Capacitor sub?

[nomadradio]

Accepted practice is to turn down the signal-generator level as low as you can and still be able to see a peak. This serves to keep the radio's AGC from flattening out the peak.

The higher the signal level, the wider the apparent 'peak' setting becomes. And the odds of having one or more slugs "nearly" on the true peak get higher with a larger test signal.

73

 

[Brian G]

Accepted practice is to turn down the signal-generator level as low as you can and still be able to see a peak. This serves to keep the radio's AGC from flattening out the peak.

The higher the signal level, the wider the apparent 'peak' setting becomes. And the odds of having one or more slugs "nearly" on the true peak get higher with a larger test signal.

73

Thanks for the tips! So no chance that could have damaged those diodes if gain was to high?

 

[nomadradio]

A signal generator should not have that kind of energy available, nowhere near enough to damage components.

73

 

[Brian G]

Accepted practice is to turn down the signal-generator level as low as you can and still be able to see a peak. This serves to keep the radio's AGC from flattening out the peak.

The higher the signal level, the wider the apparent 'peak' setting becomes. And the odds of having one or more slugs "nearly" on the true peak get higher with a larger test signal.

73

I ended up replacing those 4 diodes and i don’t see any improvement. I am going to try and retune all those coils but I’m not confident that’s going to help.

 

[nomadradio]

So, uh.. Pulling one end of D14 made no difference?

73

 

[Brian G]

So I MAY have found the problem. I was doing an extreme closeup of the board last night looking for problems. When I pulled C47 to replace it with the 1 pf, I believe I dislodged one of the legs of C48 which is coupled to 47. As you prob know, these caps are in a very tight space in-between L7,8,9,10 so it is impossible to maneuver it back into place. But of course I don't have a 5 pf cap to replace it so I had to order some. Once that comes in, I will pop that and a 2 pf C47 in and see if that fixes it. Willl let you know prob in week once I have those parts in. thanks for the help....to be continued.

 

[nomadradio]

Nothing wrong with mounting those parts on the solder side of the board.

73

 

[Brian G]

Nothing wrong with mounting those parts on the solder side of the board.

73

Yeah I thought about that at least to try and see if that was the issue. Maybe will try after. Let you know.

 

[Brian G]

Yeah I thought about that at least to try and see if that was the issue. Maybe will try after. Let you know.

Hi I would love to send you a video about 90 seconds long of what I’m hearing (or not). Might help with diagnosis. But I can’t upload videos here.

 

[Brian G]

Nothing wrong with mounting those parts on the solder side of the board.

73

Another thing. The radio is “louder” on SSB. Still not hearing any stations but it could just be quiet in the radio. But when I put it in AM, it goes almost dead quiet. I did put those 2 caps back. Seemed to help a bit but something still isn’t right. Especially in AM. Like I said, I have a video of you have an email I can send it to

 

[Brian G]

Nothing wrong with mounting those parts on the solder side of the board.

73

I did try to tune the 3, 455 kHz coils. L13,15,3. L13 doesn’t do all that much that I can see. But best I can tell they are all peaked.

 

[Brian G]

Nothing wrong with mounting those parts on the solder side of the board.

73

Also I checked out the following transistor voltages: TR 14,15,16,17,18,52. All seem ok except for the base of 16 is reading about 0.6 v and the schematic says it should be about double that at 1.19. Not sure if that means anything but that is the only significant variance I found.

 

[Brian G]

Nothing wrong with mounting those parts on the solder side of the board.

73

Also checked Tr 19,9, 10,FET 1 and 2. All seems to be ok except for maybe TR 10. The readings on that one were around 2.2, 2.3,and 2.9. Manual says 2.57,1.94,3.1 v. So not sure if that is really off by enough?

 

[nomadradio]

L13 never shows much of a peak. Part of the design far as I can tell.

Starts to sound like a weak 7.345 MHz crystal that converts 7.8 MHz down to 455 kHz.

Don't see it often, but if SSB is okay, this is pointing towards the AM-only part of the receiver.

I looked back up the line of this thread, and you don't mention lifting one leg of D14.

May not matter if SSB sounds like it should.

73

 

[Brian G]

L13 never shows much of a peak. Part of the design far as I can tell.

Starts to sound like a weak 7.345 MHz crystal that converts 7.8 MHz down to 455 kHz.

Don't see it often, but if SSB is okay, this is pointing towards the AM-only part of the receiver.

I looked back up the line of this thread, and you don't mention lifting one leg of D14.

May not matter if SSB sounds like it should.

73

No it did not. I'm not convinced SSB is "ok". It i s "louder" when you switch over to it, but I want to see if I can actually here anyone talking or not--which I didn't last night. But then again, even using my other radio, I heard nothing. I am using my other radio to wait and listen for SSB chatter. Once I do, I will check the Cobra and see if hears the chatter too.