Hi,
Im brand new here and hoping for some advice.
As you might guess i'm not educated in electronics and only understand the very basics.
My son has a pair of M-Audio Studiophile AV40 speakers which recently stopped working.
Firstly the left speaker was knocked over and stopped producing sound but the right speaker continued to work. A couple of months later and the right speaker has stopped working. When plugged in and switched on the power light fails to come on and the speaker shows no signs of life.
The two-way speakers are powered by an amp inside the left speaker that plugs into the wall socket (240V UK), an output from the left speaker then feeds the amplified audio to the right speaker. Each speaker also houses its own crossover circuit.
My troubleshooting steps so far are (using a DMM):
1. Checked fuse in plug (for mains wall socket) and it is fine.
2. Checked fuse in left speaker (between mains input and transformer) and it is fine.
3. Checked voltage at transformer input [primary] (fine reading around 244V).
4. Checked voltage at transformer output [secondary] and it shows no voltage. This to me shows the transformer is faulty.
5. Partially stripped the transformer and removed the thermal cutoff component and checked for resistance/continuity. The continuity test failed to produce a beep. The resistance test indicated an open circuit (DMM display read 1 before test and stayed on 1 when contacts were touched). It seems to me the transformer got too hot and blew the thermal cutoff.
Now for some questions...
a) Does my reasoning sound right so far?
b) The thermal cutoff is an A4-F as listed here...
http://www.aupo.com.hk/egproduct/af.htm
As im based in the UK, where can I get a replacement (same or equivalent) for this component.
c) Would it be easier to replace the whole transformer as im not confident I could solder the new cutoff with causing it to blow from the soldering heat.
d) The label on the current transformer has this text...
MODEL: BDT-57A178n(AV40) LF
I/P: ~115V/60Hz WHITE/GREEN-YELLOW/BLUE
~230V/50Hz WHITE-BLUE
O/P: ~14Vx2/1.4A RED-BLACK-RED
SHENZHEN XINGYAODA ELECTRONICS CO. LTD
The distance between the mounting holes on the PCB appears to be about 65mm center to center.
I have tried searching for a replacement transformer but just get confused by the ratings, especially when it comes to serial and parallel figures I have no idea what to choose. It seems I need one that has two secondary outputs of 14V though im not sure if it would be 1.4A current in each one or if it means combined (0.7A each).
Any help in this area would be appreciated, especially a link to a suitable replacement part, and perhaps comments on transformer make/quality if it may affect the quality of the sound output by the speakers.
e) Finally, when a transformer overheats such as this appears to have done what might be the cause? Is it likely to have caused other components to fail (no scorching on PCB that I can see or blown/mis-shaped capacitors). Could the fact that only one speaker was working for some time have caused these overheating problems.
If you got this far, thanks for reading.
Eagerly awaiting your responses and thanks.
Steve
Im brand new here and hoping for some advice.
As you might guess i'm not educated in electronics and only understand the very basics.
My son has a pair of M-Audio Studiophile AV40 speakers which recently stopped working.
Firstly the left speaker was knocked over and stopped producing sound but the right speaker continued to work. A couple of months later and the right speaker has stopped working. When plugged in and switched on the power light fails to come on and the speaker shows no signs of life.
The two-way speakers are powered by an amp inside the left speaker that plugs into the wall socket (240V UK), an output from the left speaker then feeds the amplified audio to the right speaker. Each speaker also houses its own crossover circuit.
My troubleshooting steps so far are (using a DMM):
1. Checked fuse in plug (for mains wall socket) and it is fine.
2. Checked fuse in left speaker (between mains input and transformer) and it is fine.
3. Checked voltage at transformer input [primary] (fine reading around 244V).
4. Checked voltage at transformer output [secondary] and it shows no voltage. This to me shows the transformer is faulty.
5. Partially stripped the transformer and removed the thermal cutoff component and checked for resistance/continuity. The continuity test failed to produce a beep. The resistance test indicated an open circuit (DMM display read 1 before test and stayed on 1 when contacts were touched). It seems to me the transformer got too hot and blew the thermal cutoff.
Now for some questions...
a) Does my reasoning sound right so far?
b) The thermal cutoff is an A4-F as listed here...
http://www.aupo.com.hk/egproduct/af.htm
As im based in the UK, where can I get a replacement (same or equivalent) for this component.
c) Would it be easier to replace the whole transformer as im not confident I could solder the new cutoff with causing it to blow from the soldering heat.
d) The label on the current transformer has this text...
MODEL: BDT-57A178n(AV40) LF
I/P: ~115V/60Hz WHITE/GREEN-YELLOW/BLUE
~230V/50Hz WHITE-BLUE
O/P: ~14Vx2/1.4A RED-BLACK-RED
SHENZHEN XINGYAODA ELECTRONICS CO. LTD
The distance between the mounting holes on the PCB appears to be about 65mm center to center.
I have tried searching for a replacement transformer but just get confused by the ratings, especially when it comes to serial and parallel figures I have no idea what to choose. It seems I need one that has two secondary outputs of 14V though im not sure if it would be 1.4A current in each one or if it means combined (0.7A each).
Any help in this area would be appreciated, especially a link to a suitable replacement part, and perhaps comments on transformer make/quality if it may affect the quality of the sound output by the speakers.
e) Finally, when a transformer overheats such as this appears to have done what might be the cause? Is it likely to have caused other components to fail (no scorching on PCB that I can see or blown/mis-shaped capacitors). Could the fact that only one speaker was working for some time have caused these overheating problems.
If you got this far, thanks for reading.
Eagerly awaiting your responses and thanks.
Steve