Galaxy DX 2547 & DX 959 HELP!!!

[tighthide]

I am technically capable but don't really have a clue about working on these CB radios. I wanted my radios to be in perfect operating condition so I decided to check out if anything was out of adjustment because I wasn't getting any responses from anyone and reception was very poor. I faithfully tried to follow the alignment procedures per the instructions so as not to screw anything up but it seems I may have.

Starting out with the PLL alignment, I can't get pin 8 of IC3 to read 10.2400MHz on both my Galaxy DX2547 and DX 959. When I first touched the probe to pin 8 of IC3 I was able to read 10.2406 where it should be within 20Hz plus or minus. I tried to adjust VC1 to get 10.2400 but then the best I could get by adjusting VC1 was 10.2350. Now I am unable to get it back to 10.2400. I don't know if maybe I did something to damage X1 so I ordered one. This is happening on both my CB's. Can anyone suggest what I may be doing wrong and give me a little direction?

Also when I check the AM OSC at TP5 and either of the USB OSC or LSB OSC at TP6 I can't get it anywhere near to 10.6950 when I transmit. Is something defective or am I doing something wrong? What could I have done to affect both radios? Can you help me out in any way just to get everything in working order? There is nobody nearby where I can take this too but I should be able to make the repairs myself if someone could just help direct me in what to do. Thank you in advance!

 

[Robb]

Welcome to the forum!

Having both radios go out of alignment at the same time, just because you can't hear anyone, is nearly impossible.
What do you consider 'technically proficient'; how do you define that? You have basic electronic knowledge and have all of the required equipment and have worked in this field to some extent?

Did you consider that leaving well enough alone might have been the correct course? CB radios can have lull periods of inactivity just like Ham radio can. Please pardon me for trying to wrap my head around what you have said.

What brand of freq counter are you using and had it been calibrated at some point? Did you try to use a 20pf cap between your counter probe and the test point to unload the circuit under test?

When working on RF circuits, you must have the necessary nylon adjustment tools, or else using metal tools will throw off you adjustments and most likely will damage the tuning cans.

At least you still have one of the radios that you have not attempt to adjust so that you can still use to compare the two?

 

[AudioShockwav]

Did you try to use a 20pf cap between your counter probe and the test point to unload the circuit under test?

When working on RF circuits, you must have the necessary nylon adjustment tools, or else using metal tools will throw off you adjustments and most likely will damage the tuning cans.

Good points.

And yes, odd that 2 radios exhibit same issue, suggests that equipment or procedures might be a problem.

73
Jeff

 

[tighthide]

Welcome to the forum!

Having both radios go out of alignment at the same time, just because you can't hear anyone, is nearly impossible.
What do you consider 'technically proficient'; how do you define that? You have basic electronic knowledge and have all of the required equipment and have worked in this field to some extent?

Did you consider that leaving well enough alone might have been the correct course? CB radios can have lull periods of inactivity just like Ham radio can. Please pardon me for trying to wrap my head around what you have said.

What brand of freq counter are you using and had it been calibrated at some point? Did you try to use a 20pf cap between your counter probe and the test point to unload the circuit under test?

When working on RF circuits, you must have the necessary nylon adjustment tools, or else using metal tools will throw off you adjustments and most likely will damage the tuning cans.

At least you still have one of the radios that you have not attempt to adjust so that you can still use to compare the two?

I worked as an electronics technician for 32 years but that was not with RF. I'm familiar with audio frequency but not radio. I believe I have the necessary test equipment and as far as my new frequency counter it read properly initially, although it wasn't dead nuts at 10.2400 MHz like the setup required, but it went haywire when I started trying to tweak things. It reads the proper frequencies at TP3 and adjustable with the AM at 16.2700, USB at 16.2725 and LSB at 16.2675. It's that damn pin 8 of IC3 that I can't get in specs. As for having another radio to compare it to, when I checked the second one it was close to 10.2400 but still off like the first one. When I tried tweaking it to get it to exactly 10.2400 it started acting just like the first one. I can't help but think I did something I shouldn't have and now both are screwed up. What I did not do was hook a 20Pf cap to the probe. Do you think that would make a difference?

