Not any more i removed all of them and replaced them with 540a's. Im thinking one of the power supply fets went bad whn i installed the 540ns as output transistos
A blown power supply FET won't trigger the low impedance LED.
Did you reduce the bias when you installed the 540As?
How much current does the amp draw when you power it up?
Did you reduce the bias when you installed the 540As?
How much current does the amp draw when you power it up?
Yes, i reuced all 4 bias with 1/8 of a turn counter clockwise, the amp draws about 10-12'amps at idle. When i replaced the 540a's they Are not made by ir they have an "f" logo on them but they do say 540a. Not sure if the type of manufacurer makea a difference
The F is for Fairchild Semiconductor. They are a reliable manufacturer.
Are the same outputs getting hot as before?
Did you check the ones you removed to see if they were defective?
Are the same outputs getting hot as before?
Did you check the ones you removed to see if they were defective?
The same outputs are getting hot. As soon as i replaced the outputs that were getting hot, the low ohm light went off for about 2-3minutes, after that it turned back on. As soon as the low ohm light came on the amperage jumped to about 12 amps.
Clean up the solder connections with acetone and examine the solder connections and traces for the gate legs of the outputs. Use a lighted magnifying glass so you can see the finest details. Look for tiny cracks.
Were the outputs that you previously removed from that channel defective?
Were the outputs that you previously removed from that channel defective?
The outputs that i removed were defective, when i get home from work i will check out all the connections for the gate resistors. I saw in one of youre posts that some times the bias pots are installed backwards(clockwise is really counter clockwise, and counter clock wise is really clock wise), i havnt had time to check this out yet but maybe that is my problem. I did notice a very distinct hissing noise coming from the power supply area where the transformer are. This has happened both times i replaced the the 540a's, the noise dissapears once the low ohm light turns on and the amperage jumps to 12amps
I don't remember the bias pots being reversed in this amp.
If there is no excessive current until the outputs fail, it's unlikely that the bias is the problem.
The supply is probably making noise due to the excessive current draw when the outputs fail.
Do you have all of the insulators between the transistors and the heatsink?
If there is no excessive current until the outputs fail, it's unlikely that the bias is the problem.
The supply is probably making noise due to the excessive current draw when the outputs fail.
Do you have all of the insulators between the transistors and the heatsink?
I removed the clear insulators, cleaned the heatsink down, and replaced the insulators with a strip of kapton tape all the way across, and applied thermal compound to all the components that get clamped to the heatsink.
Is there any burr or rough spot on the heatsink that's possibly cutting through the kapton and shorting to the transistor?
Is it possible that the transistor tabs are touching the clamps when they're reinstalled?
Remember to check those connections on the gates of the outputs.
Is it possible that the transistor tabs are touching the clamps when they're reinstalled?
Remember to check those connections on the gates of the outputs.
Its a possibility, i will check everything that you mentioned out when i am home from work. I will double check to make sure all the transistors are infact properly insulated, and not shorting out on the spring clamps. Thank you for all youre help i really appreciate it. I will post back when i get home.
Finally got around to doing everything you mentioned. I took the kapton tape off sanded the heatsink down a little to make sure there was no roughness and re applied new kapton tape. touched up the solder joints on the gate resistors for the channel that was causing issues, and resoldered two irf540a's and everything was working well for about 15 minutes. Thats the longest it has worked properly. Now it currently is producing distorted audio with the low ohm light on.
Where did you buy the 540As?
Has any other work been done on the amp? Can you see evidence that any solder joints are not original? If so, where?
Has any other work been done on the amp? Can you see evidence that any solder joints are not original? If so, where?
I bought them from Arrow Electronics - North American Components (NAC) . Work was done before, the only thing i saw that has excess flux on the bottom is one IRFZ44N that is isolated by itself. When i called and asked what exactly they did to the the amp they said they replaced some components in the "auxiliary power supply"
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Check the outputs (they've likely failed again). If so, replace them and instead of soldering only from the bottom of the board, solder the top and bottom to ensure that the solder connection is good. Try powering it up again to see if it fails.
Did you examine the solder connections for the driver board in the failing channel to see if any were cracked or otherwise defective?
Did you examine the solder connections for the driver board in the failing channel to see if any were cracked or otherwise defective?
I actually soldered them from the top and bottom this most recent time that i replaced those output transistors. Also i powered the amp up with out the transistors installed to ensure that there were no other issues. Everything was working perfect minus the channel that didnt have the output transistors. I have not had a chance to examine the driver board thoroughly, all though i did re solder the 473 resistor on all of the driver boards. Do i have to de solder the driver board ? Or is it on a removable pinheader ?
Are there any resistors on the driver board that appear burned or discolored?
The driver board has to be desoldered but it's not easy to do without damaging the main board. Low temp solder (ChipQuik) makes it much easier.
The driver board has to be desoldered but it's not easy to do without damaging the main board. Low temp solder (ChipQuik) makes it much easier.
Just an update, amp is finally fixed. I cleaned all the pads for the output fets with acetone, soldered them from the top and bottom and amp has been working for the last 45 minutes under load 🙂 . Thanks for all the help perry!
Amp broke again. This time the output fets that were giving me issues are still working, but now the top two lights on the driver board for that channel went out and it causes audio output issues when bridged and for the rear section. I checked the driver board everything on it seems legible. Nothing seems to be worn off.