Roland HP-860 electronic piano has HUM

ESR meter kit build it and then check the ESR in the power supply electro's

Thanks Franc. I have tried that pdf link twice and each time I get a pdf saying that the server is busy & to try again later!

I'd like to try WES in Ashfield first. Only problem is, they're closed whenever I pass by.

On Mon, 8 Sep 2008 08:15:11 -0700 (PDT), "Josh9.0" put finger to keyboard and composed:

I've uploaded it to my web space:

I looked in the WES catalogue first but was unable to find it.

This is the semiconductors section:

- Franc Zabkar

Have you ever heard the hum when you pull the cord on a guitar amplifier, or some cable going to your home stereo? What do you get? A loud hum! This is momentarily because the ground is lost. Might you have a loose ground to one of the boards ahead of the audio amplifier (or in it)? There should be a potentiometer for volume control at the head (pre-amp) section of the amplifier. Remove the wire (or cut the PCB trace) where the input goes into the amp. Connect an auxilliary source, such as the output of a cd player or a radio tuner, to that point. Do you hear a hum? If yes, the problem is in the amp itself. If not, the problem is ahead of the amp.

Of course, check the power supply first, and LOOK FOR LOOSE GROUNDS.

Mister

I've already said about the bad grounds twice so far in this thread, and once I think that he has replied that he hasn't found any, but I'm with you there. However, I don't think that he has the necessary professional background in service, to be able to run down a problem like this by disconnecting things, and running alternate grounds ... :-\\

Arfa

Reminds me of an on-site repair job at a Scottish University (on a DVM). The Phd looking over my shoulder at the circuit points to the 1uF capacitor in the integrator section and says that will be the problem. I went for the 10M resistor rather than the polypropylene cap...

Geo

Phd

Please tell me more, elaborate. This is interesting

I would suggest that he is talking theory vs practical knowledge. Given the same situation, where an integrator was formed from a polyprop cap and a 10M resistor, I too would go for the resistor every time over the cap, because years of experience tells me that resistors over about 470k are far more likely to go high / open, even in non-stress situations, than that type of cap is to go faulty in any way ...

It is this type of understanding of the fundamentals of servicing, that I was referring to when I made the comment about disconnecting and subbing grounds. The fact that the Phd picked the cap over the resistor shows that he understood the theory of the circuit involved, so was in the right area, but did not have the required practical experience to know that the cap, even though it's the more complex device, was probably a hundredth as likely as the high value resistor, to be at fault.

Arfa