Crystal off Frequency

[Plumber-G]

Hello
Aligning my Galaxy 2547 and found the X1 Crystal off by 4Khz manual says 20hz??
Having problems finding replacements
any sugestions?

Thanks
Plumber-G

 

[Robb]

X1 is the reference oscillator Xtal, which is 10.240mHz +/-20Hz. So if it off by 4kHz; then it is time to buy another Xtal and just replace it. Since there isn't enough adjustment in the VC1 trimpot cap to correct for that much deviation from specs.

RF Parts will have it

 

[Plumber-G]

Robb
Can't find crystal at RF Parts, also tried oscillators should I try a different search term??
Plumber-G

 

[Robb]

Yeah, I checked RF Parts and you are right. Strange.

One other thing; you might test and possibly replace VC1. If it has gone bad, that is also possible. Wouldn't be the first time I found a bad, cheap, compression cap. IIRC, it is rated for 2-20pf. Common.

If not; then maybe someone on this forum that knows of a source for that Xtal might jump in here and provide a link for you

 

[nomadradio]

Must have sold all their Galaxy parts to Barkett.

http://stores.goldeneagleradios.com/crystals-1/

First one listed on this page.

73

 

[Plumber-G]

I called Radio Shop Supply and they said there is none currently in the US but pulled one from a new board to get me through, I'll see if I can add the VC1 to the order

Thanks

 

[scout943]

Try here http://www.kenselectronics.com/

 

[Plumber-G]

I installed the new crystal and not much joy,
How much adjustment should VC1 have and should it be linear??
I can peak the frequency in the middle of the VC1 range, But still 2.5Khz Low
Before I replace VC1 is there anything else that would cause this??
I was thinking about the cap in parallel with VC1??

Thanks
Plumber-G

 

[Plumber-G]

I have another question many of the caps on this radio have a black mark on top of the cap?? Does anyone know what that means?

 

[Plumber-G]

New development
I have been getting my frequency readings with the ground wire from the frequency counter on the ground wire from the X1 Crystal and the positive probe on pin 8 of the PLL Chip per manual, when the ground is not grounded I am within 5hz which is in spec?? What does this mean?? Am I doing something wrong?? or is it just a quirk

Thanks

 

[loosecannon]

well, seeing as X1 is not grounded on either side, yes, that would be a problem.

not sure what gave you the impression that one side of the crystal was grounded.
you can see on the schematic that it's isolated from ground with capacitors.
http://www.cbtricks.com/radios/galaxy/dx2547_mosfet/graphics/galaxy_dx2547_main_tda2003v.pdf
LC

 

[Plumber-G]

I think you miss understood?? I used the ground from FL3 to the case of X1 crystal as my ground for the frequency counter. See Picture



Appreciate the help

 

[loosecannon]

oh ok i gotcha.

i would think that wire would be grounded to the PC board through the case of FL3, but you should confirm this with your multimeter.

you can also connect the ground side of the freq counter probe to the chassis since it is an AC signal you are trying to read.
the PC board ground is usually isolated from the chassis using ceramic disc caps, but they only block DC signals so you can use either.

try using the chassis as a ground and see how that works.

also, what is the frequency you are getting when you used the grounding point you referred to earlier (the FL3 wire)?
LC

 

[Robb]

I have another question many of the caps on this radio have a black mark on top of the cap?? Does anyone know what that means?

Means it is a 'NPO' cap, which is a designation that the cap is stable during temperature changes - among other things. Some caps need to be able to shift with temp - or temperature compensating caps Some caps need to be a little more stable in other circuits.

 

[Plumber-G]

I am getting 10,236,50 grounded and with no ground 10.240.02 (Floating)
Measured from ground on underside of board to pin 8 10,236.50 same as to EF3
Measured the resistance from the FL3 wire to chassis and 9.9 ohms
Measured from FL3 ground wire to IF cans 0 ohms
Thanks
Plumber-G