Magnavox 32mf231d please help me figure it out

[TechShui]

Re: Magnavox 32mf231d please help me figure it out

Measure the DC voltage across the startup cap again. Is it steady or fluctuating?

Ah, yes I forgot to mention I measured that too. It's 2066 right? That's 0.02v and yes I put black on -, red on +

On the edge of the board, cap 2067 reads 8.1~11.3v (it's connected to pin 1 on the SMPS IC).

The HQ photos are attached.

Read closer

If you mean probe closer, I did that too
Actually, when I press harder on the probes, it [the big cap]seems to stay at 160.1v for a few seconds longer... so maybe that's not a big deal.

There's greater fluctuation on the 24v rail, and even the 16v shows 15~16.5v, but interestingly enough, at the plug, and at the 2074 (capacitor) it's a steady 16.3v like it always has been, so that cap is doing a good job, but the new panasonic FMs are acting weird. 22~24v across both of them, and I know I soldered them properly, this isn't my my first recapping. I do mostly motherboards, and this will be my 4th TV recapping.

Edit Note: I will probably have to replace 6076 and 6071. They are the VR ICs for the 24v and 16v respectively. However, I'm still not getting 5V at the plug, and that's important since it turns on the mainboard.

If you trace pin 10 (5vsb) of the mainboard plug (lower-left on the solder-side photo). You will end up at the little white IC at 7074, which is right on top of the HOT/COLD line.
I measured pins 3 an 4 on the HOT side, and they are fluctuating between 10~12v.
Pins 1 and 2 on the COLD side are 00.0v -- is that normal?

[retiredcaps]

Re: Magnavox 32mf231d please help me figure it out

Ah, yes I forgot to mention I measured that too. It's 2066 right? That's 0.02v and yes I put black on -, red on +

On the edge of the board, cap 2067 reads 8.1~11.3v (it's connected to pin 1 on the SMPS IC).

The cap that feeds the SMPS IC VCC pin is the startup cap so it is 2067. You said you replaced this cap, but with what? I normally recommend something like a Panasonic FC because I know they work.

The startup voltage for your SMPS is 11V so it is starting, but then failing and then starting. There could be a few reasons for this.

1) the startup cap is bad. If you replaced with a quality brand name cap, then this is not the problem.
2) The SMPS IC is bad. This is a possibility since your power mosfet was shorted.
3) Something is loading down the power supply like a shorted diode somewhere on the board. You can check the diodes with your diode test function to see if any are shorted. Again since the power mosfet was shorted it would not be surprising if something else was shorted along with it.

[TechShui]

Re: Magnavox 32mf231d please help me figure it out

Can anyone guess as to why I'm not getting 5Vsb anymore?
In in my last post I pointed out the white IC at 7074, voltage across that is bouncing from 10~12v, and nothing on the cold side of it.

If you trace the startup cap, it leads to a second white IC on the opposite side if the power board, 7072 (but still on the HOT/COLD line).

I assume they are VR ICs? The second one if you haven't guessed is showing 8.1~11.3v (just like pin 1; vcc of SMPS IC). And just like it's twin it's 0.00v on the cold side. Maybe I should switch my meter to AC and check it out? Maybe these chips take AC and convert it to DC current? I'm trying to lean what each component does, and any info on that is always welcome

Why is is there fluctuation all over the place?? That doesn't have anything to do with the startup cap.

1) the startup cap is bad. If you replaced with a quality brand name cap, then this is not the problem.

2067 was Elite garbage, so I replaced it with a Panasonic that I happened to have laying around. I don't know the series or the ESR. It has slightly higher capacitance than the Elite I replaced it with (old cap: 25v 68uf, New: 25v 100uf). I've read on here that it's OK to use +/- of about 30% capacitance.

2) The SMPS IC is bad. This is a possibility since your power mosfet was shorted.
3) Something is loading down the power supply like a shorted diode somewhere on the board. You can check the diodes with your diode test function to see if any are shorted. Again since the power mosfet was shorted it would not be surprising if something else was shorted along with it.

I'm building a 12V power source out of alkaline batteries, I use this to test the SMPS IC, even if we assume it's bad, there's other components acting strange, again, I want to point out the black mosfets screwed into the heatsink on top, 6076, and 6071 show fluctuation.

