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Replace old transformer with rectifier bridge
- Thread starter pharaon
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That board apparently already has a bridge rectifier (4 diodes) on it. A transformer is a completely different animal. If the one you show has failed you will need to replace it with a similarly (or more generously) rated one, or a suitably rated wall-wart (mains to low DC voltage adapter). Either way requires the transformer output voltage to be known or deduced.
What are the markings on the 8-pin IC and the big fat capacitor?
What are the markings on the 8-pin IC and the big fat capacitor?
You might find that there is a thermal fuse fitted against the transformer windings. Look for a 'bulge' under the tape and, working carefully so you don't cut any of the winding wires, you might be able to get the fuse out and replace it.
can you explain
the winding wires already cut
The Wall Wart usually comes with a barrel connector, snip it off and solder the two ends, 12vdc, to the plus and minus output of the 4 diodes used as a bridge on the previous transformer output.
M.
^ Finding exactly the right size replacement transformer that will solder onto the space on the PCB could take a very long time and you may never find it, and it may be very expensive including shipping, compared to the low value of the speaker amp.
12VDC output AC/DC wall adapters on the other hand, are very common and inexpensive, and typically it is easy to find some rated for 1A which is probably higher current rating than that tiny original transformer was capable of, which is why I suspect it overheated and failed in the first place.
There is no reasonable/safe way to convert 220VAC to 12VDC without a transformer. This is a pretty simple repair, why are you wasting time questioning people who realize how to fix this with minimal time and expense, since it is about the cheapest, crudest low end speaker amp possible? It really is not worth great time or expense to fix this.
As Minder mentioned, you should solder the wires from an AC-DC 12V adapter to the PCB. The positive lead wire from the adapter would be soldered to the hole labeled "P9" on the PCB and the negative lead to the hole labeled "P10". If you prefer you could keep the barrel plug on the AC/DC adapter and buy a barrel socket to mount on the speaker cabinet, then solder wiring from P9 and P10 to the respective terminals on the barrel socket, but I question whether this amp is worth buying any more parts for than absolutely necessary.
Note that you don't necessarily even need to use an AC/DC adapter. If it is a desktop computer so it has a source of 12VDC, you could just power this amp board from that, just get a $1 connector for the PSU 4 pin molex plug and solder that to the amp P9 and P10, maybe needing to add a piece of wire to extend the length.
12VDC output AC/DC wall adapters on the other hand, are very common and inexpensive, and typically it is easy to find some rated for 1A which is probably higher current rating than that tiny original transformer was capable of, which is why I suspect it overheated and failed in the first place.
There is no reasonable/safe way to convert 220VAC to 12VDC without a transformer. This is a pretty simple repair, why are you wasting time questioning people who realize how to fix this with minimal time and expense, since it is about the cheapest, crudest low end speaker amp possible? It really is not worth great time or expense to fix this.
As Minder mentioned, you should solder the wires from an AC-DC 12V adapter to the PCB. The positive lead wire from the adapter would be soldered to the hole labeled "P9" on the PCB and the negative lead to the hole labeled "P10". If you prefer you could keep the barrel plug on the AC/DC adapter and buy a barrel socket to mount on the speaker cabinet, then solder wiring from P9 and P10 to the respective terminals on the barrel socket, but I question whether this amp is worth buying any more parts for than absolutely necessary.
Note that you don't necessarily even need to use an AC/DC adapter. If it is a desktop computer so it has a source of 12VDC, you could just power this amp board from that, just get a $1 connector for the PSU 4 pin molex plug and solder that to the amp P9 and P10, maybe needing to add a piece of wire to extend the length.
davenn
Moderator
pharaon, I'm going to repeat what Dave9 said so that hopefully it sinks in
""Finding exactly the right size replacement transformer that will solder onto the space on the PCB could take a very long time and you may never find it, and it may be very expensive including shipping, compared to the low value of the speaker amp.
12VDC output AC/DC wall adapters on the other hand, are very common and inexpensive, and typically it is easy to find some rated for 1A which is probably higher current rating than that tiny original transformer was capable of, which is why I suspect it overheated and failed in the first place.
There is no reasonable/safe way to convert 220VAC to 12VDC without a transformer. This is a pretty simple repair, why are you wasting time questioning people who realize how to fix this with minimal time and expense, since it is about the cheapest, crudest low end speaker amp possible? It really is not worth great time or expense to fix this.""
Dave
davenn
Moderator
If you value your life, or the lives of others, DON'T USE IT!! It has no mains isolation, so anything powered by it could float at mains potential and be LETHAL.
Technically speaking, equipment that does not use a transformer or safety earth ground conductor is constructed by being 'Double Insulated' for safety reasons.
The reason is the circuit is at the same potential as the incoming mains service in spite of dropping the circuit voltage to 12v..
Pretty much what others have said.
M.
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