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KBA40 Amp Schematic [message #10484]

Sat, 14 February 2009 22:22

jessicaandtrent
Messages: 5
Registered: February 2009
Location: Alabama

Junior Member

I have a KBA40 Bass amp and I need a schematic for it so I can figure out what part melted when I hooked it up to a 15" sub and over heated it. I know that it is black and has 3 prongs on it but that's all I know abouth the part. but the schematics should tell me what I need to be able to fix it and get the amp working agian. It has two seperate boards. One for the controle knowbs (mounted on the front plate) and the ther for power input/ effects return and send/ headphone jacks (mounted on the back plate. The power converter is mounted to the speaker box. The box has a 12" sub and it is ported. I would like to just get this amp fixed. Please help. Confused

The Circuit board says 50 watt power amp on bottom of board.

Trent

[Updated on: Sat, 14 February 2009 22:28]

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Re: KBA40 Amp Schematic [message #10485 is a reply to message #10484]

Mon, 16 February 2009 06:34

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

Hello, and welcome to the board.
I do not think anybody here on the board has a schematic for that model. I would call Hanser music group in FL 727 793 0079, as they are the parent company for Kustom and their service department will mail you a schematic as they did for me some years ago.
The problem with your amp is that you most likly blew the driver/output IC and the fuse should have blown also.
If you take the number off of the IC and go to the NTE ELECTRONICS site, they have a crossover for use on their main page.
If you type that info in it will cross it over to a NTE part number that you can then order from Mouser electronics supply.
Just to note, most all new solid state amps of under 100 watts use some type of IC pack like this and they never have enough heat sink mass. I fix Marshall amps with IC packs all the time and they even have a fan.
When I fix these amps I always add more metal screwed to the face of the pack to dump the heat better.
With a solid state output stage anytime time you half the speaker impeadance, like adding a 8 ohm to a 8 ohm speaker for a total 4 ohm load, the amp will now get twice as hot at 4 ohms as it did with the 8 ohm load at the same volume level!!
Let us know how you make out.

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Re: KBA40 Amp Schematic [message #10489 is a reply to message #10485]

Tue, 17 February 2009 21:18

jessicaandtrent
Messages: 5
Registered: February 2009
Location: Alabama

Junior Member

It is not an IC I beileve because it was never attached to a heat sink. It stands alone in front of two tall round black things that has 2200uf50v on them it might of had 4 prongs on it a plus on one side and a neg on the other. I had taken it off so I could try to find it a few years ago and I have lost it since, but I remeber what it looked like. You just couldn't read anything but the +/- on the blob of black. It was rounded on the ends and about an inch long. I marked to board before I took it off and the plus side was soldered to the neg strip on the board and the neg end soldered to a srtip that went to one of those tall round black things.

Trent

[Updated on: Tue, 17 February 2009 21:26]

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Re: KBA40 Amp Schematic [message #10490 is a reply to message #10484]

Wed, 18 February 2009 06:28

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

In that case it may have been the diode bridge if it had four leads. The circuit board would be marked with a +/- and two side ways written S, which stand for the a/c voltage input terminal points. So that would be the four leads.
If this is so you can finds bridge rectifiers at any radio shack store that still carrys seniconductors. You will need to get one that is rated for at least the voltage of those 50 volt 2200 filter caps, one with a 50 to 100 volt 3 to 5 amp rating will do fine as will something larger, but the higher rated ones may have fatter leads that will not pass thru the circuit board with out drilling the holes larger.
If that bridge popped, your fuse should have also, did it?
if so you will need to fire up the amp very carefull as other semiconductors other than the bridge may be bad also.
You can check before you even by the new part by placing a volt meter set to read ohms across that +/- point on the circuit board, after about holding the meter leads there for 20 to 30 seconds if you read less than 2000 to 1500 ohms( or 2k to 1.5k)I will take a educated guess and say that you have other circiut troubles besides the melted diode bridge.
Once again, let us know what you find out.

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Re: KBA40 Amp Schematic [message #10491 is a reply to message #10490]

Wed, 18 February 2009 22:03

jessicaandtrent
Messages: 5
Registered: February 2009
Location: Alabama

Junior Member

The fuse did not pop. And a question that I have is if I buy one of those bridge rectifyers and solder it on the board and that is not what needed to be there will it mess up the board and also the board is not marked on which side is pos and neg does it matter if it is soldered in backwards?

