connex 3300 Lost Modulation

zeppfrog · Post by **zeppfrog** » Tuesday 10th Jun 2008, 5:19

I collected this radio to try to repair for a friend, now I seem to have inherited it. It shows good carrier, about 40 watts which i plan to lower. good receive and is on frequency both send and receive, but the modulation just slightly bumps the meter and drops back. no sound output when you key up. Just dead key.
I have tinkered on radios awhile, no expert, but I can solder and test a few things on my multimeter.
I would really like to save this one and not mess it up. can anyone give me some good places to start. thanks

timrim · Post by **timrim** » Tuesday 10th Jun 2008, 5:27

I am not sure you actually have a 40 watt carrier, perhaps there is some kind of noise on the audio which is holding the watt meter at 40? I have seen this before. I would rule this out first.

zeppfrog · Post by **zeppfrog** » Tuesday 10th Jun 2008, 5:41

I wouldnt qualify my power meter too highly, i have a 5/50/500 meter and set it on 50 and hits the 40 pretty solid. i turned it back to lower the output just to see if it moved, and it did, so i moved it back up for now just to leave things as they are and not create new troubles.

zeppfrog · Post by **zeppfrog** » Tuesday 10th Jun 2008, 5:45

ahh, i think i see what you are saying... my meter has three meters in one as well. one for power, one for modulation, one for swr. the power hits 40, the mod just bumps and drops. but I think i understand you are saying there may be some internal noise killing my readings. I also have an audio mod tester, and no sound is coming out, at least not in my hearing range.

timrim · Post by **timrim** » Tuesday 10th Jun 2008, 9:56

The best way to test for noise is to monitor it with another cb if this is possible. Does your Connex 3300 have the heatsink on back? If so, then its the high power version and a 40 watt dead key is still extremely high. If you have a 40 watt dead key (assuming your meter is working ok), I would suspect that the AM voltage regulator is shorted. Thats the transistor bolted to the right side of the radio near the rear looking at it facing the front with bottom cover off. The Transistor is TR-51. Check the voltage on the small jumper PC Board located in front of the final and driver, if its 12 volts, then you have a shorted regulator. Normal reading should be between 3 and 6 volts depending on power setting.

NOTE: Also check the internal power adjustment VR-13 I believe, that will vary the voltage on the jumper PC Board, if the regulator is working and can also be used to set the dead key.

zeppfrog · Post by **zeppfrog** » Wednesday 11th Jun 2008, 4:17

thanks Timrim, will check those and let ya know how it goes

zeppfrog · Post by **zeppfrog** » Wednesday 11th Jun 2008, 4:26

btw, not the HP. single final, at this point, but its my hope to change that after i get it going right

zeppfrog · Post by **zeppfrog** » Wednesday 11th Jun 2008, 6:47

ok, better info now. i got another meter and retested, getting about 10 watts on lo, 15 on hi. also set up another radio to listen for noise, and yep, getting a kind of a low hum. you can almost hear the voice over it, but too fuzzed and low. also, i moved the echo down and it did lose the hum for the most part and also any other sound. turning the echo sw to off lowers the receive and vice versa as well (not sure what that is about) I considered bypassing the echo board altogether to see if that was the source of the problem, but its got a few more wires than i am used to on an echo board, so havent messed with that yet.

also, i tested tr51, i believe its a 2SA1012, and got the following from back of rig to front. leg 1, 12.33/12.30 . leg 2 5.28/5.24 and leg 3 13.32/12.36 first being unkeyed, second being keyed. Am not sure of the other part, the jumper, there isnt a small pcb in front of the final or driver. but i tested the jumper in front of the driver and believe i got just over 5 vdc. (i need to recheck that one to be sure)

there is also a black wire soldered to the top of one of the cans, but it has been clipped, about 1.5 inches long. this rig appears to be a non virgin, lol.

timrim · Post by **timrim** » Wednesday 11th Jun 2008, 9:33

Those readings are more in line of what you are supposed to be seeing, except the carrier should be 3 watts on low and 8 on high. Your regulator is working. The reason I was asking about the noise is because sometimes the noise will modulate the radio and it appears that the carrier is excessivly high. I would adjust the dead key to 8 watts max and try to turn up the modulation and see what happens with performance. If that does not improve the performance, then I would recommend checking the soldering around the mic amp ic and near the audio chip. A problem there could be why you are getting the hum and low modulation, but I am curious to see if the modulation will come up with the adjustment and when the dead key is lowered. The modulation adjustment should be VR-14. You can also remove the limiter if you wish the modulation to be wide open, the transistor to remove is TR-32.
Let me know what happens and we will go from there.

