Help in identifying capacitor?

[macs70GLT]

Hi,

Just found your forum last night.

I'm on a quest to repair my Klipsch subwoofer which has been blowing 2 amp slow-blow fuses.

Took it apart & observed the amp circuit with a new fuse & saw it shoot a spark out of this thing, which appears to be a capacitor.

Can anyone help me identify & locate a replacement for this part?

Also - what other components should I be looking at on the amplified circuit board? I had a couple of years of electronics in High School but that was decades ago.

I can post a picture of the amp circuit board tonight it that would help.

Thanks

Mike

 

[duffy]

Old style 0.1μF ceramic cap. Doesn't say what the voltage is, but here's one that can withstand 500V (almost certainly overkill) and costs seventy-five cents -
https://www.mouser.com/ProductDetai...ZE/3ll%2bp/aFiAYje79cQnc0064LIqhYLNRmWeQ8GRE=

One shorted filter cap like this can certainly blow fuses. With any luck, this is all it is.

 

[macs70GLT]

Old style 0.1μF ceramic cap. Doesn't say what the voltage is, but here's one that can withstand 500V (almost certainly overkill) and costs seventy-five cents -
https://www.mouser.com/ProductDetai...ZE/3ll%2bp/aFiAYje79cQnc0064LIqhYLNRmWeQ8GRE=

One shorted filter cap like this can certainly blow fuses. With any luck, this is all it is.

Thanks Duffy,

Here is a picture of the board. The capacitor was located by the outline labeled TH3, the outline above it labeled C22 was unpopulated.

Would the SCK designate the voltage &/or tolerance?
Lastly - since neither the board or capacitor are labeled it is unpolarized right?

Thanks again - I have tried both Radio Shack & Fryes electronics & the employees at both stores could not identify this.

Mike

 

[macs70GLT]

Thanks Duffy,

Here is a picture of the board. The capacitor was located by the outline labeled TH3, the outline above it labeled C22 was unpopulated.

Would the SCK designate the voltage &/or tolerance?
Lastly - since neither the board or capacitor are labeled it is unpolarized right?

Thanks again - I have tried both Radio Shack & Fryes electronics & the employees at both stores could not identify this.

Mike

sorry, having trouble uploading this picture

View attachment 64084

 

[duffy]

Hmm... I recognize that section - it's line filters and a bridge, the square caps with the voodoo symbols are called X and Y caps - but "TH3" should be a input surge limiting thermistor. You sure it came out of that spot? How thick is it? Here's a .1μF ceramic cap for comparison -


That spot on that board, with that notation, would be for a surge-limiter. One of those is thicker than a .1μF ceramic cap. it also isn't as likely to blow the fuse the way a shorted filter cap would because it's in series with the supply rather than across it.

Can we get a shot of the back of the board? A surge-limiter will lead straight to that bridge marked D6, and the other leads to the red parallel-mode filter coil. If it's wired like that, it's definitely a surge limiter.

The bad news is this probably isn't the real problem. Check the big main filter caps, see if the tops look swollen or split. That one's easy. The other probable thing would be a blown driver somewhere.

Good news is you can replace an inrush surge limiter with a wire for a testing. Have spare fuses on hand - it's mainly there to stop the fuse from blowing from the inrush current surge when the main caps charge. Start with the power supply unplugged from the amp section, just powered alone, and see if the supply blows fuses twice in a row. First time might be surge current, second time won't.

 

[Nigel Goodwin]

Assuming that capacitor is actually part of the mains filter, then the PSU will work perfectly without it - unless something else is duff.

So I wouldn't bother struggling to source a replacement until after you've confirmed it works with the capacitor removed and the blown fuse replaced.

 

[macs70GLT]

Hmm... I recognize that section - it's line filters and a bridge, the square caps with the voodoo symbols are called X and Y caps - but "TH3" should be a input surge limiting thermistor. You sure it came out of that spot? How thick is it? Here's a .1μF ceramic cap for comparison -
View attachment 64104

That spot on that board, with that notation, would be for a surge-limiter. One of those is thicker than a .1μF ceramic cap. it also isn't as likely to blow the fuse the way a shorted filter cap would because it's in series with the supply rather than across it.

Can we get a shot of the back of the board? A surge-limiter will lead straight to that bridge marked D6, and the other leads to the red parallel-mode filter coil. If it's wired like that, it's definitely a surge limiter.

