OCZ 700 Watt Bug Zapper Recap & Repair

[Sparkey55]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

oups!!
received my TNY278P (IC501) switching regulator this morning, so i installed it,
but as soon as i turned the power on, i heard a bang and saw some sparks inside the psu, the same part (ic501) had blown again, so i have to find what cause this

You should be using a series light bulb tester to reduce the voltage to the power supply. It would have saved the chip from utter destruction. Since the psu still has a short circuit the voltage would have divided between the bulb and the psu with the bulb having the greater voltage across it.

[Behemot]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

The voltage is not the most important aspect. The current limiting which the small-wattage bulb provides is important. A 60W bulb at 230 V has about quarter ampere going through which most power silicon handles.

[Sparkey55]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

The voltage is not the most important aspect. The current limiting which the small-wattage bulb provides is important. A 60W bulb at 230 V has about quarter ampere going through which most power silicon handles.

Your nit-picking is quite annoying and uncalled for. With a shorted psu most if not practically all the voltage will be across the brightly lit series bulb with only a few volts across the psu. We are assuming a supply source of 120 VAC. So if for istance the bulb sees 115 VAC and the psu sees 5 VAC well then the tester is doing its job.

[Behemot]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

You never know what is the internal resistance of shorted PSU…there are always losses on the silicon (bridge rectifier etc.), thermistor and so on. But it is never so close to zero.

Initially the voltage on the bulb is very low, if the current is high than it heats the filament and as its resistance increases it takes most of the voltage. But it still lowers the maximum current (usually the initial resistance is couple tens of ohms) so much the unit is able to withstand it for the short time before the current drops to minimum.

[Sparkey55]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

You never know what is the internal resistance of shorted PSU…there are always losses on the silicon (bridge rectifier etc.), thermistor and so on. But it is never so close to zero.

You just amaze me Sherlock.

[manthi]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

here's a picture of the regulator i soldered yesterday
can someone tell me if i fucked up, on the red arrow i notice i made a connection between the diode and the regulator leg,
what does the white line underneath means (no connection?)

[Behemot]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

I think it should be connected, otherwise the pin would be severed from the rest of the path. According to datasheet it is drain, those four common are source. But the diode may have been already bad. Or something else. Now when it exploded you have to check every component in that circuit, something else may went bad during the blast.

[manthi]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

thanks for the input,
i did some more testing and found 2 mosfet 20n60c3(q701 q702) when i set my multimeter to 200 homs, i get 5.5 between the gate (pin 1) and the source (pin 3), it means it is shorted no?

[stj]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

maybe, did you test them on the board, or removed first?

[manthi]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

maybe, did you test them on the board, or removed first?

on the board
now i removed them, and i did this test

http://itrepairguide.com/how-to-test...th-multimeter/

when i connect the black probe to the drain and red probe to the source i get a reading of 623 (continuity setting) on both mosfet, but when i try to charge them up, black probe to drain, red to gate for a few seconds, when i move the red probe to the source, i do not get any beeping, and the multimeter give me a value of 127 (both mosfet)

i try this on a working fu9024n, and it is beeping.

what do you make of this?

[stj]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

leave it for now and go meter the pads on the board.

[manthi]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

leave it for now and go meter the pads on the board.

not sure what you want me to do with the pads, you means the pads the mosfet connects to the pcb?

[stj]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

yes, see if the short is still there.

[manthi]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

yes, see if the short is still there.

ok i see, thanks for the clarifications, at the moment i put that psu aside , i am going to get back at it after the chrismass season.
have fun everybody

[Behemot]

Re: OCZ 700 Watt Bug Zapper Recap & Repair

I got the same model here, 700W. Similar situation: input cap was bad, I've replaced it. No big transistor or rectifier seems shorted. Stand-by rail outputs 5.16 V so that's OK, but it only twists when I try to turn on. Repeatedly. Lightbulb in series indicates no problem.

It's Sirtec platform for sure. I was also first thinking the FETs are bad, but they have 4R7 resistor between their gate and source pins which I think explains it. Or should I remove them as well to be sure? It would make sense something else was damaged because of the failed bulk capacitor…