[Hammarlund] HQ-180 no sensitivity and block bias question

[Jeff]

Hi all -

Been trying to troubleshoot an HQ-180.  I had it working for a while, 
but it has suddenly quit on me.

I've gone through each of the IF stages and it seems that I can get good 
peaks on all.  I aligned it before (along with two other HQ-170s), so 
I'm familiar with the process.  I had it hooked to an HX-500, using the 
"AVC" line to mute the receiver on transmit.

In moving through the radio, I have discovered that placing the 
Send/Receive switch into "Send" doesn't mute the receiver - in fact it 
is just the opposite.  When I apply a 60 kc signal to the IF strip, I 
can hear the signal out of the audio stage, but when I switch to "Send", 
the volume increases dramatically.  It appears to work the same in other 
stages.

I also notice that I can't zero the S-meter unless the adjustment pot is 
turned all the way to one end.  In addition, switching the AVC control 
between slow-med-fast causes the meter to peg left.

Finally, my documents show that the grid voltages on the 1st and second 
mixer should be -2.5 volts (approx), and this is zero on my unit.

I've replaced all the electrolytics and paper bypass capacitors. I've 
done a physical inspection, looking for grounded leads or physically 
damaged components, but so far, nothing.  The send-receive switch is 
baffling to me.  It looks like I may have a DC blocking capacitor that's 
failed? but where -- I don't know.


Can anyone offer any suggestions as to where to start looking for the 
trouble?  It's similar enough to my HQ-170, and doing a side by side 
comparison, I just am not seeing what the problem might be.

Also -- anyone have a good resolution schematic?  The one on BAMA is 
pretty horrendous; it's gotten me this far, but it's very difficult to 
follow the traces at higher zoom.


Thanks!

Jeff

WB3JIH