Topics

Help with strange audio fault #qcx


Ted 2E0THH
 

Just before I remove the QCX40 from its enclosure to fault find, I thought I would share it in case anyone else had ever experienced a similar issue.



My QCX40 rev4 has been performing beautifully for about a month now since it was built.
It is installed in a bespoke enclosure with a alternative volume control with a power switch.

The fault first manifested itself about 2 weeks ago, I had left the set on all day but when I went to listen out later in the evening, there was no audible output.
I had some work to complete so I turned it off for a few hours but when I switched it back on, all perfect again!
It remained fine for about 5 minutes and then it just went quiet again, not instantly but as though a volume control was being turned down.
It was now late so I left it overnight with a view to fault find it in the morning.
Of course in the morning all fine again!

It has been fine until a few days ago when the fault returned.
If I turn it off for an hour, it fires up again fine but then the gremlin in there turns the audio down after about 20 secs. This is fairly repeatable. If I fire it again instantly, the fault hasn't cleared.

A very quick check at low power during fault conditions demonstrates it is still able to transmit on the selected frequency.
I am suspecting a capacitor issue in the audio circuitry or earlier in the signal path.

I just wondered if anyone has experienced anything like the same issue?

Many thanks in advance.

73s Ted M7ECH


Alan G4ZFQ
 

I am suspecting a capacitor issue in the audio circuitry or earlier in the signal path.
Ted,

I'd suspect a dry joint somewhere. Maybe a capacitor charging up when it should not? Component faults are rare, construction faults not so.
But whatever, start with checking voltages against Hans' chart. Use the built-in meter. It might take a while as the fault is intermittent, maybe a good look at joints?

73 Alan G4ZFQ


James Daldry W4JED
 

Hi, Ted

Get a can of computer keyboard duster, turn it upside down so it throws liquid, and spray the board with it until you find the spot that brings the audio back. Circuit cooler and "canned air" are the same thing, except that circuit cooler cans have a dip tube so they always shoot liquid out. Canned air has no dip tube, so it always shoots gas, unless you turn the can upside down.

Spot cooling works really well for localizing thermal drift. The main problem with it is if you cool the spot enough to get condensation the water can mask the change.

Jim Daldry W4JED

On 1/10/19 9:31 AM, Alan G4ZFQ wrote:
I am suspecting a capacitor issue in the audio circuitry or earlier in the signal path.
Ted,

I'd suspect a dry joint somewhere. Maybe a capacitor charging up when it should not? Component faults are rare, construction faults not so.
But whatever, start with checking voltages against Hans' chart. Use the built-in meter. It might take a while as the fault is intermittent, maybe a good look at joints?

73 Alan G4ZFQ


Alan
 

Freezer spray may help, the condensate is not a problem   excepting on high voltages  or very high impedance circuitry which are not present here.   But a cleaner, cheaper  and more certain method is to use a paintbrush on the solder side of the pcb to put gentle pressure on every solder joint looking for the joint where a good bond has not been made.  Use the brush ( a ½” paintbrush works well on small boards) brushing across the board and note the location where things change then work up and down to home in on the bad joint. I have used this method for around 30 years, it has always worked for me in locating dry or unsoldered  joints and intermittent connectors. 

 

If the brush is too soft then trim the hairs down to ½” long, long enough to keep the metal ferrule well clear of components. You need a ½” or 1” wide home decorating style brush  with stiff  hairs not a  small artist’s Brush, you need to displace the faulty joint not paint it! If you are worried about the ferrule shorting parts then apply a few turns of insulating tape to the ferrule.

 

The freezer spray is really best for finding intermittent faults INSIDE IC’s where there is a bond wire issue internally. This class of fault is extremely rare these days but was more common many decades ago.

 

73

Alan

G8LCO

 

Sent from Mail for Windows 10

 

 

 


Ted 2E0THH
 

Hi Alan (G8LCO)

This sounds intriguing and ingenious!
Thanks also to Alan (G4ZFQ) and James.
It has now totally failed (I think) so the fault should now be easier to trace.
Tonight 's the night so wish me luck.

