[TenTec] Corsair II weak weak receive

[jon greenwood]

Ok I tried the rx switch clean, I had already done that a few times but did a bunch more slides. No change. 
As far as the filters. I am looking at the 9mhz 2.4 It is a soldered on filter? everything seems good there. I do not have any of the 6 mhz filters engaged but have turned them on off etc seems to make no difference. I did not try unplugging them from the board yet. I have poked and jiggled all over the place and find no loose or intermittent s. 

I had already plugged and unplugged most of the interconnecting coax plugs that run between boards. I should have mentioned that I have had Ten Tec's since my dad bought me a 544 new back in 78' So somewhat familiar with the simple "fixes".
I had called Paul in service and he too pointed to the filter chain as well as the tracing of signal through the boards. I guess I am not sure how to check that any further than I already have. He also suggested the  voltage checks across the boards starting with the first in line and working from there. Everything tested good up to the 80987 board. 

The only thing I am finding is the incorrect voltage reads on Q6 of the 80987 board. The manual has so many errors I really don't trust it. It does say that Q3 of that board is a preamp and that Q6 then amps the signal again. My signal sounds the same with Q6 on the board or removed. Signal seems to be there just not getting amplified by Q6. My RF gain has to be at max to hear anything if turned down just one notch everything goes away completely.
If I touch the metal case of Q6 I get a huge rise in white hash noise but it does not increase the signal. If Q3 is touched It gives a small increase in noise. I notice some of the same transistors on other boards when touched have a similar effect so that my not indicate anything. Just an observation to share. 

According to my manual Q6 on receive should have 9.5v on the collector, 1.7v on the base and .9v on the emitter. I read 11.5 on all three. I removed Q6 and get the same readings without the transistor in the circuit. I also replaced it with a new one and get the same readings.
????? Still stumped here so far. Thanks for your input though and I am sure we will get this figured out. No doubt will be a good one to have documented in the end.
73 Jon
 


     On Monday, October 5, 2015 8:10 PM, Gary - AB9M <glhuber at msn.com> wrote:
   

 Slide the AUX ANT / AUX RX switch back and forth about 20 times...... often 
corrosion / oxidation causes weak receive; cleaning the switch will put 
things back to normal.

73 & DX,

Gary - AB9M

-----Original Message----- 
From: jon greenwood via TenTec
Sent: Monday, October 05, 2015 9:40 PM
To: tentec at contesting.com
Cc: jon greenwood
Subject: [TenTec] Corsair II weak weak receive

Hope some of the good troubleshooters on here can point me in a direction. I 
have a Corsair 2 that is very weak on receive. I have checked transistor 
voltages on IF/AF board 80984, the Osc/mixer board 80975, and the RX mixer 
board 80987. All seem good or very close to specs in manual, except Q6 on RX 
mixer 80987.
I am reading 11.5 volts on base emitter and collector in receive mode. In 
Transmit these all read correctly base emitter and collector zero volts. I 
replaced the 270pf cap C24 as well as C25 5-25pf variable cap. No change. I 
removed the Q6 transistor and the radio receives exactly the same. I 
replaced with a new transistor with no change. So my thought is a bad  a 
component around Q6 but at this point I am stumped on what it is. I also 
checked D7 and D8 pulling them off the board and just checking with my ohm 
meter. Flow in only one direction on each so they seem good.
Any thoughts/ test procedures would be much appreciated. I have a 100mhz 
digital scope and an older Fluke DMM that I have to work with. 
Questions/Thoughts? Jon N8MUS
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