Klipsch ProMedia 5.1

**USchabon** · 06-12-2016, 04:11 PM

Re: Klipsch ProMedia 5.1

So I just started watching videos on how to test CAPS with a multimeter, but I can't figure out whether it is ok to test while they are still attached to a board. I guess you have to unplug for sure, but will you get a good reading without removing the cap from the board?

Because I followed this method and both of the big caps seem to give me a measurement that gradually discharges when I do this: https://www.youtube.com/watch?v=FDuN7QHn1-s

**CapLeaker** · 06-12-2016, 04:49 PM

Re: Klipsch ProMedia 5.1

the L7805 is a 5V regulator not a mosfet. You have a higher DCV going in and it regulates it down to 5V. The regulator you picked out is fine. Is the mosfet you are talking about the one that has no heat sink on it? Is it shorted or something?
To test electrolytic capacitors, you do that with an ESR meter. When in doubt with a measurement, test it out of circuit.

**USchabon** · 06-12-2016, 05:00 PM

Re: Klipsch ProMedia 5.1

Originally posted by CapLeaker

the L7805 is a 5V regulator not a mosfet. You have a higher DCV going in and it regulates it down to 5V. The regulator you picked out is fine.
second: you test electrolytic capacitors with an ESR meter. When in doubt with a measurement, test it out of circuit.

Hello Leaker! Thanks for popping in to help.

Just before you replied I noticed that those 3 mosfets are different... oops!

So I replaced the close up photo with one of the actual one that is missing the heatsink and I also edited my first post.

It reads "ST 0248 MOROCCO TIP31C". ST seems to be the brand STMicroelectronics", not sure what 0248 means, MOROCCO might be where they make them I guess, and TIP31C seems to be the actual part. I found this http://www.mouser.com/ProductDetail/...FUKUfgodEQkJ6g

Would you know how to test that part? If it makes a difference the multimeter I bought is this one: Craftsman 82141

**momaka** · 06-12-2016, 10:21 PM

Re: Klipsch ProMedia 5.1

Originally posted by USchabon

I have a multimeter, but don't know how to test CAPS. Could someone explain how to do that?

You *cannot* test capacitors with a multimeter.

I know some tutorials/videos on YouTube and elsewhere online show that you can... by setting your multimeter to resistance scale and seeing if you get "increasing/climbing" resistance numbers when "measuring" the caps. But that is actually not a useful test at all. When I started messing with electronics, that's how I thought you could test caps too... until I found some clearly bulged and leaking caps that passed this "test" as good and started reading more on the matter.

As mentioned in the Gateway 24" LCD thread, you need an ESR+capacitance meter to test capacitors *more reliably*.

Originally posted by USchabon

SECOND THING I NOTICED
I looked at all the caps and one is clearly bulging. These are the biggest and seem to be 820uF 200V. The one next to it on the left doesn't seem to be bulging, but I guess might as well do both..?

Those big caps have a plastic sleeve on top. Sometimes, that plastic sleeve will warp with age and/or heat. Press firmly on the plastic sleeve of the bulged cap and see if it "gives in". If YES, then it's just the plastic sleeve that's warped and the cap may not be bulged. But if the plastic sleeve is hard, that cap is definitely bulged.

I see those are G-Luxon brand, which is a brand not well regarded here... so yes, they could have failed.

Originally posted by USchabon

Here is what my very untrained eye found:

FIRST THING I NOTICED
I noticed there is a missing metal clip that was attached to 1 of these MOSFETS in the photo below. I found the metal heatsink in the subwoofer box, so I might be able to stick it on there with some thermal tape or something.

Loose metal parts falling from the circuit board - that's not good!

Shame on you Klipsch!!

Anyways, all goofiness aside, you can use regular PC thermal compound to create a good thermal transfer between the heatsink and the Transistor (it's actually not a MOSFET, but more on that in a bit). Then use glue to attach the heatsink to the PCB.

And speaking of glue... your circuit board appears to have the dreaded tan glue that likes to go conductive when it turns brown with heat and age. So try to remove as much of it as you can from any components or traces you see it on.

Originally posted by USchabon

It reads "ST 0248 MOROCCO TIP31C". ST seems to be the brand STMicroelectronics", not sure what 0248 means, MOROCCO might be where they make them I guess, and TIP31C seems to be the actual part. I found this http://www.mouser.com/ProductDetail/...FUKUfgodEQkJ6g

Would you know how to test that part?

Yes, TIP31C is indeed the actual part number. ST is simply one of the many companies that makes them.

That "MOSFET" is actually BJT (Bi-polar Junction Transistor). There are two types of BJTs: NPN and PNP. Your's is NPN.

These you *can* test with a multimeter. To do that for a *NPN* BJT:
1) Set multimeter to Diode / Continuity test mode (the setting with the diode symbol).
2) Put the red (+) multimeter probe on the BJT's Base pin and the black (-) multimeter probe on Emitter pin. You should get a reading of 500 to 800 mV (or 0.5 to 0.8 V.)
3) Now move the black (-) multimeter probe to the Collector pin. You should get a reading of 500 to 800 mV (or 0.50 to 0.80 V) again.

If you ever need to test a PNP BJT, simply reverse the multimeter probes. (That is, put red probe where you had black probe and put black probe where you had red. Readings should be the same.)

Since you are beginning to learn how to test these, I encourage you to post your reading here so we can verify your results.

Note that this test above is only valid for when the BJT is removed from the circuit. When testing in circuit (you CAN), note that the reading may be slightly *lower*. But in any case, you should never get a reading much higher than those listed above and if you get a short-circuit (audible beep or less than 100-ish mV / 0.10 V), then remove the BJT and test out of circuit again. Also, when out of circuit, you should *never* get any reading on your multimeter between Collector and Emitter pins, regardless of which way you have the probes.

Originally posted by USchabon

If it makes a difference the multimeter I bought is this one: Craftsman 82141

My uncle actually has that multimeter. I've used it quite a bit a few summers ago to repair a washing machine.
It's basically a standard "830" design, but built a much better than the regular cheapo Chinese versions you find on eBay elsewhere online. And the probes are decent and won't fall apart on you.

...
...
Last but not least, please post some pictures if possible. In particular, post a top- and bottom-side pictures of each board. That way, we can see what is going on in the amplifier and how components and boards are connected.

**USchabon** · 06-13-2016, 11:33 PM

Re: Klipsch ProMedia 5.1