73s Ted M7ECH


Chris Wood
 

Ted

I had a problem with my 30m QCX which had some similarities to yours.  I think it was a dry joint and I seem to have solved it without knowing exactly what it was, by resoldering everything in sight.  One thing to check is C21 and C22.  They are now '105' in version 4 - mine were buff coloured blobs.  From memory, they were not easy to read but appeared to be polarised - if yours are, you might want to check they are the right way round, if you haven't done so already. 

Good luck

Chris
G4CWS


Alan de G1FXB
 

Another source for a stiff bristle brush are tooth brushes.
Best ensure the brush is no longer in use to maintain domestic harmony,
else yours may get similarly repurposed elswhere.

To kill any "chinese whispers" check out Hans excellent assembly manuals,
V3 and earlier C21 /C22 were listed as 10uF polarised electrolytics, so polarity conscious, the silk screen was marked accordingly.
With V4, they became 1uF ceramics, and the silk screen suggest the polarity markings have being removed?.

If someone who is building a V4 kit and in doubt, perhaps take a photo of the component silk screen & both sides of an 105 capacitor and post them here?

Alan


On 11/01/2019 18:52, Chris Wood via Groups.Io wrote:
Ted

I had a problem with my 30m QCX which had some similarities to yours.  I think it was a dry joint and I seem to have solved it without knowing exactly what it was, by resoldering everything in sight.  One thing to check is C21 and C22.  They are now '105' in version 4 - mine were buff coloured blobs.  From memory, they were not easy to read but appeared to be polarised - if yours are, you might want to check they are the right way round, if you haven't done so already. 

Good luck

Chris
G4CWS


Ted 2E0THH
 

Just a quick update.

I am still struggling to track this fault down but I do now have some data from my latest investigation.
Do note that this QSX40 set aligned perfectly and was working fine for 2 weeks.

The fault is no receiver output. However if I turn it off for an hour, it fires up again for about 5 seconds and then fades out. This is repeatable. If I fire it again instantly, the fault hasn't cleared and stays silent.

I have been around every solder joint with the iron, not very scientific but sometimes it is a quick fix.

So I though I would start at the beginning with a factory reset and realignment.
8.7 Peak BPF worked fine and produced its normal deafening output.
However 8.8 I-Q Bal, 8.9 Phase Lo and 8.10 Phase Hi are all at 0
Given this alignment needs audio from the output stage, this I think is a fairly good pointer.

IC9 Voltages
1) 4.78
2) 4.78
3) 4.45
4) 0
5) 2.44
6) 2.45
7) 2.45
8) 12

And now IC10, these voltages are clearly wrong
1) 11.06
2) 11.06
3) 11.09
4) 0
5) 5.88
6) 5.36
7)11.10
8) 12

I have been over and over the PCB looking for shorts and dry joints around IC10 and IC09 to no avail (that doesn't mean they don't exist)
The weird part is that after leaving the set off, after time it will always fire up for a few seconds before fading away.

I am going to get my supper and then have another bash but any pointers at all would be most gratefully received.

73 Ted M7ECH


On Thu, Jan 10, 2019 at 02:13 PM, <qrp@...> wrote:
Just before I remove the QCX40 from its enclosure to fault find, I thought I would share it in case anyone else had ever experienced a similar issue.



My QCX40 rev4 has been performing beautifully for about a month now since it was built.
It is installed in a bespoke enclosure with a alternative volume control with a power switch.

The fault first manifested itself about 2 weeks ago, I had left the set on all day but when I went to listen out later in the evening, there was no audible output.
I had some work to complete so I turned it off for a few hours but when I switched it back on, all perfect again!
It remained fine for about 5 minutes and then it just went quiet again, not instantly but as though a volume control was being turned down.
It was now late so I left it overnight with a view to fault find it in the morning.
Of course in the morning all fine again!

It has been fine until a few days ago when the fault returned.
If I turn it off for an hour, it fires up again fine but then the gremlin in there turns the audio down after about 20 secs. This is fairly repeatable. If I fire it again instantly, the fault hasn't cleared.

