Johnson Messenger 223 low sensitivity

[sas73]

Hello guys,
I got a problem with an J. Messenger 223 23ch. CB radio - low sensitivity on all channels.
Measured with my RF generator: at -73dbm I can barely hear a signal, and that after alignment of IF 455KHZ coils and input RF coils Tested switchover relay (K1) , and D4, D5 (X4, X5). Measured resistance at V1 between PIN1 and a GROUND 120K, according to SM should be 21K.
I know it's hard to troubleshoot remotely, but any help will be really appreciated.

Thanks!

 

[buddrousa]

The messenger 223 is over 50 years old I had one when they were new. You will have bad Capacitors, Bad Coils, and Parts that may not no longer be found including Tubes. Good Luck.

 

[sas73]

I understand , this is my friend first radio (emotional and nostalgic value) .
Electrolytics capacitors been replaced.

 

[buddrousa]

Have you tested all the Tubes with a good known Tube Tester?

 

[sas73]

No Sir,
Unfortunately I don't have one, I usually work on solid state equipment, tube equipment is new to me.

 

[prcguy]

Have you tested all the Tubes with a good known Tube Tester?

Tubes and check voltages listed in the diagram. Don't overlook the local oscillators, their drive level and if everything is close enough on frequency. If the radio has drifted many KHz over the years it may be receiving ok but just way off frequency.

 

[sas73]

DC voltages looks ok, tested local osc, frequencies is OK, need to check local osc. level.
What I don`t understand : Service manual states that on V1 pin1 to ground should be 21k , I measured 120k.
Looking at schematic, how it's even possible to have 21k ?

 

[prcguy]

DC voltages looks ok, tested local osc, frequencies is OK, need to check local osc. level.
What I don`t understand : Service manual states that on V1 pin1 to ground should be 21k , I measured 120k.
Looking at schematic, how it's even possible to have 21k ?

R13 connects to stuff off to the right of R12 so there may be other paths to ground or other circuits. You might check the value of R13 and continuity back through coil A9.

 

[sas73]

Yes, I checked values of R12 and R13, all correct, coil A9 is good, and react on adjustment (peak)
V1 and V3 has incorrect pin1 to ground resistance (120K instead of 21k) V2 has correct value of 22k.
Here is the full schematic diagram

 

[prcguy]

Yes, I checked values of R12 and R13, all correct, coil A9 is good, and react on adjustment (peak)
V1 and V3 has incorrect pin1 to ground resistance (120K instead of 21k) V2 has correct value of 22k.
Here is the full schematic diagram

Have you tested the tubes?

 

[sas73]

No Sir,
Unfortunately I don`t own a tube tester , this is my first time working on tube electronic equipment

 

[prcguy]

No Sir,
Unfortunately I don`t own a tube tester , this is my first time working on tube electronic equipment

You could be chasing a non existent problem and its just a bad tube. You can get a good 6BJ6 off eBay for about $5. I might even have one here I would give you if I find one.

 

[N1EXA]

Just my 2 Cents but your not using a Tube Voltmeter with High impedance and your using some digital readout portable your using the wrong meter to work on tube equipment.
Next - seeing your on frequency and everything is just weak replace the SBJ6 RF amp Tube (V1) First and see if the Radio Wakes Up !

I have fixed many Browning Golden Eagles by just replacing the RF amp Tube right off the Antenna !

Pete
N1EXA

 

[prcguy]

Just my 2 Cents but your not using a Tube Voltmeter with High impedance and your using some digital readout portable your using the wrong meter to work on tube equipment.
Next - seeing your on frequency and everything is just weak replace the SBJ6 RF amp Tube (V1) First and see if the Radio Wakes Up !

I have fixed many Browning Golden Eagles by just replacing the RF amp Tube right off the Antenna !

Pete
N1EXA

I think he's just measuring DC voltages around the tube, no need for an RF probe for that. Any modern DVM is plenty high impedance for measuring AC/DC voltages in a tube circuit.

 

[N1EXA]

I was thinking that if he's using an RF generator he could look at V1 and see if there is any Amplification before its point of being
Mixed and being Demod. Thats where the RF probe and a Tube Voltmeter would help.
Id do A new V1 before any big thinking is applied to the probem !

Pete N1EXA