Beocenter 7002 - Amplifier problem

Reply

Eugenio Posted: Fri, Jan 18 2013 5:06 PM

rated by 0 users

Hi all

I have some problems repairing my Beocenter 7002 amplifier; main fuses burned.

One channel is good, the other needs the replacement of IC200/Ic201 and 0,36 ohm resistor.

With this solution the IC began to be hot at 2 volts (2 of 30V); so replaced all the transistors and diode (step by step).

Actually the amplifier could be powered at 30Vac of 220Vac and all the values on the circuit are similar on both channel BUT cannot lower enough the idle current trimmer between the two IB Base terminal (trimmer is new - 220 ohm).

If I raise the feed to 35Vac the voltage on the Ic200/201 emitter lower to 0,002 v and the voltage across the 0,39 resistors increase a little causing the IC temperature to raise slowly (because the IC base voltage increase to 1,3V).

The thing that I don't understand is why the IC temperature increase if the base tension on the other Transistors is the same as the other one in the working channel.

Actualli I'm making a "voltage document" and I will have more details tomorrow.

Best regards to all! :)

Eugenio 

Reply

Dillen replied on Fri, Jan 18 2013 5:19 PM

rated by 0 users

Always a headache to repair burned DC-coupled amplifiers. Even when you think, you have
it all fixed, some marginal component suddenly decide to show off and you can start all over.
In your case it could be that a resistor in the idle current circuit, or the trimmer itself, has changed value - or
a transistor somewhere lost a B-E connection.
Best solution, if possible, is to replace all components in the affected channel - or in case of this Beocenter
the whole module.

Martin

Reply

Eugenio replied on Sat, Jan 19 2013 11:40 AM

rated by 0 users

Thanks Martin, following your hints I found the problem!

My beo is a 7002 version BUT it has the 7007 ampli version so when I replaced the burned R225 reading the (wrong) schematics with a 100 ohm resistor I made the TR211 working with a different VBE voltage. The other channel has the correct 180 ohm resistor. Never replace aniting in the deep of the night! ;)

I found the 7007 ampli version in another beo 7002, so I think they could be the last version unit before the launch of 7007 version?

Thanks again.

Eugenio