A very quick check at low power during fault conditions demonstrates it is still able to transmit on the selected frequency.
I am suspecting a capacitor issue in the audio circuitry or earlier in the signal path.

I just wondered if anyone has experienced anything like the same issue?

Many thanks in advance.

73s Ted M7ECH


Alan G4ZFQ
 

And now IC10, these voltages are clearly wrong
1) 11.06
2) 11.06
3) 11.09
4) 0
5) 5.88
6) 5.36
7)11.10
8) 12
Ted,

Is C22 the correct way round? I am presuming you are using your DVM, not the one incorporated?

73 Alan G4ZFQ


Ted 2E0THH
 

Many thanks Alan

On the rev 4 board C22 changed from 10uF electrolytic to to ceramic 1uF.
Also just checked again the electrolytics c24 and c51, they are inserted correctly.

You are correct! my trusty old Fluke took the measurements

I'll give it another few hours tonight but thanks a million for your help.

73s Ted M7ECH


Ted 2E0THH
 

OK
That's me done for tonight, no closer as yet.
One curious thing, I am running from a battery and while I was looking through settings I turned on the battery level icon, however it is empty.
Probably unrelated and some other setting is incorrect.
73s from Cambridge UK
Ted M7ECH


James Daldry W4JED
 

Hi, Ted

On the top side of the board, check the resistance from pin 5 of IC10 to ground. It should be around 10K. Now short the battery terminals out. It should now be about 5K. If it fails these 2 tests you have a connection problem at pin 5.

If you connect your voltmeter to pin 5 (top side, not bottom) and then connect the battery it will probably start at 5-ish volts and gradually drift upward. That's your 5 seconds of audio. One end of R39 should be zero ohms to battery negative and the other end zero ohms to pin 5 of IC10, measured on the top of the board. I keep stressing "top of the board" because there may be a bad solder joint or an open piece of foil at pin 5. The break may be invisible. It's possible that R39 is open but so unlikely that I would exhaust all other possibilities before changing it out. Oh, the other foil that could have a problem is from R39 to ground.

Jim Daldry W4JED

On 1/14/19 2:01 PM, qrp@... wrote:
Just a quick update.

I am still struggling to track this fault down but I do now have some data from my latest investigation.
Do note that this QSX40 set aligned perfectly and was working fine for 2 weeks.

The fault is no receiver output. However if I turn it off for an hour, it fires up again for about 5 seconds and then fades out. This is repeatable. If I fire it again instantly, the fault hasn't cleared and stays silent.

I have been around every solder joint with the iron, not very scientific but sometimes it is a quick fix.

So I though I would start at the beginning with a factory reset and realignment.
8.7 Peak BPF worked fine and produced its normal deafening output.
However 8.8 I-Q Bal, 8.9 Phase Lo and 8.10 Phase Hi are all at 0
Given this alignment needs audio from the output stage, this I think is a fairly good pointer.

IC9 Voltages
1) 4.78
2) 4.78
3) 4.45
4) 0
5) 2.44
6) 2.45
7) 2.45
8) 12

And now IC10, these voltages are clearly wrong
1) 11.06
2) 11.06
3) 11.09
4) 0
5) 5.88
6) 5.36
7)11.10
8) 12

I have been over and over the PCB looking for shorts and dry joints around IC10 and IC09 to no avail (that doesn't mean they don't exist)
The weird part is that after leaving the set off, after time it will always fire up for a few seconds before fading away.

I am going to get my supper and then have another bash but any pointers at all would be most gratefully received.

73 Ted M7ECH

On Thu, Jan 10, 2019 at 02:13 PM, <qrp@...> wrote:
Just before I remove the QCX40 from its enclosure to fault find, I thought I would share it in case anyone else had ever experienced a similar issue.



My QCX40 rev4 has been performing beautifully for about a month now since it was built.
It is installed in a bespoke enclosure with a alternative volume control with a power switch.

