Toshiba 32AV502U fuse blows

[tucocaps]

Re: Toshiba 32AV502U fuse blows

So black lead on chassis, what do you measure on each pin going to main board, DC voltage?

Changed the power cord? Do any US power plugs have fuses? Different socket?

I don't know what you mean by the "black lead". Yes, the power cord is fine, and so is the fuse. Else, I don't see how I'd be able to trace the AC power across the fuse and down the circuit. The power board has problem(s). Just trying to figure out what , or if I'll have to replace with a new board instead of fixing

[tom66]

Re: Toshiba 32AV502U fuse blows

Meter probe connected to COM is probably black lead?

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Meter probe connected to COM is probably black lead?

I don't think we are communicating well. Yes, I have 120v AC power going to the board, and it is also going across the fuse and into the circuitry on the board. There is no doubt about that.

[tom66]

Re: Toshiba 32AV502U fuse blows

I'm asking where you're putting the black meter probe. In this case, for testing the outputs of the power supply, it should be on some part of the metal chassis of the set.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Tom,

So you mean strictly the DC outputs? The board shows two pins for both 5 and 12 volt dc output. I'm assuming this was pos/neg, and used my probe black/red on each of those.

For the AC side, I have been just touching line and neutral to either red or black at the plug , and the other probe to whatever point I am trying to test. Is this not correct? I'm able to read the voltages properly (i think)

[budm]

Re: Toshiba 32AV502U fuse blows

Set Meter to DC mode, Black probe of the meter on the metal part of the TV chassis, the red probe for measuring each pin of the DC output at 5v, 12v pin, etc.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Set Meter to DC mode, Black probe of the meter on the metal part of the TV chassis, the red probe for measuring each pin of the DC output at 5v, 12v pin, etc.

Could I touch it to one of the mounting screw holes? I've been working on the power board completely removed from the TV.

[budm]

Re: Toshiba 32AV502U fuse blows

You will have the mount all boards back in place first before making the measurement, then you can use the screw head or the chassis for the meter (black probe) for the secondary circuit (cold side) ground point.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Darn Wish I knew that before. I already have the TV up on a shelf, as I'm needing the space for other work. OK, thanks again. I'll have to get the TV back down and remount the power board and test in the next day or so.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Screwed the power board back on, and plugged in power. As best I can tell, no voltage on the 5v. Touched all of the pins on that plug several times with black touched to the metal case. Somehow I expected this, as the tv has not shown any led's or signs of life. Is there any further testing I can do from here? On the high voltage side?

[budm]

Re: Toshiba 32AV502U fuse blows

Check the DC voltage right at the two pin of the main DC filter cap C102, it should have about 160Vdc on it.
Also post the pictures of the whole board, both sides.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Thanks for the reply, budm. Yes, I do have 160vdc at C102.

Here are the pictures of the board as requested.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Any ideas on this ? Thanks.

[budm]

Re: Toshiba 32AV502U fuse blows

OK, your main DC is OK, there are two power transformers, the small one is for the 5V stby power supply which is not working right now, we need to get it running first.
Can you read the P/N of that 7-pin IC (U501) which is the switched mode power supply IC. Check the snubber Diode D502 to see if it show low resistance reading on both directions. If it tested good, then With the TV not plugged into the outlet, heat up those 3 small caps with hair dryer for about 3 minutes, then plug the TV into the outlet, no need to turn on the TV, then check and see if you get the 5V or not.
I also need good closed up pictures of the board (both sides) in 1/4 section at least so I can tell you the test points and the components to test.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

OK, your main DC is OK, there are two power transformers, the small one is for the 5V stby power supply which is not working right now, we need to get it running first.
Can you read the P/N of that 7-pin IC (U501) which is the switched mode power supply IC. Check the snubber Diode D502 to see if it show low resistance reading on both directions. If it tested good, then With the TV not plugged into the outlet, heat up those 3 small caps with hair dryer for about 3 minutes, then plug the TV into the outlet, no need to turn on the TV, then check and see if you get the 5V or not.
I also need good closed up pictures of the board (both sides) in 1/4 section at least so I can tell you the test points and the components to test.

OK, I used a small analog volt/ohm meter to check the snubber in "both directions". I'm not sure if I did this right, but I ensured the meter was set to ohms x10. I then tested with terminals touched together which moves the needle all the way to the right to 0. I used the 0 adjust to put needle at zero. Putting the probes on both sides of the diode, I got a reading of about 3. Reversing the probes, I get no reading (infinite resistance?). Does this mean the snubber diode is no good? I did this check with the board disconnected completely from the tv.

[tom66]

Re: Toshiba 32AV502U fuse blows

You really need a digital multimeter to check a diode like that. In fact I would say a digital multimeter is essential for almost all modern electronics repair jobs.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

You really need a digital multimeter to check a diode like that. In fact I would say a digital multimeter is essential for almost all modern electronics repair jobs.

Tom,

THanks for the reply. I do have both, and have been using a digital meter, but am unsure about the ohm setting. I notice on the digital, if I short the terminals together , it goes from reading 1, to a low resistance reading. On the diode, it's confusing me. It seems to flash from one to another reading quickly, and then back to 1. How should I properly test with this?

[tom66]

Re: Toshiba 32AV502U fuse blows

Your meter would appear faulty.
A single "1" indicates the reading is out of range.
A reading of ".000" or nearabouts should be obtained when the leads are shorted.
If the reading of ".000" does not hold, the meter is defective.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Your meter would appear faulty.
A single "1" indicates the reading is out of range.
A reading of ".000" or nearabouts should be obtained when the leads are shorted.
If the reading of ".000" does not hold, the meter is defective.

I actually have two of these meters. One new in box which I tested per your reply. These are cheap quality (harbor freight) cen-tech meters. I notice that I only get to zero with the newer meter and the higher ohm ranges (200K) setting. So, I went with that, and tested the diode again. This time, at the 200K range , it read about 65-75 in both directions. Would this be a proper test, and if so, is the diode OK?

[tom66]

Re: Toshiba 32AV502U fuse blows

It's normal to see a small offset in the lower ranges; maybe 3 or 4 ohms if the probes and leads are very cheap. So don't be afraid if you see that, it's just measuring the resistance of the probes/leads -in addition- to the component under test. Better meters have this zeroed out at the factory. My meter shows 0.1 ohms when shorted.