Quote:
Originally Posted by Gradofan2
Did that help much... does the fan kick on less often?
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Not really, but it makes me think that it helps.
Like buying life insurance - does you no good but makes you feel better.
I have replaced them twice and now do not touch the tubes in the amp until it has been off for 12 hours or more. This allows all power in the circuit to dissipate. Here is how to replace a mosfet:
Be careful handling mosfets - can short them easily with static from your fingers.
To remove mosfet, first remove bottom plate. Then remove the fan (don't lose the 4 screws and nuts holding it in) to allow you to put bottom cover aside, or if you prefer, disconnect two wires that run from fan through the side plate cover, to the front of circuit board where it plugs in. Unplug it (may be difficult, some plugs have a vinyl glue covering) then pull it through the side and out the back, and put aside.
Remove 6 screws by the tubes and two screws holding the two Toshiba K1529 mosfets.
Lift cables (on each side of circuit board) out and up from the sides so the main circuit board can be lifted up from the rear where the mosfets are. Lift the board up allowing the front to remain down - tilt it up at the mosfet end. Put a screwdriver in, at the middle of the rear of the board, to prop it up at the rear so it is elevated an inch or so.
The installed mosfets have a insulator between the frame and the mosfet body, and have a small lock washer, then a larger flat washer, under the screw holding it to the frame. Don't lose any of these.
Attach a bare ground wire to your wrist that connects to the ground of you AC wall inlet (not the hot pin) and to the frame of the amp, when working on the amp's mosfets, or when handling new mosfets. This will prevent a static charge from your skin that could short the mosfet and ruin it. Do not handle mosfets unless you are grounded.
Now, snip each of the three pins of the bad mosfet, underneath the circuit board, close to the mosfet body and take the bad mosfet out. Then use needle nosed pliars or a tweezer to grasp the mosfet pins remaining in the circuit board while applying a solder iron on top of the pin, and gently pull the pin through the borad - be gentle so as not to damage copper cylinder inserts in each board hole.
Use a grounded soldering iron of about 40 watts with a pointed (not chisel or screwdriver) tip, along with a separate solder (vaccum) sucker, to remove all the solder you can from the mosfet pins (three per mosfet) from the top. A desoldering iron may also do this. You need the pin holes to be open and clear with no solder in them. If your soldering iron is not a 3 prong plugged grounded one, then touch the tip to the grounded frame of the Bada, to discharge any static, each time before touching the tip to the Bada/'s circuit board.
In putting in a new mosfet, take a new mosfet and (with a ground wire attached to your body) bend the three pins near the body of the mosfet so that they bend bend up (90 degrees) and toward the other end (another 30 degrees or so) of the mosfet body. Use two small pieces of tape on the sides of the mosfet insulator piece to attach the insulator piece to the bottom of the mosfet body, so the insulator will not drop off of it. Put the mosfet body down under the circuit board with the pins sticking upwards and slide the pins under the board, then upwards through the three holes of the board. Bend one (or more) pin tip to hold it in place so it won't slide out. Make sure the insulator piece is in place. Lower the board and screw the mosfets firmly in place, allowing the pins to bend in place as you force the mosfet in position to be screw it in place.
Take two 15V diodes and slide one each in the two outside holes of the mosfet pins so that ends of the diodes with the black bands is sticking upwards, away from the mosfet body. Do this for each of the two mosfet bodies.
Put the 6 screws besides the tubes in, and attach the board.
Solder each pin (with the diodes in place). Briefly touch the tip of the iron to the frame edge in order to ground it and remove static, each time you go to solder a connection. In soldering the pins of the mosfet, try to get the solder to wick down the pin to the other side of the board for good conductive contact with the other side of the board. Now join the two ends of the diodes together (where they come from the black banded side of the diode body) and solder the joint to bridge the middle pin of the mosfet.
Put the two cables on each side in place so they are inside the bottom plane of the frame. Run the wire from the fan through the side plate to the front of the board and plug it in. Replace the bottom cover.