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(Update: Apr 24, 2017)

Klipsch KSW-300 Subwoofer

I've had the Klipsch KSW-300 Subwoofer [SW] for about 16 years! And it has worked perfectly until recently. So time to repair it!

A short story. About 16 years ago, I decided to build my own SW by purchasing the parts/case/box/pwr-amp/etc from a specialty audio shop in Madison, WI. They had most everything including electronic parts and speaker "kits" for the DIYer. I believe they are gone as of today.

After doing the required homework to ensure that my design would work (WinSpeakerz Version 2.5.2), I purchased the parts. The cost was apx $500 which I justified as being a "top shelf" SW when complete. At the same time, I happened to see that a local electronics store was clearing out their Klipsch SWs. The Klipsch KSW-300 was on sale for $159.00. . . BION!

Well, I cancelled the order with the Madison store and bought the Klipsch. I think I did ok!


Klipsch KSW-300 Subwoofer Repair

Klipsch KSW-300 Subwoofer

The SW weighs in at 76 lbs and it's solid! It doesn't look like much but, when you think about it, it doesn't have to!

The KSW-300 specs are shown here:
It definitely produces enough power to "vibrate" the 12 sq ft concrete slab that supports my raised family room. The famous Star Wars - Attack of the Clones - track #45 [Duel with Dooku] where they both fight with their light sabres. The low frequency power is amazing.

A Little Hum . . .
The other day, when near the SW, I heard a low level hum. You have to be close [apx 2 ft] to the SW in order to hear it but it's there!

I checked the 15" speaker with my hand and nothing could be felt. So what does that mean?? It's obviously not right but it still works ok . . . for now. Of course, knowing me, I can't have hum so time to find out what is wrong.

I searched the Internet for some clues and found a "online-repair-site". I'm sure you know what I mean. The "owner" pops up and asks what he can do. He volunteers the following answer ". . the output stage is shorted so that produces an extreme load on the power supply, so it hums."

Searching further, I found a great picture of the KSW-300 SW's Control Panel and Power Supply. The input caps look to be large, both in size and value. Since it's humming, that is the most likely failure mode, namely dried-up caps! After 16 years, you'd be dry too!

KSW-300 Insides . . .
Time to take the SW apart. To remove the PS panel, loosen the twelve (12) screws that hold the panel to the case. Use a small flat blade screwdriver to loosen the seal so that you can lift out the PS panel. After its removal, the backside looks like this.

There is the copious use of insulation to prevent resonances in the MDR cabinet. The small Molex pin connector plugs into the PS PWB board. The two RED wires are the AC input from the 120Vac power plug located on the Control Panel.

The 4" ID x 15" length port lowers the cabinet's resonant frequency down to 30hz . . . .
Power Supply Panel Removed . . .
The PWB is only two sided w/o a ground plane so the board come out easily, by removing the four (4) screws that hold it to the Heat Sink [HS].

To gain access to the BOTTOM of the board, you will need to remove four (4) screws that hold the board and four (4) metal 'bars' that hold the power transistors down ensuring good heat transfer into the HS. These screws are accessed from the outside portion of the HS and shown in the picture. Next, there are three (3) screws holding the smaller driver transistors that must be removed. These screws are loosened from the board-side of the heat-sink.

The caps have FOUR (4) leads so you're in for a treat to remove them. I used an 800F iron with a medium tip and solder wick employing standard de-soldering techniques. After doing so, the board looks as shown.

When the pwb is lifted up and turned over, the output transistors had only two (2) pads of thermal grease as shown in the BLUE rectangle in the picture. That is incorrect! I recommend that you use four (4) pads under each of the large transistors being careful to not use too much. Thinner is better than thicker. You do not need to add any to the HS b/c when the transistors are 'clamped' down, the paste will spread out due the clamp pressure. Of course, be sure to clean off the old thermal grease on the HS using acetone.

I added apx 8 inches of additional lead length to both speaker wires. To say they were a bit too short would be too kind! When the PS Assy is lifted up, the speaker wires are pulled off the speaker's terminals.
Caps Removed . . .
The removed caps are a bit different than what you are probably used to. There are four (4) terminals; 1-positive, 1-negative, and two (2) are just there for "stability". Those leads are not connected internally but are supposed to provide a stable mounting for the cap.

