Magnovox 32MF231D

[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?

[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

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?

[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

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

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

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.

[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?

[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.

[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.

[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...

[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?

[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.

[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

[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

[budm]

Re: Magnovox 32MF231D

@techshui, the IC supposed to have shorted circuits protection, but it does not act fast enough and so it blew the MOSFET inside. The 9v and 10 Ohm trick should work, it will be even better if you have Adjustable power supply with Voltage and current limiter. You should monitor the voltage drop across the resistor to see how much current you are drawing from the 9V batteries, the batteries may not have enough current capacity to supply the power, the IC is rated up to 2.5A output current capability.

[TechShui]

Re: Magnovox 32MF231D

Sorry for not posting in a while, I sort of expected the thread would continue in my absence.

Broksonic, your voltages look alright to me... I'm no expert though. Hopefully, budm or Tom will give their opinions.

Of course, the burning question is where to check next?

I've put my rev3 board on the back burner, because I just don't feel safe putting another 12VS smps IC, since a) it will probably blow, and b) another of the solder pads flaked off. (these are very delicate PCBs).

I've checked 6001 on the rev4 board that I got from ebay.

In circuit, with diode test it's 150 on forward bias, 565 on reverse. Is this a cause for concern?
Seems unusual, it should be infinity, right? So I de-soldered it, and it tests 150 on forward bias, infinity on reverse.

So it must be good, but I wonder if something else in the circuit is causing the 565 reading.

broksonic, please put your multimeter in diode test and check your board's 6001 schottky, is it also 150 / 565?

UPDATE: I was just looking at your photos, here: https://www.badcaps.net/forum/showthread.php?t=20153#7

Click the first one, and zoom into the upper left corner, there's an 8-pin smps IC, and just above that a SOT-23 transistor labeled 7P16.
I want you to check that transistor, there's a mark on it that look suspicious, like a hole or a tiny gash.
Use the Ohm setting on your multimuter, check all 3 pin combinations, (1-2, 1-3, 2-3). The side with one pin, is pin 1 (aka base pin of the transistor). The numbers go clockwise.

[TechShui]

Re: Magnovox 32MF231D

OK everyone,

While we wait for broksonic to reply, I really need help figuring out my rev4 scaler board. It seems like a better candidate for repair since the IC I put into it did not explode

This will be the first time I post pictures of the rev 4 board.
I hope some people will take a look and let me know if anything looks suspicious.

To summarize what has happened with this board:

When it arrived, I could tell it had been worked on by someone even more novice than me. The 6002 schottky diode was missing, luckily the solder pads are intact.

The SMD resistor at 3u22 was yanked off, probably with pliers? Leaving a missing pad and trace damage.

I got a new diode, exact match (from Digikey) also got a 10 Ohm resistor. Repaired the trace by soldering a small red wire to the trace and new resistor. (see photo)

Note: The resistor is not an exact match, the SM describes
3u22 as a fusible 10 ohm resistor, made by Vishay.
After an hour of searching all I could find was a normal 10
ohm resistor by Panasonic. The wattage is the same though.
Does it really matter if it's fusible or not?

I replaced 7003, the 12VS smps IC. (remember I ordered 2 from DK)

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...

More observations: I see a couple of crooked components,
I circled them in red in the photos.
One's a white smd (resistor??) the others a blue smd
inductor with 330 printed on top.

I guess the dude tried to pull those out too? What are they?

[selldoor]

Re: Magnovox 32MF231D

Hmm - not easy- will look closer tomorrow.

If you get it working you should replace resistor with a fusible one - it, as name implies acts as a fuse.
Assume you are happy the trace went off in the opposite direction to what one might have expected?


What is at 8510 and 8511 solder on 8511 looks odd.

Dont know what the white block is- probably best you can do is to check it for resistance and see if the one on your other board is the same - and I think I see one other like it- you could check that also.


Blue barrel Inductor - they seldom go wrong just make sure it is soldered down. On that same picture is that a fuse - bottom right corner white block with gold ends possibly 1U01 perhaps a T 3amp

Also bottom left corner up from the 4 pin connector there is a green thing with F75? on it which suggests it is a fuse.

Are these the same two you mention.

[TechShui]

Re: Magnovox 32MF231D

Hmm, I wonder what happened to broksonic?

Assume you are happy the trace went off in the opposite direction to what one might have expected?

Yes, that's where the trace leads.

What is at 8510 and 8511 solder on 8511 looks odd.

Those are the solder joint of the L-shaped heatsink in the upper right corner of the board. (above the tuner).

Dont know what the white block is- probably best you can do is to check it for resistance and see if the one on your other board is the same - and I think I see one other like it- you could check that also.


Blue barrel Inductor - they seldom go wrong just make sure it is soldered down. On that same picture is that a fuse - bottom right corner white block with gold ends possibly 1U01 perhaps a T 3amp

Also bottom left corner up from the 4 pin connector there is a green thing with F75? on it which suggests it is a fuse.

Are these the same two you mention.

Yes, those are the two fuses I checked. I've re-soldered the white block now too.

Did you download the service manual from my link? I'm guessing whatever is preventing the board from starting is somewhere near the IC at 7003.

I tested the schottky 6001 out of circuit, it's still 150 on forward, but infinity on reverse, so it's good. 6002 is, of course, also good, since that's the one I ordered from DigiKey.

I starting checking those tiny SMD resistors near 6002

These resistors connect to pin 5 of the 7003 IC.

408 = 2.77k Ohms
273 = 3.4k Ohms
221 = 220 Ohms

According to what I know about resistor labels, the last digit is the number of zeros. From this we can determine 221 is spot on...
273 however should be 27k, NOT 3.4k.

And what about 408? That's a VERY unusual ohm rating... 4,000 Mega ohms, seriously? Perhaps I'm imagining the line in the last digit, and it's actually 400 (i.e. 40 Ohms) but that's also unusual. 40 Ohms is so low.

Yes, I did use a magnifying lens, there are not a lot of numbers that look like zero, so it has to be a zero or an eight, maybe an R, but I don't think so.

The photo I posted has pretty good resolution, you could look at the resistor and make your best guess as to the marking.

In any case 2.77k Ohms is not consisting with the marking. Does this mean these two resistors are bad? Or they're being affected by each other and gives off reading? I don't think removing them for further is an option for me. The lamination on this board peels easily, and I don't want to risk damaging another trace.