QCX mini died


Norm. N7NSD
 

Got my 20m mini all built and working. After several bouts of torroid wrangling to get the wattage up to snuff, cleaning off all the flux and stuffing it into the box I started setting up all the options when the lights went out. Un-stuffed it and traced the power rail to find the LM 1117 is gone along with the 15uF 20v tantalum. The cap is a dead short and the VR is shorted input to ground. The 3 amp fuse in line with the station main supply did it’s job. A definite murder-suicide but I don’t know who the guilty was. 

Before I order a new LM 1117 from Mouser, what other damage should I look for?
73

PS. I don’t like tantalums


Steven Dick
 

Are you sure the tantalum was installed with the right polarity? Tantalums can short out if installed with the wrong polarity. 
-Steve K1RF

------ Original Message ------
From: "Norm. N7NSD" <n7nsd@...>
Sent: 1/1/2021 8:27:05 PM
Subject: [QRPLabs] QCX mini died

Got my 20m mini all built and working. After several bouts of torroid wrangling to get the wattage up to snuff, cleaning off all the flux and stuffing it into the box I started setting up all the options when the lights went out. Un-stuffed it and traced the power rail to find the LM 1117 is gone along with the 15uF 20v tantalum. The cap is a dead short and the VR is shorted input to ground. The 3 amp fuse in line with the station main supply did it’s job. A definite murder-suicide but I don’t know who the guilty was. 

Before I order a new LM 1117 from Mouser, what other damage should I look for?
73

PS. I don’t like tantalums


Virus-free. www.avast.com


Fred Spinner
 

Try replacing the tantalum with a 22uF 25V electrolytic before you think it's dead dead.  I am suggesting that value as the largest that will fit that I had...

The shorted tantalum probably didn't take out anything upstream including the regulator but you could check with a DMM to see if it is shorted input to output first if you would like. 

On Fri, Jan 1, 2021, 6:52 PM Steven Dick <sbdick@...> wrote:
Are you sure the tantalum was installed with the right polarity? Tantalums can short out if installed with the wrong polarity. 
-Steve K1RF

------ Original Message ------
From: "Norm. N7NSD" <n7nsd@...>
Sent: 1/1/2021 8:27:05 PM
Subject: [QRPLabs] QCX mini died

Got my 20m mini all built and working. After several bouts of torroid wrangling to get the wattage up to snuff, cleaning off all the flux and stuffing it into the box I started setting up all the options when the lights went out. Un-stuffed it and traced the power rail to find the LM 1117 is gone along with the 15uF 20v tantalum. The cap is a dead short and the VR is shorted input to ground. The 3 amp fuse in line with the station main supply did it’s job. A definite murder-suicide but I don’t know who the guilty was. 

Before I order a new LM 1117 from Mouser, what other damage should I look for?
73

PS. I don’t like tantalums


Virus-free. www.avast.com


Norm. N7NSD
 

The original cap was installed correctly. When it stopped working I first did a continuity check of the input power path and found the dead short to ground thru the tantalum, removed and replaced it with a new one. Re-powered with no joy then discovered the blown regulator. The radio worked fine on first power up, during all of the IQ adjustment, multiple power out tests while playing with the torroids and even 10 - 15 minutes of listening in to several QSOs before installing it in the case. About 4-5 minutes into going through a bunch of setup adjustments once it was in the case it just stopped, blowing the fuse. My main concern is other potential damage that might have been done. What did others who lost the VR find?
 Thanks 


