|nosaj||7/24/2018 8:19 PM|
|Yamaha PSR260 dead.|
I have this Yamaha PSR260 keyboard someone asked me to look at. They gave me a 24v powerpack( wrong power pack. I found a 12v center posistive which is correct. Get nothing but loud hum. Backlight comes on now digits on lcd. How much voltage input can 5v regulators handle?. My big question is there anything in this circuit to prevent the use of a too high voltage coming in. If not where is an example of what it would look like. I would think something like an input diode to limit the voltage ( a zener maybe?)
circuit is on the last page.
|The Dude||7/24/2018 8:31 PM|
|Check input and output voltages on your regulators. Most of the time, a wall wart puts out more than it says depending on load. If the voltage was much higher than 24, it may have taken out C106, which should filter out any remaining hum from the wall wart. There's a series diode there, but I don't see anything for over voltage at first glance.|
|Enzo||7/24/2018 8:37 PM|
|No protection other than a reverse diode. But nothing for over voltage.|
You have a couple 5v regs and a 3.3v reg. You got those voltages leaving those regs?
The power amp is more directly exposed. It runs on 9v (Which is really your 12v, normal) The speakers are isolated with caps, but check the two outputs from the IC for DC. They should be at about half the power supply, lik 5-6vDC. If they are at 12vDC, the IC is likely blown.
Oh, does volume control affect this hum?
|nosaj||7/25/2018 8:03 PM|
Hooked keyboard up to a current limited DC supply soon as I turn it on it pegs the amp side of the meter. Series diode test ok on meter.
Vol does not affect hum.
Still have to check the IC outputs for DC. I really need to put a computer in the shop.
|Enzo||7/25/2018 8:21 PM|
|OK, if you only get 3v at the power in jack, there is no way to have anything larger than that inside. No point in worrying about the regulators until you find what is loading down the power supply.|
It is possible the INPUT side of a regulator is shorted.
But approach it systematically. Power comes in and branches off. It goes through filters to the power switch. Does it load down your supply if the power switch is OFF or unplugged? If so, it points to the power input filters. If the power switch off removes the load, it is inside. Measure resistance to ground on the circuit side of the powr switch (The regulator inputs). Any indication of a short?
You tested C106, but there are at least three other caps to ground.
There are two 5v regulators. You can remove one or the other to see if it is dragging us down.
|nosaj||7/27/2018 6:27 PM|
When I go back out I will see if everything else functions ok display, etc. Will check signal at IC501 pins 10 and 11 ( like a preamp out?)
|Enzo||7/27/2018 6:55 PM|
|IC501 obviously shorted then. 11 and 12 are the inputs.|
|nosaj||7/28/2018 9:46 PM|
Thanks for your help Enzo