Buzzing noise on RF 250.2

[Perry Babin]

OK, 6 of the 540s are showing a short. Measure the resistance between the first leg and the second leg of the 540s. If one of each group reads significantly lower than the other two in the group, it's the defective one.

If there is only one defective one in each group, you can cut ALL 3 legs of the defective one free from the board and the amp should power up (if the supply isn't blown). This will tell you if there are other problems.

Remember to power it up through a 10 amp fuse.

[tavo04]

While taking the mosfets out, I "accedentaly" pulled a few of the solder holes along with a tiny peice of plated through hole trace. And now when trying to install new fets the there is nothing where to solder them to. Is there any repair holes i can purchase and istall myself? Also, after reading a few posts, when replacing burnt fets is it a good idea to replace the resistors? If so what is the value? Please advise thanks.

[tavo04]

Also how could i go about posting pics?

[2pist]

Are the legs on the fets long enough to wrap around to the trace? If not you could solder some bare wire from the trace to the legs. Not pretty but it works in a pinch.

[Perry Babin]

Any of the following will provide reliable connections. If the broken connection is between the FET and a surface mount resistor, you should use a small flexible wire so no stress is put on the SMD pads. The insulated wire below is from a computer IDE cable. It works well for low current connections. Using a drop of adhesive to hold the wire will prevent the wire from breaking (in case the amp is subjected to heavy bass/vibration). For connections that will have to pass significant current, you will need to use something that can handle more current than the insulated wire shown. The method used on the red board below is suitable for high current.













To post photos, you can use the browse button below. There are strict limitations on size (file size and dimensions). If the file is too large, you will receive an error message. If you get the error message, there's a good chance that the message will be lost. Either post the photos and text in separate messages or copy and paste the text of the message into a text editor before submitting so it's not lost.

The photos above were uploaded to a server. I used the IMG button to insert the URL of the images. You can do this with various photo sites (flicker, photobucket, shutterfly...).

[sdoom]

Perry showed some nice pictures of how you can install the transistors and make the connections if the lines are broken. If there was no chance of fixing the lines Perry showed you can cut out a small part of the curcuit board completely and insert (using heat resistance glue) a small part of standard printed curcuit board from Radio Shack.

If you have your mosfets out off the curcuit board you can test the N-channel FETs with the following curcuit. (For P-channel FETs switch the diode next to the relay, the LED and also switch polarity of the power supply)