Dean Smith
 

Hi Norm.,
I had the same issue with my mini-30m.
All worked ok (minus alignment issue, low rx) til i cased it and moved the unit to a psu, rather than an SLA battery!
I assembled mine before the cap in the regulator issue advice was distributed. A price for being first in the queue :(
The power connector was my first thought as the soldered pins were tall and probably touched the case, so i clipped those.
By this time the AM1117 had gone, this meant the ATMEGA 328 had fried along with FST3253, Si5351a (diode d1 popped also),Q6, LCD, and the 74ACT00 on the back of the pcb..
Yup, quite a mouthfull!
All of these have been replaced starting with the capacitor mod & am1117 to restore the on board psu before replacing the more expensive components.
D1 and D2 replaced, checked for 3.3v to Si 5351a slot , yep all good! so replaced all of the parts now .
Unit powers up, but still have same initial alignment and low rx faults.
Alignment fault, in my case turns out the FST3253 i replaced was faulty also, just no crater?!
I know there are many with a problem simular to this,just look on this forum and you'll see them.
mine was a really simple check you can make with no power applied to the mini.
The CLK0 and CLK1 line from the Si5351a goto pins 2 & 14 on the FST device, pin 2 was grounded. confirmed with a dvm on continuity, one lead on bnc outer for ground, and one to pin two.
Internally on the FST3253 this line was shorted to ground?!
Replaced FST3253 yet again.
Now i have alignment (yyeesss!)
Still have low receive.
IC5???
Well i removed this and replaced with dip version (cockroach style) as i have no soic8 types in my junk box
All wired up correct, but no it didn't help.
Popped the soic8 lm4562 back in, and guess what......lcd lights up with splash screen then, Pop noise and magic smoke!   nnnooooo :(
Time to pick up some LM4562's.. The soic8 versions are very pricey :( Looking at 5 or 6 pounds each here in the uk! trying to get my head around the fact I can get 50 Dip versions for 3GBP on ebay.
Have ordered 5 from rsonline for around 4gbp each, time they reach you.
So will replace LM4562, and will still expect low receive.
So, to sum up, its an ongoing journey that has probably cost me more than the mini is worth.
I have built two original QCX's one on 40m and one converted to QCX-SSB both work and aligned straight after build. Also have QCX+, which worked with no issues after building.
Would i buy another mini??
IMHO... well they look superb, but IF you have any problems with them,they could well end up, not being cost effective to repair.
Now Looking at a QCX+ for 30m now (Art in a box Hi)!
Norm, i hope your mini is an easier fix than my electronic horror show Hi!
Good luck..
Dean (G7EOB)




Steven Dick
 

I can think of a scenario where, when the tantalum capacitor failed, the AMS1117 regulator got damaged.  This could occur if the input is suddenly shorted while the output has 5V on it with a large cap. The QCX mini has a 470uF output cap (C47)  on the 5v supply at the processor, fed through a 47uH inductor (L6).  The regulator does have an internal reverse polarity protection diode.  However, the AMS1117 data sheet states: " If high value output capacitors are used, such as 1000µF to 5000µF and the input pin is instantaneously shorted to ground, damage can occur. A diode from output to input is recommended, when a crowbar circuit at the input of the AMS1117 is used (Figure 1)".  I would consider the 470uF as a large cap. Though smaller than the "such as 1000 to 5000uF", it's still a seriously large cap, and the input was suddenly shorted while operating by the failed tantalum cap.

-Steve K1RF

------ Original Message ------
From: "Norm. N7NSD" <n7nsd@...>
Sent: 1/2/2021 1:13:49 AM
Subject: Re: [QRPLabs] QCX mini died

The original cap was installed correctly. When it stopped working I first did a continuity check of the input power path and found the dead short to ground thru the tantalum, removed and replaced it with a new one. Re-powered with no joy then discovered the blown regulator. The radio worked fine on first power up, during all of the IQ adjustment, multiple power out tests while playing with the torroids and even 10 - 15 minutes of listening in to several QSOs before installing it in the case. About 4-5 minutes into going through a bunch of setup adjustments once it was in the case it just stopped, blowing the fuse. My main concern is other potential damage that might have been done. What did others who lost the VR find?
 Thanks 

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Tim and Janet
 

I am with you Norm.  I don't like tantalums.  They have caused a lot of issues over years.  Hope you get your problems sorted out.

73

Tim
KB2MFS

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On Fri, Jan 1, 2021 at 7:27 PM Norm. N7NSD <n7nsd@...> wrote:

Got my 20m mini all built and working. After several bouts of torroid wrangling to get the wattage up to snuff, cleaning off all the flux and stuffing it into the box I started setting up all the options when the lights went out. Un-stuffed it and traced the power rail to find the LM 1117 is gone along with the 15uF 20v tantalum. The cap is a dead short and the VR is shorted input to ground. The 3 amp fuse in line with the station main supply did it’s job. A definite murder-suicide but I don’t know who the guilty was. 

