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[zmix]

Here is a weird problem which taunted me relentlessly and inexplicably:

On the BA191 card of the 2245, tr-6 is shorting B-C and open B-E  whenever I engage the link switch...

All voltages are fine, the comp works perfectly until link is engaged.

I am down to my last BC184 (actually subbed in a 2N3904..  ) and desperate.. any ideas?




EDIT:  With a 2N3904 substituted in each channel, the unit operates perfectly, and linking does not destroy the transistors.

[Geoff_T]

Hi

As the fault appears to be unique to your situation... I have never heard of it before.. I think you ought to look for the fault rather than just correcting the symptom... replacing the transistor.

The transistor emitter must be connected to a short or load that draws more than the 100ma or so the BC184C can handle.

All you have done is fit a beefier transistor. I would check the B185 pin C area.

[zmix]

Geoff,
 Thanks for the reply.  I posted this question because it is an entirely unusual problem.
This initial symptom was "no gain reduction".   The shorted transistors appeared to be the cause of the loss of compression.  When I replaced them the units operated perfectly, however when linking the two the compression went away again, and the two transistors were again shorted. This is a new symptom, hence the post.   As I was in the middle of a mix and really only concerned about getting the unit up and running, which I did, I did not have time to look further into the issue, and hoped that someone might have encountered a similar situation.  It's interesting to note that tr-6 on the BA191 card is not itself connected to the link function, but I will investigate the BA185 suggestion.

PS: the 2N3904 isn't 'beefier' then the BC184, each is only rated at 200ma, but it does have a much lower Hfe.. which makes me want to test for oscillation when the BC184 is in the circuit.

[ssltech]

What's happening in terms of differential voltages at the link when the link is DISconnected?

Keith

[zmix]

ssltech wrote on Tue, 23 February 2010 15:57

What's happening in terms of differential voltages at the link when the link is DISconnected? Keith

Nothing abnormal, at full limiting I get around 5V form each, but typically it's between 1 and 2v...