Hi everyone
I have an Adam Audio Sub7 subwoofer that would not power on. After taking it apart and doing some diagnostics, I found a faulty rectifier on the SMPS secondary and blown TDA8950TH and one bulging cap. After replacing the rectifier and cap and removing the TDA, the PSU came back to life. A quick check of all voltages showed no problems so I put in a brand new NXP TDA8950TH. I also replaced the rest of the small electrolytics apart from the four 2200uf 25V caps as they seem fine. After powering the amp on there was about 7V of DC offset. Both with and without a load and both with and without the input connected to the power amp board. Connecting my throwaway test speaker showed that it pushed the cone out but seemed fine otherwise, there was still regular background hiss and the amp would pass audio. Due to a lack of time, I put the sub on my shelf and forgot about it. Now I had some time today so I pulled it back out and had another go at it. Interestingly I took it apart, measured some voltages and everything seemed fine. It had only about 10mV of DC offset and played just fine on my workbench and had plenty of power. So I put it back together and powered it on and again, pushed the cone out. Slowly and calmly, takes about a second for it to rise to 7V DC.
Now the weird thing is that after a while it starts to drop back down. I took some measurements and everything seemed normal. Supply voltages were okay, no significant DC on the input. During the time of poking around, about 10 minutes, the DC had dropped to about 1.5V. Only pushes the cone out slightly and plays fine. I have an old 16 ohm Turbosound driver to test bad amps. Then after some time it raised again, about 3.something V DC. Then dropped back down.
I checked my soldering and it's good, looks like new
Don't think there is a problem there.
Any common problems that can make these behave weird? Or is the new chip defective most likely?
No schematics for this unfortunately but it's not a very complex amp. Regular SMPS with +-20V supply, chip configured to run in BTL mode, nothing more on the amp board but the SMPS, TDA chip and it's supporting components.
I have an Adam Audio Sub7 subwoofer that would not power on. After taking it apart and doing some diagnostics, I found a faulty rectifier on the SMPS secondary and blown TDA8950TH and one bulging cap. After replacing the rectifier and cap and removing the TDA, the PSU came back to life. A quick check of all voltages showed no problems so I put in a brand new NXP TDA8950TH. I also replaced the rest of the small electrolytics apart from the four 2200uf 25V caps as they seem fine. After powering the amp on there was about 7V of DC offset. Both with and without a load and both with and without the input connected to the power amp board. Connecting my throwaway test speaker showed that it pushed the cone out but seemed fine otherwise, there was still regular background hiss and the amp would pass audio. Due to a lack of time, I put the sub on my shelf and forgot about it. Now I had some time today so I pulled it back out and had another go at it. Interestingly I took it apart, measured some voltages and everything seemed fine. It had only about 10mV of DC offset and played just fine on my workbench and had plenty of power. So I put it back together and powered it on and again, pushed the cone out. Slowly and calmly, takes about a second for it to rise to 7V DC.
Now the weird thing is that after a while it starts to drop back down. I took some measurements and everything seemed normal. Supply voltages were okay, no significant DC on the input. During the time of poking around, about 10 minutes, the DC had dropped to about 1.5V. Only pushes the cone out slightly and plays fine. I have an old 16 ohm Turbosound driver to test bad amps. Then after some time it raised again, about 3.something V DC. Then dropped back down.
I checked my soldering and it's good, looks like new
Don't think there is a problem there.Any common problems that can make these behave weird? Or is the new chip defective most likely?
No schematics for this unfortunately but it's not a very complex amp. Regular SMPS with +-20V supply, chip configured to run in BTL mode, nothing more on the amp board but the SMPS, TDA chip and it's supporting components.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.