Topics

QCX was OK #chat


G4GIR
 

Got the kit built up aligned and working. Was seeing a good 5 Watts out at 15V.  
 
However, I noticed some intermittency in the output varying 0.5 a watt or so.
 
This morning I can’t get more than 1 – 1.5  W at supply Voltage 9 – 15v!
 
Checking the Gate on the PA  when keyed up I only see 2.5v Pk-pk on the scope should be 5v pk-pk?
 
Has anyone any idea why this should be?

Thanks in advance Ian

G4GIR


Simas Pudziuvelis
 

I've had a similar problem, I could only get about 1W output, the transistors were really hot and it consumed 1.1A of power on 13V. I've fixed it by replacing Q5 transistor labeled as a RX/TX switch. then I got about 5W on 14.5V 0.6A
I hope this helps!

Simas, LY3EU


G4GIR
 

Hi Simas
 
Thanks for your reply. My symptoms are opposite to yours, I only get around 158mA @ 15V the PA transistors are cold, I have tested further and found that the output of IC1 Pin 6 is only around 1v pk-pk. I am worried it maybe a fault with IC1!!
 
I have removed all 3 PA devices and I still see only 2.5v PK-PK on the gates of the PA devices.
 
So it looks like a drive problem.
 
Will look at Q5  to see what the state of that is.
 
Again thanks for the info.
 
73
 
Ian G4GIR

From: Simas Pudziuvelis
Sent: Wednesday, October 4, 2017 5:12 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX was OK #chat
 
I've had a similar problem, I could only get about 1W output, the transistors were really hot and it consumed 1.1A of power on 13V. I've fixed it by replacing Q5 transistor labeled as a RX/TX switch. then I got about 5W on 14.5V 0.6A
I hope this helps!

Simas, LY3EU


Simas Pudziuvelis
 

Hello Ian,
Maybe The Q6 (MPS2907) has burned out. (mine did after the overcurrent issue)? I would replace it with a higher amperage rated PNP transistor (its only 600mA).

I hope it helps

Simas, LY3EU


Steve MW0KST
 

Hi all, got my QCX up and running on 30m and receiving very nicely but only with about 1W power output on tx. I confirmed about 23V p-p on the drains of the PA transistors. I only get about 3.5 p-p on the gates, so it looks like low drive. The gate waveform is not a clean on-off but more of a triangular shape so that's not right either. On tx the rig draws about 350mW and the PA transistors get warm to the touch.

I've seen some similar issues in various posts, but so far nothing conclusive. Just wondering if anyone has found a fix to this. 

thanks,

Steve MW0KST


G4GIR
 

Hi Steve
 
Well, your problem is very similar to mine.
 
However When I first powered up and aligned it all was fine.
But after probably around 1/2 hour of sporadic CW TX and WSPR TX (got signals across the pond at 20:00z)  I noticed the power was fluctuating a bit like only 0.5 a watt variation.
 
Any way I switched off and the following morning the same problem as yours.
 
After a few e-mails with Hans I got the power back. It turned out to be Q6 that had failed, I was also using a duff dummy load which didn’t help. Originally my dummy load was ok. Some how it got swapped for one O/C, FINGER TROUBLE.
 
I like you saw similar wave forms at the gate, Hans said that was due to the 50MHz scope I was using but he was concerned  about the levels.
 
I changed the MPS 2907 for an MPS751. My TX was restored. A good 5W out.  However!! at initial key down the TX draws 1.0A with about 1 watt out, re key and its fine again. I found that there was 13 v on the drains at initial key down and after keying once that returned to 0v.
 
I have asked Hans about this anomaly but still waiting.
 
 
However mine has gone to pot now. I decided to carry out the re-alignment process, NO 700Hz  during the alignment just a horrible noise coming from the speaker and none of the adjustments vary which you may expect. To add to the problems I can still get 5 Watts out but the CW note is terrible.
 
This one has taken a large amount of time and have put it on the shelf for a while.
Will look at it again with a fresh outlook on it. But to date a bit disappointed with it. Mine is the 17m version.
 
 
Hope you get sorted.
 
73
 
Ian G4GIR

From: Steve
Sent: Sunday, October 15, 2017 12:11 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX was OK #chat
 
Hi all, got my QCX up and running on 30m and receiving very nicely but only with about 1W power output on tx. I confirmed about 23V p-p on the drains of the PA transistors. I only get about 3.5 p-p on the gates, so it looks like low drive. The gate waveform is not a clean on-off but more of a triangular shape so that's not right either. On tx the rig draws about 350mW and the PA transistors get warm to the touch.

