My kurzweil micro piano will come on and the lights are on but theres no sound,even the demo will not play.the unit is plugged in correctly.i have not used it for several years.

You're correct, that's a power supply problem, but it may also be the power supply connector on the keyboard. If you have access to a voltmeter, check the power supply first.

Try to re-initialize the unit(factory reset). If the keys are the problem then the rubber key contacts need to be cleaned or replaced. Contact a local service center for help.

The place to get the best help for Kurzweil gear is Sweetwater Sound.
Other than that, always use it in stereo mode with a decent sound system. Always use speakers with at least a 15" woofer and a horn to get the full range of sound it's capable of.

The Kurzweil SP3X is a popular stage piano known for its high-quality sound, responsive keyboard, and versatile features. Some of the advantages of the SP3X include its excellent sound quality, which is achieved through Kurzweil's advanced sound engine and a variety of realistic instrument sounds. It also has a highly responsive keyboard that is suitable for playing a wide range of musical styles. Additionally, the SP3X has a variety of features that make it a versatile and useful instrument for live performances, such as its built-in sequencer, arpeggiator, and various effects. Overall, the Kurzweil SP3X is a reliable and powerful stage piano that is well-suited for both professional and amateur musicians.

It sounds like there may be an issue with the piano sounds on your Kurzweil sp4-7 keyboard. One possibility is that there may be a problem with the software or firmware of the keyboard, in which case you may need to update the software or contact the manufacturer for assistance. Another possibility is that there may be a problem with the internal hardware of the keyboard, in which case you may need to have it repaired by a professional technician. In either case.

It may be the line current at those venues.

If you have a lightweight switchmode supply, you can try adding some ferrites to the power cord from the wall. but you almost need to switch to an older style heavy transformer supply for reliablity. It is my guess there is a great deal of noise on the supply current at those vehues you have had problems at. That noise does not play well with switchmode.

When you turn a device on it is usual for it to test all lights. The three lights left on is an error code. It could be that one of the keys has got stuck down or that the instrument see it as stuck. There might be debris in the keys. Try shaking out any crumbs. Try vacuuming. Check all controls are in default position. Check noting stuck in any of the ports. The manual may have the error codes listed.

If the unit uses a wall transformer power supply, verify that it is correct and in good shape. If it is DC and half of the rectifier is gone, then result would be what you are observing.

Given its age, this unit needs a little TLC. Units of that vintage used some capacitors that may have dried out a bit and need to be replaced. There are also op-amp ICs internally that may be defective. I would suggest a visit to a service shop that works on keyboards as not all do.

Keep us posted.

Dan

I would also be inclined to check all the larger electrolytic capacitors in the power circuits as well for AC bleed.