Galaxy radio drift

[Larry A McClanahan]

I focused my investigation on Galaxy DX Series radio because I own a few of them and always have. I was aware of the drift problem and constantly reading and studying and working through different radio problems I decided to tackle this one. I've learned a few things in regards to the DX series of radios.

 

[loosecannon]

here is a cool video on what can be done to determine the "polarity" of some non-polarized capacitors.

for those that don't already know of this youtube channel, it is full of great content.


LC

 

[Larry A McClanahan]

The two things that no one else caught was the interaction between C130 and D49. That was causing a major drift problem. The other thing that no one caught was that Ranger on the 2950 put the 5p cap across the crystal terminals to lend some stability to the Circuit. Both of which are major.

 

[Martian]

There is no R130 in relation to D49.
There is a C130 in parallel which without crunching the numbers is probably going to need to be there - meaning it's not something you can just swap willy nilly.
So there is no interaction to catch. It's how it was designed to get the tuning range with that particular varactor.

Unless you mean R150, which sits right next to it on the board and that resistor was somehow getting warm which is indicative of another problem.

But keep trying. Eventually you might make it stable.

 

[Larry A McClanahan]

More local talk today. No Dx. Still no drift. There is no longer a heat problem. Thanks for the heads up on the typo. Yes, it is C-130.

 

[Larry A McClanahan]

Also take note that C131 is emitting its own field effect. Sounds like C130, C131 and D49 need to be shielded and isolated from one another.

 

[Handy Andy]

Does the radio use any foil shielding on the foil side of the board?

 

[Martian]

Going all out...
Try SMD parts. (0603/0805 for caps and SOD style packages for the diodes)

 

[Handy Andy]

Whoa!

We're in a time capsule here, working with what we got not what we could have...

Hmmm...

The reason for the question was because Cobra 19+ in their heyday's used foil shielding around their "Exciters" - even though they were only AM.

Even cobra realized the value of the function. And used shielding to make the radio stable enough to work.

That's why I asked...

 

[Larry A McClanahan]

Does the radio use any foil shielding on the foil side of the board?

Not yet, but adding it.

 

[Larry A McClanahan]

I'm also fabricating crystal cans to contain the components that are interacting with others in a field effect manor.

 

[Larry A McClanahan]

Anyone operating a Galaxy DX 2547 will see the frequency counter change sometimes. This is not necessarily a result of the frequency of the radio changing. The frequency counter and its board and the processor are sensitive to heat.

 

[Larry A McClanahan]

I also need to re-tin components on the clarifier on/off button board.
I need to take the face off so that I can tighten the nut on the RF power knob post. I remove all the knobs and two screws on the left and two screws on the right. What else do I need to remove to access under the plastic face? And just the face.

 

[Larry A McClanahan]

I need to remove the lip on one and shorten it. There are some places that Have to be filed out so as not to short other components. Line the inside base edges and bottom outside of them with liquid tape. Ground.
The small one contains D49. The large can contains C-130 and C-131. They will be soldered together.

 

[Larry A McClanahan]

I need to take the face off so that I can tighten the nut on the RF power knob post. I remove all the knobs and two screws on the left and two screws on the right. What else do I need to remove to remove the face?
I know someone on here has the experience and the expertise to have removed one. Never mind. I get it. Have a nice day.