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Connex 3300 rx help needed
- Thread starter Mk121
- Start date
SIGH - My Bad...
You don't leave TR17 in circuit, you're simply looking for signal to arrive to the base. (A DC Voltage) I am approaching this as if I would have a "dead transistor" I need to check "Bias voltages" to make sure the part I put in will survive as well as function.
That would be fine if I didn't have a brain fart...
And I see I meant "Emitter" when it comes to signal - now I know where you got confused - this is a common base design - meaning that it acts more like a simple current follower than an amplifier. You don't need gain, just power - this helps it's selectivity - too much gain can overload TR18.
The Base - see above, taps from the arriving 8 volts available at the COLLECTOR side (L7)
Sorry about that...
Then if a signal is arriving to the EMITTER, then we can rule out any relative problems with the path the RF takes to get there.
I didn't have a V8 this morning...
BELOW is another configuration used in Cobra and Uniden early models...
This is a Common EMITTER design - BASE has SIGNAL
If it were me, I'd do the same thing remove the part and test it out of circuit.
Remember we are trying to find out why TR17 isn't working - let's make sure the part isn't the problem, the way it's put in, is it Blown or shorted out due to ANOTHER voltage problem the board has...
You don't leave TR17 in circuit, you're simply looking for signal to arrive to the base. (A DC Voltage) I am approaching this as if I would have a "dead transistor" I need to check "Bias voltages" to make sure the part I put in will survive as well as function.
That would be fine if I didn't have a brain fart...
And I see I meant "Emitter" when it comes to signal - now I know where you got confused - this is a common base design - meaning that it acts more like a simple current follower than an amplifier. You don't need gain, just power - this helps it's selectivity - too much gain can overload TR18.
The Base - see above, taps from the arriving 8 volts available at the COLLECTOR side (L7)
Sorry about that...
Then if a signal is arriving to the EMITTER, then we can rule out any relative problems with the path the RF takes to get there.
I didn't have a V8 this morning...
BELOW is another configuration used in Cobra and Uniden early models...
This is a Common EMITTER design - BASE has SIGNAL
Check voltages at where the leads would go - VERIFY that the part I put back in there won't go bad like the other one.Remember we are trying to find out why TR17 isn't working - let's make sure the part isn't the problem, the way it's put in, is it Blown or shorted out due to ANOTHER voltage problem the board has...
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Now, as far as waveform, you may need to look for those Pin Diodes.
Do you have any history on the radio - was it working with a Linear / Amp and the Amp went bad?
Was it in a Mobile, and the vehicle was caught in a storm - was working - now it don't scenario.
Both usually arrive to the same conclusion - input signal path damage, but how bad?
This is why I'm having you look for signal - and by what I see - RF Gain or not, looks like the diodes are doing something - just not sure if a short or blown open - so you may need to look into removing pulling the diodes and observe the waveform. If you now get it as a pure signal like you'd see at TR18 - then suspect the PIN diodes got damaged and replace them both. This also raises the bar on what other parts in the section can be affected.- for there is now more evidence that power, more than it was designed for - was sent thru into the RF amp section.
Do you have any history on the radio - was it working with a Linear / Amp and the Amp went bad?
Was it in a Mobile, and the vehicle was caught in a storm - was working - now it don't scenario.
Both usually arrive to the same conclusion - input signal path damage, but how bad?
This is why I'm having you look for signal - and by what I see - RF Gain or not, looks like the diodes are doing something - just not sure if a short or blown open - so you may need to look into removing pulling the diodes and observe the waveform. If you now get it as a pure signal like you'd see at TR18 - then suspect the PIN diodes got damaged and replace them both. This also raises the bar on what other parts in the section can be affected.- for there is now more evidence that power, more than it was designed for - was sent thru into the RF amp section.
I'm thinking TR17 - Common Base - Emitter "Takes in" L6 - to L7 then to B.P.F. Coupling Cap to L8 then "Gate" of TR18 (FET J310) - Common Base side being that I didn't want a reverse breakdown voltage showing up and blowing the next TR17 replacement he tries to put in.
