Hi, I have an old roland D 20 that just makes a really loud constant white noise type sound when turned on. Any ideas to the problem?

SOURCE: It's a Roland HP-7e digital piano about three years old.

You may need to clean the contacts which are usually conductive rubber. I explained stuff for another Roland problem with two keys that were intermittent. I have an EP-7 that I had to do the cleaning of the key contacts. Use 91 or 99 % Isoprophyl alcohol to clean BOTH the conductive "pill" (Black under silicone rubber domes) AND the traces on the board where they press. Clean gently as the traces have a hard black coating.

SOURCE: Deville 212 overdrive channel making Loud humming noise

It sounds like a filter capacitor(s) has failed. The electrolytic caps dry out and cease to perform allowing unfiltered power to reach the preamp sections and get amplified.

Being this is tube with high voltages, an experienced person should work on it due to shock danger.

I assume you checked the tubes for shorts as well as emission since a heater to cathode short could cause this as well.

Testimonial: "Thanks man. and thanks for the fast response"

SOURCE: I have a Roland HP 101 digital piano however certain dont sound

White spirit is NOT what you should use. Mineral spirit leaves a residue film.

Use 99% isoprophyl alcohol.

ALSO inspect the contactboard for cracks by candeling with bright light behind it.

Testimonial: "bur isnt it strange that certain keys have stopped working? ie most the A keys"

SOURCE: Marshall MG50 DFX makes a squealing noise on power up

Yep, chalk that one up to poor design...The amplifiers are going out of balance during power up and down. Two seconds is pretty long... Try turning down the gain during power on and see if that affects it.

The pop on turning off is normal... None of these have speaker disconnecting hardware that is necessary for very high power amps. The biggies have hardware that checks amplifier is balanced before connecting the speakers and a relay also cuts the speakers immediatley on power down. As power goes up and down the circuitry comes to equilibrium and until it does, strange things happen.

I would investigate the CONDITION of the filter caps for the main power because if they age to a higher internal resistance that COULD cause the high freq oscillation on power up... Two seconds is MUCH too long.

There should also be some non-electrolytic caps NEAR the power output transistors to handle high frequency supply power bypassing.

Check the power bypasses that service the preamp stages. Look for pregnant electrolytic caps that have failed.

Ultimately, you MAY need an oscilloscope to isolate the high freq problem.

Testimonial: "Thanks - great advise! The gain position makes no difference. I'll try to chase the problem with my Tek Oscilloscope ;-)"

SOURCE: Roland U-20 no sound

you need to check your midi connection into the unit, check the cable and the channel that you are sending.