The fault first manifested itself about 2 weeks ago, I had left the set on all day but when I went to listen out later in the evening, there was no audible output.
I had some work to complete so I turned it off for a few hours but when I switched it back on, all perfect again!
It remained fine for about 5 minutes and then it just went quiet again, not instantly but as though a volume control was being turned down.
It was now late so I left it overnight with a view to fault find it in the morning.
Of course in the morning all fine again!

It has been fine until a few days ago when the fault returned.
If I turn it off for an hour, it fires up again fine but then the gremlin in there turns the audio down after about 20 secs. This is fairly repeatable. If I fire it again instantly, the fault hasn't cleared.

A very quick check at low power during fault conditions demonstrates it is still able to transmit on the selected frequency.
I am suspecting a capacitor issue in the audio circuitry or earlier in the signal path.

I just wondered if anyone has experienced anything like the same issue?

Many thanks in advance.

73s Ted M7ECH


Bill Cromwell
 

Ted,

Do not intentionally short the battery terminals out. If you do be sure to wear adequate eye protection. Have a new fuse on hand and the present fuse between your crowbar and those battery terminals. Batteries can and do explode when the terminals are shorted out.

73,

Bill KU8H

On 1/14/19 8:37 PM, James Daldry W4JED wrote:
Hi, Ted
On the top side of the board, check the resistance from pin 5 of IC10 to ground. It should be around 10K. Now short the battery terminals out. It should now be about 5K. If it fails these 2 tests you have a connection problem at pin 5.
If you connect your voltmeter to pin 5 (top side, not bottom) and then connect the battery it will probably start at 5-ish volts and gradually drift upward. That's your 5 seconds of audio. One end of R39 should be zero ohms to battery negative and the other end zero ohms to pin 5 of IC10, measured on the top of the board. I keep stressing "top of the board" because there may be a bad solder joint or an open piece of foil at pin 5. The break may be invisible. It's possible that R39 is open but so unlikely that I would exhaust all other possibilities before changing it out. Oh, the other foil that could have a problem is from R39 to ground.
Jim Daldry W4JED
On 1/14/19 2:01 PM, qrp@... wrote:
Just a quick update.

I am still struggling to track this fault down but I do now have some data from my latest investigation.
Do note that this QSX40 set aligned perfectly and was working fine for 2 weeks.

The fault is no receiver output. However if I turn it off for an hour, it fires up again for about 5 seconds and then fades out. This is repeatable. If I fire it again instantly, the fault hasn't cleared and stays silent.

I have been around every solder joint with the iron, not very scientific but sometimes it is a quick fix.

So I though I would start at the beginning with a factory reset and realignment.
8.7 Peak BPF worked fine and produced its normal deafening output.
However 8.8 I-Q Bal, 8.9 Phase Lo and 8.10 Phase Hi are all at 0
Given this alignment needs audio from the output stage, this I think is a fairly good pointer.

IC9 Voltages
1) 4.78
2) 4.78
3) 4.45
4) 0
5) 2.44
6) 2.45
7) 2.45
8) 12

And now IC10, these voltages are clearly wrong
1) 11.06
2) 11.06
3) 11.09
4) 0
5) 5.88
6) 5.36
7)11.10
8) 12

I have been over and over the PCB looking for shorts and dry joints around IC10 and IC09 to no avail (that doesn't mean they don't exist)
The weird part is that after leaving the set off, after time it will always fire up for a few seconds before fading away.

I am going to get my supper and then have another bash but any pointers at all would be most gratefully received.

73 Ted M7ECH

On Thu, Jan 10, 2019 at 02:13 PM, <qrp@...> wrote:

Just before I remove the QCX40 from its enclosure to fault find, I
thought I would share it in case anyone else had ever experienced
a similar issue.



My QCX40 rev4 has been performing beautifully for about a month
now since it was built.
It is installed in a bespoke enclosure with a alternative volume
control with a power switch.

