X, Amplifier, problem

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Jeff Lance2004-02-23 22:21

Hello. I own a pair of Acoustat X speakers with the Servo Charged Amplifier. There my 5 amp fuse on one of theme burned out and I could see quite the flash of light where the string of diodes are located beneath the circuit board. We will be rebuilding the diodes but a schematic of the original circuit would be very helpful. Is this available? Also, any history on this problem would be helpful. I can see that this has been a recurring problem. Thank you, Jeff Lance


Mike Savuto2004-02-23 22:21

Jeff, when the 5amp fuse burns out it is because of a problem in the high voltage section of the amplifier. It is usually from one of two problems.

The first is that the high voltage transformer has shorted. This requires replacement of the transformer. It can be tested by desoldering one of the two high voltage leads from the transformer underneath the circuit board. The two leads are red and yellow inside of a sheath. When one is desoldered, tape it off with electrical tape and make sure that it won\'t make contact with any other parts underneath. Then replace the 5 amps slow blow fuse and plug the amp back in. It does not need to be connected to the speaker for this test. If as soon as the high voltage circuit comes on the fuse burns out, the transformer is bad.

The second is that one of the large high voltage diodes underneath has failed. These are hard to test without replacing them, so it is not something you can do easily. You can get the parts though and replace them yourself if you are reasonably handy with a soldering iron and observe the polarity carefully. I suggest this be done by a technician as the voltages here are very high.

There are some other causes for the 5amp fuse to blow, occasionally the big grey capacitors next to the transformer short out, and there can be carbonizing of the circuit board underneath the tubes that will allow the tubes to go into thermal runaway.

The \"string of diodes\" you refer to are probably either the 150vt or 17vt power supply diodes. If they fail, and the stock 150vt parts often do, the 1/2amp slow-blow fuse blows, not the 5amp. You need to check both fuses to be sure.

The schematics are available from links on this website, but if that is a problem and you only need the schematic and not the whole manual, I can email it to you.

The second problem, that is of failing diodes in the 150vt p/s, is one reason why we suggest that these be upgraded. It was a common problem with early stock amps and a bit less so with later amps. After those parts are upgraded, the fix is pretty permanent. Michael Savuto

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