Peavey KB2

[Zipslack]

Ooops

My bad...I don't have the schematic and assumed it was like other KB models I've seen...sorry for the disinformation.

[andyjazz]

Hey thanks to everyone who bothered to help! You coulda just said "tough titty figure it out yourself." I ask the dumb questions here because those with experience can often offer insights that reading a troubleshooting guide or a data sheet cannot. I am truly grateful for the help. One more question: Seeing as how I have U2 and U3 detached and sitting on my desk and one seems to be testing "open." Should I get new ones, install them and go from there?

[J M Fahey]

one seems to be testing "open."

Well, not really.
These are not transistors but complex circuits (over a dozen components there) so diode testing simply does not apply.
Anyway, *if* you have a couple new devices over your bench , it won't hurt using them.
Here the big suspect is the LM3886, which should be carefully replaced, as in : pamper the board, use a good solder sucker, you may finish with a little solder wick; the idea is to pull the old part *easily*, definitely not wiggling which tears pads and tracks.

[andyjazz]

Thanks JM for the reply.

Once it was determined that these were not transistors but IC's I dispensed with the "diode" checking. Obviously a diode check is about forward voltage etc. A diode is a valve that should test relatively low Ohms one way and high Ohms the other, this is probably the most basic explanation I guess. The "open" I'm refering to is just a basic continuity check that I did on the two V reg's. One tested good continuity the other didn't. Kind of a primitive test but WTF. I ordered 2 each of the 7915 and 7815 anyway, might as well replace them they're only like $.49 a piece.

Anyway thanks for the advice on the LM3886. I ordered one yesterday. I have a pretty good vacuum solder sucker and I have some experience in damaging boards/breaking pads with too much heat. (They don't put a temperature knob on those things for looks!) And so I am aware of the care that needs to be taken in dealing with these devices. Thanks for your input and I'll post again when the parts come in.

[Enzo]

If you can suck out the solder and lift the IC, great. But a couple tips. First, if you are having trouble getting a good melt in a hole, it often helps to add a little fresh solder. That will be easier to melt. And also, it is often easier to snip the part off, leaving just its legs. Now you can individually melt the solder and pull each leg out, then clean the newly legless holes. That many times will leave the holes cleaner than trying to clear them with a component lead still in the way.

[andyjazz]

Just a note to tell everyone that most of the parts came in today. The V reg's and the big 11-pin LM3886. The LM1875which drives the tweeter is on back order. I went ahead and installed the parts that came. I don't want to power up until the 1875 comes. Probably wouldn't hurt anything but I guess I can wait. All parts went in/out with no issues. (Whew! I hate breaking pads) Got a Peavey Supreme 160 I'm working on now.....Happy Thanksgiving to all in the US and those who celebrate it overseas.

[Enzo]

The LM1875 is National's version of a TDA2030, so if you have any TDA2030 or 2040 in stock, you can use one of those.

[andyjazz]

Thanks Enzo. No I don't have IC's of this nature in stock. I'm just beginning to build up some inventory and it's mostly discreet components and tubes, harware etc... I ordered these parts from JAMECO - first time I've used them. I ordered from them mainly because their website was relatively easy to find my way around on. I wonder if when I get the LM1875 it will have TDA2030 stamped on it!

[Enzo]

Probably not, any more than your new Ford Hubcap will have Chevy on it.

National makes the LM part, and other companies make the TDA part. They are equivalent and work in one another's place, but they are not the same part. SO, no I wouldn;t expect any label surprise.

[andyjazz]

Just a note to tell everone that I got impatient and went ahead and fired up the KB2 and everything seems to be working fine. Turns out a replacement LM1875 wasn't needed. I'm hoping that it will find a good home as a practice home for someone. Thanks everyone for your help.

[mexico1280]

Saludos desde Mexico. Espero puedas ayudarme, ya que necesito el diagrama de la sección de control de volumen (mezcla). Ya que se quemaron algunas resistencias. Gracias al diagrama pude reparar parte de mi bafle (fuente de poder) muchas gracias. Espero puedas ayudarme.

Greetings from Mexico. I wait for you can help me, since I need the diagram the section of gain control (it mixes). Some resistance were burned. Thanks to the diagram I could repair part of my speaker thank you very much (power main). I hope you can help me.

- - -

ANdy, you are beiing misled. I have to point out to the well-meaning folks posting above that this amp uses a LM1875 to drive its tweeter, and an LM3886 to drive its woofer. So those won;t be in three-leg TO218 cases, or for that matter, three leg anything. There is a small push pull discrete amp for the headphones, runs off +/-15.

If there is DC on the woofer, your LM3886 is almost certainly shot. The two ICs I mention are indeed on the heatsink, but you won;t be making meaningful tests on them with a meter unless you find the output pin shorted to a supply pin. We still don;t call them op amps, they are full fledged power amp ICs.

The LM3886 is that 11-leg thing. I'd remove it, and check that there are both +20 and -20 volt power supplies getting to it.

I attached the powr amp diagrams for those who need them.

[Enzo]

Hola

Look above here in post #14 for the power amp schematic

Hola de los Estados Unidos. Earler I el dibujo del amperio de energía KB2 en el poste #14. Usted lo encontrará allí. También, aquí ahora está la sección del preamplificación. Y siempre que usted necesite nunca cualquier diagrama esquemático del Peavey, usted puede entrar en contacto con customerservice@peavey.com y él le lo proporcionará.

[mexico1280]

Disculpa el retraso para contestar. Muchas gracias por tu ayuda e informacion . Ya pude reparar mi bafle . Un fuerte abrazo desde mexico.

It excuses the delay to answer. Thank you very much by your aid and information . I already could repair my speaker . A hug from Mexico.

Atte. Fernando "Mexico1280"

Hola

Look above here in post #14 for the power amp schematic

Hola de los Estados Unidos. Earler I el dibujo del amperio de energía KB2 en el poste #14. Usted lo encontrará allí. También, aquí ahora está la sección del preamplificación. Y siempre que usted necesite nunca cualquier diagrama esquemático del Peavey, usted puede entrar en contacto con customerservice@peavey.com y él le lo proporcionará.

[barri]

how many volts is coming out from transformer secondary ihave kb2

i have kb2 peavey amp i check the voltage fro, transformer after the bridge diode and it reads 45volts dc also in the neg. side is it right please help

[52 Bill]

The schematic posted above shows a bipolar supply of + & - 20 volts dc as measured to ground. If you are reading across the two supplies, you could get about 45 volts.

How are you reading this voltage?