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Galaxy DX 88HL - Tone when transmitting AM, SSB

C

Chipensaw

Member
Nov 18, 2018
13
2
13
50
Hello All,

I have a Galaxy DX 88HL with an issue and it is kicking my backside. I have the radio on my bench connected to my 12 volt PS. Mic connected to radio, antenna port connected to a power / SWR meter then to a 50 ohm dummy load. The problem is constant, experiences the same issue with different microphones and when connected to an antenna.

When I transmit in AM I see a carrier, which is normal but I also hear a tone which is roughly 600hz in frequency. My AM output is roughly 7 watts. In SSB I see the same carrier and hear the same tone, output is around 14 watts. This is with no input to the microphone, echo off, mic gain minimum or maximum, all channels.

What I have checked,
Tried new microphone, PLL alignment, receiver alignment, verified voltages on TR32 and IC4. Tried to manipulate the carrier balance - no luck. Attempted to use my oscilloscope to trace the source of the tone. Checked over the Galaxy DX Radios Symptoms and Cures Database, no smoking gun so far. When I remove the TP7 - TP9 jumper bar the output power drops to zero as it should but the tone is still present, just at a lower level as I would expect. I do not have an AF signal tracer at my disposal which is why I was hoping I could use my scope to find the area causing the issue. Any help is greatly appreciated.

Thank you,

Jay
 

I did find this tonight although for the 77HML. How would I verify DC voltage leaking through a capacitor?

Galaxy DX Radios
Model DX77HML
Chassis EPT3600-14B
Symptom Excessive noise on transmit with mic gain off, DC voltage is leaking into the audio through C128
Cure Replace C128
Additional Comments
Category TX
Posted By Galaxy Tech Support
 
First, after trying what nomad suggested, try replacing C199 this little critter has caused much trouble in the past for Galaxy radios especially the older chassis like the 88 44's etc. You may also try while in transmit mode try arranging and or touching the cable routing along the front of the radio and see if that has any effect on the amplitude of the tone. But do try that C199 replace it first and get that possible issue out of the way.
 
Update - I removed one leg of R179 with no loss or change in tone. I then replaced C199 as suggested with no loss or change of tone. When probing around on the board looking for cold solder joints I did notice I can make the tone oscillate if I press in certain areas, near or on the cans etc. I will attach a file from my 1500 so you can hear and see the tone. Towards the end of the audio clip you will hear what happens after pushing on cans and probing the board a bit.

Thanks all!
 

Attachments

Last edited:
Thank you...

The tone - sounds like a "carrier" all the time.

That's not a "Beep" tone either...unless it's very muffled...

So in looking over the schematic and this things got a Frequency counter - remove, just pull, the connector - J107.

Why? the FC may be injecting the noise thru it's polling in the display...just pull J107 from the main PCB - if no change then just reinstall it - I'm trying to find places in the radio that can possibly inject this noise.

This tone - reminds me of CW - like you'd need to use in a talkback CW tone for keying - C128 is by the Audio Chip side of the 4558 chip - part of the Mic audio "offset" for the inverted input - wonder if that cap is getting leaky. IT would change "dramatically" as you touched it.

Has any mods been done to the radio - like additions to it?
 
Handy Andy said:
Thank you...

The tone - sounds like a "carrier" all the time.

That's not a "Beep" tone either...unless it's very muffled...

So in looking over the schematic and this things got a Frequency counter - remove, just pull, the connector - J107.

Why? the FC may be injecting the noise thru it's polling in the display...just pull J107 from the main PCB - if no change then just reinstall it - I'm trying to find places in the radio that can possibly inject this noise.

This tone - reminds me of CW - like you'd need to use in a talkback CW tone for keying - C128 is by the Audio Chip side of the 4558 chip - part of the Mic audio "offset" for the inverted input - wonder if that cap is getting leaky. IT would change "dramatically" as you touched it.

Has any mods been done to the radio - like additions to it?
Click to expand...


Unfortunately no luck. I removed the connectors from the Freq. counter module, assuming one of them was J107. Freq. counter went dark yet I still have the carrier.

As far as mods go, yes it has been modded in the past. I would say it has all except the modulation mod as outlined on the cbtricks site. I will post a picture of some interesting cut wires that have been there since I bought it. It did work perfectly for a number of years before this issue arose.

Thanks,

Jay
 
Then that isolates the "Tone" to as I would call it, and internal Birdie...

Although "mods" I'm thinking of, are related to Audio - this may be more of a internal carrier that is an image result of some type of subtraction. A mixing artifact.

Near the end of the MP3 - you touch one spot and it "Chortles" then no tone - did you make it stop? Where on that board?
 
IT also has FM - so a leaky cap like two posts above - the 4558 one with R 179. That uses C126 or R160 goes to the FM diode splitter / Varactor - pull it - or at least break the connection to the VCO from the Audio Amp.

What I see with Mikes post, you should remove all connections from the Audio Amp - to remove the Mic amp from being suspect.

Then if tone still exists, then something in the IF the radio has, right back to the "birdie" being something in the CFilter for 10.690 or something from the PLL is leaking past and possible part out the way out.

You'd hear the tone really warble about the IF cans for Clarifier and PLL. IF all other audio sources were removed.

Try L19 ~ L22 for PLL or L26 thru L28 Clarifier side.
 
Handy Andy said:
Then that isolates the "Tone" to as I would call it, and internal Birdie...

Although "mods" I'm thinking of, are related to Audio - this may be more of a internal carrier that is an image result of some type of subtraction. A mixing artifact.

Near the end of the MP3 - you touch one spot and it "Chortles" then no tone - did you make it stop? Where on that board?
Click to expand...

L12 - L17 area. Although it is very random as far as changing the tone, making it warble can be had in may different areas of the board. One thing I noticed last night and in the past. I hook the ground lead of my probe to the chassis when using my scope to check voltages etc. The chassis does not provide a good ground. I have to go directly to the negative terminal on the power input connector. Or like I did last night run a jumper wire from the negative lead to the chassis. This does not seem normal to me but maybe is done to isolate the chassis from ground?
 
Handy Andy said:
IT also has FM - so a leaky cap like two posts above - the 4558 one with R 179. That uses C126 or R160 goes to the FM diode splitter / Varactor - pull it - or at least break the connection to the VCO from the Audio Amp.

What I see with Mikes post, you should remove all connections from the Audio Amp - to remove the Mic amp from being suspect.

Then if tone still exists, then something in the IF the radio has, right back to the "birdie" being something in the CFilter for 10.690 or something from the PLL is leaking past and possible part out the way out.

You'd hear the tone really warble about the IF cans for Clarifier and PLL. IF all other audio sources were removed.

Try L19 ~ L22 for PLL or L26 thru L28 Clarifier side.
Click to expand...

Will do!
 

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