Paul, is that a typo on your psu settings, or is that really only 70mA on TX? If so that definitely will give you low output. What current are you drawing as metered on your psu during TX? 73 Nick G0OQK

Your current limits look low.

Expect about 100 milliamps in Rx and close to 1A when Tx-ing. 

Maybe set your current limit to say ...  1.25 A?

GREG KI4NVX 

Hi Paul,

1) turn back on your SWR protection to prevent damage if something happens.

2) your power supplies and bias current are fine

3) it should be pulling somewhere near 1A on transmit

4) although most of your filter scans look like a pretty good shape, looking at the left-hand scale, you see they are not getting activated properly: the scale should be going from about 0dB down to about -35dB.  Confirmation that your transmit is not working properly.

5) your SWR scans are irregular, further confirmation that something is wrong with tx.

 

First, make sure you haven't put your QMX keyer in Practice mode (a P will be in the display after the frequency).  That would cause all of the above symptoms, because transmit is disabled in firmware, and stays disabled even while running diagnostics.

 

Otherwise, this type of failure almost always means that one of the following assembly issues is happening:

1) One of the ends of L502 is not connected well.  This is not uncommon, especially if your kit used the larger gauge wire.  It must be scraped well at the ends to remove the insulation, since it will not burn off.  Even the smaller gauge wire, which has insulation that will burn off with solder does not always contact well if not heated well enough - even if the solder connection looks perfect.  I recommend removing and scraping the ends of the wire, and replacing (if you had the larger gauge wire), or if you used the same gauge as for the toroids, heat it again with a soldering iron set to at least 370C, and heat each connection for at least 10 full seconds.

2) One of the connections of T501 is not good.  You said you already re-wound this.  It is not typically the windings that are the problem if you have no tx, it is the connections.  Especially the center-tap connection with the twisted wires.  Even if the soldering looks perfect, the insulation can prevent proper contact.

3) One or more of the connections of T507 is not good.  Only the one single-wire 'turn' that connects the signal to the output could prevent transmit, but I suspect that is not your problem because you are receiving well.  However, if any one of the other connections is bad, it will prevent the SWR and power readback in the diagnostics from working properly.

 

Since your current draw is so low on transmit, I suspect it is one of the first two issues above.  There are several other things that can cause transmit to fail, including improperly installed BS170 transistors, and failures in some of the pre-installed surface-mount components, but these are very rare problems.  By far the above mentioned things are the most common failures.  Even if you are sure you soldered well.

 

I hope this helps, and you find the problem quickly,

Stan KC7XE

 

 

 

Ge

 

Many thanks for the information I will get back to you with how I got on in a couple of days. 

Thanks again.

 

Paul

 

m0pnn

 

 

Hi

 

Stan

 

I removed and resoldered L502, checked reheated T501 and T507 at 370c for 10 seconds, and then checked with a multimeter in Ohm’s mode; all made good connections.

I have uploaded some pictures to  https://www.flickr.com/photos/202049058@N06/

 

There is a short between the BNC's centre pin and the ground. Is this normal? There is still no Tx, and the SWR is random.

 

Cheers

 

Paul

 

M0PNN

Paul, it sounds like you are doing the correct things, but unfortunately without resolving the problem.

The photos look good - seems like a nice assembly job.  But it is very hard to tell good connectivity from photos alone.  A photo or two of the bottom side of the board may be useful.

 

Note that although you tested for proper connections with your ohm-meter, it is very hard to really tell on some of the connections, because they get shorted to each other or ground when installed: so one end of the connection may be good, and the other end bad, but you can't tell with a DMM.

Did you scrape the enamel coating off the wires of T501 and L502 and T507 very well before soldering?  This is truly the most common issue.  The insulation will not burn off with a soldering iron.  Or you might get a partial connection that looks OK at DC but is bad with the transmit RF signal.

The reason I revisit this same issue that you already tried to solve, is that there are not many other items in assembly of the QMX that can fail and give the symptoms you have.  And there are many others on this list that have finally found that their "known good" soldering of these was indeed the real problem.

 

Other possible sources of failure:

If you can probe very carefully while QMX is powered on (probe slips can cause shorts that damage components), one thing to check is the voltage at the 'top' end of L502, which is also the drain (tab) of Q507.  This should be just a little less than your supply voltage during receive and transmit.  If this voltage instead is near zero, it would also defeat transmit power, and would indicate a rare failure in the surface-mount circuitry.  Likewise, the 'gate' leads of the BS170 driver transistors should be at about 2.5V during transmit (actually a 5V square wave, which will look to your DMM like and averaged 2.5V.  Both of these can be measured with just the bottom cover off, if you carefully identify the correct thru-holes to probe.  If both of these voltages are correct, then the coil connections are about the only thing which can cause the failure mode you have.

 

Stan KC7XE