EDIT: Let me know if bypassing the echo gives better modulation, the echo really should not be affecting the receive however. Its possible that the echo board is the source of the hum.

zeppfrog · Post by **zeppfrog** » Wednesday 11th Jun 2008, 13:11

Mod adjust does very little, goes to nothing at all, or slight bump. i have been pressing around on the area around the audio ic, ic8 and ic 4 and i seem to get the mod to go up, appears that tr 52 has been removed, and there are a pair of resistors tied to diodes near there. also looks like a capcitor can was removed next to that transistor. the solder holes are open, but not sure if they were meant to be there or not.
going looking for tr 32 now to see if its there or not. btw, tested audio through the PA and it works. seems i have seen that before... must jog the brain a bit
(pressing with wet fingertip across contacts)

zeppfrog · Post by **zeppfrog** » Wednesday 11th Jun 2008, 19:24

did some testing on the ic voltages, ic 4 and ic 8. both are somewhat off from spec, but not sure enough to matter. wish there was a real decent radio tech nearby, not a parts changer. (aka thief).a good vco and pll alignment might illuminate the problem. i suspect either one of these ic's or the regulator(am modulator) or the driver... but may be a resistor or anything in the circuit. since the limiter is in place, and the am mod VR does nothing at all, it seems it must be before it. though it does seem the needle jumped a few time as i turned it, but not when i keyed and sounded in the mic. will look through my parts and see what i have. i think i have a spare for ic 4, and been eyeballing that cobra 148 for parts... been on that one for over a year and cant get it on frequency...

timrim · Post by **timrim** » Wednesday 11th Jun 2008, 20:49

did dropping the dead carrier increase modulation?

zeppfrog · Post by **zeppfrog** » Thursday 12th Jun 2008, 5:29

no change to the mod, but i did bring the hi and lo deadkey back to 3/12. I also found a better diagram last night of the VR's. seems the one I have is more for the ssb models, doesnt show the hi and lo power settings. going to have a go on that in a bit, but I suspect I already messed with those a bit too.

Rick · Post by **Rick** » Thursday 12th Jun 2008, 9:14

Is it working on FM?
What voltages do you have on IC 4 Pins 1 to 4 in the TX mode?

zeppfrog · Post by **zeppfrog** » Thursday 12th Jun 2008, 11:40

nada in FM. 1 Thru 4= 4.14, 4.16, 4.26, 0.09

woody · Post by **woody** » Thursday 12th Jun 2008, 16:24

I would check the eletrolitic caps in the circuit these will be located next to the audio amp (ta 7222 ap) wich is located on the right hand side the the parts side of the board IC8.C151 4.7MFG,C150 22MFG.sometimes these caps dry up or leak.if you have an ohm meter check to see if they are shorted

zeppfrog · Post by **zeppfrog** » Thursday 12th Jun 2008, 16:42

going to maybe save myself a headache, and just ask a dumb novice question. Using which setting on my ohm meter and what reading should i look for in the capacitors, also, should the radio be plugged in/on/or neither when checking... thanks (novice i said, heh)

did a quik search so should be able to handle that one, off for some testing

Rick · Post by **Rick** » Thursday 12th Jun 2008, 20:53

You have check that the mike and it is OK yes?

Your TX audio has nothing to do with IC8 this is only for RX and PA.

Try replacing C128 and C129, make sure you put the replacement caps in the right way round.

As for testing electrolytic caps this is best done with them removed from the radio.
Do a Google search on testing capacitors with a DVM.

I did ask you if the radio was working in the FM mode?

zeppfrog · Post by **zeppfrog** » Saturday 14th Jun 2008, 5:21

well, still didnt get those caps tested, though the solder under the larger looks suspiscious. had a baby boy at 12:05 this am, (well, not me, my wife did) here's cyber cigars to everyone and I will get back on this one as soon as she lets me.