Before I order a new LM 1117 from Mouser, what other damage should I look for?
73

PS. I don’t like tantalums


Zdenek OK2BQN
 

Hi Tim ,
You scared me now. I also put Tantalum there. It is still from the totalitarian communist era from the TESLA company. I chose with the smallest ESR. When I did the service for TESLA ELTOS DIZ Prague, there were no problems with these tantalums.
73
Zdenek


Gregg Myers
 

One thing that I noticed also is that the 2.1mm power connector solder lugs seemed to be so long that they will very nearly short to the mini case once the boards are in place. I clipped my power connector lugs short after soldering the power connector in place just to be sure that wouldn't happen. You can sort of see the clearance in this picture.

73,
Gregg W7GRM



On Sat, Jan 2, 2021 at 8:22 AM Zdenek OK2BQN <ok2bqn@...> wrote:
Hi Tim ,
You scared me now. I also put Tantalum there. It is still from the totalitarian communist era from the TESLA company. I chose with the smallest ESR. When I did the service for TESLA ELTOS DIZ Prague, there were no problems with these tantalums.
73
Zdenek


Bill Cromwell
 

Hi Zdenek,

I have been avoiding tantalum caps for a long time. I think the
reported failure rate is due to the tantalum and the chemistry of the
caps and nothing to do with the manufacturing company that makes them
nor the politics in the country of origin. Those pack a lot of
microfarads in a tiny package. Like the Lithium batteries I also don't
trust. Lots of amp-hours in a very small, lightweight package. The
elements and chemistry just seem awfully risky.

73,

Bill KU8H


On Sat, 02 Jan 2021 07:22:05 -0800
"Zdenek OK2BQN" <ok2bqn@...> wrote:

Hi Tim ,
You scared me now. I also put Tantalum there. It is still from the
totalitarian communist era from the TESLA company. I chose with the
smallest ESR. When I did the service for TESLA ELTOS DIZ Prague,
there were no problems with these tantalums. 73 Zdenek


ohwenzelph
 

The pins on the voltage regulator go ground out in, so there is very little distance between the out and in pins. But the tab is also out, so there might be room to place a reverse polarity protection diode between the tab and the in pin.
jt aa1of


Steven Dick
 

More than you wanted to know about tantalum caps failing short. The
aerospace industry uses them because they have low ESR compared to
comparable electrolytics, When we used them, we had to insure that they
had a "surge rating" specification, which implies that then, they were
extremely unlikely to fail. With no surge rating specified, though
unlikely, the risk is increased for a short circuit failure when voltage
is instantaneously applied and a high (surge) current is seen by the
capacitor during the capacitor's charging up. In safety critical
cases where very low ESR was needed, , we used tantalum caps with
built-in fuses. This was frowned upon as not being cost effective and
tended not to have multiple sources. These are ridiculously expensive
and a bad solution for this application. In general, electrolytic
capacitors don't have this failure mode of failing short, and we don't
really need super low ESR here.

-Steve K1RF

https://escies.org/download/webDocumentFile?id=62199#:~:text=When%20a%20Tantalum%20Capacitor%20fails,drawn%20from%20the%20power%20supply.&text=This%20may%20cause%20the%20capacitor's,with%20a%20low%20power%20level.

------ Original Message ------
From: "Bill Cromwell" <wrcromwell@...>
To: QRPLabs@groups.io
Sent: 1/2/2021 10:38:21 AM
Subject: Re: [QRPLabs] QCX mini died

Hi Zdenek,

I have been avoiding tantalum caps for a long time. I think the
reported failure rate is due to the tantalum and the chemistry of the
caps and nothing to do with the manufacturing company that makes them
nor the politics in the country of origin. Those pack a lot of
microfarads in a tiny package. Like the Lithium batteries I also don't
trust. Lots of amp-hours in a very small, lightweight package. The
elements and chemistry just seem awfully risky.

