Krazy Ken's Realistic TRC-451 needs help....again.

[Night Ranger]

My friend "Krazy Ken" has a Realistic TRC-451 40 channel sideband mobile that needs a little help. I've been through this radio several times, and so far I have not found the cause. For those of you who have visited my website,this is the same TRC-451 that Krazy Ken hurled out his closed window after I drove him batty back in the 1980s. It took out several panes of glass on the way along with the little wooden dividers in between. In any case the flying radio survived Kens fit of rage to see another day. Unfortunately the Arizona heat may have taken it's toll as Ken had this radio in his car when he and I moved to Phoenix in 1991.
Here is the problem. I have the radio working again along with a new meter, but the RF output is low. It will only key about 1/4 of a watt on AM and about 5 watts on sideband. I have replaced the finals (2sc1969), the driver (2sc2166), and one of the pre-drivers. I checked the voltages on the driver, final, and two pre-drivers. One voltage is off by .2 volts, but other than that they look fine. I even replaced the s042p mixer IC before the drivers, but the output is still low. I also aligned the radio according to the service manual. There is an emitter resistor and bypass capacitor on one of the predrivers, so that is a possibility. Maybe the coupling capacitors? I did notice if I touched one of the pins on the s042p mixer with my multimeter the mixer would break in to self oscillation and the power output would rise to the expected output (20 watts sideband). As soon as I remove the probe the self oscillation stops. That suggest to me the finals are not getting enough drive. Any ideas or suggestions?

Below is the TRC-451 schematic;

www.shadowstorm.com/cb/schematics/Realistic-TRC-451-Manual-schematic.jpg

Night Ranger

[Sandbagger]

Dec 28, 2013 0:09:11 GMT -5 Night Ranger said:

My friend "Krazy Ken" has a Realistic TRC-451 40 channel sideband mobile that needs a little help. I've been through this radio several times, and so far I have not found the cause. For those of you who have visited my website,this is the same TRC-451 that Krazy Ken hurled out his closed window after I drove him batty back in the 1980s. It took out several panes of glass on the way along with the little wooden dividers in between. In any case the flying radio survived Kens fit of rage to see another day. Unfortunately the Arizona heat may have taken it's toll as Ken had this radio in his car when he and I moved to Phoenix in 1991.
Here is the problem. I have the radio working again along with a new meter, but the RF output is low. It will only key about 1/4 of a watt on AM and about 5 watts on sideband. I have replaced the finals (2sc1969), the driver (2sc2166), and one of the pre-drivers. I checked the voltages on the driver, final, and two pre-drivers. One voltage is off by .2 volts, but other than that they look fine. I even replaced the s042p mixer IC before the drivers, but the output is still low. I also aligned the radio according to the service manual. There is an emitter resistor and bypass capacitor on one of the predrivers, so that is a possibility. Maybe the coupling capacitors? I did notice if I touched one of the pins on the s042p mixer with my multimeter the mixer would break in to self oscillation and the power output would rise to the expected output (20 watts sideband). As soon as I remove the probe the self oscillation stops. That suggest to me the finals are not getting enough drive. Any ideas or suggestions?

Below is the TRC-451 schematic;

www.shadowstorm.com/cb/schematics/Realistic-TRC-451-Manual-schematic.jpg

Night Ranger

Hmm, I thought the radio he tossed was a base rig. Anyway, I had a similar problem with a Midland base. Power was low across the board. Of course the finals, and driver etc. were immediate suspects, but like you, it didn't solve the problem. I was pretty much into the "banging head against the wall stage" when I noticed one of the picofarad disk caps that make up the final matching network and low pass filter, was very warm to the touch. Replacing that very leaky cap solved the problem. So perhaps you're facing a similar situation.

[Night Ranger]

Dec 28, 2013 10:13:36 GMT -5 Sandbagger said:

Dec 28, 2013 0:09:11 GMT -5 Night Ranger said:

My friend "Krazy Ken" has a Realistic TRC-451 40 channel sideband mobile that needs a little help. I've been through this radio several times, and so far I have not found the cause. For those of you who have visited my website,this is the same TRC-451 that Krazy Ken hurled out his closed window after I drove him batty back in the 1980s. It took out several panes of glass on the way along with the little wooden dividers in between. In any case the flying radio survived Kens fit of rage to see another day. Unfortunately the Arizona heat may have taken it's toll as Ken had this radio in his car when he and I moved to Phoenix in 1991.
Here is the problem. I have the radio working again along with a new meter, but the RF output is low. It will only key about 1/4 of a watt on AM and about 5 watts on sideband. I have replaced the finals (2sc1969), the driver (2sc2166), and one of the pre-drivers. I checked the voltages on the driver, final, and two pre-drivers. One voltage is off by .2 volts, but other than that they look fine. I even replaced the s042p mixer IC before the drivers, but the output is still low. I also aligned the radio according to the service manual. There is an emitter resistor and bypass capacitor on one of the predrivers, so that is a possibility. Maybe the coupling capacitors? I did notice if I touched one of the pins on the s042p mixer with my multimeter the mixer would break in to self oscillation and the power output would rise to the expected output (20 watts sideband). As soon as I remove the probe the self oscillation stops. That suggest to me the finals are not getting enough drive. Any ideas or suggestions?

Below is the TRC-451 schematic;

www.shadowstorm.com/cb/schematics/Realistic-TRC-451-Manual-schematic.jpg

Night Ranger

Hmm, I thought the radio he tossed was a base rig. Anyway, I had a similar problem with a Midland base. Power was low across the board. Of course the finals, and driver etc. were immediate suspects, but like you, it didn't solve the problem. I was pretty much into the "banging head against the wall stage" when I noticed one of the picofarad disk caps that make up the final matching network and low pass filter, was very warm to the touch. Replacing that very leaky cap solved the problem. So perhaps you're facing a similar situation.

I did not think about the low pass filter, but that could be it. When I caused the s042p mixer to break into self oscillation it may have been on a frequency that was able to pass through the low pass filter thus the expected 20 watt output with the radio on sideband. I'll check it. Thanks.

Night Ranger

[Sandbagger]

Dec 28, 2013 10:51:51 GMT -5 Night Ranger said:

Dec 28, 2013 10:13:36 GMT -5 Sandbagger said:

Hmm, I thought the radio he tossed was a base rig. Anyway, I had a similar problem with a Midland base. Power was low across the board. Of course the finals, and driver etc. were immediate suspects, but like you, it didn't solve the problem. I was pretty much into the "banging head against the wall stage" when I noticed one of the picofarad disk caps that make up the final matching network and low pass filter, was very warm to the touch. Replacing that very leaky cap solved the problem. So perhaps you're facing a similar situation.

I did not think about the low pass filter, but that could be it. When I caused the s042p mixer to break into self oscillation it may have been on a frequency that was able to pass through the low pass filter thus the expected 20 watt output with the radio on sideband. I'll check it. Thanks.

Night Ranger

Either that or the spurious that you caused was simply a collection of signals which power added to make that 20 watts. If you key the transmitter for a period of time, you can do the touch test on the disk caps to see if any are hot to the touch. Also check underneath the board for cold solder joints in the same area.