Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

[garry7263]

I bought this TV for $45. The guy said that it had steady green light when turned on. When I went to pick it up he hands me a bunch of 680uf caps and whats left of a pack of 1A fuses. He told me he tried to fix it but didnt have the time. I located the one cap he replaced, on the ysus board I believe. Every fuse in the TV has been replaced with a 1A glass fuse. I pulled out the power supply and want to trouble shoot it first just in case there is a problem with it and to save me from ruining any other boards. ( hear to many times when someone just replaces the fuse and then end up frying something replaceable)

I took pictures of the power board to start. Maybe to many and a little overkill, but better than not enough

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

Bottom of the power board

[tom66]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

The connectors going to the Y and X main are located near the top left of the board. You should see voltages Vs and Va marked, possibly others. Test each in succession and compare to the plasma panel's rating sticker (on the metal plate of the panel.)

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

connectors

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

various pics

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

more pics

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

If a picture is worth 1000 words then I just rewrote War and Peace.

Last of the pics of the power supply board

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

I have to get the right fuses before I can power it up and check voltages. The main AC input is an 8A ceramic, There is one 2.5A, one 4A, and one 1A from what is written on the board.

So waiting to get the fuses I was checking the bridge rectifier (I think) 4 legs and attached to a heat sink. I was getting some weird inconsistent readings so I removed it and tested. Results are

pic 4 of post#6 (imag0100.jpg)

R82505M
V642

pin 1 pin 2 pin 3 pin 4
(+) OL (-) (+) OL (-)
(+) OL (-)
(+) ----OL---- (-)
(+) ---- OL ---- (-)
(+) -------- OL--------- (-)
(-).439 (+) (-).442 (+)
(-) OL (+)
(-) ---.454 ---- (+)
(-) ----.447 ---- (+)
(-) --------.826---------(+)

Should I be getting anything across pins 1&3, 2&4, and 1&4?

[tom66]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

The bridge -looks- good. If correct fuses are installed, and the fuse does not blow, more than likely it is OK.
And thanks for the good pictures. It's a rare treat here!

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

Im guessing that the kid that was trying to fix this figured that if the fuse was the same size then it was the right fuse. I need to contact hi and find out just what he did and what happened when it stopped working.

I think he thought it was a cap on the Ysus board because there is one on there that matches the other caps that he gave me. 680uf. There are fuses on the two boards that were also replaced with a 1A fuse. (missing a few screws a well but not problem)

Pictures of the rest of the TV

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

XS board

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

YS Board and Y Buffers

In pic #3 (IMAG0128) on the far right, the smaller of the two caps is the one that is the replacement. Looks like C5000

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

I have been reading a lot here and I know it is much better to have a visual of the actual thing you are trying to troubleshoot than yo conjure an image through some telepathic mind meld.

I dont do much on TV repair. I mostly just work on guitars and basses, and minor amp or mixer repair, but would like to know enough to be able to fix what I need and a better understanding of testing and troubleshooting is in order.

I will put the BR back in and look for fuses tomorrow

While I am here.
I am sure it is better to check Diodes by unsoldering one leg and testing.
I would assume the same goes for resistors, but think that finding a general short or blown would show up still in circuit.
Caps should be checked with an ESR meter (can be done in circuit) but also possibly removed.
Transistors should be taken out. Not really sure on testing them yet(still learning) NPN had + to the base and PNP has - to the base?

Im sure that it would be better to test everything out of circuit but not practical, so trouble shooting and finding where to look and isolate problems can reduce the definitive removal and testing procedure.

Any input would be greatly appreciated. Thanks for your quick responseTom

[tom66]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

The first thing you need to do when repairing a TV (indeed, anything) is to find the fault.
You need to install all of the fuses and get it to the original broken state.

Then, please check the Vs/Va as mentioned earlier. If they're low, check the other supply voltages such as 5V2. Listen for clicks from the relay when plugged in and power button pressed. Does the LED flash red? If so, count the blinks.

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

This didn't turn out like I had originally written it so I will re do it

R82505M
V642

pin 1 pin 2 pin 3 pin 4
(+) OL (-) (+) OL (-)
(+) OL (-)
(+) ----OL---- (-)
(+) ---- OL ---- (-)
(+) -------- OL--------- (-)
(-).439 (+) (-).442 (+)
(-) OL (+)
(-) ---.454 ---- (+)
(-) ----.447 ---- (+)
(-) --------.826---------(+)


(pin 1 +) OL (pin 2 -) (pin 2 +) OL (pin 3 -) (pin 3 +) OL (pin 4 -)

(pin 1 -) .439 (pin 2 +) (pin 2 -) OL (pin 3 +) (pin 3 -) .442 (pin 4 +)

(pin 1 +) OL (pin 3 -) (pin 2 +) OL (pin 4 -)

(pin 1 -) .454 (pin 3 +) (pin 2 -) .447 (pin 4 +)

(pin 1 +) OL (pin 4 -)

(pin 1 -) .826 (pin 4 +)

[tom66]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

The bridge would -appear- good to me, at the very least, there are no dead shorts.

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

Fuses installed, am getting 5v and 12v where they should be. Will put it back in the TV and leave the Y and X boards unplugged then check the voltages and report back

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

put the board in and checked voltages, power on, but the X and Y boards not plugged in

Va: 64.7
Vsc: -200.4
Vs: 181.9
Ve: 90.1
Vset: 174.7
Vsc_h: Didn't know where to test, noticed that there was Vsc_h on a transformer on a sub-board on the Ysus
5v2: Didnt find something designated with that but most 5v locations were 5.3v-5.5v
5v_sw: 5.31
8v6: 8.63
12v: 12.2
SND_P: 16.98
SND_N: -17.15



Supposed to be

Va: 65
Vsc: -185
Vs: 198
Ve: 105
Vset: 190
Vsc_h: -65
5v2: 5.2
5v_sw: 5.2
8v6: 8.6
12v: 12.2
SND_P: 18
SND_N: -18

[garry7263]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

Also....The power button was solid green when turned on.

[tom66]

Re: Magnavox 50MF231d 37 Blown Fuse/supposedly solid green light when turned on

Vs is much too low. Please set this carefully to the panel rating (+/-1V)
Ve, Vset and Vsc are also very wrong, and will need to be set within +/-2V.
Check in a dark room: does the plasma panel glow slightly?