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Hmmm...If you have time - this might help for if the SQUELCH knob running the Squelch control - opened up - it will QUENCH all signal - act like this because it's really a VERY non-linear switch that looks to a voltage across the SQUELCH control to set "trigger" - if it opened up as in a bad pot, you just need to "short" the wiper arm wire to ground and see if it pops open. Remove the wiper lead to the SQ pot and touch it to a case of one of your IF cans to see if it "pops" open - then you know you have a bad pot.

TR6 - act as the non-linear switch that ties both the AGC (to track signal strength and operate to OPEN the Squelch as the signal gets stronger) and RX voltage to set a "hysteresis" event - it sends this result to TR10 - your On - Off Switch
TR6 is a 2SC1815 - It can short out - due to static pokes popping the substrate when someone has a lot of static charge - another Achilles heel due to the construction of the front panel and the way it was made back then. When it blows shorted - sucks all the signal out - but shouldn't turn off Mic Audio power.
TR10 is the "Final Call" to send RX audio to the Amp - TR10 doesn't normally go out but pulling it to help troubleshoot - gives you the chance to at least hear MIC audio - removing it won't hurt the radio - again for troubleshooting only ok?
This is just for checking MIC Audio in TX mode only.
TO hear RX (weakly) - you'll need to short C54's output to (towards base of) TR10 to C56 to get any RX audio thru - a simple jumper helps here...then replace any parts to restore TR10's operation so you're not mixing RX and TX together.
In this case, the Squelch control works in RX, but in TX - no audio is still a different beast...

TR16 is a PNP - might need to check it and put in a 2SA733 - it's the TX switch - this controls the TX line, and looks at MiC Jack Pin 3.
- as it falls when you go into TX, TR16 is supposed to
- send power to the Mic amp to turn on the audio for PA to the Audio amp
- MIC Amp (TR13) powers up to allow Mic audio to get amplified then onto Audio Amp (R73 SENDS power to the Mic amp from the TX line)
- MIC Jack Pin 3 line also has power for RX when the Mic is not keyed up
- so when you switch to TX
- MIC Pin 3 Line gets grounded
- RX light goes out
- power going to RX drops on the line
- RX stops working
- if you get a TX light, then that means TR16 may not be the issue.
Might need to check traces and make sure all soldering is good and this means continuity checks - to make sure the Foil traces are not opened up.

<blockquote data-quote="Handy Andy" data-source="post: 774098" data-attributes="member: 52309">Hmmm...If you have time - this might help for if the SQUELCH knob running the Squelch control - opened up - it will QUENCH all signal - act like this because it&#039;s really a VERY non-linear switch that looks to a voltage across the SQUELCH control to set &quot;trigger&quot; - if it opened up as in a bad pot, you just need to &quot;short&quot; the wiper arm wire to ground and see if it pops open. Remove the wiper lead to the SQ pot and touch it to a case of one of your IF cans to see if it &quot;pops&quot; open - then you know you have a bad pot.TR6 - act as the non-linear switch that ties both the AGC (to track signal strength and operate to OPEN the Squelch as the signal gets stronger) and RX voltage to set a &quot;hysteresis&quot; event -&nbsp; it sends this result to TR10 - your On - Off Switch<ul>
<li data-xf-list-type="ul">TR6 is a 2SC1815 - It can short out - due to static pokes popping the substrate when someone has a lot of static charge - another Achilles heel due to the construction of the front panel and the way it was made back then. When it blows shorted - sucks all the signal out - but shouldn&#039;t turn off Mic Audio power.</li>
</ul>TR10 is the &quot;Final Call&quot; to send RX audio to the Amp - TR10 doesn&#039;t normally go out but pulling it to help troubleshoot - gives you the chance to at least hear MIC audio - removing it won&#039;t hurt the radio - again for troubleshooting only ok?<ul>
<li data-xf-list-type="ul">This is just for checking MIC Audio in TX mode only.</li>
<li data-xf-list-type="ul">TO hear RX (weakly) - you&#039;ll need to short C54&#039;s output to (towards base of) TR10 to C56 to get any RX audio thru - a simple jumper helps here...then replace any parts to restore TR10&#039;s operation so you&#039;re not mixing RX and TX together.</li>
</ul>In this case, the Squelch control works in RX, but in TX - no audio is still a different beast...TR16 is a PNP - might need to check it and put in a 2SA733 - it&#039;s the TX switch - this controls the TX line, and looks at MiC Jack Pin 3.<ul>
<li data-xf-list-type="ul">- as it falls when you go into TX, TR16 is supposed to</li>
<li data-xf-list-type="ul">- send power to the Mic amp to turn on the audio for PA to the Audio amp<ul>
<li data-xf-list-type="ul">- MIC Amp (TR13) powers up to allow Mic audio to get amplified then onto Audio Amp (R73 SENDS power to the Mic amp from the TX line)</li>
</ul></li>
<li data-xf-list-type="ul">- MIC Jack Pin 3 line also has power for RX when the Mic is not keyed up</li>
<li data-xf-list-type="ul">- so when you switch to TX 
<ul style="margin-left: 20px">
<li data-xf-list-type="ul">- MIC Pin 3 Line gets grounded</li>
<li data-xf-list-type="ul">- RX light goes out</li>
<li data-xf-list-type="ul">- power going to RX drops on the line</li>
<li data-xf-list-type="ul">- RX stops working</li>
<li data-xf-list-type="ul">- if you get a TX light, then that means TR16 may not be the issue.</li>
</ul>
</li>
</ul>Might need to check traces and make sure all soldering is good and this means continuity checks&nbsp; - to make sure the Foil traces are not opened up.</blockquote>

