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Trc457 modulation clicking

KneeBiter

KneeBiter

Well-Known Member
May 21, 2014
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Trc457. New filter cap in power supply and the known tantalum cap changed to an electrolytic. No mods. TX audio on SSB the receiving party hears a clicking sound with my voice. I put on a monitor radio with headphones and sure enough it's there. I turned up the alc to see if maybe it was from that clipping the audio but it's still there. Any suggestions?
 

You can also get a "click" or "rattle" from the "sense cap" the ALC uses off of the TX strip.

That "spike" is from a breakdown in that tiny value cap - the resistor network tries to smooth that spike down so the ALC signal doesn't look so much like a square wave - all tied to the ALC
 
Handy Andy said:
You can also get a "click" or "rattle" from the "sense cap" the ALC uses off of the TX strip.

That "spike" is from a breakdown in that tiny value cap - the resistor network tries to smooth that spike down so the ALC signal doesn't look so much like a square wave - all tied to the ALC
Click to expand...
Is there a mod or fix to that? Part locations and what to try would be a great help. Thanks
 
nomadradio said:
I'd be looking at electrolytic capacitors in the SSB ALC circuits. Hmm, I only count one. C158 smooths the signal envelope from D46 and FET5. If this cap loses value, or goes open, you could get this sort of symptom.

Maybe.

73
Click to expand...
I have a cap kit coming from Klondike so I will swap that one out first and see what happens. Thanks Chris
 
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nomadradio said:
I'd be looking at electrolytic capacitors in the SSB ALC circuits. Hmm, I only count one. C158 smooths the signal envelope from D46 and FET5. If this cap loses value, or goes open, you could get this sort of symptom.

Maybe.

73
Click to expand...
Ok, I had a new 1uf 50v here so I swapped out c158. Same thing. Clicking with my voice. Really hear it with a whistle. Sounds like clipping
 
Is the Relay dropping out?

This normally doesn't happen but when you have that type of noise presence - can't help but wonder if your relay is clicking - as it - it wants to drop out.

Otherwise - the "ALC" sense circuit "sense" trace arrives to FET5 from the back of the board between 2 coils L29 and L28 - - but it does thru a capacitor to keep the "live" signal current (DC Block) and lets the RF pass - but it goes thru a divider set up with a "variable" and a fixed value - and to keep DC off of it, so the FET doesn't blow up - a simple coil to act as that "shunt" across to ground - then onto a Diode and 10K resistor then the FET itself (simpler 0.047uF smoothing cap is located here)

The FET - if these radios been in storage after a storm of has been left connected after a couple of close lightning strikes - the FET itself can turn into a "transistor" (Fused pellet junction) and might need to be replaced.

The Diode and resistor are a type of constriction valve - looking for Negative peaks to act quickly with, but the 10K also with the Diodes one-way valve action - allows positive peaks to be sensed as well.

So, what this tells me the FET may be damaged or shot - the junction is too sensitive now and although a simple SK192 would work - the whole circuit needs a good going over in parts and even the diode itself - might need replacement.

But to answer that, the whole mess should get "pulled" off or disabled to verify that the ALC is causing this.

The issue of the relay becomes more paramount when the relay contacts are not perfectly clean and "bounce" or have a resistive element in them. This generates an SWR bump that blows up the Final in this scenario - so if the Relay has suffered damage or you don't know it's condition - then no matter what you do to fix the "click" the relay may be the whole problem.
 
Handy Andy said:
Is the Relay dropping out?

This normally doesn't happen but when you have that type of noise presence - can't help but wonder if your relay is clicking - as it - it wants to drop out.

Otherwise - the "ALC" sense circuit "sense" trace arrives to FET5 from the back of the board between 2 coils L29 and L28 - - but it does thru a capacitor to keep the "live" signal current (DC Block) and lets the RF pass - but it goes thru a divider set up with a "variable" and a fixed value - and to keep DC off of it, so the FET doesn't blow up - a simple coil to act as that "shunt" across to ground - then onto a Diode and 10K resistor then the FET itself (simpler 0.047uF smoothing cap is located here)

The FET - if these radios been in storage after a storm of has been left connected after a couple of close lightning strikes - the FET itself can turn into a "transistor" (Fused pellet junction) and might need to be replaced.