73,

Bill KU8H


On Sat, 02 Jan 2021 07:22:05 -0800
"Zdenek OK2BQN" <ok2bqn@...> wrote:

Hi Tim ,
You scared me now. I also put Tantalum there. It is still from the
totalitarian communist era from the TESLA company. I chose with the
smallest ESR. When I did the service for TESLA ELTOS DIZ Prague,
there were no problems with these tantalums. 73 Zdenek




--
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https://www.avast.com/antivirus


Bernie <bmcintosh@...>
 

There’s been some discussion about blown voltage regulators and capacitors that have led to subsequent IC damage.     In my humble opinion there have been a few little inaccuracies too – but hey, we’re a discussion group and it might be me that’s all wrong anyway.   I actually got a little bit of stick over it all earlier  but I remain  adamant that this is all about fun -  it’s a  a hobby after all  so lets not get too serious.

 

There’s been some particularly good stuff on this topic  from regular contributors like Fred VK2WS and Steve K1RF who know what they’re talking about.

 

This new kit, the QCX mini is just brilliant.    

 

I wanted to take the trouble to take the dialogue further with some detailed aspects of PSU design and proper selection of tantalums  but I don’t want it to be a distraction from the great work of this group and I don’t want it to be misinterpreted as advice for anyone. It would  just  be my technical musings.

 

So be happy and always follow Hans' advice unless you're sure you know what you're doing.

 

If you want to do PSUs, Tanatalums, ESR  to death then you’re welcome to have a look at the PDF you’ll find linked to below.  I kind of enjoyed bringing it together.  Sometimes a forum goes  off topic or goes on too long.    That’s why I thought it best for everyone’s sanity to  not make a long posting here. 

 

So read at your own risk!  Humour aside, if you are already a bit fed up of this topic don’t go any further.

 

 LDO.pdf

https://www.dropbox.com/s/00snpe94vf7s8gc/ldo.pdf?dl=0

 

 

73

 

 

Bernie


Janez S58J
 

Bernie thank you for that! I enjoyed reading your PDF article and learning new things/facts. For sure this will lead to the implementation on my QCX-mini.

Kind regards

Janez, S58J

V V sob., 2. jan. 2021 ob 18:28 je oseba Bernie via groups.io <bmcintosh=paceprofessional.co.uk@groups.io> napisala:

There’s been some discussion about blown voltage regulators and capacitors that have led to subsequent IC damage.     In my humble opinion there have been a few little inaccuracies too – but hey, we’re a discussion group and it might be me that’s all wrong anyway.   I actually got a little bit of stick over it all earlier  but I remain  adamant that this is all about fun -  it’s a  a hobby after all  so lets not get too serious.

 

There’s been some particularly good stuff on this topic  from regular contributors like Fred VK2WS and Steve K1RF who know what they’re talking about.

 

This new kit, the QCX mini is just brilliant.    

 

I wanted to take the trouble to take the dialogue further with some detailed aspects of PSU design and proper selection of tantalums  but I don’t want it to be a distraction from the great work of this group and I don’t want it to be misinterpreted as advice for anyone. It would  just  be my technical musings.

 

So be happy and always follow Hans' advice unless you're sure you know what you're doing.

 

If you want to do PSUs, Tanatalums, ESR  to death then you’re welcome to have a look at the PDF you’ll find linked to below.  I kind of enjoyed bringing it together.  Sometimes a forum goes  off topic or goes on too long.    That’s why I thought it best for everyone’s sanity to  not make a long posting here. 

 

So read at your own risk!  Humour aside, if you are already a bit fed up of this topic don’t go any further.

 

 LDO.pdf

https://www.dropbox.com/s/00snpe94vf7s8gc/ldo.pdf?dl=0

 

 

73

 

 

Bernie


Fred Spinner
 

At the risk of annoying everyone, especially Hans, I suspect at this point that regulator is a time bomb.

I personally am going to try to design it out or at least put a crowbar in somehow.  That probably means 3D printing a case bottom and sides to get a little room to add another board. Which for me means "long term project" now.   Or taking out the barrel connector and off boarding the 5V.  Either way would not hurt my two use cases for the little rig. 

I finally am letting it out and probably will get black balled from the group for doing so.  But it is useful information for people to have that have who are having issues and are probably being too polite about them. 

I think his board house used out of spec (reject, including non functional) or counterfeit opamps, regulators and possibly other parts.  It a risk of keeping the price of all of this low. 