[QUOTE="Handy Andy, post: 774098, member: 52309"] Hmmm...If you have time - this might help for if the SQUELCH knob running the Squelch control - opened up - it will QUENCH all signal - act like this because it's really a VERY non-linear switch that looks to a voltage across the SQUELCH control to set "trigger" - if it opened up as in a bad pot, you just need to "short" the wiper arm wire to ground and see if it pops open. Remove the wiper lead to the SQ pot and touch it to a case of one of your IF cans to see if it "pops" open - then you know you have a bad pot. TR6 - act as the non-linear switch that ties both the AGC (to track signal strength and operate to OPEN the Squelch as the signal gets stronger) and RX voltage to set a "hysteresis" event - it sends this result to TR10 - your On - Off Switch [LIST] [*]TR6 is a 2SC1815 - It can short out - due to static pokes popping the substrate when someone has a lot of static charge - another Achilles heel due to the construction of the front panel and the way it was made back then. When it blows shorted - sucks all the signal out - but shouldn't turn off Mic Audio power. [/LIST] TR10 is the "Final Call" to send RX audio to the Amp - TR10 doesn't normally go out but pulling it to help troubleshoot - gives you the chance to at least hear MIC audio - removing it won't hurt the radio - again for troubleshooting only ok? [LIST] [*]This is just for checking MIC Audio in TX mode only. [*]TO hear RX (weakly) - you'll need to short C54's output to (towards base of) TR10 to C56 to get any RX audio thru - a simple jumper helps here...then replace any parts to restore TR10's operation so you're not mixing RX and TX together. [/LIST] In this case, the Squelch control works in RX, but in TX - no audio is still a different beast... TR16 is a PNP - might need to check it and put in a 2SA733 - it's the TX switch - this controls the TX line, and looks at MiC Jack Pin 3. [LIST] [*]- as it falls when you go into TX, TR16 is [B][U]supposed to[/U][/B] [*]- send power to the Mic amp to turn on the audio for PA to the Audio amp [LIST] [*]- MIC Amp (TR13) powers up to allow Mic audio to get amplified then onto Audio Amp (R73 SENDS power to the Mic amp from the TX line) [/LIST] [*]- MIC Jack Pin 3 line also has power for RX when the Mic is not keyed up [*]- so when you switch to TX [INDENT][LIST] [*]- MIC Pin 3 Line gets grounded [*]- RX light goes out [*]- power going to RX drops on the line [*]- RX stops working [*]- if you get a TX light, then that means TR16 may not be the issue. [/LIST][/INDENT] [/LIST] Might need to check traces and make sure all soldering is good and this means continuity checks - to make sure the Foil traces are not opened up. [/QUOTE]

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