, yes it does receive in fm, but no mod there either. also , wattage changes in tx with each band change, but thats probably normal

zeppfrog · Post by **zeppfrog** » Sunday 20th Jul 2008, 16:01

welp, i sKwewwed the pooch. swapped out several of the capacitors with new, then i was tweaking around the VR's (hi/lo pwr and mod) to see if i could get anything, (nope) the looked away and zoik poof... yep, i was using the metal screwdriver. lost all output. can hear it key up but thats it, no signal.

already replaced the driver and finals. nothing. getting a negative reading on the outer legs of the final, and very low voltage to the center. when i key, it goes negative.

any takers? other than to just start randomly replacing diodes and transistors I dont have any idea what i smoked.

ramblingman · Post by **ramblingman** » Monday 21st Jul 2008, 3:51

Does the tx red led come on when you key?????
If not check your tx/rx switching transistors.
They are TR-36/TR-38
Tr-36 collector should be 8.5 vdc in RX mode and
0.0 vdc in TX mode.Then Tr-38 collector should read
0.0 vdc in RX mode and 8.37 vdc in TX mode.
Also check D-77 for O/C,,This diode is located
under your mic socket.Also re-check your voltages
at TR-50/TR-51.There should be 5.6 v.d.c on the collectors
of these transistors.Also check voltages at TR-41 which is
the voltage regulator.You should have 8.5 vdc on the collector
and 12.5 vdc on the base and 13.2 vdc on the emitter of
this transistor.

zeppfrog · Post by **zeppfrog** » Tuesday 22nd Jul 2008, 1:34

Thanks RamblingMan. the tx/rx light is coming on and the meter still moves on key up. So I skipped the first two, tr 36-38. checked the diode just for voltage and got 6vdc rx/ 5.83 tx

TR 51 TX/RX 1.76/1.36 1.05/-0.51 10.93/10.87

TR 50 TX/RX 1.75/0.30 1.05/-0.51 1.79/0.35

TR 41 TX/RX 10.15/10.02 7.64/7.61 10.85/10.70

(All read left to right looking from back of mic plug inside radio)

sorry I didnt look up the BCE's but the voltages are all moofed, hehe

ramblingman · Post by **ramblingman** » Tuesday 22nd Jul 2008, 3:40

Wel from these voltages you gave.
It seems that you have took out the
Am mod amp.Change TR-50/TR-51
And see if tx power is restored.

zeppfrog · Post by **zeppfrog** » Wednesday 23rd Jul 2008, 1:16

Replaced tr51. the odds of me havin a new 2sa1012 are bout as good as me winning the lottery, but i did.

Got the dead key back now and good watts. thanks ramblingman. now you dont know a substitute for the 2sa934 do ya? still hunting for my missing modulation, thinking of swapping out the audio regulator-i/c and that little 8 pin square one. I have a new one for the 8pinner, but nothing here right now for the chassis mounted one. (pc isnt in the radio room so i cant spout off any numbers)...
any other ideas? know which wires i need to connect to remove the echo board completely. i am sure it will be the two plugs with three wires on the side of the echo board, but dont know which ones to which.

thanks again ramblingman. appreciate the help on that one.

zeppfrog · Post by **zeppfrog** » Wednesday 23rd Jul 2008, 2:23

by the way, should have mentioned this before at the start. The Mod does bump to about 20% when you first key then drops to zero. if you continue to key it, the percentage drops as well.

(replaced IC 4 and tr 50 with no effect)

ramblingman · Post by **ramblingman** » Wednesday 23rd Jul 2008, 7:57

Did you check the caps,that rick mentioned in his earlier post???

ramblingman · Post by **ramblingman** » Wednesday 23rd Jul 2008, 8:51

B.T.W.. Just part changing aint gonna get it..You need to start
taking some voltage measurements and relaying it to us.
By giving us your readings this will better help us help you.
You can keep changing parts till kingdom come and still might
not fix it..Start by giving us your voltage readings at ic-4
as rick said earlier..Also at tr-34 and tr-32 if it hadnt been
yanked out.IC-4 is your mike amp/t/r switching..TR-34 is your
amc/alc amp..and TR-32 is your amc shunt

zeppfrog · Post by **zeppfrog** » Wednesday 23rd Jul 2008, 17:11

thanks for the response again ramblingman, i did swap a few of the electrolytics rick mentioned, yet to find a few of them. I will get those voltages for you in the morning. thanks

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connex 3300 Lost Modulation

connex 3300 Lost Modulation

Re: Connex 3300 No TX Modulation.

Re: Connex 3300 No TX Modulation.