Galaxy 44 goes off freq. when warm.

[Low_Boy]

Another one off the head scratch pile.
Galaxy 44 when warm goes off freq. First problem L20 is supposed to be 16.2700 MHz I can only get 16.2665 MHz. Warm or cold. L20 good and crystal is good. Also 1he 10.240 MHz crystal is good. and I get the right reading on pin 4 of the PLL. Both varactor diodes which I thought was the problem to begin with are good. TR25 VCO is also good. L22 adjusts but is not real clean. I am not sure what to check next. Could it be IC10 PLL mixer?

 

[M0GVZ]

Typical CB quality oscillator TBH. You should only be tuning it for the correct frequency once it has been on for a while, not from cold, and then it'll be out until it warms up. Going on what L20 is then you're not going to be so far out that it is an issue talking to people on AM or FM.

 

[Low_Boy]

Oh no when it warms up it is gone. And can not be adnusted. Shure would like to figure that one out.
Thanks

 

[nomadradio]

And can not be adnusted.

Does this mean that L20 doesn't do anything?

Ought to.

Any chance the 9-Volt regulator is the source of the warmup drift?

73

 

[Low_Boy]

L20 has some adjustment but little. I Tried another coil out of another radio with the correct numbers but it does the exact same thing. But when it gets to the point that it loses frequency that 16.2665 MHz is all over the place also. I also tried putting a variable capacitor across the legs that are connected to the internal cap in the coil and got it up to 16.2668 MHz but when it got to the temp that also went crazy.
Thanks

 

[nomadradio]

L20 has no internal capacitor. It's a straight-up two-terminal variable inductance.

Is the oscillator/mixer chip the crystal is hooked to the original one-piece 7310 chip? I remember having trouble with some of the Korean copies of that chip, the KA7310.

Or is it the thick-film hybrid circuit coated in black goo?

Sure does start to sound like the 7310 chip is the culprit.

73

 

[Low_Boy]

I will check it out when I get home.
Thanks

 

[Tallman]

I wonder if this is similar to the DX949-959-979 drift problems. I believe exithirteen did an article on fixing those. Seems like bad/cheap capacitors were the cause.

 

[nomadradio]

L20 should run the channel frequency down a channel and a half, sometimes more.

If it does nothing, there's a problem in that circuit beyond the typical drift behavior.

73

 

[Low_Boy]

Nomad. The service manual shows Ta7301P But I have to remove it to see what it actually is. It could be the Korean KA7301 I will remove it after dinner.

 

[nomadradio]

Original part is Toshiba TA-seventy three ten.

Not "oh-one". And the one that begins with "K" is the Korean copy.

73

 

[Low_Boy]

I wonder if this is similar to the DX949-959-979 drift problems. I believe exithirteen did an article on fixing those. Seems like bad/cheap capacitors were the cause.

I changed the caps in that area. But did not recap the whole radio. But if I put the heat gun in that area for a second frequency goes out of control crazy. If I let it act up on it's own I would say 4 or 5 Min. it will go crazy. Going to try the PLL Mixer first.
Thanks.

 

[Low_Boy]

I think it is fixed. I pulled the TA7301P and had a old connix board someone gave me. I pulled the TX mixer the Korean one KIA6410S and all is well after 3 Hrs. running. and after heating the PLL area with my heat gun. Still L20n will only very between 16.2630MHz and 16.2665MHz. It will not go to 16.2700 but still sounds good on a near by radio.

 

[nomadradio]

Rock on! Good to hear you drilled down to it and got 'er going.

73

 

[Low_Boy]

0ne question Nomad. where would I get a TA7301 or a KIA6410S? I did a search and looked on e bay and can not find either.