I recently let bad judgment get the better of me and purchased and amp on ebay that the seller claimed "Worked Great" when it was removed from his car but since he had no means to test it he was selling it as is...
Well turns out his idea of "Works Great" is that both the power and the low ohm LEDs light up...
I have read through all the threads here and through Perry's repair guide but I have a couple of questions I hope you guys can help with before I attempt to repair this myself.
First question is on the IRF540 fets. Locally I can get NTE2396 fets, is that acceptable or should I just order the actual IRF540's from Digikey?
Second, being that the fets are only a couple of dollars each and this is an older amp is there any reason not to replace all of them?
Is there any other items worth replacing while I have it apart?
Thanks for any help you might be able to offer and please be patient with me. I am sure I am going to have a lot of stupid questions through this process but I promise to be grateful for all constructive input!
Well turns out his idea of "Works Great" is that both the power and the low ohm LEDs light up...
I have read through all the threads here and through Perry's repair guide but I have a couple of questions I hope you guys can help with before I attempt to repair this myself.
First question is on the IRF540 fets. Locally I can get NTE2396 fets, is that acceptable or should I just order the actual IRF540's from Digikey?
Second, being that the fets are only a couple of dollars each and this is an older amp is there any reason not to replace all of them?
Is there any other items worth replacing while I have it apart?
Thanks for any help you might be able to offer and please be patient with me. I am sure I am going to have a lot of stupid questions through this process but I promise to be grateful for all constructive input!
NEVER use NTE parts in a class D amp. There's almost no way for them to work properly. Order the IRF540 (NOT from ebay).
You only need to replace the outputs and any failed components in that channel. No other parts.
You should look add solder to, desolder and re-solder the connections on the large 47k resistors on the driver board (if you can do so without disturbing any other parts on those boards).
You only need to replace the outputs and any failed components in that channel. No other parts.
You should look add solder to, desolder and re-solder the connections on the large 47k resistors on the driver board (if you can do so without disturbing any other parts on those boards).
Thanks for the reply Perry. Do you have a brand you can recommend?
I also noticed in a previous thread that you mentioned sending some files to someone for this amp. Any way you could send me those same files?
I also noticed in a previous thread that you mentioned sending some files to someone for this amp. Any way you could send me those same files?
There was a previous post where you asked the posted if they received the files that you had sent. I was hoping that you had some files for this amp.
Now on to stupid question #1...Do I have to remove the fets to test them? When testing on place I have a direct short between all three legs of the second fet on channel #2.
If needed I can give you the readings for all the other fets but channel 2 is the only one that shows a direct short.
I am also reading a direct short on the power supply transistors D500 and D501.
Any thoughts?
Now on to stupid question #1...Do I have to remove the fets to test them? When testing on place I have a direct short between all three legs of the second fet on channel #2.
If needed I can give you the readings for all the other fets but channel 2 is the only one that shows a direct short.
I am also reading a direct short on the power supply transistors D500 and D501.
Any thoughts?
If you read 0 ohms between terminals in the board, the FET is likely defective.
For shorted FETs, you don't have to remove them to check them. Otherwise, for more definitive testing, you have to remove them.
D-prefix parts are diodes. You're likely reading the windings of the transformer if you're not reading 0 ohms to the center leg.
For shorted FETs, you don't have to remove them to check them. Otherwise, for more definitive testing, you have to remove them.
D-prefix parts are diodes. You're likely reading the windings of the transformer if you're not reading 0 ohms to the center leg.
I am assuming that when ordering the FETs that the only difference between an "IRF540" and an "IRF540PBF", is that one is lead free and the other is not. Is that correct?
On the diodes mentioned in the post above they also do not match an appear to have been replaced previously.
The one in location "D500" is labeled "619 SF1604G" location "D501" is labeled "623 SF1604GA". Is there anyone that may have some information on what values are supposed to be here?
On the diodes mentioned in the post above they also do not match an appear to have been replaced previously.
The one in location "D500" is labeled "619 SF1604G" location "D501" is labeled "623 SF1604GA". Is there anyone that may have some information on what values are supposed to be here?
These are both rectifier diodes but I haven't been able to find an exact replacement. Any chance someone has the schematic for this amp that can check the values for me?
I am not sure at this point. They are reading a direct short on all three legs at this time but they are still on the board and could be reading through the windings.
I am trying to put together a potential parts list so that I know where I can source the parts. NTE is the only company I have found with both values.
Not recommending it but UTsource has them at 2.00 ea.. Ive personally had no problems with the parts I've received from them but that's just my personal experience. Id be surprised if they are damaged. They are rated 400v @16 amps. I think you should try a diode test hooking positive lead of the meter to the outside leg and negative lead to the middle. You should read some where between to .4 to .7 volts . The rectifier is comprised of two diodes facing each other as indicated on the rectifiers body. A diode should read low ohms in a forward bias. Flip the connection of the leads on your meter to see if u still read near zero or zero ohms.If so its likely shorted.
http://www.google.com/imgres?imgurl...ved=0CCIQ9QEwAGoVChMIsvKLnMfqxwIVA4YNCh0l_ARU
http://www.google.com/imgres?imgurl...ved=0CCIQ9QEwAGoVChMIsvKLnMfqxwIVA4YNCh0l_ARU
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They are only 200v rectifiers.
SF1601G Datasheet pdf - 16A SUPER-FAST GLASS PASSIVATED RECTIFIER - Won-Top Electronics
The MUR1620CTG and MUR1620CTRG should be good subs and are readily available. Mouser has them.
https://octopart.com/search?q=MUR1620CT #_
To clarify, if the meter is set to ohms, the reading will likely be in the M-ohms range for forward biasing and infinite ohms when the probes are reversed. this is when testing out of the board.
SF1601G Datasheet pdf - 16A SUPER-FAST GLASS PASSIVATED RECTIFIER - Won-Top Electronics
The MUR1620CTG and MUR1620CTRG should be good subs and are readily available. Mouser has them.
https://octopart.com/search?q=MUR1620CT #_
To clarify, if the meter is set to ohms, the reading will likely be in the M-ohms range for forward biasing and infinite ohms when the probes are reversed. this is when testing out of the board.
I finally got around to checking the outputs for this amp and sure enough there were two outputs that were bad.
In addition the trace around the board where the legs go through is also damaged. See attachment.
Does this need to be repaired and if so how do I go about doing that?
In addition the trace around the board where the legs go through is also damaged. See attachment.
Does this need to be repaired and if so how do I go about doing that?
Attachments
If you solder the connections on both the top and bottom of the board, you don't need to do anything else.
Acetone and cotton swabs will remove the flux and make it easier to see how bad the damage is.
You need to bend the center leg out (will allow the leg to flex) as shown in the attached photo.
Acetone and cotton swabs will remove the flux and make it easier to see how bad the damage is.
You need to bend the center leg out (will allow the leg to flex) as shown in the attached photo.
Attachments
I just ordered 50 IRF540 (no N) from jameco. They were half the price of everybody else. No idea why but this is the 3rd batch of them I've bought no problem yet. Still can't find a good deal on the non N IRF9540 tho.
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