TV Fuse Keeps Blowing - Electronic Circuits Projects Diagrams Free

aibelectronics · 7th May 2008, 11:50 AM

A surge tore my tv power supply fuse apart. I thought buying a new fuse will do the trick - it blew it as well. My troubleshooting took me farther to the Capacitor and the big guy said he was OK. The 4 diodes 2 were OK. So I was wondering whether the new 3A fuse I bought was too small?

I also series-ed the television with a 100W bulb, according to this site: http://www.repairfaq.org/REPAIR/F_smpsfaq.html a persistent problem in the PSU would make the bulb go very bright, mine didn't even light up at full load. My question what else could be the problem? Could I have wrongly connected something, switched polarity? I'm avoiding uprooting the regulator for the moment..

**Nigel Goodwin** · 7th May 2008, 12:05 PM

The power supply is probably blown - a large mains surge could have taken the transistor and/or IC out - or it may just have failed?.

aibelectronics · 7th May 2008, 12:41 PM

The series bulb test gave me the doubts, so I got a 5A fuse. I don't if that's too high? Curiously enough the manufacturers (Zaiko) didn't indicate a wattage/current rating for their television. The bulb didn't even light up!

crutschow · 7th May 2008, 05:32 PM

I don't understand. Do you have the bulb connected with a good fuse in place and it doesn't light? Yet when you connect it without the bulb the fuse blows? That doesn't seem correct. If the fuse blows, then the bulb should light.

aibelectronics · 8th May 2008, 01:03 PM

The transistor (a 2S4236) is off. It was short-circuited throughout. I got 2 new ones. When connected with series bulb the bulb went bright, reduced drastically then came up brightly again. I guess the Cap was charging at the time. The TV even came on although it would go off and come on again.

However on disconnecting the bulb and connecting directly to mains my 3.15A fuse blew. My transistor wasn't spared as well.

Now I've soldered a second transistor, but I'm yet to find the courage to connect direct to source again! Starts up with the bulb like before. What could be up? A weakened capacitor? Some fault elsewhere?

Need your i/p.

**Nigel Goodwin** · 8th May 2008, 03:09 PM

You need to replace every faulty component, blowing a second transistor may have damaged further components as well - a lot depends on the exact circuit, but a common cause is electrolytic capacitors drying out and going high ESR.

Error editted, thanks crutschow.

killivolt · 8th May 2008, 03:23 PM

Sounds like it's not oscillating right or not at the right voltage. Try looking at the regulator. Check all the diodes in around the flyback.

crutschow · 9th May 2008, 04:12 AM

Quote:

Originally Posted by Nigel Goodwin

but a common cause is electrolytic capacitors drying out and going low ESR.

Hate to be picky Nigel, (and I have a feeling you know this) but normally you want a low ESR (equivalent series resistance), the lower the better, especially for those caps used to filter switching regulator outputs. A resistance that goes low in a bad cap is the parallel (leakage) resistance.

**Nigel Goodwin** · 9th May 2008, 10:37 AM

Quote:

Originally Posted by crutschow

Hate to be picky Nigel, (and I have a feeling you know this) but normally you want a low ESR (equivalent series resistance), the lower the better, especially for those caps used to filter switching regulator outputs. A resistance that goes low in a bad cap is the parallel (leakage) resistance.

Sorry, a typo

Obviously it's HIGH ESR that is bad!.

aibelectronics · 16th May 2008, 04:47 PM

In a summary, there was another transistor in a darlington with the main power transistor. The capacitors were all OK. Changing the two transistors as well as the fuse did the trick. There's no satisfaction that beats the one derived from fixing a dead equipment...

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7th May 2008, 11:50 AM	(permalink)
aibelectronics	TV Fuse Keeps Blowing A surge tore my tv power supply fuse apart. I thought buying a new fuse will do the trick - it blew it as well. My troubleshooting took me farther to the Capacitor and the big guy said he was OK. The 4 diodes 2 were OK. So I was wondering whether the new 3A fuse I bought was too small? I also series-ed the television with a 100W bulb, according to this site: http://www.repairfaq.org/REPAIR/F_smpsfaq.html a persistent problem in the PSU would make the bulb go very bright, mine didn't even light up at full load. My question what else could be the problem? Could I have wrongly connected something, switched polarity? I'm avoiding uprooting the regulator for the moment.. __________________ Everybody can but not everybody will.

7th May 2008, 12:05 PM	(permalink)
Nigel Goodwin	The power supply is probably blown - a large mains surge could have taken the transistor and/or IC out - or it may just have failed?. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

7th May 2008, 12:41 PM	(permalink)
aibelectronics	The series bulb test gave me the doubts, so I got a 5A fuse. I don't if that's too high? Curiously enough the manufacturers (Zaiko) didn't indicate a wattage/current rating for their television. The bulb didn't even light up! __________________ Everybody can but not everybody will. Last edited by aibelectronics; 7th May 2008 at 12:44 PM.

7th May 2008, 05:32 PM	(permalink)
crutschow	I don't understand. Do you have the bulb connected with a good fuse in place and it doesn't light? Yet when you connect it without the bulb the fuse blows? That doesn't seem correct. If the fuse blows, then the bulb should light. Last edited by crutschow; 7th May 2008 at 06:25 PM.

8th May 2008, 01:03 PM	(permalink)
aibelectronics	The transistor (a 2S4236) is off. It was short-circuited throughout. I got 2 new ones. When connected with series bulb the bulb went bright, reduced drastically then came up brightly again. I guess the Cap was charging at the time. The TV even came on although it would go off and come on again. However on disconnecting the bulb and connecting directly to mains my 3.15A fuse blew. My transistor wasn't spared as well. Now I've soldered a second transistor, but I'm yet to find the courage to connect direct to source again! Starts up with the bulb like before. What could be up? A weakened capacitor? Some fault elsewhere? Need your i/p. __________________ Everybody can but not everybody will.

8th May 2008, 03:09 PM	(permalink)
Nigel Goodwin	You need to replace every faulty component, blowing a second transistor may have damaged further components as well - a lot depends on the exact circuit, but a common cause is electrolytic capacitors drying out and going high ESR. Error editted, thanks crutschow. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk Last edited by Nigel Goodwin; 9th May 2008 at 10:38 AM.

8th May 2008, 03:23 PM	(permalink)
killivolt	Sounds like it's not oscillating right or not at the right voltage. Try looking at the regulator. Check all the diodes in around the flyback. __________________ Truthiness Monkeys : Obedience, Ignorance, Fear.

16th May 2008, 04:47 PM	(permalink)
aibelectronics	In a summary, there was another transistor in a darlington with the main power transistor. The capacitors were all OK. Changing the two transistors as well as the fuse did the trick. There's no satisfaction that beats the one derived from fixing a dead equipment... __________________ Everybody can but not everybody will.