The Diode and resistor are a type of constriction valve - looking for Negative peaks to act quickly with, but the 10K also with the Diodes one-way valve action - allows positive peaks to be sensed as well.

So, what this tells me the FET may be damaged or shot - the junction is too sensitive now and although a simple SK192 would work - the whole circuit needs a good going over in parts and even the diode itself - might need replacement.

But to answer that, the whole mess should get "pulled" off or disabled to verify that the ALC is causing this.

The issue of the relay becomes more paramount when the relay contacts are not perfectly clean and "bounce" or have a resistive element in them. This generates an SWR bump that blows up the Final in this scenario - so if the Relay has suffered damage or you don't know it's condition - then no matter what you do to fix the "click" the relay may be the whole problem.
Click to expand...
The relay is not dropping out. I had a brand new nos relay here and popped that in just as a test. Same clipping. Audio is loud and clear on ssb just has this clipping sound with my voice peaks
 
KneeBiter said:
The relay is not dropping out. I had a brand new nos relay here and popped that in just as a test. Same clipping. Audio is loud and clear on ssb just has this clipping sound with my voice peaks
Click to expand...
And the sound is low under my voice. Not cutting my voice out.
 
KneeBiter said:
And the sound is low under my voice. Not cutting my voice out.
Click to expand...

So, you encounter this same condition with the Limiter removed?

Locate C98, the output side of TR24 - the "8V" Regulator.

When you get that peak effect, does that voltage output - drop?

Then the answer is in that area - your regulation is dropping out.
 
I also am curious to know of you have that mic amp IC 592H2 (IC3) - that uses a diode from the "bootstrap" C47 (22uf 16V) with it's banded end towards Pin 2 of the IC - this is a "protection" from the input going too negative. You're experiencing clipping and I wonder if it even has this installed.

Else there is a "EQ" Equalization network using a cap (C63) of 10uF 16V between two resistors (R80 4.7K and 56K R195) - kind of like an RIAA EQ emphasis they used to do for Phono inputs on stereos.

The board I think you have is the PC-196? Right?
 
Handy Andy said:
So, you encounter this same condition with the Limiter removed?

Locate C98, the output side of TR24 - the "8V" Regulator.

When you get that peak effect, does that voltage output - drop?

Then the answer is in that area - your regulation is dropping out.
Click to expand...
I have not removed the limiter. Only turned up the alc. What should I remove to test if it happens without the limiter? I will also get the board number when I go back into the shop. This radio was virgin. Screws never removed until I got it.
 
The thinking I have is you may not really have any serious issues except the age - and those caps are a part of the "Age" equation.

Relay aside - the "chortle / click" I've experienced in this or on a Robyn 520D has been due to "sags" in the cheaper voltage regulation they made discrete capable of 500mA draw (maybe 4W?) - versus using a more robust 7808 1A type.

When you remove the limiter don't be surprised if the condition becomes worse - then we know it's a sagging voltage in the supply somewhere.

The original message said you had replaced a tantalum in the power supply - one of the first clues to me the rest of that tantalum mess may also need an upgrade - but only as an age issue - not really a performance quirk. The Quirks are from the age and dielectric the tantalums are

So, my previous ramblings are from the aspect of the ALC chortle and clipping "limitations" from the ALC getting zapped
 
Handy Andy said:
The thinking I have is you may not really have any serious issues except the age - and those caps are a part of the "Age" equation.

Relay aside - the "chortle / click" I've experienced in this or on a Robyn 520D has been due to "sags" in the cheaper voltage regulation they made discrete capable of 500mA draw (maybe 4W?) - versus using a more robust 7808 1A type.

When you remove the limiter don't be surprised if the condition becomes worse - then we know it's a sagging voltage in the supply somewhere.

The original message said you had replaced a tantalum in the power supply - one of the first clues to me the rest of that tantalum mess may also need an upgrade - but only as an age issue - not really a performance quirk. The Quirks are from the age and dielectric the tantalums are

So, my previous ramblings are from the aspect of the ALC chortle and clipping "limitations" from the ALC getting zapped
Click to expand...
I replaced the big cap in the power supply just because and the tantalum in front of the relay that is a known one to give problems just because. The radio was working good except for the clipping.
 
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