Realistic TRC-448 not working....why?

[Turbo T]

I have a Realistic TRC-448. The radio does not transmit on AM or sideband.

It does not receive regardless of how far the squelch is dialed back or how much the RF gain is advanced.

The PA function does not work. The needle doesn't even move.

Heck the LED's for the AM or either of the SSB's come on when the dial is put in the correct position.

The only thing I even hear is a clicking noise inside the radio when the mic is keyed. Sounds like a relay clicking.

Where do I begin looking to repair this radio? Would the mic being faulty cause these conditions on this model radio?

Thanks in advance.

 

[Robb]

http://www.worldwidedx.com/cb-band-cb-radios/23179-realistic-trc-448-am-ssb.html

Lotsa info right there.

It may be a transistor in the Audio circuit, since it doesn't use an IC.

I have one of these radios in my junk pile. No output transistors; uses the rare 1307 & 1306 final/driver.

Might be able to be changed over to a 2166 and 1969 driver/final.
Perhaps MOSFET's too.

 

[ExitThirteen]

Sounds like the VCO is unlocked, and probably needs an alignment, off the top of my head. That could cause all the symptoms you mentioned.


~Cheers~

 

[Turbo T]

Sounds like the VCO is unlocked, and probably needs an alignment, off the top of my head. That could cause all the symptoms you mentioned.

Curious why would the VCO be unlocked? Where inside should I check for this?

 

[Robb]

Curious why would the VCO be unlocked? Where inside should I check for this?

If the VCO voltage is too high or too low; it will allow the PLL to unlock.
There is an alignment page for this radio on CB Tricks. Look up where it says 'VCO voltage'. It will tell you where to connect your voltmeter/DVM to and what channel to put the radio on for the test.

http://www.cbtricks.com/radios/realistic/trc_448/graphics/realistic_trc_448_sm.pdf

 

[Radioman1]

Inop Radio

First thing I would do is check the PLL Crystal, a 10.240 (it's marked)

Plug an external speaker into the PA jack, put the radio in the PA mode and

verify the audio stages are working, if they are good, I would almost betcha that the crystal mentioned earlier is not oscillating........

 

[Zman]

Good radio when it is working. if you need a few spare parts i have a junker that id sell parts off of.

 

[slprydk]

First thing I would do is check the PLL Crystal, a 10.240 (it's marked)

I have had a few of these and I seem to remember replacing the crystal before.

I like the look of these radios, even better when they are all blue

Jim

 

[Turbo T]

Ok I'll admit I've never tried working on one of these before....is the VCO under those 2 chrome shields....????

Also...Radioman1, this radio has no output whatsoever...no RX, no PA mode....it doesn't even receive.

 

[slprydk]

The mode LED's come on or dont come on?

 

[Robb]

Ok I'll admit I've never tried working on one of these before....is the VCO under those 2 chrome shields....????

Also...Radioman1, this radio has no output whatsoever...no RX, no PA mode....it doesn't even receive.

If you looked at this link on page 10, it gives you all of the test point locations and adjustment points.
Just 'go by the book'; best results will follow . . .

http://www.cbtricks.com/radios/realistic/trc_448/graphics/realistic_trc_448_sm.pdf

In fact, all of the test points on this radio have their own connectors standing up off of the board for easy access. V.cool.

IIRC, the metal covers can be easily removed.
Been awhile since I've been in this radio - though.

 

[Turbo T]

The mode LED's come on or dont come on?

The LED lights do not come on at all....none of them.

 

[Robb]

Then I would find the voltage regulator on the board and test/replace if necessary.

 

[slprydk]

You are looking for Q229 (TO220 in the back), you should have 13.8v on the collector, about 9.3v on the emitter, and just under 10v on the base. R314 or R315 off of the collector could be open, C328 could be shorted, or D244 could be shorted.

Q229 supplies / links to voltages all over the place including the mode LED's and the PA.

Good luck,

Jim

 

[Turbo T]

You are looking for Q229 (TO220 in the back), you should have 13.8v on the collector, about 9.3v on the emitter, and just under 10v on the base. R314 or R315 off of the collector could be open, C328 could be shorted, or D244 could be shorted.

Q229 supplies / links to voltages all over the place including the mode LED's and the PA.

Good luck,

Jim

Ok Jim. Thank you so much this helped quite a bit.

With the neg lead on the neg terminal of the power supply, and the pos lead touching the transistors legs, with the radio on, below are the following readings:

Base: 0

Collector: 12.1

Emitter: 0