 

[tighthide]

Good points.

And yes, odd that 2 radios exhibit same issue, suggests that equipment or procedures might be a problem.

73
Jeff

I will try it with a 20PF cap on the probe, THANKS!

 

[Robb]

I will try it with a 20PF cap on the probe, THANKS!

Also make sure the power supply is set to 13.8v AND let the radio run for at least 30 min to stabilize.
Vrrrry important!

 

[tighthide]

Yes the radio is set for 13.8V and the VCO is set to 2.5VDC with the PCB Jumper removed from TP7, TP8 & TP9. I'll try this tomorrow! Thanks!

 

[Handy Andy]

If you can understand the above...

When you do up your RF probe, best to locate several schematics of different radios that use the 10.240 Crystal, pretty much most of todays CB's still use that Xtal as their reference and Main Clock.

​

Just wanted to help you more in getting a probe that won't LOAD DOWN or Change / Alter or otherwise Upset the Apple Cart your oscillator section is, due to the probe itself adding a tuning issue upon it.

Even Galaxy's own Frequency Counters have excessive input

​

The best method to help is use less capacitance than that which is used in the circuit.

When you look at the values in your 2547 above, that is an amplified signal - but it's still able to be DE-tuned by using a variable capacitor - by either in series or ACROSS the output on the Xtals leads.

As Robb Suggested - 20pF (OR LESS) would work. In SERIES - not parallel NOT across the tip.

Because, if this capacitance across the leads occurs - IT (The tip) could/would suck the Clock's delicate balance of signal away from the circuit and you lose signal and the signal strength struggles to attain what it once had as a stable oscillator because of the loading the tip put on it. This usually winds up (SIC) LOWERING the frequency by several kHz below your intended adjustment range.

Try to keep the input as high-Impedance load as possible - smaller Caps and Higher resistor input values reduce the load effects.

The Cap in SERIES - one leg to the world the other to the bridge...

​

So as they say in Acting - Break a Leg, usually means give it your all. But in this case, just offer one leg of the cap - the Bait will bite and you'll have a good signal feed underway...

So when you see your Clock heading south, Use LESS capacitance to reduce the loading.

A simple buffer circuit
ADJUST Resistor values to attain the best trade off of degradation to signals' STABLE capture
Note the Resistor ACROSS this input is AFTER the input cap - helps to stabilize the expected loading
.and keep stray voltages from skewing your readings.
Use a value of resistance ACROSS starting at 100K to help develop a low-loading RF probe lead.
A INPUT resistance of 1Meg is suggested but you can change that as your systems you use this probe on,
will dictate their needs of required low-load application, adjust resistance as possible.
​

It's your focus on Pin 8 PLL that has me worried, for that output RELIES on the input from Pin 7 - it's not a pass thru, it's a buffered output from the internal amp used to clean up the Clock and let it get used by the system.

• I find it ODD the Galaxy, along with others, do not use the output of this pin to help with signal and it's propagation thru the board, for many timing references use it, but they "originate" at other spots on the board.
• This technique lends more to the notions that Galaxy is a Drifter, and rightfully so, 30 minutes of Warm-up - is sometimes not enough.
• Part of this propagation effect is the required use of other Xtals for the mixing, but they too, when you look at trace lengths as well as the parts used to communicate these signals throughout the board, the inherited delays in the signal flowing to and being used by the other support "blocks"
  • - there can easily be self-induced PHASE Relationship changes to the arrivals of a specific signal at a given specific level of quality
  • - it's a self induced degradation I've seen the some of the best radios out there
  • - they purposely add trace lengths to offset this sensitivity by letting the trace (or cable), wind thru areas and land at a specific spot in both length of cable and location on the board
  • - and to think I get chastised for Coax Length issues, the techs do this to prevent degradation - go figure?

