Gemtronics GTX-5000 Transmit Problem

[maichael]

Hi at all;I am in the middle of this base radio restoration but i have a reall strange problem in this radio.The radio has a perfect RX,LEDs,Meter but if i try to transmit with the base at the normal position the radio has no TX but if i place the radio with the top side of the radio over the bench the radio transmit perfect.In other words,if i twist the radio 180 degres the radio works fine.

Note;I replaced all of the tubes with a new ones and my RG8 jumper cable is in perfect condition.And Many Thanks Anticipated for any help.

[Sandbagger]

Jan 11, 2010 18:02:04 GMT -5 maichael said:

Hi at all;I am in the middle of this base radio restoration but i have a reall strange problem in this radio.The radio has a perfect RX,LEDs,Meter but if i try to transmit with the base at the normal position the radio has no TX but if i place the radio with the top side of the radio over the bench the radio transmit perfect.In other words,if i twist the radio 180 degres the radio works fine.

Note;I replaced all of the tubes with a new ones and my RG8 jumper cable is in perfect condition.And Many Thanks Anticipated for any help.

Usually when I see something like that I think "Gravity assisted intermittent solder joints". There is most likely a loose connection in the radio which makes better contact when the radio is inverted. I would venture to guess that you might be able to tap around with a blunt insulated instrument and track down the source of the bad connection.

Also I have have an intermittent short in a coax jumper which would go away when it was twisted into a different position.

[cbrown]

I'd tend to think you have a bad solder connection, too. Take a wooden chop stick and poke around (being careful, of course). You should be able to track it down this way.

[Sniper..Unit 305]

May also be the so-239 panel connector on the rear of the radio that has lost its proper connection. You can check to make sure its making a good connection inside the radio. If this is loose it can be intermittent in transmit or no transmit at all, but more than likely will receive. When you are twisting the rig around with the coax connected or flipped over, you may be making the chassis connector make contact. Just something to check while you are checking everything else. Sniper

[maichael]

Ok;I did all of the test and everything looks ok.I did a search resistor by resistor,capacitor by capacitor,all of the wiring connections,the SO239 with the same results.The reception of the base is perfect with the base in the normal position.I did the test of all of the voltage in the TX section and i have the -84 bias voltage,i have the correct plate voltage and the oscillation reads good too.I suspect about one of the final section coil is bad because when i turn the base just 90 degrees the base has a TX but less than 1 watt.But if i twist the base 180 degrees the TX is back with about 2.5 watts rms.I noticed that the base has TX in this position but without any swing and the base has a poor TX audio output but in the receive mode the base has a great audio.


Pssssss;I did a test of my coaxial connectors and everything is in good condition and i can use any other radio without any problem.I have over 120 old school radios because i have a big collection of CB radios and every radio works good in my 4 element Hy Gain Quad and in my Penetrator 500 base antenna and this includes my Yaesu FT-1000MV with my Dentron MLA-2500 and my Yaesu FL-2100 amp.And i have the same type of CB radio that is a Robyn T-240D and everything works perfect except the Gemtronics GTX-5000.This base is too close at my garbage box if i cant find the problem in the next couple of days.Ji,Ji,ji



73sss... Maichael- Unit 67,Puerto Rico

[Sandbagger]

Jan 13, 2010 19:29:02 GMT -5 maichael said:

Ok;I did all of the test and everything looks ok.I did a search resistor by resistor,capacitor by capacitor,all of the wiring connections,the SO239 with the same results.The reception of the base is perfect with the base in the normal position.I did the test of all of the voltage in the TX section and i have the -84 bias voltage,i have the correct plate voltage and the oscillation reads good too.I suspect about one of the final section coil is bad because when i turn the base just 90 degrees the base has a TX but less than 1 watt.But if i twist the base 180 degrees the TX is back with about 2.5 watts rms.I noticed that the base has TX in this position but without any swing and the base has a poor TX audio output but in the receive mode the base has a great audio.


Pssssss;I did a test of my coaxial connectors and everything is in good condition and i can use any other radio without any problem.I have over 120 old school radios because i have a big collection of CB radios and every radio works good in my 4 element Hy Gain Quad and in my Penetrator 500 base antenna and this includes my Yaesu FT-1000MV with my Dentron MLA-2500 and my Yaesu FL-2100 amp.And i have the same type of CB radio that is a Robyn T-240D and everything works perfect except the Gemtronics GTX-5000.This base is too close at my garbage box if i cant find the problem in the next couple of days.Ji,Ji,ji



73sss... Maichael- Unit 67,Puerto Rico

One other thing to check: The SO239 coax socket on the back of the radio. Many times the spring tension on the center contact relaxes enough that the center pin of a PL-259 can sit in there and only make intermittent contact.

If that doesn't pan out, I'm tempted to think that one or more of the tuning slugs or coils may be loose and by inverting the radio the tuning may shift a bit.

[maichael]

Thanks a lot at everybody.I found the mistery problem.After many hours of work i founded the problem in the L702.The L702 coil has two adjustments with two separate carbon hex adjustments.The previous owner of the base made a mistake because i founded the lower carbon bolt broken of the L702 coil.When i twisted the radio 180 degress the piece of the broken carbon moves at the correct adjustment in inside of the coil and when i placed the radio at the normal position the carbon adjustment moves in inside of the coil out of the correct adjustment.This is incredible ahhhhhhh!!!!!!!!


Pssssss;I replaced the R901 resistor (10 ohms) with a (1 ohm) resistor and i peaked the output coils and now the radio has a much better swing.And Many Thanks for the help again.