, started to have sound problems. I would have to turn it off/on many times for it to get sound with the picture to work and finally one day it would not turn on at all. So I took the behemoth off the wall and down to my local professional TV repair guy. He called me the next day and said it needed new "caps" and if I remember it cost me about $250... Keep in mind this was several years ago. I knew nothing about bad caps and didn't have any equipment or the know how to do my own repairs....
No activity results to display
Leave a comment: