Magnovox 32MF231D

[broksonic]

Re: Magnovox 32MF231D

@broksonic,
I have some information that could help both of us.

After pouring over the service manual, I see that the 12VS chips feeds the white smd fuse labeled 1u01.

When you get a chance please check your board's fuse. If you click on my photo (the 2nd from the right, in my last post). And look at the top-left, there's a big green sticker labeled "M9", the fuse is directly under it. You should have 12v on one side of it.

From there the 12v goes into many transistors (or are they volt regulators?) and comes out as 1.2v, 3.3v and 2.5v. This is all illustrated on page 47 of the SM.

Also check the chips 7u03, 7u01 and 7u25. What are their voltages? I believe they are each converting the 12v into the smaller voltages that I mentioned.

Heres the readings i got when checking...

Fuse
1u01-12.04

7u01
pin 1-2.96
pin 2-4.49
pin 3-0.00
pin 4-8.26
pin 5-5.19
pin 6-5.19
pin 7-5.19
pin 8-5.19

7u03
pin 1-0.00
pin 2-10.06
pin 3-1.22
pin 4-2.20
pin 5-12.02
pin 6-12.02
pin 7-1.23
pin 8-1.23

7u25
pin 1-5.18
pin 2-11.92
pin 3-5.18
pin 4-11.92
pin 5-5.19
pin 6-5.19
pin 7-5.19
pin 8-5.19

[broksonic]

Re: Magnovox 32MF231D

@broksonic,
I have some information that could help both of us.

After pouring over the service manual, I see that the 12VS chips feeds the white smd fuse labeled 1u01.

When you get a chance please check your board's fuse. If you click on my photo (the 2nd from the right, in my last post). And look at the top-left, there's a big green sticker labeled "M9", the fuse is directly under it. You should have 12v on one side of it.

From there the 12v goes into many transistors (or are they volt regulators?) and comes out as 1.2v, 3.3v and 2.5v. This is all illustrated on page 47 of the SM.

Also check the chips 7u03, 7u01 and 7u25. What are their voltages? I believe they are each converting the 12v into the smaller voltages that I mentioned.

If you get your board fixed, you can sell it on eBay to cover your losses, or better yet, make a profit.

Will check and post results.

As far as the board from E-Bay, i got a refund on it today. The seller noted that they found the board was "bad". BUT, i seen another of their buyers left a note about them "never being able to get ahold of the seller or ever getting the product".

So i am still looking.

FYI... e-bay seller was 591tracie

[tom66]

Re: Magnovox 32MF231D

@broksonic,
I have some information that could help both of us.

After pouring over the service manual, I see that the 12VS chips feeds the white smd fuse labeled 1u01.

When you get a chance please check your board's fuse. If you click on my photo (the 2nd from the right, in my last post). And look at the top-left, there's a big green sticker labeled "M9", the fuse is directly under it. You should have 12v on one side of it.

From there the 12v goes into many transistors (or are they volt regulators?) and comes out as 1.2v, 3.3v and 2.5v. This is all illustrated on page 47 of the SM.

Also check the chips 7u03, 7u01 and 7u25. What are their voltages? I believe they are each converting the 12v into the smaller voltages that I mentioned.

If you get your board fixed, you can sell it on eBay to cover your losses, or better yet, make a profit.

@budm
On my board that keeps blowing 12vs chips. I was thinking about soldering a 9v battery to the pads where the IC was. Positive to pin 1, negative to GND.

Then take voltage measurements from the same places I mentioned above (fuse 1u01, chips, transistors...) and see if I'm getting 9v at those locations.

Wherever the voltage stops is where my problem component will be.

Is this a good idea? Could something go wrong?

The 9V trick should work, but use a 10 ohm 5W resistor in series "just in case". A 9V battery won't source much current without dropping voltage a lot, consider a 12V wall wart or similar.

[TechShui]

Re: Magnovox 32MF231D

@broksonic,
I have some information that could help both of us.

After pouring over the service manual, I see that the 12VS chips feeds the white smd fuse labeled 1u01.

When you get a chance please check your board's fuse. If you click on my photo (the 2nd from the right, in my last post). And look at the top-left, there's a big green sticker labeled "M9", the fuse is directly under it. You should have 12v on one side of it.

From there the 12v goes into many transistors (or are they volt regulators?) and comes out as 1.2v, 3.3v and 2.5v. This is all illustrated on page 47 of the SM.

Also check the chips 7u03, 7u01 and 7u25. What are their voltages? I believe they are each converting the 12v into the smaller voltages that I mentioned.

If you get your board fixed, you can sell it on eBay to cover your losses, or better yet, make a profit.

@budm
On my board that keeps blowing 12vs chips. I was thinking about soldering a 9v battery to the pads where the IC was. Positive to pin 1, negative to GND.

Then take voltage measurements from the same places I mentioned above (fuse 1u01, chips, transistors...) and see if I'm getting 9v at those locations.

Wherever the voltage stops is where my problem component will be.

Is this a good idea? Could something go wrong?

[TechShui]

Re: Magnovox 32MF231D

budm,
I posted photos below.
The schotty diode 6001, that has low ohms both ways. It must be shorted.

Look at broksonic's readings, he has 11.8v at 6001. His is functioning properly.

Here's the IC datasheet: http://www.alldatasheet.com/datashee...ICS/L5973.html
The thing is, this IC is suppossed to shut off by itself when the load gets too high, right? So is something preventing that... is it really safe to use my 2nd new IC. Even if I replace that schottky, there may be more shorted components and I can end up with another toasted chip?

One more thing I noticed: The GND pin of the switchmode IC is always where it blows. In my first photo below, you will see the original chip, and a tiny hole near the GND pin. This appears to be a common problem for Magnavox scaler boards.

I have another of these scaler boards, got from eBay, listed "For Parts and Repair". The difference is it's a Rev 4 (my orignal is a rev 3, hence the the pic are labeled that way). The eBay board has a burnt IC 7003 in the same exact spot, on the chip near GND.

It also has trace damage, and at least one missing component (6002 schottky, the one on the 5.2Vsb circuit). The board has obviously been worked on, presumably by the seller, who gave up on it.

The advantage is I can use it as a source for components for the first board, and vice-versa.

UPDATE: Call me crazy, but I went and put my 2nd L5973 chip into the eBay scrapper. I repaired the trace on Friday and there's new diode for 6002.

The good news: The chip did not explode this time!

The bad news: The TV does not turn on at all with this board, not even a split-second flash, like I was getting with the other one. I checked both fuses and they're good.

Voltages for the new IC:

1 - 0.00v
2 - 0.00v
3 - 0.00v
4 - 4.82v
5 - 0.07v
6 - 0.02v
7 - 0.00v
8 - 17.3v

So the IC is turned OFF, hmm...

[budm]

Re: Magnovox 32MF231D

@techshui, sorry to hear that the new IC burnt up, I will really draw out the IC connection and see how it is being connected and compare it to the service manual then we can see what they have done and if it makes senses when compared it to the IC manufacturer suggested connections, the Vref is supposed to be 3.3V.
The gold holes are VIA for connecting the top copper layer to the bottom copper layer of the circuit board, so they must be going somewhere.
One thing that can cause the IC to burn up like that, the output pin (which is the switch power transistor inside the IC) feeding into shorted load, you should check the flywheel diode 6001 or the pin 1 and ground when you remove the bad IC and see what resistance you are getting.
This 12vs is fed to alot of other regulators, I think you have something that is loading down this IC real bad.

[broksonic]

Re: Magnovox 32MF231D

Well, i found a board on E-Bay ($55.00) from a broken screen unit and should be here next week sometime.

Will let you know if it fixes the problem.

[TechShui]

Re: Magnovox 32MF231D

I went against my better judgement, I installed the new chip leaving the Vref pin open.

When everything was back together, I plugged in the TV, and it turned on by itself, backlight came on, but I could not change ch/vol or menu. It was just a black screen. TV stayed about 15-20 seconds before the smell of burnt plastic filled the air, and a nice gray plume of smoke emmited from the TV.

The new IC is toast.

I think whatever killed the original one must've killed this one too, but what about that pin 6 Vref? Did my leaving it open have anything to do with this?

[TechShui]

Re: Magnovox 32MF231D

budm, I forgot to attach my photo

I could be wrong, but seems pins 5, 6, 7 and 8 go to that little gold circle (the one by the number 5)?

That circle probably goes through the PCB right? To another circuit on the opposite side. Or GND maybe?

The trace also goes down to the other gold circles... and the three SMD resistors.

EDIT: The chassis is the same, TPE1.0LA

DOUBLE EDIT: The voltages I took before removing the IC tell a different story:

Pin 5 (FB) = 11.5v
Pin 6 (Vref) = 12.2v
Pin 7 (GND) = 0.0v
Pin 8 (Vcc) = 14.4v

Resistors:
562 - 23.8v
473 - 23.8v

So the trace is not connected? It sure looks like it though, since the dark green area criss-crosses and surrounds those four pins.

[budm]

Re: Magnovox 32MF231D

According to the service manual, the Sync and the Vref pin are not used in this application. If it is connected to something then you will need to connect them back since the circuits may need Vref for something, but you need to verify for sure, also look at the data sheet of the IC on how it beinh used. I wonder if the SCH we are using matches the chassis you are working on. It is analog signal, and it should not be connected to the FB (feedback pin).

[TechShui]

Re: Magnovox 32MF231D

The parts I ordered arrived yesterday, including two L5973 chips.

Desoldering the old L5973 (at 7003) did not go smoothly.
The pins would lift up after just 3 seconds, those were not an issue, but the chip itself would not budge, like it was glued. Prying it only served to break off little bits of it.

I finally took a pair of cutters to it and hacked off most of the chip.

Then put the the tip of the iron on what was left, I figured it would heat any glue still holding it.

Guess what? It was solder, not glue. :surprised: No wonder it wouldn't budge!

Unfortunately, the pad for pin 6 flaked off. This is the Vref pin of the IC and doesn't appear to connect to anything? See the schematic at https://www.badcaps.net/forum/attach...6&d=1335669269

But that trace was there for a reason... it seems to connect both pin 5 (FB) pin 6, 7 and 8 to a tiny gold circle. (see photo).

How important exactly is this Vref pin? It's a digital signal, right?

Can I bridge the pin since the trace seems to connect them all on that side? Is it better to leave it disconnected?

[budm]

Re: Magnovox 32MF231D

@techsui, the 7004 has input of 0.1V, I think that 5v you are seeing is coming from some where else through high impedance line, to find out, connect a 500 Ohm resistor so it will draw about 100mA from it and see if it will still staying at 5V. You will have to look and see also why you do not have the +24A/+24BV feeding it from connector1089 pin 3 on power supply board, the +24A/+24B are always on, +24V is switched for feeding the Inverter board, if you look at the Power supply board PDF.
Your 7003 is bad for sure since the Inhibit line PIN 3 is HI which will cause the out put to shut off, it looks like it had internal shorts circuits inside the IC.
The +5V2-STBY (Generated by 7004 on the scaler board) is needed for a lot of circuits to function, also the 12VS (generated by 7003 on the scaler board).

Summary:
When the TV is plugged in, you should have these voltage at the power supply board.
+16Vdc at connector 1089 pin1 and 2.

+24Vdc at connector 1089 pin 3

[TechShui]

Re: Magnovox 32MF231D

Broksonic, your 7003 (12V suppply) is functioning correctly. Your problem is not caused by the same thing. However, I have a feeling your on the right track, keep going!

Test the resistors and caps in that circuit too. Look at the PDF file budm attached for the locations of all the components in the 12V circuit. You can also trace the 5.2V (4.9v) circuit to see if that has any burnt or shorted components in it, but I doubt that.

The 12V circuit is your best bet, but also check 3U22 SMD resistor, should read 10 Ohms.

I see you have 24V on your 7004. Hmm, I wonder why I didn't get that on mine? Yet it's still outputing 5.2V, so it *seems* to be working.

budm, should I order IC 7004 just in case?

[broksonic]

Re: Magnovox 32MF231D

Thanks budm for pointing me in the right direction.

Yeah, there's a lot of ICs, but I only had to check the first one. Look:

12V supply IC (7003):
 
Pin 1 (OUT) = 11.8v
Pin 2 (Sync) =11.8v
Pin 3 (Inh) = 11.8v
Pin 4 (Comp) =11.9v
Pin 5 (FB) = 11.5v
Pin 6 (Vref) = 12.2v
Pin 7 (GND) = 0.0v
Pin 8 (Vcc) = 14.4v

I can see a small crack, and a pin-sized hole on the chip. So I'm off to Digikey to order a new one.

broksonic, I suggest you check this chip on your board too.

Well, i checked 7003 (5 times) and this is what i have..

Pin 1 - 11.86
Pin 2 - 0.75
Pin 3 - 0.0
Pin 4 - 1.81
Pin 5 - 1.22
Pin 6 - 3.32
Pin 7 - 0.0
Pin 8 - 15.62

I did check a few other things:

Schottky rectifiers:
6001 has 4.60v on cathode lead
6002 has 4.80v on cathode
6003 has 23.8v on cathode
 
IC at location 7004
 
Pin 1 (OUT) = 5.2v
Pin 2 = 0v
Pin 3 = 0v
Pin 4 (comp) = 0.9v
Pin 5 (FB) = 1.2v
Pin 6 = 0v
Pin 7 = 0v
Pin 8 (Vcc) = 0.1v

Why is the Vcc only 0.1v on this one? Shouldn't it be 24V?

I also checked these.... (5 times again)
6001 - 11.83
6002 - 4.95
6003 - 18.5

7004....

Pin 1 - 4.91
Pin 2 - 0.0
Pin 3 - 0.0
Pin 4 - 0.89
Pin 5 - 1.22
Pin 6 - 0.0
Pin 7 - 0.0
Pin 8 - 24.2

Alot of differences in my numbers compared to yours there..

[TechShui]

Re: Magnovox 32MF231D

Thanks budm for pointing me in the right direction.

Yeah, there's a lot of ICs, but I only had to check the first one. Look:

12V supply IC (7003):

Pin 1 (OUT) = 11.8v
Pin 2 (Sync) =11.8v
Pin 3 (Inh) = 11.8v
Pin 4 (Comp) =11.9v
Pin 5 (FB) = 11.5v
Pin 6 (Vref) = 12.2v
Pin 7 (GND) = 0.0v
Pin 8 (Vcc) = 14.4v

I can see a small crack, and a pin-sized hole on the chip. So I'm off to Digikey to order a new one.

broksonic, I suggest you check this chip on your board too.

I did check a few other things:

Schottky rectifiers:
6001 has 4.60v on cathode lead
6002 has 4.80v on cathode
6003 has 23.8v on cathode

IC at location 7004

Pin 1 (OUT) = 5.2v
Pin 2 = 0v
Pin 3 = 0v
Pin 4 (comp) = 0.9v
Pin 5 (FB) = 1.2v
Pin 6 = 0v
Pin 7 = 0v
Pin 8 (Vcc) = 0.1v

Why is the Vcc only 0.1v on this one? Shouldn't it be 24V?

[budm]

Re: Magnovox 32MF231D

16vdc to the scaler board, and comes out as 12v by the busking switching regulator. there are so many regulator, switching power supplies on this scaler board to check.

[broksonic]

Re: Magnovox 32MF231D

It is rather confusing (manual for scaler board).
I finally got a download using safari.

I have been searching for a different diagram too (bing, google, even ask) with no luck.

Got my friends/co-workers watching the e-recycling for a possible replacement as well as watching e-bay.

Unless someone else has an idea i see no other option than scaler replacement right now.

[TechShui]

Re: Magnovox 32MF231D

We're still back at square one.

We have to troubleshoot the scaler board at the component level, or shell out $80-$100 for a new one on eBay. :-/

The RiddleTV guy (from post #28 on this page) said to check the SMD capacitors at 2H08 and 2H09. Heck, that location isn't even there!

It must be an unmarked location, but the manual's only reference is in the parts revision list. There's no diagram of the entire scaler board. Or am I too dumb to find it?

[broksonic]

Re: Magnovox 32MF231D

broksonic, have you tried testing that plug while it's disconnected from the scaler board? Obviously, they should stay steady when it's by itself.

Pins 1 & 2 were steady at 16.9
pin 3 steady at 24.2
pin 4 steady at 3.2
rest were signal pins or 0.0 (as per other post)

Oh and the flashing from the Master Backlight inverter board has changed again.

Now when scaler board green light kicks out, the red light flashes twice, pauses, flashes twice, pauses then flashes once.

[selldoor]

Re: Magnovox 32MF231D

What browser are you using- doesnt like Opera - optimised for firefox