I need help for repair an old GE 3-5825A

[XE1BPS]

Hi Folks.

Actually I am working in resurrect a old CB, a GE 3-5825A SSB Radio.

Luckly I can adjust and lock the PLL( 5 volts in the PIN 6 of PLL02A), but I dont have RF power out. In some channels receive, but whit very low audio. I don?t not tested it agaisnt a RF signal source, only by other CB.

The mic are ok, the mic plug are ok, old but good. If I apply mi finger in the AF IC amplifier i have noise .

I have scope and multitester and a scheme. The board are PTBM0048COX.

Any help, advise, sugesstion and of course service manual are welcome.

73 from MEXICO

[lbcomms]

First of all, check the supplies. Pin 16 of the PLL should have 5V on it, and the BB supply (middle terminal of the squelch control) should be just over 9V.

The most common part to fail in these was the mixer ICs - these have about 10 pins in a single row. They are marked "3001" usually in sets that old.

Another common problem is shorted tant. capacitors... those sets are about 25 years old, so cap problems can be expected.

Good luck!

[XE1BPS]

Update

1) The VCO and the PLL02A are OK. The same for the 10.0525 oscilator/doubler stage.

2) The first mixer and the 1? RF preamplifier are operational. I can receive distant cb station whit regular level and quality.

3) I proceed to check the second mixer and the firts TX RF preamplifier. The RF power are about .001 Watt !

The next time I will atach some pictures with scope mesurements and levels.
Happy repairs !

[lbcomms]

Like I said before, Ive had a few dead mixer chips die over the years. They are marked "3001" in the earlier sets, and "7310" in the later ones.
The GE uses two - one for the VCO / downmix and the second for the TX mixing. The first one is obviously OK, so one trick is to swap the two over and see if the fault stays the same. If so, this clears the ICs.

If the IC is OK, then just trace the signal with a CRO from the output of the IC, through the two TX bandpass cans, onto the predrivers, then onto the driver and final.

Check the DC conditions first though - the second mixer IC has a 9V supply on TX only, and check the DC levels on the predrive transistors. The voltages are shown on the schematic - don't forget the voltages marked with a triangle must be measured on transmit.

Good luck...

[XE1BPS]

Ok Thanks for your advise,

The first mixer TA7310 are ok( I replace ), But I have a question. What are the correct level for the output of th doubler/oscilator 10.0525 to 20.0150? I have only 200 mVolts in TP3 for 20.0150 MHz, and 2 volts for 30.100 Mhz !. I have a triplifier ?

And the adecuate level at the output for the first mixer TA7310 at 37 MHZ?

I attach a scheme for the PLL / VCO.

One correction, the board are PTBM058COX. Thanks

[lbcomms]

You said: "I can receive distant cb station whit regular level and quality"

By that, I presume you mean the thing is receiving OK. If that is the case, then the level of the 20.0150 is OK. If this is too low, the receive will be low too.
This also clears the first mixer IC (the one that connects to the VCO block).

It's the other mixer and the transistors following it that you need to be looking at. As you have measured the RF voltages, I presume you have an oscilliscope - put the radio on AM transmit and have a look at the first base and collector. You should have a 27 meg carrier there.
If you have, then work your way along the transistors from the one you checked, up to the final - when you find one with more RF voltage on the base than on the collector, you have found the trouble. Before condeming the transistor, check that the biasing (the DC voltages) are correct first.

If you have nothing on the first base, then either the transmit mixer IC is dead (thats why I suggested swapping them over, to clear it from the list of suspects) or you've lost the transmit IF (about 10.695Mhz) signal to the transmit mixer. One fault I see occasionally with that type of radio is very low output from the carrier oscillator - this both kills the transmit and stops it receiving properly on USB and LSB.

Do what I suggested, as you are looking in the wrong place, assuming the thing is receiving OK like you said it was.

[XE1BPS]

Hi lbcomms

I think the cb are a little "deaf". I don?t have a lab RF generator, and I don't made sensitivity test. I have a RS handie CB with rubber antenna for signal generation/inyection.

In fact I restore the first mixer and replace Q3, but when test in TP3, I have 2 RF volts @ 30.100 Mhz and 0.200 RF volts @ 20.015 Mhz. The output are .01 Volts @ 37 Mhz.

Yes, the rig receive in all 40 channel but with regular-low level level compared with newer rigs. When I picked the rig, they are dead, no rx/tx... I adjust the VCO, the first mixer and peaked T1 T2. After that the rig receive.

I agree with you: RX are functional. Its time to check the TX chain.

Thanks for all. It?s very instructive for me your knowledge.

XE1BPS Adalberto

Saludos de M?xico/ Greetings from M?xico

[lbcomms]

If the thing has never worked from when you got it, there is a possibility the tx mixer is severely misaligned. Do you have a second CB set or something else, like a shortwave receiver, that can receive a CB frequency?

If so, solder a short (1 foot long) piece of wire at one end to the base of the first predrive transistor on the GE, put it into AM transmit, and adjust the first 5 slugs (the ones near the PLL - two pairs and the single 20.105 peaker) for max. signal on the second set. If it goes over S9, cut the foot long wire shorter... but by that stage, you should see RF output from the GE and be able to peak it in the normal way. When you start to get a reading on a power meter, remove the wire.

If you get NO signal on the second set, and are sure you are on the right frequency, then you've lost the 10.695 signal to the TX mixer.
To check the GE PLL is on the correct frequency, put it in receive and hook up a counter to the 10pF recieve LO capacitor (located near the first mixer IC, close to the shield, going to a mini-coax centre conductor). Subtract 10.695 to give you the freq the set is tuned to.
Example: if you measure 37.900Mhz, the GE is on channel 20 (because 37.900-10.695=27.205, i.e. channel 20).

Good luck

[XE1BPS]

HI!


I was working in the GE a little. I discover that the PLL/VCO lost lock in the channels 1 to 10. Very interesting. I replace the second TA7310 and I dont have TX out. But I have a big cuestion: The level in the MIXER OUT pin 9 of the first mixer are??. I can?t see a 37 MHZ signal in this pin with the scope. Maybe the "new" TA7310 are defective

Does anybody have the service manual for this thing?

SALUDOS !!
73.

[XE1BPS]

HI FOLKS !
THE THING PUTS OUT 10 WATT RMS IN AM MODE AND 12 PEP IN SSB ! I FINALY FIND THE FAIL. A CAP INSIDE T3 ARE OUT OF SPEC, I PUT A VAR CAP ACROSS T3 AND ANOTHER CAP VAR INSTEAD C7. THAT CHANGES GIVE ME 20.105 MHZ. I WILL POST A SCOPE MEASUREMENT FOR SOME RF STAGES OF THE 3-5825A.

SALUDOS DE MEXICO ! 73.