Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

[caphair]

I have this Klipsch Pro Media computer speakers that I originally found a blown mains fuse and two shorted switching mosfets.

Has all kinds of glue on the board covering the daughter board and secondary side so can't really test much but I did find a schematic for it. Any help would be appreciated

http://www.thompdale.com/bash_amplif...ic-986x707.gif

[ReeceyBurger123]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Heres a tip remove that glue ! It becomes kind of conductive and causes issues.

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

How? There's SO much of it

Does it get conductive to the point that you can ohm test it and see a reading or?

[RJARRRPCGP]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

That's the same kind of glue that CWT used in my 2003 True 430.

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

How do I clean it off? And/or determine its the root cause?

[stj]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

scrape it off with a small flat-ended screwdriver.

but leave the coils alone - too much chance of damaging them.

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Ok so removed most of the glue and before simply soldering in a new fuse and two blown mosfets, I tacked on wires to the driver ic's Vcc and Com with 11v from adjustable supply.

I'm only seeing frequency on one of the MOSFET gates (LO as shown in the schematic) nothing on the other gate (HO). Im not sure if that's normal or if both should be receiving a freq at same time.

Does this conclude the ic is good or?

Here's what I'm measuring:

[budm]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Do the blown MOSFETs have resistance between Drain and Gate which will take out the drive output of IC U1.

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

The blown mosfets measure 0 ohms in any gate, source, drain configuration

[budm]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

The blown mosfets measure 0 ohms in any gate, source, drain configuration

Then the IC is damaged, you need to check those resistor/diode network on the Gate pin to make sure they are not damaged either.
BTW, the AUX winding on this one is T1:2 PIN 1 and PIN 6. for generating running DC (D3, protection resistor R10, filter cap C13), same concept as other SMPS power supply.
SMPS IC IR2153

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Ok just to verify, was I testing resistance between drain and gate of blown mosfets in circuit or at their pins on the circuit board?

Also I'm still bit confused about the AUX of a transformer. Is AUX voltage generated on the secondary side (opposite of primary windings of T) but the pins are routed to the "hot" side of the circuit board?

[budm]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Ok just to verify, was I testing resistance between drain and gate of blown mosfets in circuit or at their pins on the circuit board?

Also I'm still bit confused about the AUX of a transformer. Is AUX voltage generated on the secondary side (opposite of primary windings of T) but the pins are routed to the "hot" side of the circuit board?

What resistance do you get when tested off the board?

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

0 ohms in any direction. Does that usually means blown ic when you get that reading?

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Also did my powering the ic externally and those measurements mean anything? For future reference

[budm]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

0 ohms in any direction. Does that usually means blown ic when you get that reading?

The IC was more likely has the Gate drive output damaged when you have shorts between Drain and Gate due to high Voltage from power supply dumped in to the Gate drive pin of the IC, that is why must check the resistor and diode on the Gate pin also as shown in the diagram

[budm]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Also did my powering the ic externally and those measurements mean anything? For future reference

R7, D1 supply the startup Voltage to the VCC so you really do not need to use external power supply to start the circuit, beside you are dealing with the hot primary side so what ever you use it must be isolated power supply that does not have output that is connected to the Safety GND.

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

R7, D1 supply the startup Voltage to the VCC so you really do not need to use external power supply to start the circuit, beside you are dealing with the hot primary side so what ever you use it must be isolated power supply that does not have output that is connected to the Safety GND.

I used external psu because I couldn't test with just plugging in. The fuse blew and when I tried powering without the mosfets to test ic the thermistor went bad

[budm]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

I used external psu because I couldn't test with just plugging in. The fuse blew and when I tried powering without the mosfets to test ic the thermistor went bad

So the TH1 was OK, but the fuse was blown due to shorted MOSFETS? I cannot see how the TH1 will blow if the MOSFETs are not installed unless the bridge was also shorted out.

[caphair]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Fuse and mosfets went first. I connected ammeter in fuse location and powered on with mosfets removed to see current draw/try testing ic operation but thermistor blew instantly. So decided to try powering ic externally

Friend said because there's voltages on the gates after powering ic externally that means the ic is bad? Wouldn't voltage be there in normal operation to turn mosfets on?

[budm]

Re: Klipsch Pro Media 2.1 Speakers - Keep blowing mosfets

Fuse and mosfets went first. I connected ammeter in fuse location and powered on with mosfets removed to see current draw/try testing ic operation but thermistor blew instantly. So decided to try powering ic externally

Friend said because there's voltages on the gates after powering ic externally that means the ic is bad? Wouldn't voltage be there in normal operation to turn mosfets on?

When the power MOSFETs are removed, then there will no longer be any heavy load to cause the TH1 to blow like that, shorted bridge will be the one or shorted Caps.
The Gate drive outputs will be switching ON and OFF at high frequency not steady DC.