I see that there is a soft start (inrush current limiter) on the primary of the transformer. In that case, 1.6AT or 2AT is used for the 300VA transformer. Without soft start, a twice as strong fuse must be placed in the primary, that is, 3AT or 4AT, so that it does not burn when switched on. A short circuit to the secondary will certainly blow the 4AT fuse. In this case, it burned 10AT without a problem. In case of long-term overload of the transformer, the thermal fuse in the primary will melt, if there is one. The transformer can usually be thrown away if that thermal fuse blows, that is, it must be rewound because that fuse is deep in the primary, where it is the warmest. Usually, that rewind is not worth it. I don't think that happened here, but it is not excluded.
Now the steps would be to first check everything, that means first the transformer with an ohmmeter, then at idle if it has the required voltages. Next is the replacement of the rectifier diodes. Then try the power supply and that at idle. Then everything else as mentioned here, new amplifier modules, checking with an ohmmeter that there are no short circuits, etc. Insert 22ohm 0.6W resistors into the plus and minus lines of the amplifier for the first switch-on. Measure the voltage drop on them, calculate the current. If it has a quiescent current setting, the trimmer pot must be in the minimum current position. Connect the amplifier module one by one, to reduce possible material damage if there are any problems again. An incandescent bulb in series with a primary for first switching on is a good recommendation. After each trial, discharge large electrolytic capacitors in PS with a 220ohm 10W resistor.
Now the steps would be to first check everything, that means first the transformer with an ohmmeter, then at idle if it has the required voltages. Next is the replacement of the rectifier diodes. Then try the power supply and that at idle. Then everything else as mentioned here, new amplifier modules, checking with an ohmmeter that there are no short circuits, etc. Insert 22ohm 0.6W resistors into the plus and minus lines of the amplifier for the first switch-on. Measure the voltage drop on them, calculate the current. If it has a quiescent current setting, the trimmer pot must be in the minimum current position. Connect the amplifier module one by one, to reduce possible material damage if there are any problems again. An incandescent bulb in series with a primary for first switching on is a good recommendation. After each trial, discharge large electrolytic capacitors in PS with a 220ohm 10W resistor.
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Yeah unfortunately there wasn’t much I could do about it. However I’m keeping the AC wiring up high and the signal wire is shielded and passes along the bottom of the case. I hope this is good enough.
When testing the transformer what is it I’m looking for? Where am I measuring from?
Measure the ohmic resistance of all windings, primary and both secondary. First, disconnect the transformer leads from the rest of the device. Then connect the transformer via fuse 3AT to the mains and measure the voltage on the secondaries. If you don't have any experience, consider a life insurance policy first. 🤣
Way too complicated and it seems unnecessary as you already verified it to be OK. It got a firm kick under its *** but survived. Inductive stuff is also next level material. The diodes are the ones that need preventive replacement as these had lightning currents.
I would replace those and carefully check that they are soldered in OK and then again test/measure the PSU and pray it will stay that way for years to come 🙂 IMHO it seems that your experience is (yet) insufficient but you learn fast 😀
The learning curve of heavy destruction is not steep, it only costs some money and after a while you laugh at it.
I would replace those and carefully check that they are soldered in OK and then again test/measure the PSU and pray it will stay that way for years to come 🙂 IMHO it seems that your experience is (yet) insufficient but you learn fast 😀
The learning curve of heavy destruction is not steep, it only costs some money and after a while you laugh at it.
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My view on the rail fuses and a pair for each channel are that they will protect your speakers (not the amp) provided ofc that their value is chosen with this in mind.
The mains fuse will need to cope with both channels and the startup current which depending on your speakers might not be enough to save your speakers if one channels fails in a bad way.
The mains fuse will need to cope with both channels and the startup current which depending on your speakers might not be enough to save your speakers if one channels fails in a bad way.
I don't know exactly, let's say for that transformer, the primary is about 3 ohm, each secondary maybe 0.7ohm