optic drive 700x2

[megael9]

hello everyone,
this opti drive 700x2 have 65 volts at one of its channels, however no shorted output or driver transistors.
any idea?

 

[Perry Babin]

Photos?

 

[megael9]

here is the picture.
also, i purchased the repair tutorial a long time ago, can I download the latest version?
thank you

 

[Perry Babin]

Yes. Email me.

babin_perry@yahoo.com

I think I'd start by pulling the pre-drivers to see if it still had offset.

Does it draw excessive current if you touch a load across the speaker terminals?

Is the bad channel the one with the transistor that was replaced?

 

[megael9]

with a speaker as a load it it consumes about 10 amps.

 

[megael9]

with Q208, and Q209 out of the board there is no voltage at the out put.

 

[Perry Babin]

Check them and reinstall them if OK.

Then try it again, removing the predrivers (Q206 and Q207?). Work your way back until you narrow down the section that's driving the DC.

 

[megael9]

i took out every semiconductor, and i went back as far as taking out of the board q202, q203, q204 and q 205.
all semiconductor checked ok, and no voltage at the output up to this point, but it is kind of difficult to trace back from here.
are q601, and q602 part of what i need to check?

 

[Perry Babin]

I can't really read the numbers on the board. I'm assuming that the 600 series are something like the regulators.

I'm assuming that Q202-205 are the small transistors that make up the two differential amplifiers. Is that correct?


Are you saying that with all semis but the 4 above in the circuit that there is 0v DC on the output of that channel?

Is there excessive DC driving into the differential amp stage?

Did you check those 4 transistors (as well as any you pulled) for leakage and open junctions?

Is there a Q201 that's used for muting?

 

[megael9]

I pulled out all semis from the board and tested them. And while I pulled them out of the circuit ( by sets ) I tested for voltage at the output and there was no voltage at the speakers terminals.
I also pulled out Q601 and Q602 and there was voltage at the speakers terminals.
Both transistors checkered Ok.
About Q201, I don’t see it on this board.

 

[Perry Babin]

What are Q601/2 doing in the circuit? To me, they appear to be the ±15v regulators.

I don't quite understand. When, after you started removing stages did the initial (62?) volts across the output drop to 0v?

 

[megael9]

Yes, the voltage dropped to 0 volts after the removal of any set of components

 

[megael9]

Perry, do you have the schematic or a similar one for this Amp?

 

[Perry Babin]

Not anything that has matching circuit board designations. It's likely just a generic amp like any of the power acoustik or others with more/larger parts.

 

[megael9]

i found this schematic on the web, the components location numbers match on a 95%, i was able to confirm that the pre amp for both channels are working fine, and it looks like the driver circuit is the problem, however, except for the output transistors, i exchanged all driver circuit components from the good channel to the bad one and vice versa, and the problem remains on the bad channel. i also noticed that the bad channel have a square wave at its output, instead of audio signal. the output filter composed of c190 and r296 is working ok

 

[Perry Babin]

Is R251 connected to the differential amp bases on one end and the emitter resistors on the other end?

 

[megael9]

yeap, R251 (20k ohms) was open.
replaced it and it all working fine now.
thank you

 

[Perry Babin]

The information about it producing a square wave narrowed it down. The gain was essentially infinite without the feedback through that resistor.

 

[megael9]

Thank you for the extra information.