TRC-453, no AM tx, Uniden President Grant meter needle doesn't move, TRC-209 no rcv

[Critter98]

Hello all. I have a few problems.
1. My TRC-453 AM/SSB transmits fine on USB/LSB. When I switch to AM it throws a good carrier (as seen on another radio) but no audio is transmitted.
2. The President Grant's meter appears dead. The light is on but the needle doesn't move on TX or RX. I pulled it out and did the screw turn on top & Bottom but that didn't help.
3. On the TRC-209 I don't have any Rcv on any channel. It transmits OK.
I don't have an education in electronics or any experience in the field. I do have a couple of Multi testers & can solder. Any help would be appreciated since nobody around here repairs CB radios.
Tks in Adv.
Dennis

 

[doffo]

My only random guess on that TRC-453 is that maybe near the back just under the power connector, maybe that transistor may be the issue? It acts as the voltage regulator and AM regulator I believe. I just know that sometimes that part does go bad. There is a motorola counterpart that is much better if that day ever comes.

Otherwise, maybe a capacitor somewhere near the area may be the issue?

 

[Critter98]

If you're referring to the 2SA1012 transistor as a AM regulator, it appears OK. I've replaced 6 capacitors so far and nothing has changed. I'm going to get an ESR Transistor/Diode/Capacitor tester on Monday. I know it's an old radio but I'd rather not have to replace every capacitor, some are really hard to desolder.

 

[doffo]

If you're referring to the 2SA1012 transistor as a AM regulator, it appears OK. I've replaced 6 capacitors so far and nothing has changed. I'm going to get an ESR Transistor/Diode/Capacitor tester on Monday. I know it's an old radio but I'd rather not have to replace every capacitor, some are really hard to desolder.

My old desoldering gun I picked up in 2017 does ok. I think its a ZD-985. I will never go back to a desolder wick unless it is for ground areas on a board with larger solder to remove.

 

[nomadradio]

Grant's meter appears dead

First thing to see is if rocking the radio right-to-left around the center of the meter causes the needle to move. If it does, the problem could be upstream from the meter.

But if the needle refuses to budge when rocked around the axis of the pointer's pivot it's just mechanically seized.

Taking a multimeter set to ohms, and touching the probes to the meter's terminals should make the needle move. If not, the problem lies in the meter, not the radio.

73

 

[Johnny Mullet]

I am pretty sure you know the service manual for the TRC-453 is here......

Realisitic TRC453 Service Manual

 

[Critter98]

OK I replaced the c2312(TR538) with a TIP42C, replaced a dozen capacitors. I have audio for about 30 seconds then fades out to static. The LED signal strength lights do not light up any more for Tx but they do for Rx. More trouble shooting tomorrow & more cap replacements. I'll get this radio working eventually (I hope).

 

[nomadradio]

Hmm. In the schematic it shows TR538 has the type number "2SC2312". The device markings usually leave out the "2S", leaving the "C2312" marking to identify it.

Just one problem. TR538 requires a RF power transistor. The TIP42 series is a low-frequency transistor that's only good for audio and power supply circuits. NOT a proper substitute. Looks the same, but what's inside is what counts.

Did you check the "C2312" you removed? That one has become expensive to find, and it has been widely counterfeited. Got discontinued years ago, and has been reproduced only by a couple of legitimate sources. And it's been counterfeited by folks who sand off the marks from a cheap part and print the bogus number for a discontinued part. If that part checks okay, the fault lies elsewhere.

So, just why did you replace that part?

73

 

[Critter98]

The metal plate was blackened so I thought it was burned out. After I replaced it I bought a simple tester & it showed hFE=38, Uf=635mv. The TIP was listed as an alternate on the Alltransistors web site. We have one small electronics shop in town & he had the TIP42C so I thought I'd give it a try.

 

[nomadradio]

A quick inspection of the published specs will show that the TIP42 has a much-lower "ft" rating, meaning the highest frequency it wil amplify is way, way below 27 MHz.

Wait a minute. My idiot light just came on. The TIP42 is a PNP transistor. The 2SC2312 is a NPN device. Never mind the other differences, this one would be a deal breaker all by itself.

Any database that says this part will sub for a 2SC2312 is just plain wrong.

73

 

[Critter98]

Jeez, makes it hard to fix anything when published specs are wrong. Anyway last night I took the 42 out & put back the 2312 and now radio is working in degraded mode. Looks like the more caps I replace the better it gets.

 

[nomadradio]

the more caps I replace the better it gets.

Funny how that works.

73

 

[Critter98]

I've got this radio working (well, sort of). After about a minute or less it gives off a lot of pops & crackles. Back to the drawing board.