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Connex 3300HP No Modulation

digitalwacker73

digitalwacker73

Active Member
Sep 15, 2014
32
3
38
53
O'fallon, MO
Picked up an old Connex 3300HP for cheap. Radio receives fine. It has full output on high and low power, but NO modulation. PA also does NOT work. I've tried a couple different microphones as well. Checked voltage at TR51 and the audio chip, both tested good. Also reflowed solder in these areas. Changed C129, still no luck. Still need to check voltage at ic4. Anyone have any other suggestions?? Thanks
 

And this is with an external speaker correct and seeing this on an external watt meter? I know it sounds like stupid questions, but it happens!! Hope you get it fixed. Robb and the other techs here should be able to help you. Maybe post up some photos of the board, both sides, so the techs can look more at things. Just some food for thought. They always seem to catch something when they have pics to look at and aren't just shooting in the air. JMHO. Hope you get it fixed. Have a good day.
 
you say full output , does this mean you have a full dead key ?if you have a full dead key that is usually the sign of a bad tr51. clarify what you mean by full output. are you getting a 2 watt dead key on low and say a 6 watt on high and can you turn them up and down with the VR's in the radio. how about posting voltages you are getting on tr51.

after thinking more about this have you verified you do not have a broken lead to the mic jack ? have seen a side mic version the nut come loose and it would short D77 or pull a lead off the plug inside the radio. you said you do not have the PA mode either so this makes me also think some thing is wrong at the plug inside the radio.. assume this is a side mic version since you said it was a old one. losing audio is one other thing I am thinking. more detailed info would help.

one other item to check, make sure your echo board connections are good. if you have to bypass the echo at the audio wire to see if you get audio out. if you have bad dirty connections or one came loose you will lose audio out.
 
Last edited:
sonoma said:
you say full output , does this mean you have a full dead key ?if you have a full dead key that is usually the sign of a bad tr51. clarify what you mean by full output. are you getting a 2 watt dead key on low and say a 6 watt on high and can you turn them up and down with the VR's in the radio. how about posting voltages you are getting on tr51.

after thinking more about this have you verified you do not have a broken lead to the mic jack ? have seen a side mic version the nut come loose and it would short D77 or pull a lead off the plug inside the radio. you said you do not have the PA mode either so this makes me also think some thing is wrong at the plug inside the radio.. assume this is a side mic version since you said it was a old one. losing audio is one other thing I am thinking. more detailed info would help.

one other item to check, make sure your echo board connections are good. if you have to bypass the echo at the audio wire to see if you get audio out. if you have bad dirty connections or one came loose you will lose audio out.
Click to expand...
Radio is the side mounted microphone version. Full output meaning I'm getting around 2 watts low power on an external watt meter and 8 on High power. Getting B12.03v C4.83v E 12.87 at TR51. I did reflow the solder on the mic plug but will check D77 next. Echo board was also a thought of mine as it looks like someone has reflowed solder at some point.
 
nothing special
just lead with a cap in series for isolation and appropriate volume level and a tone of a pitch in your speech range (lol 1khz will do )
(radio keyed of course)
inject at the points where there is coupling caps .. between stages to determine if the stage before or after has lost modulation to localize the area takes alot of guess work out if it and voltage testing is only half the fault finding ride ..
voltages cant tell you if a coupling cap is not soldered or shorted or a resistor in series with audio path is open circuit or even a trace is open circuit also if a chip/transistor is open internally voltages dont always show this (like the audio preamp ic )
get ya learn on ..sorry i dont give step by step stuff anymore life is too short

the "buzz" test was around before avo made test meters
 
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good info Yeti. you have to have the proper equipment to test and repair. most guy's now days have access to a lot more than we did back in the 70's and 80's. I have some nice 60's signal generators that I still use from time to time. back in the early 70's I started selling cb equipment and then got into heavy repairs about 2001 . by then I had all the equipment I needed to do my repairs. at 65 now I just do it as a hobby and only work on close friends and family and my own equipment I buy. it takes too long to try to explain step by step to repair a radio. over on a forum I have been on since 2001 a couple of guy's still write it out for some one and it will take 2 to 3 pages to print out some info they will type out.
 
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Yeti Communications Ltd said:
a audio injection in the tx audio path at key points from the mic socket towards the audio amp will find the source of your problem in a matter of less than a min
heaps of tone gen apps out there
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I've gone as far as I can from home. Will take the radio to a friend with a scope and other test equipment to probe where I'm losing a signal. Will post results when found.
 

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