The bad news is this probably isn't the real problem. Check the big main filter caps, see if the tops look swollen or split. That one's easy. The other probable thing would be a blown driver somewhere.

Good news is you can replace an inrush surge limiter with a wire for a testing. Have spare fuses on hand - it's mainly there to stop the fuse from blowing from the inrush current surge when the main caps charge. Start with the power supply unplugged from the amp section, just powered alone, and see if the supply blows fuses twice in a row. First time might be surge current, second time won't.

I'm attaching a picture of the back of the board. The TH3 does connect from the D6 Bridge to the parallel coils. The component, TH3 is about 4.5 mm thick where the wires attach to the face.

I have extra fuses so can do some testing with a piece of wire, but I'm not clear on how I can power up just the power supply but not the amp. The board (picture attached) has both the terminals for the speaker (amp output) and the terminals for the power from the switch/fuse thing.

Also - what does a driver look like? If it's a surface mount component with designation "D" followed by a number there are a number of those. I can't find any other components on the board that look overheated. Except there is some type of yellowish glue on several things that turned brown in a couple of places - not sure if it is normal coloring from slight heat or if the components are overheated.

Please let me know how I can power up the power supply w/o the amp. I would rather not risk blowing the whole thing if that may result from putting a wire in.
View attachment 64134View attachment 64135
Thanks again

Mike

 

[duffy]

Sure enough, the connections show it is NOT a capacitor, but a surge-limiting thermistor! I didn't realize it was an "L" shaped board, I thought the amp section was separate, which is why I suggested disconnecting them.

The big caps don't look swollen or popped, so a bad driver is looking more probable. The drivers are attached to those heatsinks. The power supply drivers will be bolted to that black anodized heatsink in the middle. The audio drivers are sandwiched in the aluminum heatsink on the right.

In light of this, here's Plan A:
1. Check the audio drivers to find a bad one
2. Replace it, replace the thermistor
3. Power the whole thing up again

Got multimeter? Put the meter in "diode check" mode, and start looking at the junctions on the drive transistors, swapping the + and - lead to check each junction *twice*. Leave them soldered in the board for now, with any luck the bad one will show itself with a little careful checking and comparing. The drivers are probably MOSFETS, so there will be 3 pins - gate, source and drain. Your diode check should show an "open" either way to one of the pins on the left or right side of the package to the other 2. This will be the gate. A mosfet often blows a gate short in failure, so a connection that shouldn't be there is a giveaway.

Here's the main thing: You are looking for the odd one out. There's 4 audio drivers, probably 2 P-channel and 2 N-channel (or maybe all 4 are N-channel), and probably only one of them is blown. So by comparing readings (write them down) there's an excellent chance of finding the bad one.

 

[pfofit]

Any Sck devices I've seen are NTC thermistor inrush current limiter.

Found this one datasheet **broken link removed**

Yours is probably 10 ohms cold that can handle 4 amps.

As has been stated, since it blew its brains out it most likely saw more than 4amps and it is most likely the result and not the cause.

cheers

 

[macs70GLT]

Thanks Duffy,

I took a number of measurements - posting in the attachment here.

The one driver labeled Q7 seems to be the culprit with several "open" measurements. Among the others there seemed to be 2 pairings with consistent measurements. One of the drivers in of the first 2 had very low readings of 0.002V. But it was consistent - maybe ok?

Thanks again for the help. I did finally find something last night showing SCK Thermisters, have not checked the link above yet from pfofit but imagine it's the same.

View attachment 64159

Mike

 

[duffy]

Q7 might be it, get it's part number. Not sure what that 5th one is for, though, a bridged amp is only 4 drivers.

The top one with the real low .002 readings also looks suspect. It might be driving the transformer, which can short out some of the readings. You will have to remove it to check it properly.

 

[ectt]

that should be a PGT or NGT therisistor, resistance value related to temperature.
usually found in ATX psu, near the AC pins part.
code on it will help u find its value.

 

[redpackman]

Dis you ever get the problem solved. I have a Klipsch Sub-10 amp that's continually blowing fuses. It has at least 3 bad mosfets and the therisistor needs to be replaced. So: Did you fix the amp and did you find if the therisistor was a 4 amp 10 ohm or a different value?