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Low RX volume on dx 44v
- Thread starter ethomas
- Start date
I could be wrong; but all of the Galaxies between 44 and 99 use the same board. So -therefore- any troubleshooting applications can be used.
If that isn't enough, you can email Galaxy for info if need be. I did - and they were fairly prompt in writing back.
LooseCannon - a member on this forum - might read this thread tonight or some time over the next few days and give some tips. He works at a radio shop and is quite knowledgable - and may provide the best scoop/the real skinny on what to check. Haven't seen him stumped yet!
If that isn't enough, you can email Galaxy for info if need be. I did - and they were fairly prompt in writing back.
LooseCannon - a member on this forum - might read this thread tonight or some time over the next few days and give some tips. He works at a radio shop and is quite knowledgable - and may provide the best scoop/the real skinny on what to check. Haven't seen him stumped yet!
My Galaxy DX 77HML has developed this same symptom. I realize this is an old thread, but was hoping someone might know what the issue is.
just saw this thread for the first time.
some more info would help.
does the S meter still work normally when this happens?
does the NB/ANL switch have any effect when this happens?
can you still TX as normal with modulation in all modes when this happens?
any details you can provide will help narrow the problem area down.
for now, i would suspect an electrolytic cap around the audio amplifier area.
(thats IC8 mounted on the wall)
you can try bridging a good electrolytic cap of a similar value across the traces of a cap you suspect, and see if the receive volume comes back.
that way you dont have to unsolder a bunch of caps looking for the problem.
just be very careful about the polarity of the cap you are bridging across the old one. backwards can be very bad.
good luck,
LC
some more info would help.
does the S meter still work normally when this happens?
does the NB/ANL switch have any effect when this happens?
can you still TX as normal with modulation in all modes when this happens?
any details you can provide will help narrow the problem area down.
for now, i would suspect an electrolytic cap around the audio amplifier area.
(thats IC8 mounted on the wall)
you can try bridging a good electrolytic cap of a similar value across the traces of a cap you suspect, and see if the receive volume comes back.
that way you dont have to unsolder a bunch of caps looking for the problem.
just be very careful about the polarity of the cap you are bridging across the old one. backwards can be very bad.
good luck,
LC
On the DX 77HML:
The S-meter seems normal. The RX speaker volume is loud when you first turn the radio on after leaving it unplugged for a while. After a few seconds, the RX volume slowly drops to the point where you have to turn the volume control wide open just to hear anything. Once you unplug the radio and let it sit for a while, the RX volume will go back to normal levels for a few seconds. Talkback volume seems normal.
Other symptoms (may or may not be related);
1. NB seems to have no effect.
2. Squelch works, but does not completely cut the sound off, you can hear some faint audio still coming through. This may be because the volume is turned all the way up.
3. When you put the radio in PA mode, the S-meter jumps to about 3/4 of the way, and holds there.
4. There is a low pitched squeal on USB TX, but not on LSB TX. This happens even with the mic gain turned all the way off.
I've replaced D1,D2,D23,D24 and TR17 with parts from a junk radio that used the same board. No effect.
I'm going to start checking voltages on all the TRs and ICs and post results.
Also, C190 and C193 appear to be swollen, but I haven't replaced them yet. They appear to be part of the SSB circuit, and may be causing #4 above, but I wouldn't think they would affect AM. I am going to change them out and see what happens.
The S-meter seems normal. The RX speaker volume is loud when you first turn the radio on after leaving it unplugged for a while. After a few seconds, the RX volume slowly drops to the point where you have to turn the volume control wide open just to hear anything. Once you unplug the radio and let it sit for a while, the RX volume will go back to normal levels for a few seconds. Talkback volume seems normal.
Other symptoms (may or may not be related);
1. NB seems to have no effect.
2. Squelch works, but does not completely cut the sound off, you can hear some faint audio still coming through. This may be because the volume is turned all the way up.
3. When you put the radio in PA mode, the S-meter jumps to about 3/4 of the way, and holds there.
4. There is a low pitched squeal on USB TX, but not on LSB TX. This happens even with the mic gain turned all the way off.