I've seen some similar issues in various posts, but so far nothing conclusive. Just wondering if anyone has found a fix to this.

thanks,

Steve MW0KST


Steve MW0KST
 

Many thanks Ian, very much appreciated. It seems I connected my scope badly last night - this morning I'm seeing a square wave at 5V p-p, at the gates of the PA transistors, so it looks like it isn't the drive. Ha, I'll have a look at Q6. I think I might have accidentally tx'd into an open circuit when I switched on for the first time. I did muck up the initial set up, with a display pin not soldered, and lots of random button pressing before I found my error. Poor Hans must be tearing his hair out. Good luck with yours and I'll let you know how it goes!

Thanks and 73,

Steve MW0KST


G4GIR
 

Ok Steve yes please let me know how you get on. I’m not deterred though, just ordered a 20mtr version! + the GPS module.
 
73
 
Ian G4GIR
 

From: Steve
Sent: Sunday, October 15, 2017 11:55 AM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX was OK #chat
 
Many thanks Ian, very much appreciated. It seems I connected my scope badly last night - this morning I'm seeing a square wave at 5V p-p, at the gates of the PA transistors, so it looks like it isn't the drive. Ha, I'll have a look at Q6. I think I might have accidentally tx'd into an open circuit when I switched on for the first time. I did muck up the initial set up, with a display pin not soldered, and lots of random button pressing before I found my error. Poor Hans must be tearing his hair out. Good luck with yours and I'll let you know how it goes!

Thanks and 73,

Steve MW0KST


Steve MW0KST
 

Thanks Ian, I’ve ordered some more transistors so will resume later! Yes, when the backlog calms down I’ll be ordering another as well. I too have the GPS unit and some other bits on their way.

 

73 Steve MW0KST

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of IAN FRITH via Groups.Io
Sent: 15 October 2017 12:40
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX was OK #chat

 

Ok Steve yes please let me know how you get on. I’m not deterred though, just ordered a 20mtr version! + the GPS module.

 

73

 

Ian G4GIR

 

From: Steve

Sent: Sunday, October 15, 2017 11:55 AM

Subject: Re: [QRPLabs] QCX was OK #chat

 

Many thanks Ian, very much appreciated. It seems I connected my scope badly last night - this morning I'm seeing a square wave at 5V p-p, at the gates of the PA transistors, so it looks like it isn't the drive. Ha, I'll have a look at Q6. I think I might have accidentally tx'd into an open circuit when I switched on for the first time. I did muck up the initial set up, with a display pin not soldered, and lots of random button pressing before I found my error. Poor Hans must be tearing his hair out. Good luck with yours and I'll let you know how it goes!

Thanks and 73,

Steve MW0KST


Armin, DJ2AG
 

I also already had to replace a smoking an electrically smelling MPS 2907. Don't know why this happened. I was using WSPR beacon with manually set time. It was working for some cycles. Then I attached a GPS receiver kit and immediately after switching on it started to transmit and moments later fume was coming out from under the display. After switching of power  supply of and inspection I didn't see any damaged parts tried again and everything looks good, besides no entries in WSPRnet. Turns out transmit power was low, dont remember  exactly but arround 100mW and or.  Poor MPS 2907 was dead. I replaced it with another one and up to know it's working again without any problems.

73 de Armin - DJ2AG


GD
 

A good 5W out.  However!! at initial key down the TX draws 1.0A with about 1 watt out, re key and its fine again. I found that there was 13 v on the drains at initial key down and after keying once that returned to 0v

Hello Ian

It has the characteristics of RF floating on the board on intial key down removed by virtue of the next key down. A search for a missing direct Gnd around the PA, and a Multi Meter might not be the right unit to troubleshoot this, more visual. i.e PA gnd not local

The clue may go back to your original problem with your dummy load.


Geoff G4CAO 73


G4GIR
 

Hi Geoff

Maybe I worded it wrongly.

I should have said 13v On the Drains before initial key down, Found using the DMM which slowly decreased by virtue of the DMM being across them. Once it had reduced to <1v, then key down no problem.

However as you see in the e-mail there are other problems to overcome first!!!

Will look for any Gnd problems.

Tnx for the help.

73

Ian G4GIR

-----Original Message-----
From: GD
Sent: Sunday, October 15, 2017 9:21 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] QCX was OK


A good 5W out. However!! at initial key down the TX draws 1.0A with
about 1 watt out, re key and its fine again. I found that there was 13 v
on the drains at initial key down and after keying once that returned to 0v

Hello Ian

It has the characteristics of RF floating on the board on intial key
down removed by virtue of the next key down. A search for a missing
direct Gnd around the PA, and a Multi Meter might not be the right unit
to troubleshoot this, more visual. i.e PA gnd not local

The clue may go back to your original problem with your dummy load.


Geoff G4CAO 73