Hi,
I have been working on an MBQuart PAB 1200.1D for some time. When I received the amplifier, it was immediately obvious that the power supply had gone (some mosfets had burst).
The rest of the amplifier looked fine after measurements. So I hoped that after restoring the power supply, the amplifier would work again.
What has been replaced so far:
Unfortunately, it turned out that there were other problems. As soon as the amplifier is switched on, it starts to oscillate, the output stage transistors get very hot and it constantly draws a lot of current. This is only limited by my power supply. I assume that this led to the original power supply damage.
What have I tested so far?
- Rectifier desoldered
Without the rectifier, the power supply runs without problems (idle current etc.).
- Output stage transistors desoldered.
Amp starts without problems (idle current etc.). but no oscillation
- Checked the output stage transistors with a component tester.
But could not find anything negative.
- Drive card removed and all components tested and the drive IC replaced.
But still the same problem.
Other components were also checked, but nothing was found. Unfortunately, I can't get any further and I hope there are still a few ideas to solve the problem.
With kind regards
I have been working on an MBQuart PAB 1200.1D for some time. When I received the amplifier, it was immediately obvious that the power supply had gone (some mosfets had burst).
The rest of the amplifier looked fine after measurements. So I hoped that after restoring the power supply, the amplifier would work again.
What has been replaced so far:
- All power supply mosfets
- All gate resistor
- Drive IC
Unfortunately, it turned out that there were other problems. As soon as the amplifier is switched on, it starts to oscillate, the output stage transistors get very hot and it constantly draws a lot of current. This is only limited by my power supply. I assume that this led to the original power supply damage.
What have I tested so far?
- Rectifier desoldered
Without the rectifier, the power supply runs without problems (idle current etc.).
- Output stage transistors desoldered.
Amp starts without problems (idle current etc.). but no oscillation
- Checked the output stage transistors with a component tester.
But could not find anything negative.
- Drive card removed and all components tested and the drive IC replaced.
But still the same problem.
Other components were also checked, but nothing was found. Unfortunately, I can't get any further and I hope there are still a few ideas to solve the problem.
With kind regards
Post a good quality photo of the component side of the entire main board and the component side of any driver boards if no one can help.
These amps can draw a lot of current on startup.
Try pulsing the remote voltage repeatedly to see if the amp eventually powers up. You may have to remove all current limiting and use a 15 amp fuse to offer protection.
Where did you get the replacement 4060 driver IC? The replacements are sometimes counterfeit and the original may be a better option.
Try pulsing the remote voltage repeatedly to see if the amp eventually powers up. You may have to remove all current limiting and use a 15 amp fuse to offer protection.
Where did you get the replacement 4060 driver IC? The replacements are sometimes counterfeit and the original may be a better option.
Hey Perry,
I ordered the replacement drive IC from Aliexpress expecting it to be a fake, but it behaves just like the original. To be on the safe side I soldered the original one back in.
Remote voltage to pulse repeatedly I have already tested unfortunately without success the rail voltage does not rise above +/- 10V
Without current limit with a 15A fuse unfortunately also does not work the fuse blows directly.
I ordered the replacement drive IC from Aliexpress expecting it to be a fake, but it behaves just like the original. To be on the safe side I soldered the original one back in.
Remote voltage to pulse repeatedly I have already tested unfortunately without success the rail voltage does not rise above +/- 10V
Without current limit with a 15A fuse unfortunately also does not work the fuse blows directly.
When trying to power up as you previously did, which output transistors heat up after repeatedly powering up?
With all output transistors in circuit, all become hot after 1-2 minutes. With only one high site and one low side transistor, both get extremely hot after a few seconds. For this reason I first thought the output transistors were defective, but all output transistors seem ok (tested with a component tester outside the circuit).
Which terminals of the driver IC and which resistor terminals connect to the base of Q3A? List all.
When I bridge Q1A G-S the amp turns on normally with 0,7A idle current but of course without drive signal. Rail Volatge +/- 60V and the auxiliary power supply also looks good. The volatge regulator for the drive IC also work +/- 9V
When I inject a 100hz sine wave I can see it on pin 9 but as soon as I turn up the volume I can hear a crackling sound from the drive card when I turn up the input signal further the amp goes into protection.
Pin 8 without signal is at 0V as soon as I inject the signal and you hear the crackle pin 8 jumps between 0-0,5V
Pin 8 without signal is at 0V as soon as I inject the signal and you hear the crackle pin 8 jumps between 0-0,5V
Yes they reach the chip, from the +/- 9V input of the drive card I have a direct connection from +9V to pin 5 and 12 -9V to pin 1,4,7,15,16,18,19 and 23 of the drive IC. Unfortunately I didn't find a datasheet for the IC so I can't check if this is correct.
What's the exact DC voltage (precisely what your meter reads) on pins 8 and 9 (measured using the same reference). The base is Q1A may be a good reference.
I just zoomed in on the driver board an it appears that there are a LOT of pulled vias. If there are that many pulled vias, this may be very difficult to repair.
I just zoomed in on the driver board an it appears that there are a LOT of pulled vias. If there are that many pulled vias, this may be very difficult to repair.