If you think I am crazy, otherwise how could he sell these with $9.50/ea (Mouser/Digi-Key qty one price) opamps for the price?   Even in 1K quantity, even from China? 

The cleverness of this design and the low price point is really quite THE factor in buying one.   I GET IT. It's still a bargain for what we got and personally having to troubleshoot the circuitry is forcing a lot of us to learn it.  At least in my case that is why I am doing it.  I don't have a lot of time to actually operate. 

On top of that, those SMD LDOs are typically not used to drop the voltage levels that we are doing.  Although within spec depending how you read it, some of the data sheets state absolute max as 15V in but then state 12V in in their examples as a maximum.  I suspect if something was done to drop the input down to 9V or less it would be fine. 

The older 78xx series were designed in a different time and are good to 20V in and absolute max at 35V from most manufacturers.  (If the power dissipation is okay).  The output stage on them is different and fail open, too. 


Tantalums are an interesting creature.  I bought a bag of very expensive ones at the surplus store when I worked at Collins and they still had a local surplus store.  I built a linear supply with a bunch of them and ran it overnight with a light load.  In the morning I had every single one of them in ashes. I must be a heavy sleeper, a few of them exploded. 

I later learned that only ones that have internal fuses were allowed anymore and that is why they were selling off stock.  I was unlucky apparently on top of that with that bag.  These were genuine Vishay parts and their stuff is normally very good.

I don't know what else to say.  Many people are blaming themselves for ESD popping the opamps, especially on the Facebook side.  I think there are too many reports of this for that statistically to be the case. 

I still want to praise Hans for doing this for us and a living.  It has to be terribly difficult to do this at the price point he sells all of this for.  I feel real empathy for him with this but trying to figure out a fix for it would do nothing but help him. 

Still I am afraid to power mine up at this point, honestly. 

I think adding the diode is a good idea and there is room for it on both sides of the board.  It also could be added at C37/C38 on the bottom with great care. 

I am going to still say that the measured by me 8.4uF output cap isn't big enough, either.  If the 470uF was right at the output that would be a different story.   I think a electrolytic at the regulator would help there too, but I haven't yet figured out how.  

Fred W0FMS 


On Sat, Jan 2, 2021, 10:28 AM Bernie via groups.io <bmcintosh=paceprofessional.co.uk@groups.io> wrote:

There’s been some discussion about blown voltage regulators and capacitors that have led to subsequent IC damage.     In my humble opinion there have been a few little inaccuracies too – but hey, we’re a discussion group and it might be me that’s all wrong anyway.   I actually got a little bit of stick over it all earlier  but I remain  adamant that this is all about fun -  it’s a  a hobby after all  so lets not get too serious.

 

There’s been some particularly good stuff on this topic  from regular contributors like Fred VK2WS and Steve K1RF who know what they’re talking about.

 

This new kit, the QCX mini is just brilliant.    

 

I wanted to take the trouble to take the dialogue further with some detailed aspects of PSU design and proper selection of tantalums  but I don’t want it to be a distraction from the great work of this group and I don’t want it to be misinterpreted as advice for anyone. It would  just  be my technical musings.

 

So be happy and always follow Hans' advice unless you're sure you know what you're doing.

 

If you want to do PSUs, Tanatalums, ESR  to death then you’re welcome to have a look at the PDF you’ll find linked to below.  I kind of enjoyed bringing it together.  Sometimes a forum goes  off topic or goes on too long.    That’s why I thought it best for everyone’s sanity to  not make a long posting here. 

 

So read at your own risk!  Humour aside, if you are already a bit fed up of this topic don’t go any further.

 

 LDO.pdf

https://www.dropbox.com/s/00snpe94vf7s8gc/ldo.pdf?dl=0

 

 

73

 

 

Bernie


Hans Summers
 

Hi Fred

As I mentioned in my other post just now that I was writing apparently at the same time you were writing this... I am working very hard on solutions to all these problems. 

I'm disappointed that there are production issues (SMD rework, C38, and some failed op-amps). It's cause me an enormous amount of stress. 

I do not believe counterfeit components are involved. There are always volume pricing differences when you buy 10,000 of something rather than 1. This is normal. And when you go closer to the source, than component distributors that are relatively expensive anyway. It's a huge topic. But suffice it to say, QRP Labs kits are so very well priced because I have put so much effort into design and sourcing and learned so much over the years. 