I've replaced D1,D2,D23,D24 and TR17 with parts from a junk radio that used the same board. No effect.
I'm going to start checking voltages on all the TRs and ICs and post results.
Also, C190 and C193 appear to be swollen, but I haven't replaced them yet. They appear to be part of the SSB circuit, and may be causing #4 above, but I wouldn't think they would affect AM. I am going to change them out and see what happens.
Forgot to mention that AM TX seems normal with normal modulation. The only TX issue is the USB squeal.
yeah the radio does seem to have a few issues. LOL
since the S meter seems to still function when this happens, that means that the signal is still being detected, but just isnt being amplified.
try this, when the volume problem occurs, turn the volume up most if not all the way, and touch your finger to pin 4 of the audio IC (IC8).
you should hear a loud hum in the speaker. if you do, then the audio amplifier is doing its job and the problem probably lies before the audio amp.
if you dont hear the hum, then the audio IC itself and the surrounding parts (especially electrolytic caps) are suspect.
check the voltages on the audio IC when the problem is happening and see if they jive with what the service manual says they should be.
some things to check are C157, C156, TR42 and TR41.
the caps could go short when the radio heats up, so bridging a good one across it wont work. you'll have to remove them and replace them with good caps to see if it works.
the transistors should be pulled and checked with the diode function of your DVM.
google "testing transistors with a DMM" if you dont know how to do this.
good luck, let me know what you find,
LC
since the S meter seems to still function when this happens, that means that the signal is still being detected, but just isnt being amplified.
try this, when the volume problem occurs, turn the volume up most if not all the way, and touch your finger to pin 4 of the audio IC (IC8).
you should hear a loud hum in the speaker. if you do, then the audio amplifier is doing its job and the problem probably lies before the audio amp.
if you dont hear the hum, then the audio IC itself and the surrounding parts (especially electrolytic caps) are suspect.
check the voltages on the audio IC when the problem is happening and see if they jive with what the service manual says they should be.
some things to check are C157, C156, TR42 and TR41.
the caps could go short when the radio heats up, so bridging a good one across it wont work. you'll have to remove them and replace them with good caps to see if it works.
the transistors should be pulled and checked with the diode function of your DVM.
google "testing transistors with a DMM" if you dont know how to do this.
good luck, let me know what you find,
LC
C190 and C193 replaced. No effect, but I feel better now. 
No noticeable hum from a finger on pin 4 of the IC8, even when the volume is working normally for the first few seconds. Perhaps my fingers aren't compatible.
C157, C156 replaced. No effect.
TR41 was upgraded to a 2SA1012 as part of earlier troubleshooting today, so I think that can be ruled out.
TR42 is ok.
C143 looked a bit swollen, so I replaced it. No effect.
It's getting late, so I won't do any more checking until tomorrow. I'll start documenting voltages on TRs and ICs next.
No noticeable hum from a finger on pin 4 of the IC8, even when the volume is working normally for the first few seconds. Perhaps my fingers aren't compatible.
C157, C156 replaced. No effect.
TR41 was upgraded to a 2SA1012 as part of earlier troubleshooting today, so I think that can be ruled out.
TR42 is ok.
C143 looked a bit swollen, so I replaced it. No effect.
It's getting late, so I won't do any more checking until tomorrow. I'll start documenting voltages on TRs and ICs next.
that is strange about the lack of a hum. hmmmm...
try it again only this time touch your finger to the center pin of the volume control. AKA the "wiper".
this should also produce a noticeable hum from the speaker.
