QCX Mini - Failure of AMS1117 on connection of GLG-1


Mike Easterbrook
 

Hi Everyone

Mini build and basic alignment all good.

When I tried to connect the QLG1 to adjust frequencies looks like the regulator failed short-circuit and sent 12v down the 5v line.  Didn't see any magic smoke cos I was paying more attention to the QLG which was working OK!  Display went to line of dark boxes - removed power immediately but found several components very warm (including IC2).

Guess sensitive items on the 5v line will have failed but can't check anything without having the regulator working. To this end is it recommended to replace AMS1117 like for like or is there an equivalent more likely to fail O/C than S/C?  Local suppliers don't have AMS but offer LM1117 instead - this looks like a simple drop-in.  Maybe I'll need to write this one off and start with a new build but in any case would like to understand what happened.

Any suggestions most welcome
Thanks Mike 9M2LXM


N3MNT
 

I strongly recommend not hot plugging anything on QCX Mini.


Daniel Conklin
 

The regulator and associated smd capacitor is a weakness and Hans recommended putting either an electrolytic or tantalum capacitor across it in the latest instructions to avoid that burn out. The newest kits have a different regulator. Here is a link: https://groups.io/g/QRPLabs/message/60391 
73, Dan - W2DLC


Daniel Conklin
 

For some reason the link appears to be invisible, but I think it's there...
--
73, Dan - W2DLC


N3MNT
 

Another option is to download latest assembly manual.  Describes the capacitor mod.  I recommend an electrolytic vs tantalum. 


Gary W9TD
 

Rather than a capacitor, the standard way to protect regulator ICs from damage is to connect a reverse-biased diode across them. This bypasses the current from the output capacitor directly to the input rather than flowing through the regulator and damaging it.
Gary
W9TD


Mike Easterbrook
 

Thanks for feedback. Yes I had the latest instructions so fitted a 22uF electrolytic across the regulator - which is still intact - wanted to steer clear of tantalums!
Mike 9M2LXM 

On Mon, 18 Jan 2021, 21:32 Daniel Conklin, <danconklin2@...> wrote:
The regulator and associated smd capacitor is a weakness and Hans recommended putting either an electrolytic or tantalum capacitor across it in the latest instructions to avoid that burn out. The newest kits have a different regulator. Here is a link: https://groups.io/g/QRPLabs/message/60391 
73, Dan - W2DLC


Mike Easterbrook
 


OK Daniel - read whole message now! I'll search out 78M05 tomorrow.
Tks Mike 

On Mon, 18 Jan 2021, 21:32 Daniel Conklin, <danconklin2@...> wrote:
The regulator and associated smd capacitor is a weakness and Hans recommended putting either an electrolytic or tantalum capacitor across it in the latest instructions to avoid that burn out. The newest kits have a different regulator. Here is a link: https://groups.io/g/QRPLabs/message/60391 
73, Dan - W2DLC


Mike Easterbrook
 

Thanks Gary
If it looks recoverable maybe I'll add the diode as well as changing to the 78M05. 
Mike


On Mon, 18 Jan 2021, 23:00 Gary W9TD, <w9td@...> wrote:
Rather than a capacitor, the standard way to protect regulator ICs from damage is to connect a reverse-biased diode across them. This bypasses the current from the output capacitor directly to the input rather than flowing through the regulator and damaging it.
Gary
W9TD


Mike Besemer - WM4B
 

Be aware that the 78M05 has a different pinout.

 

Mike

WM4B

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of Mike Easterbrook
Sent: Monday, January 18, 2021 10:33 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX Mini - Failure of AMS1117 on connection of GLG-1

 

Thanks Gary

If it looks recoverable maybe I'll add the diode as well as changing to the 78M05. 

Mike

On Mon, 18 Jan 2021, 23:00 Gary W9TD, <w9td@...> wrote:

Rather than a capacitor, the standard way to protect regulator ICs from damage is to connect a reverse-biased diode across them. This bypasses the current from the output capacitor directly to the input rather than flowing through the regulator and damaging it.
Gary
W9TD


Gregg Myers
 

As Mike B. has said,

You will find the 78M05 pinout is not the same as a AMS1117 so you will need to do some lead swapping to solder it onto the board. Its doable, but might look a little messy. The good news is that Hans confirms that the tab pad on the board is floating so you don't have to worry about the electrical contact to the tab.