When you see your difficulty in adjustments - knowing you're going lower, the idea is to lessen the LOAD you place on it. Your tip is causing this along with the shielding - adds a complex impedance to the clock circuit - mostly as capacitance ACROSS the tip to ground.

It's why I wanted you to locate other clock circuits' the PLLs' in other CB's use to help you gain back control of your radios...

Each one uses the 10.240 signal to help with their IF imaging in some form. Usually as a mixer product to DERIVE the lower 455kHz IF image they eventually detect and amplify the Audio Envelope from the Carrier that finally after all the levels of processing - shows up as the actual signal you're listening for.

 

[tighthide]

If you can understand the above...

When you do up your RF probe, best to locate several schematics of different radios that use the 10.240 Crystal, pretty much most of todays CB's still use that Xtal as their reference and Main Clock.

View attachment 42850
View attachment 42851​

Just wanted to help you more in getting a probe that won't LOAD DOWN or Change / Alter or otherwise Upset the Apple Cart your oscillator section is, due to the probe itself adding a tuning issue upon it.

Even Galaxy's own Frequency Counters have excessive input

View attachment 42852​

The best method to help is use less capacitance than that which is used in the circuit.

When you look at the values in your 2547 above, that is an amplified signal - but it's still able to be DE-tuned by using a variable capacitor - by either in series or ACROSS the output on the Xtals leads.

As Robb Suggested - 20pF (OR LESS) would work. In SERIES - not parallel NOT across the tip.

Because, if this capacitance across the leads occurs - IT (The tip) could/would suck the Clock's delicate balance of signal away from the circuit and you lose signal and the signal strength struggles to attain what it once had as a stable oscillator because of the loading the tip put on it. This usually winds up (SIC) LOWERING the frequency by several kHz below your intended adjustment range.

Try to keep the input as high-Impedance load as possible - smaller Caps and Higher resistor input values reduce the load effects.

The Cap in SERIES - one leg to the world the other to the bridge...

View attachment 42855​

So as they say in Acting - Break a Leg, usually means give it your all. But in this case, just offer one leg of the cap - the Bait will bite and you'll have a good signal feed underway...

So when you see your Clock heading south, Use LESS capacitance to reduce the loading.

View attachment 42854

A simple buffer circuit
ADJUST Resistor values to attain the best trade off of degradation to signals' STABLE capture
Note the Resistor ACROSS this input is AFTER the input cap - helps to stabilize the expected loading
.and keep stray voltages from skewing your readings.
Use a value of resistance ACROSS starting at 100K to help develop a low-loading RF probe lead.
A INPUT resistance of 1Meg is suggested but you can change that as your systems you use this probe on,
will dictate their needs of required low-load application, adjust resistance as possible.
​

It's your focus on Pin 8 PLL that has me worried, for that output RELIES on the input from Pin 7 - it's not a pass thru, it's a buffered output from the internal amp used to clean up the Clock and let it get used by the system.

• I find it ODD the Galaxy, along with others, do not use the output of this pin to help with signal and it's propagation thru the board, for many timing references use it, but they "originate" at other spots on the board.
• This technique lends more to the notions that Galaxy is a Drifter, and rightfully so, 30 minutes of Warm-up - is sometimes not enough.
• Part of this propagation effect is the required use of other Xtals for the mixing, but they too, when you look at trace lengths as well as the parts used to communicate these signals throughout the board, the inherited delays in the signal flowing to and being used by the other support "blocks"
  • - there can easily be self-induced PHASE Relationship changes to the arrivals of a specific signal at a given specific level of quality
  • - it's a self induced degradation I've seen the some of the best radios out there
  • - they purposely add trace lengths to offset this sensitivity by letting the trace (or cable), wind thru areas and land at a specific spot in both length of cable and location on the board
  • - and to think I get chastised for Coax Length issues, the techs do this to prevent degradation - go figure?

When you see your difficulty in adjustments - knowing you're going lower, the idea is to lessen the LOAD you place on it. Your tip is causing this along with the shielding - adds a complex impedance to the clock circuit - mostly as capacitance ACROSS the tip to ground.