The fault first manifested itself about 2 weeks ago, I had left
the set on all day but when I went to listen out later in the
evening, there was no audible output.
I had some work to complete so I turned it off for a few hours but
when I switched it back on, all perfect again!
It remained fine for about 5 minutes and then it just went quiet
again, not instantly but as though a volume control was being
turned down.
It was now late so I left it overnight with a view to fault find
it in the morning.
Of course in the morning all fine again!

It has been fine until a few days ago when the fault returned.
If I turn it off for an hour, it fires up again fine but then the
gremlin in there turns the audio down after about 20 secs. This is
fairly repeatable. If I fire it again instantly, the fault hasn't
cleared.

A very quick check at low power during fault conditions
demonstrates it is still able to transmit on the selected frequency.
I am suspecting a capacitor issue in the audio circuitry or
earlier in the signal path.

I just wondered if anyone has experienced anything like the same
issue?

Many thanks in advance.

73s Ted M7ECH
--
bark less - wag more


Roger Hill
 

I think the resistance tests would be done with the battery disconnected...DO NOT intentionally short the battery itself.

Of course the voltage checks would need the battery connected, but at that stage you are not shorting anything.

Roger
G3YTN


Roger

---
***************************
Roger Hill
***************************

On 2019-01-15 02:13, Bill Cromwell wrote:
Ted,
Do not intentionally short the battery terminals out. If you do be
sure to wear adequate eye protection. Have a new fuse on hand and the
present fuse between your crowbar and those battery terminals.
Batteries can and do explode when the terminals are shorted out.
73,
Bill KU8H
On 1/14/19 8:37 PM, James Daldry W4JED wrote:
Hi, Ted
On the top side of the board, check the resistance from pin 5 of IC10 to ground. It should be around 10K. Now short the battery terminals out. It should now be about 5K. If it fails these 2 tests you have a connection problem at pin 5.
If you connect your voltmeter to pin 5 (top side, not bottom) and then connect the battery it will probably start at 5-ish volts and gradually drift upward. That's your 5 seconds of audio. One end of R39 should be zero ohms to battery negative and the other end zero ohms to pin 5 of IC10, measured on the top of the board. I keep stressing "top of the board" because there may be a bad solder joint or an open piece of foil at pin 5. The break may be invisible. It's possible that R39 is open but so unlikely that I would exhaust all other possibilities before changing it out. Oh, the other foil that could have a problem is from R39 to ground.
Jim Daldry W4JED
On 1/14/19 2:01 PM, qrp@... wrote:
Just a quick update.
I am still struggling to track this fault down but I do now have some data from my latest investigation.
Do note that this QSX40 set aligned perfectly and was working fine for 2 weeks.
The fault is no receiver output. However if I turn it off for an hour, it fires up again for about 5 seconds and then fades out. This is repeatable. If I fire it again instantly, the fault hasn't cleared and stays silent.
I have been around every solder joint with the iron, not very scientific but sometimes it is a quick fix.
So I though I would start at the beginning with a factory reset and realignment.
8.7 Peak BPF worked fine and produced its normal deafening output.
However 8.8 I-Q Bal, 8.9 Phase Lo and 8.10 Phase Hi are all at 0
Given this alignment needs audio from the output stage, this I think is a fairly good pointer.
IC9 Voltages
1) 4.78
2) 4.78
3) 4.45
4) 0
5) 2.44
6) 2.45
7) 2.45
8) 12
And now IC10, these voltages are clearly wrong
1) 11.06
2) 11.06
3) 11.09
4) 0
5) 5.88
6) 5.36
7)11.10
8) 12
I have been over and over the PCB looking for shorts and dry joints around IC10 and IC09 to no avail (that doesn't mean they don't exist)
The weird part is that after leaving the set off, after time it will always fire up for a few seconds before fading away.
I am going to get my supper and then have another bash but any pointers at all would be most gratefully received.
73 Ted M7ECH
On Thu, Jan 10, 2019 at 02:13 PM, <qrp@...> wrote:
Just before I remove the QCX40 from its enclosure to fault find, I
thought I would share it in case anyone else had ever experienced
a similar issue.
My QCX40 rev4 has been performing beautifully for about a month
now since it was built.
It is installed in a bespoke enclosure with a alternative volume
control with a power switch.
The fault first manifested itself about 2 weeks ago, I had left
the set on all day but when I went to listen out later in the
evening, there was no audible output.
I had some work to complete so I turned it off for a few hours but
when I switched it back on, all perfect again!
It remained fine for about 5 minutes and then it just went quiet
again, not instantly but as though a volume control was being
turned down.
It was now late so I left it overnight with a view to fault find
it in the morning.
Of course in the morning all fine again!
It has been fine until a few days ago when the fault returned.
If I turn it off for an hour, it fires up again fine but then the
gremlin in there turns the audio down after about 20 secs. This is
fairly repeatable. If I fire it again instantly, the fault hasn't
cleared.
A very quick check at low power during fault conditions
demonstrates it is still able to transmit on the selected frequency.
I am suspecting a capacitor issue in the audio circuitry or
earlier in the signal path.
I just wondered if anyone has experienced anything like the same
issue?
Many thanks in advance.
73s Ted M7ECH
--
bark less - wag more