73,
Gregg

On Mon, Jan 18, 2021 at 8:33 AM Mike Easterbrook <mike.easterbrook.2012@...> wrote:
Thanks Gary
If it looks recoverable maybe I'll add the diode as well as changing to the 78M05. 
Mike

On Mon, 18 Jan 2021, 23:00 Gary W9TD, <w9td@...> wrote:
Rather than a capacitor, the standard way to protect regulator ICs from damage is to connect a reverse-biased diode across them. This bypasses the current from the output capacitor directly to the input rather than flowing through the regulator and damaging it.
Gary
W9TD


Mike Easterbrook
 

Thanks Greg 
I think if I have to replace all the 3/5 v devices the board's going to get messy anyway with my shaky hands! 
Maybe time to just avoid the stress & order a new kit but I guess my stubborn streak will cut in & I'll plough on regardless
Mike 9M2LXM 

On Mon, 18 Jan 2021, 23:43 Gregg Myers, <gregg.w7grm@...> wrote:
As Mike B. has said,

You will find the 78M05 pinout is not the same as a AMS1117 so you will need to do some lead swapping to solder it onto the board. Its doable, but might look a little messy. The good news is that Hans confirms that the tab pad on the board is floating so you don't have to worry about the electrical contact to the tab.

73,
Gregg

On Mon, Jan 18, 2021 at 8:33 AM Mike Easterbrook <mike.easterbrook.2012@...> wrote:
Thanks Gary
If it looks recoverable maybe I'll add the diode as well as changing to the 78M05. 
Mike

On Mon, 18 Jan 2021, 23:00 Gary W9TD, <w9td@...> wrote:
Rather than a capacitor, the standard way to protect regulator ICs from damage is to connect a reverse-biased diode across them. This bypasses the current from the output capacitor directly to the input rather than flowing through the regulator and damaging it.
Gary
W9TD


Mike Easterbrook
 

Thanks - yes I had the latest manual & already had 22uF electrolytic in place when problem occured 
Mike 9M2LXM 

On Mon, 18 Jan 2021, 21:43 N3MNT, <bob@...> wrote:
Another option is to download latest assembly manual.  Describes the capacitor mod.  I recommend an electrolytic vs tantalum. 


Michael Greene
 

uh-oh. I've hot swapped in the GPS numerous times without problems. Guess I better connect it at a cold start.


Steve Z
 

The problem is that you also don't want to start the QCX with the GPS attached, as that will begin transmitting with the potential to fry the BS170s. The GPS should only be connected when in Beacon mode or Alignment mode.

Which is more dangerous for the health of the QCX, hot plugging the TRS plugs or booting with the GPS attached?

Steve N9SZ


Michael Greene
 

Steve,
I have always hot plugged the GPS and put the unit in practice mode prior and put it in Beacon mode, then gone to the alignment menu,done the 2 calibrations, gone back to turn off practic mode and returned to beacon mode and tried to keep any keying to a minimum. I have not tried putting it in practice mode, and beacon mode then turning power off, connecting the GPS and then turning power on. I think if one is quick about it, it is an experiment to try.
Michael


Michael Greene
 

Yes, I am now able to use the cable for both QCX-mini and QCX+ since I made the trace cuts and jumpers on the QCX+ described by Hans in the manual. This also allows the same cable to be used for the PTT connection to the 50W amp. See page 100 of the QCX+ manual version 1.04. I would certainly go through the description there and the QCX-mini manual to be sure you understand the details and confirm this has not changed. (I don't have the 50W PA, but I've been using the same cable to connect the GPS to my QCX+ and QCX-mini since I modified the QCX+ (and changed the +5V cable connection in the GPS).
If you read through all 3 carefully, you should be successful.


N3MNT
 


I have a header on the GPS and hot plug the GPS end of the cable and have never has an issue.  It is also very important to note that the cable used for the QCX+ can not be used for the QCX mini.  It is possible to use the mini cable if the QCX+ is modified.   See the RED warning on page 82.

On Tue, Jan 19, 2021 at 12:17 PM, Michael Greene wrote:
Steve,
I have always hot plugged the GPS and put the unit in practice mode prior and put it in Beacon mode, then gone to the alignment menu,done the 2 calibrations, gone back to turn off practic mode and returned to beacon mode and tried to keep any keying to a minimum. I have not tried putting it in practice mode, and beacon mode then turning power off, connecting the GPS and then turning power on. I think if one is quick about it, it is an experiment to try.
Michael


Allen N4NN
 

Mike - I had a similar experience and got several recommendations to never plug or unplug anything when the mini is powered. Also, in another post Hans said "In the 2nd batch I have changed to 78M05. This has 0.5A current rating, 30V maximum input voltage, doesn't fail short-circuit, and doesn't significantly increase the cost."


howard winwood G4GPF
 

I think the reason not to hot plug anything is because of the fragile nature of the voltage regulator used in the first batch of kits, once  it has been replaced with a 78 device you should have no problems.

G4GPF

On 19 Jan 2021, at 18:17, Allen N4NN <allen.n4nn@...> wrote:

Mike - I had a similar experience and got several recommendations to never plug or unplug anything when the mini is powered. Also, in another post Hans said "In the 2nd batch I have changed to 78M05. This has 0.5A current rating, 30V maximum input voltage, doesn't fail short-circuit, and doesn't significantly increase the cost."