It's why I wanted you to locate other clock circuits' the PLLs' in other CB's use to help you gain back control of your radios...

Each one uses the 10.240 signal to help with their IF imaging in some form. Usually as a mixer product to DERIVE the lower 455kHz IF image they eventually detect and amplify the Audio Envelope from the Carrier that finally after all the levels of processing - shows up as the actual signal you're listening for.

Thanks for these tips!

I tried putting a cap in series with the probe and it seemed to improve but what I ended up trying was using my oscilloscope probe and I was then able to adjust pin 8 to 10.24001MHz within the +/- 20Hz. The funny thing was that if I connected the ground lead to the probe it must be loading it down because it won't adjust properly and drifts when grounded. I was able to lock in the 10.2400MHz on both radios using the oscilloscope probe. The radio seems to be working okay from my radio check response on AM. Don't know if I'm still doing something wrong here but still seem to have issues as described below.

Continuing down the alignment list, when I checked my TX Offset Frequency on TP3 and when I push to transmit the reading should be 16.2675MHz +/-20Hz but I can only get it down to 16.2692MHz and that's with VR7 maxed out CCW.

The next step is AM OSC which in AM TX mode should read 10.6950MHz+/-10HZ but can only get it down to 10.6975MHz using L23 with probe connected to TP5.

The next step is USB OSC which in USB TX mode should read 10.6925MHz+/-10HZ but it reads 84.0MHz (floating) using L24 with probe connected to TP6.

The next step is LSB OSC which in LSB TX mode should read 10.6925MHz+/-10HZ but it reads the same 84.0MHz (floating) using L25 with probe connected to TP6.

I don't know how critical these frequencies are and I don't hear anyone on the SSB channels that I can get a radio check with. Aside from that, it seems to be working but I don't know if it is marginal or working 100% perfectly.

 

[Handy Andy]

Look at the FC347 Frequency Counter used in a Galaxy...

IT uses a Cap on the Ground wire-lead also, to shield it from multipoint ground loops that induce losses in the system it uses to "count"

Similar happens in a O-Scope unless you "bond the case" of the Scope to the Case of the Radio - then they can resonate - you'll get noise, but in reality, that is what you want to see.

So you can neutralize it.

Or Tune it...

Either way, the Scopes have "Quirks" in how they approach their subject of probes. You need an accurate schematic to understand the way the Scope interfaces with the world, so you can adapt a probe for it.

It's how companies make a killing on "buy this Probe kit for this Model xxx e&c..."

There are lots of RF Probe designs, but not all work for every scope it's used on.

Some will rectify the signal to a point it will skew the small signal RF readings you're looking for.

 

[Handy Andy]

When you are looking for "On Frequency" - good luck in using it, Due to scope to probe to board capacitance - lead length, shielding and other factors come into play can change the tuning - so why take on such a hassle?

Most radios are pre-centered to help with Quality control - so to think you've got a Mountain of problems - quit making these Molehills into them, don't OVERTHINK something - they've already been there and done that...They aren't going to take you to another Galaxy, at least not like CompuServe and Herbie...

​

Leave the Scope and it's Probes to do their job, your next task is to make that radio something others really would like to listen for, and to, for crying out loud!

What I do, is re-build, tune or adjust a normal AM only (OR SSB) CB radio to offer a channel to throw a simple weak carrier to help in the RX side to find "center" radio - use it, TX it, on a dummy load.

Tune it and set it up - so it's TX's can generate a carrier to tune to on all aspects of AM and SSB, FM - not so much - it's bandwidth on that side - it's kinda like using a Elephant to tromp Grapes, it's simply too difficult to accomplish the task.

