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#qcxmini Can't adjust I-Q Balance, Phase Lo or Phase Hi #qcxmini

 

Hi, I just finished building the QCX Mini. I am trying to align it, but when I try to adjust the?I-Q Balance, Phase Lo or Phase Hi, turning the screw has no affect on the signal. I can adjust the Peak BPF and get it to 7. Also, I tested the radio and I can see my CQ call on RBN. So the radio transmits. And I can hear other operators.

I have very little electronics experience and my only test equipment is a digital multi-meter. I read several of the threads about the same issue, and I read the troubleshooting manual about the same issue. I checked all my solder joints and checked for solder bridges and everything looks good. But I have no idea what or how to test.

Any recommendations on what I would test?

Thanks
 

Pat, use your DVM to check all the bias voltages on the op amps. First look for 2.5v on pins 7 and 9 of IC4

Ron

On Mon, Feb 12, 2024 at 11:05 Pat <pxforti@...> wrote:
Hi, I just finished building the QCX Mini. I am trying to align it, but when I try to adjust the?I-Q Balance, Phase Lo or Phase Hi, turning the screw has no affect on the signal. I can adjust the Peak BPF and get it to 7. Also, I tested the radio and I can see my CQ call on RBN. So the radio transmits. And I can hear other operators.

I have very little electronics experience and my only test equipment is a digital multi-meter. I read several of the threads about the same issue, and I read the troubleshooting manual about the same issue. I checked all my solder joints and checked for solder bridges and everything looks good. But I have no idea what or how to test.

Any recommendations on what I would test?

Thanks

 

Hi Ron,

Thanks. I checked IC4 pins 7 and 9, I think. I attached a picture and show what I tested. Voltage at 7 is 2.52 and at 9 2.37
 

OK, that's reasonable. Now check pins 1,2,3,5,6&7 of ICs 5,6,7&8 looking for 2.5v. You should also see 2.5v on pins 5,6&7 of IC9, 4.9v on pins 1,2&3 of IC9 and half the input voltage on pins 1,2,3,5,6&7 of IC10.?

Ron

On Mon, Feb 12, 2024 at 12:45?PM Pat <pxforti@...> wrote:
Hi Ron,

Thanks. I checked IC4 pins 7 and 9, I think. I attached a picture and show what I tested. Voltage at 7 is 2.52 and at 9 2.37

 

Hi Ron,

Voltage is correct on all ICs except for ic10 where it is 0 on all pins.
 

Ok. Well that will certainly affect the readings you get in the phasing adjustments section. Check R39 and R40. They form a voltage divider to put half the line voltage on pin5 of IC10 and it propagates to the other 5 pins from there. These are SMD components on the Mini and I suspect R40 is either missing or broken. Look at it under magnification and also measure it. But also check for line voltage (like 12v) on one side of R40 and then see what’s on the other side.?

Ron

On Mon, Feb 12, 2024 at 13:49 Pat <pxforti@...> wrote:
Hi Ron,

Voltage is correct on all ICs except for ic10 where it is 0 on all pins.

 

Hi Ron. I checked both R39 and R40. They are both there and seem to be soldered to the board and look intact. There is no voltage at either of them.
 

Start with the end of R40 that isn't connected to R39.? It should have the 'high' voltage used by the PA etc on it . .? ?
 

OK Pat. Then that indicates there is an open trace between the 12v line and the end of R40 that isn’t connected to R39. You can carefully solder a jumper wire between those two locations to bring it up. I would use left over 28 gauge wire from the kit to make the jumper.?

Ron

On Mon, Feb 12, 2024 at 15:30 Bruce Akhurst <bruce@...> wrote:
Start with the end of R40 that isn't connected to R39.? It should have the 'high' voltage used by the PA etc on it . .? ?

 

Hi Ron,?

I'm willing to try the jumper, but I'm not sure where the jumper goes. Can you show me where on the board I put the jumper?
 

Pat, Jumper as shown in the photo. Please ignore the horizontal jumper in the photo. This was necessary to correct an issue with this particular radio...73 ... Ron


On Mon, Feb 12, 2024 at 5:10?PM Pat K7GUD <pxforti@...> wrote:
Hi Ron,?

I'm willing to try the jumper, but I'm not sure where the jumper goes. Can you show me where on the board I put the jumper?

 

Pat, just to be clear the top end of that jumper connects to the left side of R40. Good luck….Ron

On Mon, Feb 12, 2024 at 17:38 Ronald Taylor via <wa7gil=[email protected]> wrote:
Pat, Jumper as shown in the photo. Please ignore the horizontal jumper in the photo. This was necessary to correct an issue with this particular radio...73 ... Ron

On Mon, Feb 12, 2024 at 5:10?PM Pat K7GUD <pxforti@...> wrote:
Hi Ron,?

I'm willing to try the jumper, but I'm not sure where the jumper goes. Can you show me where on the board I put the jumper?

 

Thanks Ron. I'll give it a try. Can I use the magnetic toroid wire and just clean the ends? Or do I need coated wire?

If that doesn't work, I'll send it to an expert/you ;)
 

Yes. A piece of the toroid magnet wire with enamel removed from both ends is what I meant. Should work fine.?

Good luck…Ron

On Mon, Feb 12, 2024 at 19:58 Pat K7GUD <pxforti@...> wrote:
Thanks Ron. I'll give it a try. Can I use the magnetic toroid wire and just clean the ends? Or do I need coated wire?

If that doesn't work, I'll send it to an expert/you ;)

 

Hi Ron,

In soldered the jumper to the left side of R40 and to the 12v location you showed in image. There is now 12.5 volts at R40, and 6.5 volts coming out of R40 and into R39. But still can't adjust?I-Q Balance, Phase Lo or Phase Hi. Turning the screws has no effect on the signal level.

Any more ideas or is it time to send it to you?

Thanks.
 

Kind of hard to diagnose remotely Pat. Feel free to go ahead and send it.?

73….搁辞苍

On Tue, Feb 13, 2024 at 14:49 Pat K7GUD <pxforti@...> wrote:
Hi Ron,

In soldered the jumper to the left side of R40 and to the 12v location you showed in image. There is now 12.5 volts at R40, and 6.5 volts coming out of R40 and into R39. But still can't adjust?I-Q Balance, Phase Lo or Phase Hi. Turning the screws has no effect on the signal level.

Any more ideas or is it time to send it to you?

Thanks.

 

Thanks for help with this Ron. I'll send the radio tomorrow.

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