Toshiba 32AV502U fuse blows

[pauldow]

Re: Toshiba 32AV502U fuse blows

These power supplies use very good capacitors, were they bulging on this model? (Chemicon and Rubycon caps.)

Unfortunately, I'm working (well, playing with) two different TVs, so I don't have the capacitors anymore. There were some bulging, but they were on the secondary side. Investing in an ESR meter may have been useful.

As far as that inrush limiter, I have another supply, and that reads about 1.2 ohms. For some reason, all the thermistors my local electronic store has are 1K, 2K, 3K, 5K or 10K. Harrumph!

Thanks for the light bulb idea. It could save the smoke coming out of things.

It's tough to figure out where the "just one more part" obsession should end, and just buy the replacement supply. I think I'm getting close though.

Thanks for all the replies,

[tucocaps]

Re: Toshiba 32AV502U fuse blows

I wanted to reply on this thread , because I have the same board and tv, and am also trying to fix a no power issue.

First, I must say I am no expert. Just an interested hobbyist with a meter and a solder gun

The fuse is not blown. The problem I have seems to be no power going through the fuse. If I check voltage up to the varistor at UA101, I have power. However, on the other side of UA101, I do not have power. I'm a bit confused, because it seems this varistor actually "bridges" the neutral connection, and in this case is burned out?

Thanks for any idea on confirming what's wrong, and if it is the varistor, can I replace with one out of a computer PSU?

[tom66]

Re: Toshiba 32AV502U fuse blows

The varistor goes across live and neutral. If and when there is a mains surge it will short circuit shunting the current and limiting the voltage to a relatively safe level. After too many shunt events it may fail short circuit blowing the fuse.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

The varistor goes across live and neutral. If and when there is a mains surge it will short circuit shunting the current and limiting the voltage to a relatively safe level. After too many shunt events it may fail short circuit blowing the fuse.

So any ideas on what might be wrong with the fuse instact? The TV had been hit by a power surge which caused it to go down. I guess I'm confuse about the varistor. With the circuit live, should I have current from live to neutral on both sides of the varistor? I'm just using a basic digital meter. I get nothing on the other side. Maybe .1 or .2. There is another varistor leading off neutral, and it shows current on both sides (larger blue). This is the smaller , yellow one, that appears open.

[tom66]

Re: Toshiba 32AV502U fuse blows

Have you checked the outputs from the power supply like 5V standby?

[budm]

Re: Toshiba 32AV502U fuse blows

Can we see the pictures of YOUR board? Both sides of the board and around the area that you have checked the AC voltages.
By the way, the board has TVS (P6KE220C) also for the surge suppressor.
So you are not getting 120VAC at the two pin of the MOV UA101? Remoev and reinstall the fuse.
The line (HOT) is fed through one end of the fuse, the other end of the fuse is connected to one end of the MOV, the other end of the MOV is connected to the Neutral. If you are not getting 120v right at the two legs of the MOV, you either have open fuse of bad solder joints. Fuse reistance reading using 200 Ohm scale?

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Thanks for the replies. Here are some pictures as requested.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Can we see the pictures of YOUR board? Both sides of the board and around the area that you have checked the AC voltages.
By the way, the board has TVS (P6KE220C) also for the surge suppressor.
So you are not getting 120VAC at the two pin of the MOV UA101? Remoev and reinstall the fuse.
The line (HOT) is fed through one end of the fuse, the other end of the fuse is connected to one end of the MOV, the other end of the MOV is connected to the Neutral. If you are not getting 120v right at the two legs of the MOV, you either have open fuse of bad solder joints. Fuse reistance reading using 200 Ohm scale?

Have removed and re-installed fuse. I get continuity across fuse, so I assume it is good. Based on what you said, it would appear I do not have voltage across the MOV. I'm puzzled, because the solder is there as you can see. Voltage at the first leg directly off the neutral trace, but not on the other side, so no voltage at fuse.

[budm]

Re: Toshiba 32AV502U fuse blows

There is not that many connections in that areas, something is being overlooked. Resistance reading of the fuse?

[budm]

Re: Toshiba 32AV502U fuse blows

Resolder connection at the L, N of the AC input connector, fuse holder pins, TH101 (in rush current limitter) pins.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Thanks Budm. I set my meter at 200 ohms , and got a reading of 3 across the fuse. Do you have any suggestions or links as to how I should properly resolder? I have a solder sucker and a 40 watt (i think) iron with a basic base station. It's a weller setup with a 1-5 adjust for heat on the station.

[budm]

Re: Toshiba 32AV502U fuse blows

Just heat up the old joints and add new solder to the joints.
I expect the fuse that large current rating to have less than 1 Ohm reading, unless you test leads have very high resistance. Meter's battery is good?

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Meter battery is good. Are you saying it's possible even with continuity the fuse could be bad? I gather you also are saying that the MOV is not likely to be bad and open?

[budm]

Re: Toshiba 32AV502U fuse blows

MOV should read open, it is connected between Line and Neutral, it should on conduct only when the voltage exceed the breakdown voltage of the MOV. The TV will still function without and surge protection devices installed, they are for protection, not for operation of the TV.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

MOV should read open, it is connected between Line and Neutral, it should on conduct only when the voltage exceed the breakdown voltage of the MOV. The TV will still function without and surge protection devices installed, they are for protection, not for operation of the TV.

Going to retest again and try to understand this. I realize it's second nature to you, but I'm having trouble getting it

Looking at the board, it would seem that I could have a problem or multiple problems down the circuit? I say this because from neutral at the power source, the board traces to TH101 and UA101 varistors. I have power on both sides of TH101, but haven't checked further down the circuit. Am I correct that no power/neutral on the other side of UA101 could be because of another problem after TH101?

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Going to retest again and try to understand this. I realize it's second nature to you, but I'm having trouble getting it

Looking at the board, it would seem that I could have a problem or multiple problems down the circuit? I say this because from neutral at the power source, the board traces to TH101 and UA101 varistors. I have power on both sides of TH101, but haven't checked further down the circuit. Am I correct that no power/neutral on the other side of UA101 could be because of another problem after TH101?

I wasn't testing properly. I think I now understand the varistor bridging hot to neutral, and being open. I do have power on both sides of the UA101. However, I think it's getting more complicated. Tracing down, there is power at several points along the circuit. The only thing I was able to identify is no power across CX101 (yellow box). Again, don't know if this is correct or not.

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Is this a clue? I tried to spot any visible damage on the board. There were some additional deposits around the large cap here that I scraped off with fingernail. I think I have power leading up to this cap.

[tom66]

Re: Toshiba 32AV502U fuse blows

Did you use AC or DC voltage?

[tucocaps]

Re: Toshiba 32AV502U fuse blows

Tom, I am testing with AC voltage, but not sure how to test much beyond the first few points on the hot side. I did test DC at the plug, and appear to have nothing for 5 volt standby.

[tom66]

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?