I Perry i now replaced the IRF540 and now the amp
is upp and running again!
But i noticed that one of the FETs in the vertical
board had 3.6 volts refered to ground terminal.
It should be 3 or 3.3volts... Not 3.6.
Do you think it matters? I checked all the
gate resistors and they were in tolerance.
Maybe i should check all surrounding resistors
also?
Or maybe i just testrun it for a while and se
if they run hot.
Thanks again! =)
is upp and running again!
But i noticed that one of the FETs in the vertical
board had 3.6 volts refered to ground terminal.
It should be 3 or 3.3volts... Not 3.6.
Do you think it matters? I checked all the
gate resistors and they were in tolerance.
Maybe i should check all surrounding resistors
also?
Or maybe i just testrun it for a while and se
if they run hot.
Thanks again! =)
With no power applied, measure the resistance between the gates of each transistor in each parallel group. For the 540s, if you set the meter to ohms and place one meter lead on the gate leg of one 540, it should read 2x the gate resistor value to the gate leg of each of the other two 540s in that group. This confirms that the gate resistors are OK and that there are no broken connections. All drain legs for the group should be directly connected. All source legs for the group should read ~0.2 ohms (2x the resistance of the source resistors) to the other two source legs for the group. A difference of 0.2 ohms is significant here.
Since your meter isn't likely to read 0.00 ohms, touch the leads together for ~5 seconds. Subtract the lowest reading (when the leads are shorted together) from the resistance between the source legs to get the true resistance.
Since your meter isn't likely to read 0.00 ohms, touch the leads together for ~5 seconds. Subtract the lowest reading (when the leads are shorted together) from the resistance between the source legs to get the true resistance.
Hi again. Seems like none of the new FETs were a perfect
match.
pin3
Q224 and 225
0.7 ohms
Q211 and 213
0.3 ohms
Q212 and 214
0.4 ohms
On the other channel its not identical either.
Around 0.25-0.35 ohms i think.
Do you think it should be a problem?
All the gate resistors seems OK
Measured from leg1 to leg 1 paralell
0.748Kohms on every pair.
It was a direct connection on leg 2 of every
FET pair. 0ohms...
match.
pin3
Q224 and 225
0.7 ohms
Q211 and 213
0.3 ohms
Q212 and 214
0.4 ohms
On the other channel its not identical either.
Around 0.25-0.35 ohms i think.
Do you think it should be a problem?
All the gate resistors seems OK
Measured from leg1 to leg 1 paralell
0.748Kohms on every pair.
It was a direct connection on leg 2 of every
FET pair. 0ohms...
The resistors help insure equal current sharing between the parallel transistors. If one resistors has a slightly higher, the transistor in series with it will not carry its share of the load. A small difference can significantly impact reliability when the amp is driven hard.
Yes, the large white resistors are the source resistors. On the vertical board, there are two smaller/single source resistors. The 3 legged resistors are dual resistors. The center leg is common. Measure the resistance between the center leg and each of the outer legs.
Yes, the large white resistors are the source resistors. On the vertical board, there are two smaller/single source resistors. The 3 legged resistors are dual resistors. The center leg is common. Measure the resistance between the center leg and each of the outer legs.
If one of the dual resistors is defective, you could use two 0.1 ohm resistors as a replacement. You may get lucky and have one of the single resistors out of tolerance.
I'd prefer to see all 3 of the resistors replaced for the parallel group. If you want to replace all 3, I'd suggest using 1% components. 5% would be sufficient but I prefer to use 1% replacements.
I'd prefer to see all 3 of the resistors replaced for the parallel group. If you want to replace all 3, I'd suggest using 1% components. 5% would be sufficient but I prefer to use 1% replacements.
Hi again.. I checked all the resistors out of the board
and they where all in tolerance.. maybe i just didnt have
good contact last when i checked them.
Wiped of all the old grease and put some new on and
mounted everything in the chassi.
Plugged in my old Pioneer head unit and its a miracle!
(or just a lot of hard work and pain..)
But so far i have played a entire album and the amp
is still upp and running.. totaly i played music for about
an hour. then my old car battery started to get weak.
I noticed that the amp was getting quite hot. but i think
thats normal, i played quite loud for an hour
Will test mount it in my car tomorrow and hit som base!
Thanks Perry for all helping me out!
and they where all in tolerance.. maybe i just didnt have
good contact last when i checked them.
Wiped of all the old grease and put some new on and
mounted everything in the chassi.
Plugged in my old Pioneer head unit and its a miracle!
(or just a lot of hard work and pain..)
But so far i have played a entire album and the amp
is still upp and running.. totaly i played music for about
an hour. then my old car battery started to get weak.
I noticed that the amp was getting quite hot. but i think
thats normal, i played quite loud for an hour
Will test mount it in my car tomorrow and hit som base!
Thanks Perry for all helping me out!
You should remove all of the old solder, clean the terminal block (sandpaper, scrape it) where it solders to the board and resolder it.
If the outer part of the terminal is not bright/shiny/clean, you'll have to clean it also. This type of problem is often caused by dirty contacts or a loose connection. Either can cause excessive resistance. When high current is passed through that resistance (when the amp is driven hard), the terminal overheats.
Do not power up the amp without having all of the transistors clamped tightly to the heatsink. When you initially power it up, have a 10-15 amp fuse in series with the B+ line. This will help protect the amp's other components if there are more problems.
If the outer part of the terminal is not bright/shiny/clean, you'll have to clean it also. This type of problem is often caused by dirty contacts or a loose connection. Either can cause excessive resistance. When high current is passed through that resistance (when the amp is driven hard), the terminal overheats.
Do not power up the amp without having all of the transistors clamped tightly to the heatsink. When you initially power it up, have a 10-15 amp fuse in series with the B+ line. This will help protect the amp's other components if there are more problems.
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