Crate KX-80 Keyboard Amp fuse pops immediately

[kc8adu]

Re: Crate KX-80 Keyboard Amp fuse pops immediately

those caps near the resistors are cooked.they should be yellow like the others.
shorted diodes,shorted transistors on the heatsink are the top suspects.

[999999999]

Re: Crate KX-80 Keyboard Amp fuse pops immediately

The darkened area appears to have a couple diodes, but at least on one I see "1N 53..." which is usually a zener diode. Can you get the complete part # off both of those?

Is this a single output channel amp, meaning it only drives the one or pair of integrated speakers? My first guess would be it blew one of the output transistors on the heatsink.

[retiredcaps]

Re: Crate KX-80 Keyboard Amp fuse pops immediately

1) Circled in red are four diodes that probably act as a bridge rectifier. If your fuse is blowing as soon as you apply power, one or more of these diodes could be shorted.

2) Use your multimeter's diode test function to see if they are bad. Post your measurements. You should have 8 readings (2 per diode).

3) What is your budget for a multimeter with capacitance measurement capabilities?

4) Post a picture of your current multimeter for one retiredcaps' bonus point.

5) If you are going to do more troubleshooting, an ESR meter is more useful than a capacitance meter.

[ajsemtb]

Re: Crate KX-80 Keyboard Amp fuse pops immediately

photos...

[ajsemtb]

Hello, I have a Crate keyboard amp that I use as a monitor that has been dying for a while, I think, and finally bit the dust. What happened this time is I turned the power switch on and immediately I saw a bright white/blue flash inside the case around the side of the cover, and all the LED's blinked and shut off immediately.

Prior to this, when the power switch has been turned off, it clicks or pops, then a high pitched squeal that goes up in pitch for a second or so then it shuts off.
But that has been going on for a long time.

So, i opened up the case, replaced the 2Amp 250V slow blow in line fuse, tried it again, immediately it blew.

I have pictures of both sides of the board, I did notice an area that looks like it is burned or was heated. Can anyone identify what the components are in this area? I know what capacitors look like, but its the black thingies that I don't know what are.

Anything that would immediately come to mind would be appreciated also.

thanks in advance, AJ


Also, I don't have a capacitance meter, but I'm going to go buy one. I have a nice multi-meter, but it doesn't have the capacitance function. Any recommendations on a meter would be appreciated. Probably going to fry's unless you can recommend something on Amazon much higher than I could get at fry's. thanks