(make sure the squelch is down. not sure if this would affect it but better safe than sorry)
after that, i think we're down to interpreting IC voltages.
if you measure a pin that should have a certain voltage on it, say 8 volts, and it measures really low, then unsolder that pin from the board, lift it, and check the pin again. if voltage has returned you know that something on that trace is shorted and pulling the voltage down near ground potential.
anytime someone describes a problem that happens after a radio is on for a short while, i immediately think of electrolytic caps, or thermally intermittent transistors/IC's.
the caps going south are much more common.
how old is your radio?
the cheap chinese electrolytic caps in the galaxy radios do not have the same shelf life as the older radios did.
think around 10 years instead of 20-30.
if you just get frustrated and cant find the problem for the life of you, you might think about doing a re-cap job on the radio.
its not expensive, and if you are experienced at soldering, it can actually take less time than troubleshooting.
if you go this route, replace any caps that are rated at 10v or less with 16v caps (higher voltage ratings are fine too, just make sure the cap you choose will fit)
good luck,
LC
try it again only this time touch your finger to the center pin of the volume control. AKA the "wiper".
this should also produce a noticeable hum from the speaker.
(make sure the squelch is down. not sure if this would affect it but better safe than sorry)
after that, i think we're down to interpreting IC voltages.
if you measure a pin that should have a certain voltage on it, say 8 volts, and it measures really low, then unsolder that pin from the board, lift it, and check the pin again. if voltage has returned you know that something on that trace is shorted and pulling the voltage down near ground potential.
anytime someone describes a problem that happens after a radio is on for a short while, i immediately think of electrolytic caps, or thermally intermittent transistors/IC's.
the caps going south are much more common.
how old is your radio?
the cheap chinese electrolytic caps in the galaxy radios do not have the same shelf life as the older radios did.
think around 10 years instead of 20-30.
if you just get frustrated and cant find the problem for the life of you, you might think about doing a re-cap job on the radio.
its not expensive, and if you are experienced at soldering, it can actually take less time than troubleshooting.
if you go this route, replace any caps that are rated at 10v or less with 16v caps (higher voltage ratings are fine too, just make sure the cap you choose will fit)
good luck,
LC
The radio is very old, probably close to 20 years. She's been sitting in storage for the last 10 years. I stopped talking on the radio for a while, but now have regained a passion for it.
She's always been my favorite radio though and I'm determined to fix her. I'm not opposed to doing a complete recap job on it, but was hoping to narrow down the problem and document it for others.
I really appreciate all your help, loosecannon!
I'll see If I can't find some time today to document some voltage readings, and post the results.
She's always been my favorite radio though and I'm determined to fix her. I'm not opposed to doing a complete recap job on it, but was hoping to narrow down the problem and document it for others.
I really appreciate all your help, loosecannon!
I'll see If I can't find some time today to document some voltage readings, and post the results.
not sure if you have this info, but here is the srvice manual for this radio. it has all the voltage charts on this page also.,
Galaxy DX Radios DX44V Service Manual
Galaxy DX Radios DX44V Service Manual
Getting some odd voltages on the collector of TX transistor TR38. The voltage chart show that this should be at 0 volts during RX. When I turn the radio on, there is somewhere around .8 volts on the collector of TR38, and it immediately starts climbing. The rate of voltage climb seems to be proportionate to the decrease in volume. This circuit path also seems to involve pin 5 of IC8 and there is electrolytic C150 in the same circuit. Although the voltage on pin 5 of IC8 is stable and normal.
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hmmmm...
good find on the TR38 collector. to me this says that the radio is trying to switch into TX mode, but isnt quite making the switch.
im going to look at the schematic in the area of the RX/TX switching transistor and see if there might be a cap on that line that could be causing this issue.
who knows, if this is the problem, it might also be causing the other issues you mentioned.
also, the radio sitting idle for a long time, and then being brought back into service really points to faulty electrolytic caps.
ill post back if i find something,
LC
good find on the TR38 collector. to me this says that the radio is trying to switch into TX mode, but isnt quite making the switch.
im going to look at the schematic in the area of the RX/TX switching transistor and see if there might be a cap on that line that could be causing this issue.
who knows, if this is the problem, it might also be causing the other issues you mentioned.
also, the radio sitting idle for a long time, and then being brought back into service really points to faulty electrolytic caps.
ill post back if i find something,
LC
Getting close to solving this. Manually grounding the collector of TR38 brings back full RX volume. Now I just have to figure out where that stray voltage is coming from. Could TR38 be defective?
- No one is chatting at the moment.