Garey, Mike ....others as well,
The saga continues...
I lifted the lead of the Q7 base coupling cap ( the .1) and even tried
a new one of .1 and ,47..
Q7 voltages are:
Base = .5v
Emitter = 0v ( .003)
Collector = 18.5v IS IT SUPPOSD TO BE THAT HIGH?? Don't think so.
Audio at 12:00 id just ok , not loud and distorts at 3:00 but not super
loud either.
Open for ideas. Thanks for all the help...I want to fix this baby...as
it sure hears well now that I have done the full alignment.
73,
Lee
-----Original Message-----
From: Garey Barrell <[email protected]>
To: drakelist <[email protected]>
Sent: Sun, Apr 3, 2011 11:07 am
Subject: Re: [Drakelist] Fwd: My R-4B audio?
Lee -
Mike has the answer. A leaky 0.1 uF coupling cap is the only, (also
least likely!,) thing left. I wondered about that last night, but the
resistor was more likely, even a cracked solder joint! :-) Being
right
up against R137 doesn't help either.....
Easy to check, just disconnect one end and see if the Q7 voltages go
where they should be.
I would replace it with one of the Panasonic metalized polyester film
caps rather than a ceramic. It will actually be smaller than the
ceramic, and a much better audio cap.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Mike Millen wrote:
Garey Barrell wrote:
Lee -
OK. You need to measure resistor R131. Q7 is NOT turned on at all,
there is no current through it.
The middle lead is the Collector, not the Base. So the Base is 0.46
which isn't enough. The Collector is 18V, indicating that there is
NO current through R148. I suspect either R131 has way up in value,
or there is a cracked or rosin solder joint in that area.
I had the same problem & assumed Q7 had failed.
After changing Q7 with no improvement I determined that the only part
left that would explain the fault
was a leaky C167, a 100nF ceramic.
It looked fine, but fitting a new one brought everything back to
normal. (It was leaking away the bias from R131)
It's pretty unusual, but ceramics can go leaky, too.
73,
Mike
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