I also think it is still hard to judge the percentage of problems. The QCX-mini is undoubtedly a more challenging radio than both QCX and QCX+ due to the small size. Some of the problems are assembly errors, not manufacturing errors. 

Again: after adding the 10uF electrolytic or tantalum at the input I tried very hard to kill a QCX-mini with extreme intermittent power connection, and I couldn't kill it. 

For the next batch I have changed the voltage regulator to 78M05 in TO-252 package. Its a larger device but there is space for it there. 0.5A and 35V max or whatever it is, gives a substantial amount more headroom. Not being LDO, if it fails it does so open, not short. Just because I'm sick of hearing about the '1117, and 78M05 is a sure thing, and there isn't any impact on cost anyway. So why not just eliminate the risk or even if no risk, the reputation damage. 

As I mentioned in the other post, I'm also trying to find other improvements, one thing I'm trying to figure out is a test bed system so that I can put each board through a final test here before shipping any out. 

73 Hans G0UPL 


On Sat, Jan 2, 2021, 21:46 Fred Spinner <fred.spinner@...> wrote:
At the risk of annoying everyone, especially Hans, I suspect at this point that regulator is a time bomb.

I personally am going to try to design it out or at least put a crowbar in somehow.  That probably means 3D printing a case bottom and sides to get a little room to add another board. Which for me means "long term project" now.   Or taking out the barrel connector and off boarding the 5V.  Either way would not hurt my two use cases for the little rig. 

I finally am letting it out and probably will get black balled from the group for doing so.  But it is useful information for people to have that have who are having issues and are probably being too polite about them. 

I think his board house used out of spec (reject, including non functional) or counterfeit opamps, regulators and possibly other parts.  It a risk of keeping the price of all of this low. 

If you think I am crazy, otherwise how could he sell these with $9.50/ea (Mouser/Digi-Key qty one price) opamps for the price?   Even in 1K quantity, even from China? 

The cleverness of this design and the low price point is really quite THE factor in buying one.   I GET IT. It's still a bargain for what we got and personally having to troubleshoot the circuitry is forcing a lot of us to learn it.  At least in my case that is why I am doing it.  I don't have a lot of time to actually operate. 

On top of that, those SMD LDOs are typically not used to drop the voltage levels that we are doing.  Although within spec depending how you read it, some of the data sheets state absolute max as 15V in but then state 12V in in their examples as a maximum.  I suspect if something was done to drop the input down to 9V or less it would be fine. 

The older 78xx series were designed in a different time and are good to 20V in and absolute max at 35V from most manufacturers.  (If the power dissipation is okay).  The output stage on them is different and fail open, too. 


Tantalums are an interesting creature.  I bought a bag of very expensive ones at the surplus store when I worked at Collins and they still had a local surplus store.  I built a linear supply with a bunch of them and ran it overnight with a light load.  In the morning I had every single one of them in ashes. I must be a heavy sleeper, a few of them exploded. 

I later learned that only ones that have internal fuses were allowed anymore and that is why they were selling off stock.  I was unlucky apparently on top of that with that bag.  These were genuine Vishay parts and their stuff is normally very good.

I don't know what else to say.  Many people are blaming themselves for ESD popping the opamps, especially on the Facebook side.  I think there are too many reports of this for that statistically to be the case. 

I still want to praise Hans for doing this for us and a living.  It has to be terribly difficult to do this at the price point he sells all of this for.  I feel real empathy for him with this but trying to figure out a fix for it would do nothing but help him. 

Still I am afraid to power mine up at this point, honestly. 

I think adding the diode is a good idea and there is room for it on both sides of the board.  It also could be added at C37/C38 on the bottom with great care. 

I am going to still say that the measured by me 8.4uF output cap isn't big enough, either.  If the 470uF was right at the output that would be a different story.   I think a electrolytic at the regulator would help there too, but I haven't yet figured out how.  

