This amp came in for repair.
Upon starting up goes to protect instantly.
The power supply seems to be ok, since i can measure 100V before voltage starts to go down due to amp going to prot mode.
Checked the preamp, voltage regulators, seem fine, removed all IRF640Ns, none was bad.
Tried to start up without them, but again goes to protect.
Upon starting up goes to protect instantly.
The power supply seems to be ok, since i can measure 100V before voltage starts to go down due to amp going to prot mode.
Checked the preamp, voltage regulators, seem fine, removed all IRF640Ns, none was bad.
Tried to start up without them, but again goes to protect.
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Q6 and Q7 (on this board) commonly fail and will fail again if you don't take steps to keep them cool. You probably noticed that the board was discolored under the transistors from heat stress. This is a common problem that's been covered in various other threads. On the other boards, Q6/7 are designated as Q1/2 but you can't see the Q1/Q2 designations until you remove the two transistors.
Thanks for the feedback Perry.
All 11 transistors were replaced on this board.
After removing the parts with a hot air rework station, and cleaning everything
with acetone, i checked the board with a strong stereo microscope,
and didnt see any signs of heating on the board.
So i soldered the new parts (too afraid to use the hot air yet, as i am very new
to this).
All 11 transistors were replaced on this board.
After removing the parts with a hot air rework station, and cleaning everything
with acetone, i checked the board with a strong stereo microscope,
and didnt see any signs of heating on the board.
So i soldered the new parts (too afraid to use the hot air yet, as i am very new
to this).
They shouldn't fail that quickly. They fail but generally only after several months. If they fail within a few minutes, there is another problem. Q6 and Q7 are in parallel. Are you sure that they were both soldered to the board? I'm assuming that those are the ones that failed because they are the ones that most commonly fail.
The problem is different now.
With the rca connected the amp goes to protect.
Without them, it powers up fine.
I measured the output rca shield with the power gnd and showed 0 ohms.
This did not apply for the input rca. Upon grounding the input rca shield,
powers up fine.
I am worried about Q6 and Q7 though. Should i do something before giving the
amp back?
With the rca connected the amp goes to protect.
Without them, it powers up fine.
I measured the output rca shield with the power gnd and showed 0 ohms.
This did not apply for the input rca. Upon grounding the input rca shield,
powers up fine.
I am worried about Q6 and Q7 though. Should i do something before giving the
amp back?
Attachments
With no RCAs plugged in, you should not read 0 ohms between the RCA shield and the amp's primary ground. If you do, the amp is likely to have a lot of engine noise.
Did one of the smaller transistors fail on the driver board or were the RCA cables causing the amp to go into protect?
Email me if you want suggestions on keeping the drivers cool(er).
babin_perry@yahoo.com
Did one of the smaller transistors fail on the driver board or were the RCA cables causing the amp to go into protect?
Email me if you want suggestions on keeping the drivers cool(er).
babin_perry@yahoo.com
If you plug the RCAs in (before applying power) but have the audio level set to 0, does it still go into protect?
It appears that the other smaller transistors have been replaced and the numbers are not the same as what's generally in those locations. Are the transistors rated the same as the originals?
It appears that the other smaller transistors have been replaced and the numbers are not the same as what's generally in those locations. Are the transistors rated the same as the originals?
Original MMBTA42 and 92 are marked 1D and 2D and are rated at 350mW.
my ordered MMBTA 42 and 92 that came from Farnell were marked 7DW and 7EW,
and are rated at 250mW.
I think of trying to fit TO-92 devices, rated at 625mW, put the module back, and check wether with the RCAs plugged and zero audio in, the amp goes to protect.
my ordered MMBTA 42 and 92 that came from Farnell were marked 7DW and 7EW,
and are rated at 250mW.
I think of trying to fit TO-92 devices, rated at 625mW, put the module back, and check wether with the RCAs plugged and zero audio in, the amp goes to protect.
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