Trent

[Updated on: Wed, 18 February 2009 22:09]

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Re: KBA40 Amp Schematic [message #10492 is a reply to message #10484]

Thu, 19 February 2009 06:19

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

Yes it does matter, when you removed the melted one did you note which lead came out of which hole, or which way it was facing when it was mounted on the board?
One way to tell how it goes in would be to look at how those 2200 mfd caps hooked up to it.The positve marked end of one cap would go to the + connection of the bridge, the negitive marked end of the other cap would go to the - lead of the bridge.

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Re: KBA40 Amp Schematic [message #10493 is a reply to message #10484]

Thu, 19 February 2009 06:21

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

If you get this re- hookup wrong, the new bridge may not blow, but alot of other semiconductors in the amp will until the fuse does blow!

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Re: KBA40 Amp Schematic [message #10494 is a reply to message #10493]

Thu, 19 February 2009 09:35

jessicaandtrent
Messages: 5
Registered: February 2009
Location: Alabama

Junior Member

I did note which way it was facing and I marked on the board where the pos and neg was but it didn't make much since to me. The pos side of the bridge was soldered to the ground circuit on the board. But it was working fine for years like that until I blew it. And how do you tell which side of the cap is pos and neg?

Trent

[Updated on: Thu, 19 February 2009 09:38]

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Re: KBA40 Amp Schematic [message #10497 is a reply to message #10494]

Thu, 19 February 2009 18:39

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

The bridge rectifier will either be in a flat package with all 4 leads in a row, or in a square configuration with the 4 leads at the corners.

Two of the pins need to go to the power transformer secondary wires. The other two leads are the positive and the negative voltage outputs.

Check the pc board. Two of the holes will connect directly to the power transformer.

Follow the traces of the other two holes. Where do they go? In most cases they will connect to the main filter capacitors.

These can be mounted on the pc board or can be mounted directly to the chassis. See if you can find them. Most amps will have two, but your amp could have only one. They will be marked with something like 2200uF or 4700uF. They will also have a marking showing which end or which terminal is positive and which one is negative.

If you have two then each one will have one of it's terminals connected to the main circuit ground. You can tell the ground connection because somewhere it will connect to the metal chassis. It may be connected by a screw that holds down the pc board, or it may be a wire to the input jack.

Come back and let us know what you find out.

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Re: KBA40 Amp Schematic [message #10498 is a reply to message #10484]

Fri, 20 February 2009 07:00

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

yesterday I got a schematic and a board layout of this amp from Kustom, so I can email it to you.
The schematic does not show a bridge rectifier or 2200 mfd at 50 volt main filters.
Its has four seperate didoes! and 3300mfd at 35 volt main filters. There are several revisions listed, along with the parts changes and since day one the amp has never had 2200 mfd at 50 volt filters according to the schematic.
At this point you will have to look at the board layout I will send you, and then tell us what burnt up. Then we can help you ot more.

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Re: KBA40 Amp Schematic [message #10499 is a reply to message #10498]

Fri, 20 February 2009 10:49

chicagobill
Messages: 2005
Registered: April 2003

Senior Member

Steve:
My example of 2200 or 4700 was only a guess at what could be in there. I'm surprised that it fell right in between my two guesses.

So if there isn't a bridge rectifier then I would assume that the blown up device he's talking about is a power transistor, thus the three legs.

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Re: KBA40 Amp Schematic [message #10500 is a reply to message #10484]

Fri, 20 February 2009 12:12

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

I am sorry Bill, that last post of mine was for Trent, not commecting on what you posted.
Just to update you, it now seems that we have have been taking about the amps output IC pack that is bad. Just like I guessed way back at the top of this thread.

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Re: KBA40 Amp Schematic [message #10503 is a reply to message #10500]

Fri, 20 February 2009 19:42

jessicaandtrent
Messages: 5
Registered: February 2009
Location: Alabama

Junior Member

I bought a bridge rectifyer that was a 4 amp x 400 volts and now it is up and running just like it was before. Thanks for all of ya'lls help.

Trent

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Re: KBA40 Amp Schematic [message #10524 is a reply to message #10484]

Mon, 23 February 2009 12:07

stevem
Messages: 4743
Registered: June 2004
Location: NY

Senior Member

Well, all that matters is that its up and running again, although I can not belive that the amps fuse did not pop!
I also would love to know why their are two vastly different versions of this amp and the Kustom repair dept did not ask me for a serial number or something!

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