connex3300hp no transmit

[sanjosebay21]

I have a connex 3300hp It has dual1969's iv replaced both transistors and still no power out I hook my volt meter to center legs on finals and key up and it shows power and increses when I talk into the mic however I did not replace the driver because I had power at the finals but I do have a new replacement if it needs it but im not sure what to do or test next all my coax is good and when ikey I have nothing the meter don't even move on the radio any suggestions?

 

[Shockwave]

Having modulated voltage (DC voltage with audio on it) at the center pin (collector) of the transistors does not mean RF is present. It is a good sign your series pass modulator is working though. The problem is most likely in the driver or earlier stages of the radio. This assumes you haven't shorted out the insulator on the back of the transistors you installed. With power off you should measure from the center pin to the aluminum heatsink with your ohm meter to make sure there is no short here. That would stop the RF but allow the DC to remain since the chassis is not at DC ground in these radios.

 

[sanjosebay21]

thanks shockwave...ok, I replaced driver so driver and finals all new checked insulaters they good they are half as thick as the transistors but no shorts what am I missing here? any other ideas on what to check /? thanks

 

[Shockwave]

Another thing that is prone to failure would be the TX mixer IC in front of the pre-driver. The scope would be very nice to see where the RF is and is not.

 

[sanjosebay21]

would you happen to know what pins are what and witch woul have rf? also I noticed my rx/tx light is green in rx and light up half green and half orange dosent light up red like it used to

 

[Shockwave]

That changes everything. Try it on different channels to see if the red TX light will light properly on any channel. Your VCO may be out of alignment or a bad PLL.

 

[sanjosebay21]

ok it wont light up red on any of the channels and it started when my swr's went up and I changed the coax soon as I plugged it intothe radio the it would spark then the channel selector would go off I removed the coax and bought a new one now I have no transmit receives just fine radio usedto work great.......thanks

 

[Radio Tech]

would you happen to know what pins are what and witch woul have rf? also I noticed my rx/tx light is green in rx and light up half green and half orange dosent light up red like it used to

This tells me that there is a problem in the mic switching circuit. When it is orange this means both lights are on at the same time. There is a little black diode under the mic jack D77. Check that. Also there are 2 swithing transistors at the corner of the board in front of the mic jack. They are both A1282. You will need to check through that circuit to find the fault. Shotgun approach here can ring up a bill. The idea is the check voltages and scope your way through.

All this needs to be fixed before moving on the the transmit stage. The spark you mentioned at the ant jack can be caused by several things. Your antenna system need to be check over good. Antennas pick up a lot of static electricty and that may be what you are having. Due to poor ground. This can reak havok on the front end of a radio.

 

[sanjosebay21]

hi, thanks you for responding iv spent all night on this radio lastnighti replaced both those transistors and two diodes next to them but I do see that black diode with yellow strip I have not replaced that one when I took out one of those transistors I loose receive installed new one and receive comes back the other one transmit or whats left of it goes away installed new transistor same thing both lights at same time