Carvin KB1000 Keyboard Amp Help

[misterc57]

I am trying to get the output board out (green one in upper right corner of picture). Only way it is coming out is to move either the PT or the power module (upper left corner, marked 1110).

I removed the bolt connecting the PT to the bottom of the case. It is not moving (like it is glued down).

I removed the bolts holding the power module fan to the back of the case. It is not moving (like it is glued down). Wobbles a little bit. Fan housing is broken and cracked, looks like from prior attempts to move the module.

No other screws or bolts to be found connecting either the PT or the PM to the case.

Anyone been down this path? Any suggestions? Thank you!

[Enzo]

The transformer is just stuck to the chassis. There is a rubber gasket under it. Get a wedge under one side of it, and pry it loose. Only the one bolt should be holding it. They wouldn't have glued it.

Power amp module - are there any screws up through teh bottom into the heat sink?

[misterc57]

need schematic...

No screws on the bottom. I was able to remove the 4 screws holding the fan to the heat sink, at that point I was able to wiggle the entire power amp module enough to free it from the cabinet.

Now I have the output board out.

The person I got the amp from told me it died when being pushed real hard. He replaced a capacitor and said it now turns on but no sound. I quickly found that something was burning when turned on. This is where I found C13 on the output board burned. See pics. This I believe is the capacitor that he replaced. There is some cleanup of soldering and testing that needs to be done in this area. However I cannot find the schematic for this section of the amp. This board is where the power enters the amp and where the outputs are located. I need to figure out why C13 is cooking.

When I plugged it in my bulb limiter did not light up and I did not see excessive current draw, however I did smell the burning and shut it right down.

[Enzo]

The yellow caps is melted from someone leaning their soldering iron on it.

Did you CALL Carvin and ask if they could provide the schematic?

[TomCarlos]

Is this the right schematic? Carvin KB1000.

[nickb]

Here is Rev B http://bmamps.com/Schematics/carvin/..._Schematic.pdf

AH! Simulpost!

[misterc57]

I am not finding the power supply on those schematics. Trying to find that area with C13. Am I missing it?

[misterc57]

The yellow caps is melted from someone leaning their soldering iron on it.

Interesting (I did not think of that). I could smell burning plastic when I turned on the amp. I did not observe burn evidence any where else. Will keep digging.

[nickb]

I am not finding the power supply on those schematics. Trying to find that area with C13. Am I missing it?

The PSU (top left) & Power amp is here:

Carvin_KB1000 Pwr Module RevE.pdf

[52 Bill]

Interesting (I did not think of that). I could smell burning plastic when I turned on the amp. I did not observe burn evidence any where else. Will keep digging.

The plastic plug in photo 3 looks like it is burning. Fairly common problem.

[misterc57]

Hmmm, not finding it on that one either. Interested in finding C13, C14 and F1

[misterc57]

>>>The plastic plug in photo 3 looks like it is burning. Fairly common problem.

Yes it is. There is a big blob of solder next to the burn area. This is part of the cleanup I want to do but still like to see schematic of the area before starting.

[g1]

F1 in lower right area by AC line plug. May not be exact schematic, I think C13 & C14 may be across the AC primary side.

[Enzo]

Or one across and one to ground from hot.

I suspect the yellow cap is original, and he melted it replacing the cap that is brown, between the fuse and the big resistor. I also think the connector isn't burnt electrically, I think he charred it trying to solder in that same cap on the solder side.

As to burning smell, "burning" parts are not necessarily going to look blackened. Sometimes they just look shiny, sometimes they don't look different. It could be anywhere in the circuit.

I'd agree, this schematic is probably close, but not exact.

[misterc57]

still burning

C13 is the yellow cap, C14 is the brown cap between the fuse and large resistor. I think you are right that C14 is the one that was replaced.

I removed both caps and tested them, they both test good, C13 is a .047uf and C14 is a .1 uf.

With everything cleaned up and back in, I tested the amp. After turning on the amp I can see some sparking and smoke at the base of C14 (the base side next to the big white plastic connector where it looks burnt). The power indicator light is on, but that section is cooking so I shut it down. Also I do not observe any high current draw and the bulb limiter does not light up.

That 4 pin connector has two brown wires which go to/from the on/off switch, and two black wires that connect to the primary side of the PT. If I ohm out these pins feeding the PT I read about .5 ohms.

At this point I have no idea why this is happening and the schematic does not match what I have. Tomorrow I am going to try and draw a schematic of that section.

Any suggestions much appreciated. Thank you