This is what I'm thinking...
This could be something as simple as replacing C333 with a know good part...See if Power can be restored. Unless there are more issues with L6 or L7 (Open coil stuff)
This is what I'm thinking...
This could be something as simple as replacing C333 with a know good part...See if Power can be restored. Unless there are more issues with L6 or L7 (Open coil stuff)
Yes I see it now I had 4 schematics up as I was working out issues on several different radio models and got them confused. I find it happens more the younger I get.
You too eh?
Man - This Carbon Dating stuff is really getting out of hand...
Back to the Game - I mean - on break...
Man - This Carbon Dating stuff is really getting out of hand...
Back to the Game - I mean - on break...
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Never got a chance to get back into the radio yesterday. I have already checked the d15 and d16 pin diodes by lifting one leg of each. The rx stayed the same as far as being able to hear anything. Never did check to see if there was a difference in scope waveform. I also already replaced c333 along with tr17. I will go back though and pull those pin diodes again and take out tr17 and look for signal.
I asked the owner of the radio for some history. He said it was working fine but did have it laying on the floor of his truck for a while before hooking it up in a new truck.
Again thanks for all the help so far.
I asked the owner of the radio for some history. He said it was working fine but did have it laying on the floor of his truck for a while before hooking it up in a new truck.
Again thanks for all the help so far.
Ok, well, not much to work on - but thanks for helping to at least rule out certain possibilities.
What I see on the Waveform is a type of distortion - almost as if it's either noise, or a reflection - like coax not terminated into a dummy load - a reactive element. It's why I asked those questions about other parts in line to TR17 - if they may have entered in another factor or quirk - to this, and we needed to know they were not adding to the problem.
So that may mean we need to do some ohmic checks of L6 - make sure it's winds are not broken - that is an open coil and is at the whims of someone careless with a screwdriver, can damage the wires or nick the winds generating a mis-match - mistune problem - even to the point of breaking the slug or case to the point where L6 cannot be used it's too damaged.
So look for physical damage to the work as well as ohmic checks to make sure the winds are ok. This also means using a Loupe - a magnifying glass - to examine the coil up close to ensure it's physically ok.
...From Harbor Freight...
So if L6 is ok, we also may need to look at what I suggested earlier - remember the S/RF meter?
Did you even check the rear panel SO-239 to see if it was "Shorted" to case? IF so, you may need to even go back further to L51/L31 combo and check to see if the parts used to "tap" the RF output - are not adding to this - a shorted cap can ruin your day. OR an OPEN connection from one of the Coil winds can also affect the radios ability to receive (and blow up the TX side as well).
If there was a reason he threw it on the floor, you have to review and find out why it got left behind.
Ok, last note about TR17, and why I wanted you to check the board for voltages once the part was removed...
So this also brings in the variables like RF gain as well as IC 1 - which may be fine just somehow not communicating anymore - so again do your details and make sure the radio and TR17 are ok before you just presume a part failed - for even the most obvious is evident, but may not be the issue - there are too many other parts to interrupt the signal - for if they are ignored then you're stuck in a loop...
(Edits: Gotta' love it when Google changes BCE to ESR...LOL)
What I see on the Waveform is a type of distortion - almost as if it's either noise, or a reflection - like coax not terminated into a dummy load - a reactive element. It's why I asked those questions about other parts in line to TR17 - if they may have entered in another factor or quirk - to this, and we needed to know they were not adding to the problem.
So that may mean we need to do some ohmic checks of L6 - make sure it's winds are not broken - that is an open coil and is at the whims of someone careless with a screwdriver, can damage the wires or nick the winds generating a mis-match - mistune problem - even to the point of breaking the slug or case to the point where L6 cannot be used it's too damaged.
So look for physical damage to the work as well as ohmic checks to make sure the winds are ok. This also means using a Loupe - a magnifying glass - to examine the coil up close to ensure it's physically ok.
