Telefunken V672D problem (solved)

[colonel_sanders]

(Edit:  Solved!)

Hi again guys,

I am trying to fix a friends V672D pre amp.  It was racked up by a guy in Israel.

One channel is creating a funny noise that increases in frequency with the gain knob.  It starts as a 'squeal' at low gain, and just sounds like a 'thump' at high gain.  I have uploaded a recording of the faulty channel here: http://www.homerecordingconnection.com/profile.php?action=music&id=1661#

It looks like there are a lot of older capacitors in there.  There is one newer electrolytic that looks like someone has replaced recently.  I'm gravitating towards these being a problem...

I read in a previous post (http://www.groupdiy.com/index.php?topic=8821.0) I read that the easiest way to trouble shoot this pre is with a signal tracer and a list of 'V672D hotspots'.  Does any one have a link to this 'hot spot' information?  The link the the other thread no longer exists...

If any one has an idea of where to start looking, it would be greatly appreciated!

Thanks,
Arie

 

[colonel_sanders]

Managed to track down a schematic

 

[colonel_sanders]

And a photo of the channel in question...

 

[colonel_sanders]

I've traced the signal from the input, and the noise seems to start at the collector of TS 6.  There is a new 220uF electrolytic, and a couple of old ceramic 82pF caps near the transistor.  Faulty transistor or capacitors?

 

[colonel_sanders]

I replaced C11, C12, C13 ad C14 and that solved the problem.  Sounds great now!

I think the problem was C11, an old green tantalum capacitor.  I replaced this with an electrolytic of the same value.