Hello
I'm working on a RF R1200.1d that appears to have an issue with the power supply.
This version of the amp has 6 big rail caps (3 per rail) instead of the version that has many smaller caps. One of the rail caps on the positive side was noticeably budged, I removed it and will replace it later on.
The issue is that the amp will start causing the speaker to pop/pulse. This is happens with or without audio input, sometimes the popping/pulsing will stop but the speaker will move like there is a 5Hz signal despite no audio input. Sometimes it will work fine for a few minutes and it'll sound perfectly normal.
When the amp is playing normally, the rails looks good - about +/- 66V with ~2-3Vpp of ripple. The positive rail has a bit more ripple (8Vpp) because I removed the bad cap. I have to note that the rails also look good when it starts to pop/pulse as long as I disconnect the speaker.
I've attached a scope picture (CH1 - Pos rail, CH2- Neg rail) of what the rails look like when the speaker starts to pop/pulse. It looks like the rails start to oscillate and will occasionally have some overshoot events (only have seen it on the positive rail, from 66V to ~100V). The overshooting events occurs at the same time as the popping noise as well.
During one of the pop/pulsing events one of the power supply FETs (IRF3205) failed, shorting itself. There are 4 of the IRF3205s on each side of the primary transformer. I removed the bad FET to continue testing.
I've checked the gate drive to the power supply FETs and they look good even during the pop/pulsing events, although the amplitude of the gate drive will drop in sync with the popping/pulsing due to the rail voltage dropping. Could it be because one or multiple of the power supply FETs are latching up and causing this behavior?
I'm working on a RF R1200.1d that appears to have an issue with the power supply.
This version of the amp has 6 big rail caps (3 per rail) instead of the version that has many smaller caps. One of the rail caps on the positive side was noticeably budged, I removed it and will replace it later on.
The issue is that the amp will start causing the speaker to pop/pulse. This is happens with or without audio input, sometimes the popping/pulsing will stop but the speaker will move like there is a 5Hz signal despite no audio input. Sometimes it will work fine for a few minutes and it'll sound perfectly normal.
When the amp is playing normally, the rails looks good - about +/- 66V with ~2-3Vpp of ripple. The positive rail has a bit more ripple (8Vpp) because I removed the bad cap. I have to note that the rails also look good when it starts to pop/pulse as long as I disconnect the speaker.
I've attached a scope picture (CH1 - Pos rail, CH2- Neg rail) of what the rails look like when the speaker starts to pop/pulse. It looks like the rails start to oscillate and will occasionally have some overshoot events (only have seen it on the positive rail, from 66V to ~100V). The overshooting events occurs at the same time as the popping noise as well.
During one of the pop/pulsing events one of the power supply FETs (IRF3205) failed, shorting itself. There are 4 of the IRF3205s on each side of the primary transformer. I removed the bad FET to continue testing.
I've checked the gate drive to the power supply FETs and they look good even during the pop/pulsing events, although the amplitude of the gate drive will drop in sync with the popping/pulsing due to the rail voltage dropping. Could it be because one or multiple of the power supply FETs are latching up and causing this behavior?
Attachments
Are you using current limiting that could be causing the amp to shut down?
Did you try to get the diagram from Rockford?
Was that scope cap taken from the rectifiers? There shouldn't be any pulses on the rails.
Did you try to get the diagram from Rockford?
Was that scope cap taken from the rectifiers? There shouldn't be any pulses on the rails.
I have a current limit set but when I get the pops/pulses it doesn't hit the current limit (idles at ~1.4A, draws about 3A during pop events, limit is at 8A).
The scope capture is measuring at the output of the rectifiers, effectively across the rail caps. Those "pulses" are the oscillations that occur when the amp becomes unstable. When it is working fine the output is stable with some ripple if there is an audio input.
I've attached the schematic that I have on hand. It is for the same amp but the version with many smaller rail caps vs. 6 bigger ones.
The scope capture is measuring at the output of the rectifiers, effectively across the rail caps. Those "pulses" are the oscillations that occur when the amp becomes unstable. When it is working fine the output is stable with some ripple if there is an audio input.
I've attached the schematic that I have on hand. It is for the same amp but the version with many smaller rail caps vs. 6 bigger ones.
Hey Perry, I think I got it working now. It appeared to be the input daughter board (one with the gain/xover controls). I noticed tapping on it would have a direct effect on the popping/pulsing on the output. I removed it from the main board and re-soldered all the connections and now it seems to be working great.
I'm going to burn it in a little playing music. Going to order a replacement cap and replace all the power supply FETs as well.
I'm going to burn it in a little playing music. Going to order a replacement cap and replace all the power supply FETs as well.
There may have been more than one problem. There's no way that you should be able to have a pulse like that on the scope display with any good rail capacitors on that rail.
The rails didn't exactly have a pulse but more of a oscillation. The time scale was 500ms in the scope image. I think what happened with the straight drop in rail voltage was that the amp went into protect for a brief second.
At idle the rails are basically DC now and about 3Vpp of ripple when playing 20hz at 200 watts. What's acceptable ripple?
At idle the rails are basically DC now and about 3Vpp of ripple when playing 20hz at 200 watts. What's acceptable ripple?
I don't have a spec for acceptable ripple. Ripple at the audio frequency isn't a big problem. High frequency ripple near the PS oscillation frequency is a problem and shouldn't be visible on the rails.