And the P10NK80ZFP -- the mosfet I replaced -- is showing 0.02v on pin S. Doesn't that seem strange? Does anyone have a datasheet for P10NK80ZFP? I know it can't be bad, since it's brand new, but something else nearby might be.

[retiredcaps]

Re: Magnavox 32mf231d please help me figure it out

In in my last post I pointed out the white IC at 7074, voltage across that is bouncing from 10~12v, and nothing on the cold side of it.

If you trace the startup cap, it leads to a second white IC on the opposite side if the power board, 7072 (but still on the HOT/COLD line).

I assume they are VR ICs?

7072 and 7074 are optoisolators. These rarely fail because it is basically a LED. In 2 years of active participation, I think I have only seen 1 optoisolator fail.

http://en.wikipedia.org/wiki/Opto-isolator

[budm]

Re: Magnavox 32mf231d please help me figure it out

Service manual: http://elektrotanya.com/?q=showresul...oria=&kat2=all

I came in here late so here goes:
1) This power supply has PFC Voltage booster circuits, from the beginning of the post it was indicating that he only has 160Vdc on the main DC filter cap. It should be close to 400Vdc if the PFC is working. The PFC is controlled by IC7056 (L6562D).

2) I looked at the Power supply circuits (I download the service manual from the link provided in post 1). This power supply is always on, there is not 5vdc standby so I am not sure what you are referring to, may be you can please verify the diagram I attached matches your power supply first otherwise my explanations on how it works will not be applied to your board.
Per diagram: it has always on +24VA, +24VB, +16V, switched 24V.

[TechShui]

Re: Magnavox 32mf231d please help me figure it out

Service manual: http://elektrotanya.com/?q=showresul...oria=&kat2=all

I came in here late so here goes:
1) This power supply has PFC Voltage booster circuits, from the beginning of the post it was indicating that he only has 160Vdc on the main DC filter cap. It should be close to 400Vdc if the PFC is working. The PFC is controlled by IC7056 (L6562D).

2) I looked at the Power supply circuits (I download the service manual from the link provided in post 1). This power supply is always on, there is not 5vdc standby so I am not sure what you are referring to, may be you can please verify the diagram I attached matches your power supply first otherwise my explanations on how it works will not be applied to your board.
Per diagram: it has always on +24VA, +24VB, +16V, switched 24V.

Hi budm, you're not late the party has just begun.

1) Yes, it has a PFC (I had to look that term up to confirm).
The PFC controller IC is 5055 / 7056, you can see it on my solder-side photo
in post 21
I checked for shorts between all pins, all combinations. It all checks OK.

2) Yes, there is standby. The PDF you attached is page 55 of the Tpe1.0la manual, look at section F-1 of that page's grid.

"To Scalar board..."
Pin 9 - Standby

I was getting 5V at that pin at that start of all this (before the TV ran for 15 minutes and then shut down into the relay loop). I was under the impression that the 5V originated from the power board and serves to tell the scalar board to turn on? Looks like I could be wrong.

Like I said, I'm learning as I go.

7072 and 7074 are optoisolators. These rarely fail because it is basically a LED. In 2 years of active participation, I think I have only seen 1 optoisolator fail.

http://en.wikipedia.org/wiki/Opto-isolator

Thanks, I was wondering what they were for. And where is the fluctuating 10~12 volts coming from that runs accross those opto coupler chips?

[budm]

Re: Magnavox 32mf231d please help me figure it out

The pin labeled with "standby" is the PS_ON receiving pin on the power supply board which it gets from the Main board. When it received the 5v from main board, it turn on the PFC circuits and the switched 24v power supply section. There is not 5v standby power supply in this TV.

[cashkennedy]

Re: Magnavox 32mf231d please help me figure it out

I just purchased one of these (name your own price sort of deal from seller who just wanted it to not be thrown away). Symptom was the power light flashing on and off like it was trying to boot (tv performs a preboot when you plug it in). Fixed it in about 10 seconds by recapping the power supply, particularly the 25v 2200uf filter cap for the 12v line (I assume its 12v) which was obviously bad / was crapxcon. I replaced it with a panny FM 2200uf 16v cap. The other 3 filter caps are 35v for the 24v rail. Took longer to clean it up for resale then it did to fix.

Gotta love those old simple power supplies that didn't worry about active pwm and 20 forms of error sensing.