Alan G4ZFQ
 

James wrote:
If it fails these 2 tests you have a connection problem at pin 5.
Ted,

Are your voltage readings taken when the fault is present? If so then surely pin 5 is correct? (James, Ted is using his DVM which is not loading the circuit like Hans' figures show.)
I'm concerned about pin 6 which should be connected to pin 7 by R38, as there should be no other DC connection to pin 6 it should therefore be close to the pin 7 voltage.
Is R38 soldered? Check it's value, that each end is actually connected to the IC pins. Check the resistance from pin 6 to ground.

73 Alan G4ZFQ


Ted 2E0THH
 

Hi Alan

Just about to get stuck in again and saw yours and James' posts.
Yes the voltages readings were taken under fault conditions with my DVM Fluke (I only have a few seconds window when the set works)
I am pretty certain it is a 10k Alan but will get a camera in there to check. Both ends are soldered and the set performed flawlessly for nearly a month.

I will run James' tests and report back, huge thanks James and Alan (and everyone else on the safety advice), 

73s Ted
M7ECH


Ted 2E0THH
 

Hi again Alan and James

Battery disconnected
IC10 p5 to ground = 5.33K

PCB battery terminals shorted
IC10 p5 to ground = 5.33K

Just pondering what that means

73s Ted
M7ECH


Alan G4ZFQ
 

Battery disconnected
IC10 p5 to ground = 5.33K
PCB battery terminals shorted
IC10 p5 to ground = 5.33K
Just pondering what that means
Ted,

That means look at pin 6.

73 Alan G4ZFQ


James Daldry W4JED
 

Hi, guys

Let's throw some logic at the target.

My B&K 2405 meter tells me that when my Fluke 111 is measuring the resistance of a 10K resistor it is putting about 0.115 volts across the resistor. In other words, it's not turning on any semiconductors. Especially silicon ones.

Assuming that the radio draws 100 ma on receive, let's substitute a 1200 ohm resistor for the radio, making a network of 2 10K resistors with a 1200 ohm across the open ends. A triangle. The 1200 ohm resistor takes the place of the rest of the radio. If we put an ohmmeter across one of the 10K resistors, then short the 1200 ohm resistor, we will get about 5300 ohms with the circuit "normal" and 5000 with a short across the 1200. So - either the +12 volt end of R40 isn't making the trip or the ground end of R39 isn't.

Jim Daldry W4JED

On 1/15/19 4:12 AM, Alan G4ZFQ wrote:
Battery disconnected
IC10 p5 to ground = 5.33K
PCB battery terminals shorted
IC10 p5 to ground = 5.33K
Just pondering what that means
Ted,

That means look at pin 6.

73 Alan G4ZFQ



Ted 2E0THH
 

Dear James and Alan

Thank you so much for helping me out here.
I'll be back on the case in about 90 minutes and will report.
James, I am thinking about just trying small wire bridges to isolate which one is open circuit.

73s Ted
M7ECH