Both caps measure apx 82uF . . . far short of 10000uF! Look carefully and you can see that both have "oozed" a bit!

I was curious about the two (2) NC terminals, so I cut the top off to see what mysteries would be unvailed. As the right picture shows, the two pins have no connection.

Finding a replacement cap is somewhat difficult b/c of the four (4) pins. This cap is immediately a specialty item. Even Mouser, which has EVERYTHING, doesn't carry that cap. There are some sources but you need to dig in order to find them. I bought two (2) from tedss for $19.99.

If you can't find the four (4) leaded version, you can substitute a "standard" two (2) pin radial cap but it MAY be difficult to find the required capacitance (10,000uF) *and* the operating voltage (80V) in a package that will fit the 35mm dia and 50 - 60mm height.
Oops . . .
After inspecting the hole pattern on the PS pwb, I noticed that one of the "structural" leads was tied to the "+" terminal. The Marcon spec for the caps (and all other manufacturers) state that you shouldn't tie the structural pins to any potential. Those pins are there just for mounting integrity.

Vishay/Marcon Specs:
An easy fix is shown in the picture; cut the trace either side of the terminal and that isolates the pin from any potential. Make sure you cut as shown by the two pointer-lines. You have to cut clear through the front and back trace. Use an ohmmeter to check that it's open. Since the trace connection is in parallel there's no need to add a jumper. The insert shows the BEFORE cuts are made. Note that the second cap was installed properly with both structural pins left floating.

If you inspect the hole pattern carefully, you'll see that there are "pads" to mount a "standard" radial lead capacitor shown in the blue circle. It appears that the designers were actually paying some attention looking to the future.
It Works . . .almost!
The two caps arrived today and it took an hour to install the caps, clean the old thermal grease off the transistors, use a "drop" of new thermal grease in the four (4) power transistor areas, install the board and tighten the power transistors down to the HS.

Then install the PS Assy into the SW. The lengthening of the speaker leads paid dividends b/c the PS assy could be rotated around to install the Molex connector from the Control Panel w/o pulling the speaker leads off the 15" driver.

Of the 12 screws, one was missing!!! Found it attached (magnetically) to the bottom of the driver! Used the screws to attach the PS Assy to the SW cabinet. Then connected the AC plug and the LFE input from my receiver. Turned it on . . . and . . . just music . . . w/ just a little bit of hum!

The hum level was really low level but you could hear it if you put your ear next to the PS Heat Sink assy. Also, noticed that the VENT tube was loose?? Not sure how that happened but it would best be fixed by removing the PS HS assy allowing full access to the internal vent tube assy.

PS 12V Regulator Caps
[ I don't have a schematic of the either unit (Control Head and PS Assy] but the layout and choice of ICs makes it somewhat transparent for some areas such as the power supply.]
On the PS board, I found that ALL of +/-12V regulator caps were bad. One of the 470uf measured open, the other measured 41uf! The regulator output filter caps, 100uf, measured 6uf and 32uf respectively. So that's the source of the low level hum. I happened to have the required values except slightly higher operating voltage of 25V. This ckt has it's own transformer tap for the dedicated rectifier so the ckt can produce a "clean" +/-12V for board use.

The output VENT plastic end-cap worked loose so it needed to be firmly set back into place. That was easy and it is now stable.

All in all, not a difficult project. If your SW has hum, it's an easy repair. You SHOULD automatically replace the four (4) +/-12V regulator caps b/c if the main caps are dry, so will these.
Klipsch Repair Facility
The KSW-300 SW is no longer in production (stopped in 1998) and Klipsch has a designed repair facility; Sybesma's Electronics in Holland, MI. Phone (800-456-4265). The price for the repair of the KSW-300 SW is $120 with shipping from you extra. The return shipping is included in the fee.

I spoke with one of the techs and he was courteous but not very helpful except in generalities. I can understand that b/c they want the business for themselves. The repair fee is reasonable IMO. If the problem had been more complicated, I would have sent the SW for their repair.

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