...From Harbor Freight...
So if L6 is ok, we also may need to look at what I suggested earlier - remember the S/RF meter?
Did you even check the rear panel SO-239 to see if it was "Shorted" to case? IF so, you may need to even go back further to L51/L31 combo and check to see if the parts used to "tap" the RF output - are not adding to this - a shorted cap can ruin your day. OR an OPEN connection from one of the Coil winds can also affect the radios ability to receive (and blow up the TX side as well).
If there was a reason he threw it on the floor, you have to review and find out why it got left behind.
Ok, last note about TR17, and why I wanted you to check the board for voltages once the part was removed...
- Test TR17 - OUT OF CIRCUIT - use any TRANSISTOR tester if possible - get a Hfe number to see if the transistor is still ok.
- Probe the pads - from the foil side, with the Radio powered but into a Dummy load - and adjust RF gain control - does the voltage on the EMITTER side (The L6 side of the RF Amp) show a change?
- Does the Base pad, show a voltage?
- IF Base shows voltage - IS IT LESS THAN Emitter and Collector?
- If not - there's the problem -
- lets' further clarify - open resistor or poor soldering - Base Greater than Emitter?
- R68 needs to be checked for value 2.2K.
- R67 - 820 or 680 ohm resistor - check it's value...
- R66 Needs to be checked for Value 1K.
- Collector "Dead"? L7 is possibly Damaged - see above...
- C52, pulled and checked for value - easier to just replace with a known good part and leave it at that...
- Remove - Unsolder the "tabs" that hold the shield of L7 - to the main PCB and pull of the case exposing the coil - check for damages - Do this also for L8....
- For points of note, the ability of TR17 to "discern" signals in the 27MHz band, note the use of capacitance - two a 0.001uF (102) and a 10pF - both serve to provide a "springboard" or resonance that lets the 27MHz signal float across and have more current applied to get past the Bandpass filter of L7, C52 and L8 - so the IF image from TR18 can discern to a greater degree what is there.
- L6 if "overpeaked" can add more noise - this goes to the "springboard effect" listed above that the capacitance used in the BASE of TR17 uses to develop a resonance effect and amplify a given range of RF - it's crude but effective and the use of L6 for one side and L7 for the other makes this a tank circuit that can self-resonate and blow parts - hence why we are in the mess we have now...
So this also brings in the variables like RF gain as well as IC 1 - which may be fine just somehow not communicating anymore - so again do your details and make sure the radio and TR17 are ok before you just presume a part failed - for even the most obvious is evident, but may not be the issue - there are too many other parts to interrupt the signal - for if they are ignored then you're stuck in a loop...
(Edits: Gotta' love it when Google changes BCE to ESR...LOL)
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Did some more checking and finally found something! Yes I did check for continuity from so-239 to board, it's good. Removed tr17 and probed pads for voltage. .3 mv on base, 8.7v collector, 2.3v emitter. When in circuit numbers stayed the same except base was 1.8v. Now while it's out I have a good look at L6 and it's winding are broken! So what can I replace it with? Is this my problem or just something adding to the mess? Not sure where to go from here. Thanks
The numbers - well - ech... not the best, and if you see that L6 is damaged. That adds to the problem most certainly. Are just the wires going to that Coils' base, that has the mounting leads - those coil connections - are they broken? If so - then that may be salvageable but you have to pull/add or build solder up on those posts to reaffix the wires broken off - else you may need to get a part or two. Meaning Replace L6 and maybe even more for the TX side of things.
But that does not mean it's ok. Because - the Emitter Side - towards L6 is very low. It should be adjustable due to it being the RF Gain control that does handle that pad. One side of the RF gain is to 8 V from the RX side - so it usually would have some pretty good voltage presence - so you should have been able to see voltage rise and fall on this.
A blown TX section can mean something very big in problems - that fixing the receive may not as simple as we once thought. This can be a brick we can only decorate but to even put the time in for that - is best left to the customer.
