Finding pre-amp output in mini system

[chuck55]

I got my Denon UD-M31 apart again and found 5 wires to the chip-amp board:
Red / Orange / Black / Blue / White
(There are also 7 smaller white wires but I think these are for some control function).
I got the schematic from Denon but it is no help as to explaining the colored wires that go to the amp board.

So I would appreciate some help with:
1) Can I measure the voltages of these wires to find out if they are, indeed, the preamp outputs and, if so, for which channel?
2) What happens if I get, say, the (+) for the right channel and the (-) for the left channel? How would I know if I found found both which go to the same channel?
3) Would the voltage go up and down as I adjust the volume level?
4) Can I tap off these wires as to retain the original amp function of the Denon and route the tapped-off wires to separate RCA outputs to hook up a gainclone amp? The Denon has 4 RCA's for tape input/output so I would probably just cut those wires and solder the pre-amp wires to those 4 RCA's. (Note that I would not be running both amps at the same time).
5) I'm thinking the 5th wire may be some system ground. Any way to verify that?

Thanks

[chuck55]

Can I measure while wires are still soldered to amp board.
Surely someone here must know how to do this.

[Minion]

Well if you are trying to find the output of the pre-amp (input to the power amp) and it uses a chip amp then look at the chips datasheet and trace the input to the wire from the preamp output , the datasheet will tell you what pin on the chip is the input which will also help you find the wire that leads to the input...


Cheers

Once you found the wire you can tap off it.....

[chuck55]

"look at the chips datasheet and "

Thanks but I have the schematic and it does not show this.

Is it possible to measure the voltage between wires as I don't have a wiring diagram that shows the chip amps?

[Minion]

Im not talking about the schematic , the datasheet for the chip amp will tell you what pin on the IC is the input pin , now you find the input pin and follow the copper trace on the PCB back to were the signal comes from the preamp to the power amp ... should be fairly simple as long as the PCB doesn"t have more than 2 layers .....

Just find out (by visual examination) what type of chip is used in the amp and then do a datasheet search on the net...

[Enzo]

You look on the schematic and see that the chip amp is some number - for example LM3886 - and then you enter that part number into google. Google will then present you with a variety of sources of the data sheet for that IC. Not only that, but if you look up the part in Mouser, for almost all parts they sell, there is a link to a data sheet on the page.

www.mouser.com

[chuck55]

Thanks. It will be more difficult to get this PCB apart.
Aren't there two inputs and two outputs? Does the data sheet show all four?

[chuck55]

Well, it says:

7812A JRC M4013M on one

and:

7806A JRC M2026M on the other

Can't find a data sheet at Mouser, alldatasheet.com. google search either.

Theses are bolted to a heatsink with what looks like heat conducting paste so figure they are the I/C's

[pacificblue]

Those are both voltage regulators. Look for something bigger with more pins. If you have built a gainclone you should know, how a power amp IC looks.

Start your search at the speaker terminals. The wires or traces that end there start at the power amplifier section. If they lead you to transistors instead of a chipamp, you will have to send the schematic to somebody for help. Don't post it, because that might bring you into trouble with Denon.

[Minion]

The chips (if indeed it is a chip amp) will be bolted to a big piece of metal called a heatsink .....

Cheers