Fred W0FMS 

On Sat, Jan 2, 2021, 10:28 AM Bernie via groups.io <bmcintosh=paceprofessional.co.uk@groups.io> wrote:

There’s been some discussion about blown voltage regulators and capacitors that have led to subsequent IC damage.     In my humble opinion there have been a few little inaccuracies too – but hey, we’re a discussion group and it might be me that’s all wrong anyway.   I actually got a little bit of stick over it all earlier  but I remain  adamant that this is all about fun -  it’s a  a hobby after all  so lets not get too serious.

 

There’s been some particularly good stuff on this topic  from regular contributors like Fred VK2WS and Steve K1RF who know what they’re talking about.

 

This new kit, the QCX mini is just brilliant.    

 

I wanted to take the trouble to take the dialogue further with some detailed aspects of PSU design and proper selection of tantalums  but I don’t want it to be a distraction from the great work of this group and I don’t want it to be misinterpreted as advice for anyone. It would  just  be my technical musings.

 

So be happy and always follow Hans' advice unless you're sure you know what you're doing.

 

If you want to do PSUs, Tanatalums, ESR  to death then you’re welcome to have a look at the PDF you’ll find linked to below.  I kind of enjoyed bringing it together.  Sometimes a forum goes  off topic or goes on too long.    That’s why I thought it best for everyone’s sanity to  not make a long posting here. 

 

So read at your own risk!  Humour aside, if you are already a bit fed up of this topic don’t go any further.

 

 LDO.pdf

https://www.dropbox.com/s/00snpe94vf7s8gc/ldo.pdf?dl=0

 

 

73

 

 

Bernie


Jim
 

Nice write up Bernie. Thanks for posting it.
Jim W3APC


Norm. N7NSD
 

Thank you Hans et al for the reply’s. My first thought after reading the data sheet on the LM 1117 was to replace it with a venerable 7805. I would welcome any thoughts on other circuit mods necessary to make it work. I am also removing the tantalum from my now finished 30 m mini and installing an electrolytic in hopes of keeping it alive.


I want to be clear that the failure wasn’t right at power up but after been on for some time.  My hope is that the lack of any noise, smoke or heat and the good work of the 3 amp fuse may have saved me from major re-work. My love affair with the QCX is still in full bloom. 

73


Jim Painter
 

On the qcx+, there was pretty close tolerance between the board and the bottom of the case. A qsl card fit nicely between the board and the case. Might be a good idea to slip something in the mini.

Jim...kq3s


On Jan 2, 2021, at 10:32 AM, Gregg Myers <gregg.w7grm@...> wrote:


One thing that I noticed also is that the 2.1mm power connector solder lugs seemed to be so long that they will very nearly short to the mini case once the boards are in place. I clipped my power connector lugs short after soldering the power connector in place just to be sure that wouldn't happen. You can sort of see the clearance in this picture.

73,
Gregg W7GRM

<PXL_20201221_182100288_Original.jpg>


On Sat, Jan 2, 2021 at 8:22 AM Zdenek OK2BQN <ok2bqn@...> wrote:
Hi Tim ,
You scared me now. I also put Tantalum there. It is still from the totalitarian communist era from the TESLA company. I chose with the smallest ESR. When I did the service for TESLA ELTOS DIZ Prague, there were no problems with these tantalums.
73
Zdenek


Gregg Myers
 

Hi Norm,

I think you will find the pinouts of the SMD SOT version of the 7805 to not be in the same order as the LM1117. I don't even think the tab connection is the same (on 7805 it is ground and on LM1117 it is Vout). Therefore you will not find it to be an easy drop in replacement for the original regulator. FWIW, I'm not worried about my LM1117 as I added the recommended electrolytic capacitor mod.

73,
Gregg W7GRM

On Sat, Jan 2, 2021 at 1:04 PM Norm. N7NSD <n7nsd@...> wrote:

Thank you Hans et al for the reply’s. My first thought after reading the data sheet on the LM 1117 was to replace it with a venerable 7805. I would welcome any thoughts on other circuit mods necessary to make it work. I am also removing the tantalum from my now finished 30 m mini and installing an electrolytic in hopes of keeping it alive.


I want to be clear that the failure wasn’t right at power up but after been on for some time.  My hope is that the lack of any noise, smoke or heat and the good work of the 3 amp fuse may have saved me from major re-work. My love affair with the QCX is still in full bloom. 

73