bash amp repair!!!
i havent tried this yet but i hope this helps out a little. my promedia 5.1 sys. is also dead. amp works with sub only. seems that the MOSFET switches are dead. heres what to do....
this solution is for those of you with the problem of the Satellite speakers dying or cutting off and on, but the SUB is ok. This solution probably also fixes those systems which have the opposite problem: The SUB cutting out or dead, but the Satellites are ok.
Both SATS & SUB use identical components (chips) for power switching, but are on opposite sides of the same board.
OK, here what you’ll need to do
You’ll need to know basic soldering, so you’ll need a soldering iron with a fine (small) tip, solder, and soldering flux. Also get a solder sucker to remove the old solder. Don’t use the copper braid stuff to remove it; it takes too long to heat up and that extra time can heat damage your board’s components.
PARTS NEEDED:
Quantity 2: high speed MOSFET switches, part number IRFZ44N. Part number IRFZ44 can be used as well. Equivalents from other suppliers will work too.
These part numbers are equivalent to the NTE part number NTE2395. Go to
www.NTEINC.com and use the cross reference. There you can read the spec sheet if you’re into that sort of thing. There, also in the specs, you can see a drawing of the part if you need a visual clarification. Click on the parts distributors in your state link to find parts suppliers nearby. I found a store nearby who had the IRFZ44 chips. There’s also online distributors, but beware online of the minimum order; that will cut into your savings!
This NTE site is a favorite for “OLD SCHOOL” component level electronics troubleshooters like me! I’m not really “old” though, I can still dunk a basketball! (occasionally).
!!!!!!!!!!!!!!!!!!!Remember to unplug your power cord 1st!!!!!!!!!!!!!
The board you’ll be replacing parts on is the one containing the BASH circuitry. From here on I’ll refer to it as the crossover board. You can identify it by looking for the two little boards on it with the word “BASH” on the outside of each one. This board is the “switching” part of this switching power supply. This also is the signal crossover board; it separates the high and low frequencies. Notice the 2 big copper coil wound inductors, just like the crossovers found in car and home speaker boxes. This board also ties the low level preamp signals from your PC, to the high level amplifier circuitry of the Klipsch system. You can find this board by following the Red & Black wires that daisy chain across the top of the surround (SAT) boards back to where they start. Again it’s the board with the 2 smaller boards with the words “BASH” on their sides. To remove the crossover board, unscrew the 2 screws on the outside cover. You will also have to remove the 2 sets of Red & Black wires from each side of the crossover board. Label the wires accordingly. The words, SUB (+) & SUB (-) are on the board next to one heatsink, SAT (+) & SAT (-) are next the other. I will be referring to these wires again in the next section.
The crossover board has 2 identical circuits, one side is for the SATELLITE speakers, and the other side is for the SUBWOOFERS. You can figure out which side you need by looking at the Red & Black wires mentioned above. The daisy chained Red & Black wires from the 5 SATELLITE amplifier boards plug into the SAT+/-. The other Red & Black wires with SUB+/- go to the SUB amplifier board. Remember, the SUB board is the only board not connected in the daisy chain. If needed, cut the cable ties holding these wires to make sure you trace them correctly. These wires plug into both sides of the crossover board. Remember to look for SAT+/- & SUB+/- written on the crossover board itself. There are 2 black heatsinks (plates) on each side of the crossover board near each Red & Black wire plug-in. The heatsink near the SAT plug-in is for SATS and the one nearest the SUB plug-in is for the SUBS. On each heatsink there are 3 black clips. These clips have holes on one side of them. These clips hold 3 chips on to the heat sink. Remove the clips. I used a small flathead screwdriver by lifting (spreading) the clip and sliding it off. Under each clip are the following:
Quantity 2: MOSFET switches (a kind of high speed switching transistor). The number on these 2 chips is IRFZ44N.
Quantity 1: Semiconductor Diode. The Part Number on this one is U1520. (You will NOT be removing this chip). It’s hard to find it aftermarket (not impossible) so BEWARE!!
Hint: The MOSFETS have 3 legs; The Diode has 2 legs!!!!
Remove the heat sink by unscrewing it from the board (2 screws). The 3 chips will stay in place. Take care not to damage the cards with “BASH” written on them or you’ll probably regret it!
Remove the plastic liners from the back of the 2 MOSFET chips. You’ll need these for the replacement chips so do not throw them away, put them aside. You’ll notice there’s a white paste on them, this stuff is heat sink compound, available at any Radio Shack. I just re-spread & re-used the compound already on the liners and chips.
Removing the 2 MOSFETS, Part Number IRFZ44N:
I found it easier to just bend them back and forth until the legs snapped off. That way they are out of the way to get to at the solder joints. You’re going to heat the solder joints up. Put flux on the joints before you heat them. With flux, they will heat a lot faster causing less damage to the board. Suck the points clean of solder & remove the broken off legs using the solder sucker and a small needle nose pliers or tweezers.
Installing the new MOSFET chips:
Push them through the solder holes making sure the backs of the chips (silver side) are towards the “BASH” cards, identical to the U1520 diode chip. If you put them in backwards you’ll probably regret it!!!
Make sure the height of the chip is about the same as the U1520 diode chip. It doesn’t have to be perfect, but be in the ballpark. I did this by bending the legs on the solder side (back side) of the board when the height was correct.
Solder the new chips on to the board. Solder on the back side only. Remember to dab flux on the legs and solder points first, this makes the solder flow fast and heats up the replacement chips less. Add new solder to the tip of the soldering iron only, not directly to the legs. This reduces the heat on the new chips. Touch the soldered tip of the iron to each leg of the chip. With flux on the legs, the solder will quickly flow into the solder joint. Add more solder to the iron as needed.
Remember to cut the extra bit of leg off after each soldered joint when you’re done. You don’t want the legs to bend & touch or you’ll probably regret it.
Viola! You got yourself a repaired crossover/switching board, (you repaired the switching part) and you saved some time & dough $$!!
Re-install the heatsink and liners. Reconnect the plugs and remount the board.