Hello diyAudio,
I'm trying to troubleshoot an Alpine MRV-F352 5-channel amp, as per the title. I've searched and read through the other threads here and on other forums and haven't found anything that matches the issue I'm having.
Although it powers reliably, the audio cuts in and out of all channels: a second on, a second off. I've tested all the electrolytic caps with an ESR meter and replaced a few that read bad. Before I did this, the signal was extremely weak and crackly even with the gains maxed. Now it plays clearly with the gains at the setting marked "Nominal", but still a second on, a second off.
I believe the power LED is designed to go red if it's entering protect mode, which it does not do; it powers with the ignition switch and stays solid green while my truck is running.
The same speaker configuration plays normally with another amp I have, so the issue doesn't seem to be in the speaker wiring anywhere.
Given that the signal cuts in and out regardless of what output channels are connected, I suspect the issue is in the output stage or the EQ board, which is a separate unit from the main amp and power supply board. I've cleaned all the pots and switches with naptha and cycled them several dozen times each.
Any suggestions? I can post photos of the board if that would be helpful, there's not a lot out there for this amp.
Thanks!
I'm trying to troubleshoot an Alpine MRV-F352 5-channel amp, as per the title. I've searched and read through the other threads here and on other forums and haven't found anything that matches the issue I'm having.
Although it powers reliably, the audio cuts in and out of all channels: a second on, a second off. I've tested all the electrolytic caps with an ESR meter and replaced a few that read bad. Before I did this, the signal was extremely weak and crackly even with the gains maxed. Now it plays clearly with the gains at the setting marked "Nominal", but still a second on, a second off.
I believe the power LED is designed to go red if it's entering protect mode, which it does not do; it powers with the ignition switch and stays solid green while my truck is running.
The same speaker configuration plays normally with another amp I have, so the issue doesn't seem to be in the speaker wiring anywhere.
Given that the signal cuts in and out regardless of what output channels are connected, I suspect the issue is in the output stage or the EQ board, which is a separate unit from the main amp and power supply board. I've cleaned all the pots and switches with naptha and cycled them several dozen times each.
Any suggestions? I can post photos of the board if that would be helpful, there's not a lot out there for this amp.
Thanks!
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Did this amp just start doing this one day or did you receive it in this condition?
What are you using for a signal source?
Do you have a scope?
What are you using for a signal source?
Do you have a scope?
I got the amp this way; I didn't test it thoroughly when I picked it up and the seller didn't know anything about it. Bad job, me.
Signal source is either a Bluetooth module connected to my phone, or my phone connected directly to the amp's RCA jacks. This also behaves as expected with the known-good amp.
I don't own a scope but I might be able to borrow one.
Signal source is either a Bluetooth module connected to my phone, or my phone connected directly to the amp's RCA jacks. This also behaves as expected with the known-good amp.
I don't own a scope but I might be able to borrow one.
"behaves as expected with the known-good amp."
^^ An amp of the same exact model?
What's the DC voltage on the RCA shields when the audio is switching on and off?
^^ An amp of the same exact model?
What's the DC voltage on the RCA shields when the audio is switching on and off?
It's not a like model, it's a Rockford Fosgate 45.2 a friend loaned me. I just checked the voltage at the RCA jacks and I'm getting +15 to +20mV when it's playing and -170 to -200mV when it cuts out.
Use a small jumper wire to connect the RCA shields to the amp's ground terminal. Does the audio remain on?
Some. I'm by no means an expert. I replaced a control IC on a Denon integrated receiver, I've built a few little chip-amps, I know how to read a schematic. I don't have a strong grasp of circuit design.
I'm testing it in my truck because I don't have a bench power supply. I don't have any test equipment except for a multimeter and a borrowed ESR meter.
Disconnect ALL speaker wires from the terminals on the amp. With no jumper on the shields, does the pulsing vary from the first numbers you posted?
With all speaker terminals disconnected I get similar readings, but not identical, flipping between +30 to +100mV and -130 to -190mV.
Measuring the DC voltage directly across the two speaker terminals for each channel, do you see any significant DC pulsing on one or more channels?
Here's what I measured, being careful to measure with the positive probe on the positive terminal and negative on negative.
Ch1: +500mV dropping to +250, -1.5mV, -230mV
Ch2: +0-315mV and -90 to -85mV, spikes to +300, drops to zero, hovers around -90
Ch3: -0-315mV and +90 to +85mV, spikes to -300, drops to zero, hovers around +90
Ch4: same as channel 2
Ch5: +3 to 6mV and -90 to -5mV; it spikes to around +230mV before it goes back to a negative voltage and then starts the cycle over
Ch1: +500mV dropping to +250, -1.5mV, -230mV
Ch2: +0-315mV and -90 to -85mV, spikes to +300, drops to zero, hovers around -90
Ch3: -0-315mV and +90 to +85mV, spikes to -300, drops to zero, hovers around +90
Ch4: same as channel 2
Ch5: +3 to 6mV and -90 to -5mV; it spikes to around +230mV before it goes back to a negative voltage and then starts the cycle over
Does the audio play long enough to tell if channel 1 is producing clean audio?
If you connect a speaker (one that you can see the cone) to ch1, do you see the cone pulsing when the amp switches on and off?
If you connect a speaker (one that you can see the cone) to ch1, do you see the cone pulsing when the amp switches on and off?
With a 4 ohm subwoofer connected to Channel 1 I get a clean signal when it's playing and nothing when it's off; it's hard, clean transition with nothing I'd describe as pulsing. The DC voltage reads around +180 to +230mV while it's playing and -5 to -2.5mV when it cuts out.