- The TX issue may mean a replacement Final - which as these radios once used. are not cheap to replace anymore - onto more complex issues meaning more parts - like the AM Regulator
But that does not mean it's ok. Because - the Emitter Side - towards L6 is very low. It should be adjustable due to it being the RF Gain control that does handle that pad. One side of the RF gain is to 8 V from the RX side - so it usually would have some pretty good voltage presence - so you should have been able to see voltage rise and fall on this.
- (This goes back to now knowing L6 wasn't in the best of shape - so it can explain the readings we got on the EMITTER side of TR17 during the test- not out of the woods yet though.)
- This design used for Galaxy may not be the best at VOLTAGE gain, but it is effective for sensing and amplifying current thru it - to develop power and obtain a voltage into L7 - using inductance then going into a capacitor into another stage versus direct capacitive coupling to the next stage. This L to C Series-circuit (then thru another L) function has some benefits. Impedance transformation is one, Better selectivity and flexibility in design and part interchangeability are others, that SMD doesn't always give you.
A blown TX section can mean something very big in problems - that fixing the receive may not as simple as we once thought. This can be a brick we can only decorate but to even put the time in for that - is best left to the customer.
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I did try the RF gain while probing the emitter pad, voltage went up and down. That's when I noticed my tx was shot. You had said to tx into dummy load. I was using my bk 1040 and noticed the meter barely moving. S meter in radio was still moving forward though. I did a quick voltage check on driver and get 3.5v on collector. Same for first final and nothing on second final.
Anyway back to L6. Yes the windings are all snapped off it looks like. I wouldn't try to salvage it.
I'm really not sure what to do at this point. I feel like I have a lot of time into already and should just let it go. Only thing is customer probably isn't going to be happy hearing that now transmit is gone as well. I do have some nos 1969 finals hanging around. Although this one has 2312's stock. So I guess hit me with what you think this radio is going to to need to get going and I will decide if I'm up to it or not. Thanks again.
Anyway back to L6. Yes the windings are all snapped off it looks like. I wouldn't try to salvage it.
I'm really not sure what to do at this point. I feel like I have a lot of time into already and should just let it go. Only thing is customer probably isn't going to be happy hearing that now transmit is gone as well. I do have some nos 1969 finals hanging around. Although this one has 2312's stock. So I guess hit me with what you think this radio is going to to need to get going and I will decide if I'm up to it or not. Thanks again.
Well, it's good that you RF gain voltage adjustment.
Not good about L6 but it's fairly abundant as it is 27 meg and should be easy to get from any old chassis in the Connex, Galaxy or Ranger line.
The final section having voltage on the driver and one final I would unsolder the Collector of the final that is not showing voltage and check for voltage again. If there is still no voltage at the point where the collector was soldered to the board you would then suspect an open circuit or a bad solder connection where the collector voltage fed from the collector of the other.
Don't get into big of a hurry to give up it's far from a lost cause. I will check my parts for a 27meg transformer but you will have to have some patience as the customer will also have to show some as well. You could maybe find another parts unit with a good coil in it
I may have found a source for the coil there is number and URL below
the coil number is ECIFT12004
http://www.rrcom.com/radioparts/Parts Pictures/ECIFT12004.html
Not good about L6 but it's fairly abundant as it is 27 meg and should be easy to get from any old chassis in the Connex, Galaxy or Ranger line.
The final section having voltage on the driver and one final I would unsolder the Collector of the final that is not showing voltage and check for voltage again. If there is still no voltage at the point where the collector was soldered to the board you would then suspect an open circuit or a bad solder connection where the collector voltage fed from the collector of the other.
Don't get into big of a hurry to give up it's far from a lost cause. I will check my parts for a 27meg transformer but you will have to have some patience as the customer will also have to show some as well. You could maybe find another parts unit with a good coil in it
I may have found a source for the coil there is number and URL below
the coil number is ECIFT12004
http://www.rrcom.com/radioparts/Parts Pictures/ECIFT12004.html