To help...​

• The CB Radio now called Dummy Load Radio becomes your Reference signal.
• Then use ac Non-ferrous, Preferably Ceramic - tipped tool to adjust the slugs.
• You can also use that Dummy Load Radio and it's microphone to send a weak audio signal into another radio use It's handset next to a little table radio or TV to generate an ambient background of noise and audio signal combined
  • - this can provide you the best ability to make that SSB radio sound like it's on AM
  • Because of how our brain interprets conversation, you can use the subtleties of the changing audio levels in the "conversation" the mic's picking up to help you improve the tuning to even better than the Scope could EVER provide. In this method, you are using CARE to adjust that radio to listen for and to the AUDIO BAND PASS - not forcing on the <*GOSH DARN*> frequency the Coil is supposed to show on the scope...
• AM-Only radios can provide a LOT of the legwork for your References needed to get a Receiver back to Center - for the TX side also uses that same REFERENCE.
• In TX your only issues may be due to the small changes the tunnig is in VOLTAGE regulation - TOLERANCE and temperatures and Q-factors of the components making up the tuning section that radio uses.
• So if you want to go all out and make these radios work, you can use a different Dummy Load Radio like an SSB one - to do a lot more than just throw a carrier, they can provide the timing references too.

To "Center" an FM carrier - let the FC on the Radio or Scope determine the IF it runs on and let the rest fall into place.

When tuning use the Dummy Load Radio to help you find the "center" you want to be at, then once all the cans for the IF of Audio, and the IF from the PLL let you get there, using that Ceramic Tip tool - the small changes to find the Radios AUDIO Center afterwards can be done using the Dummy Load Radio

• turn the Clarifier to what worked the night before,
• check back to the Dummy Load Radio and knowing how far off you were,
• you can then "tweak" all cans to Center Slot of your next nights attempt using that Dummy Load Radio as your marker
  • adjust the Clarifier to the new location
  • - then use the Dummy Load Radio .as your Reference for tuning to this new expected center slot leaving your clarifier on that spot of rotation
  • - re-tune the radio to that new "Received" signal as your new marker beacon to Heterodyne with..
• Your Dummy Load Radio doesn't change - you change your Tune - Ups Radios Clarifier Location in it's Rotation to accomplish that last night fiasco tuning chase.
• This change is for your new center slot of the radio you're tuning.
• At a later time, it is possible to "tweak" the Dummy Load Radio to your new Center Slot to handle any further tune-ups and different SSB Radios in which to tune up and use this Dummy Load Radio as your new tuning fork for references

I said this before, but if you are really concerned about being "Center Slot" you need another hobby. It simply is up to those that want to take the lead and just sit on a frequency and let others tune to them. IF they don't want to? Well, then find another group that's a little less critical and Most CB'ers (Thank God) are those types, they are WANTING to have more fun and relax a little - this Radio thing isn't a Job...

Unless you WANT to be Married to it...
The Cost in Counseling fees can be pretty high...​

 

[kaos513]

Thanks for these tips!

I tried putting a cap in series with the probe and it seemed to improve but what I ended up trying was using my oscilloscope probe and I was then able to adjust pin 8 to 10.24001MHz within the +/- 20Hz. The funny thing was that if I connected the ground lead to the probe it must be loading it down because it won't adjust properly and drifts when grounded. I was able to lock in the 10.2400MHz on both radios using the oscilloscope probe. The radio seems to be working okay from my radio check response on AM. Don't know if I'm still doing something wrong here but still seem to have issues as described below.

Continuing down the alignment list, when I checked my TX Offset Frequency on TP3 and when I push to transmit the reading should be 16.2675MHz +/-20Hz but I can only get it down to 16.2692MHz and that's with VR7 maxed out CCW.

The next step is AM OSC which in AM TX mode should read 10.6950MHz+/-10HZ but can only get it down to 10.6975MHz using L23 with probe connected to TP5.

The next step is USB OSC which in USB TX mode should read 10.6925MHz+/-10HZ but it reads 84.0MHz (floating) using L24 with probe connected to TP6.

The next step is LSB OSC which in LSB TX mode should read 10.6925MHz+/-10HZ but it reads the same 84.0MHz (floating) using L25 with probe connected to TP6.

I don't know how critical these frequencies are and I don't hear anyone on the SSB channels that I can get a radio check with. Aside from that, it seems to be working but I don't know if it is marginal or working 100% perfectly.

What is your brand of the frequency counter