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

[Jeff]

An update...

Silver Mica Disease on T-3 (and probably T-4 and T-5 - the 455 KC IF 
transformers.)

Does anyone have any suggestions as to the value of capacitor to shunt 
across the transformers if I'm successful in removing the old mica 
sheets from the cans themselves?  I've watched a few videos of the 
process -- it looks pretty intimidating, but I'm willing to give it a 
try.  Plenty of space to mount something on the underside.

Thanks all.


On 11/11/2016 7:50 PM, Jeff wrote:
> 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
>
>
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