Re: QCX - Problem with new 30 meter QCX Initial Alignment


On Tue, May 26, 2020 at 04:15 PM, Ronald Taylor wrote:
Don, the behavior of the rotary encoder and the voltage problem on IC2 pin 13 indicates to me either a cold solder joint Or defective rotary encoder. I suggest re soldering the connections on the rotary encoder and on pins 12 & 13 of IC2 as a start. Those are the processor pins connected to the encoder.  Hold your iron on the joints for a few seconds until you see the solder flow. A bad encoder is a rarity so start with the joints. 

On Mon, May 25, 2020 at 13:10 Don W4ZYT <w4zyt.don@...> wrote:
On Sun, May 24, 2020, 23:54 Don <w4zyt.don@...> wrote:
I purchased a  new 30-meter QCX xcvr earlier this month (PCB Rev. 5, Firmware 1.04) and have finished assembling it.  I have adjusted the screen contrast without problems to show the initial information - "T1.04, 2020 30 mtr xcvr" etc.  However, I have been unable to proceed with alignment as I cannot get the boot up screen showing "Select Band" and "80m" to advance.  I turn the center knob (rotor switch) left or right and it switches to "10m" but will not show any other band.  This would reset to "80m" if I switched off and then on again. Today, I clicked the rotor switch, thinking I might progress into the alignment scheme, and later reset the band using the factory reset, and it brought up "3820.0" but no further response to rotating the switch.  Turning off power now fails to reset this, and it is now stuck showing that 80 meter frequency. Consequently, further alignment is still not possible.  I have carefully avoided pushing either of the two smaller buttons, so don't know what their effect might be.

I have been back over the board and components carefully, resoldered what appeared to be several cold joints, checked for bent and misplaced IC pins, shorts, solder bridges, component orientation, and missing hardware - all OK.  Using the voltage chart on pp. 131-132 I have done some checking with my two AVMs.  Voltages on ICs 5 through 10 are all consistent nominally with what is shown in the troubleshooting section.  That is also true of the voltages for IC3, which I suspect reflects "receive" mode - all 14 points agree with the chart.  I also checked voltages at the several points on T1 and the points on C2 and D2, and those are correct.  On IC2, Most values are approximately what the chart on page 131 shows, although some are almost a volt higher.  I attribute this to the alignment not yet having been completed, but I don't know that these may also represent a problem.  The 20 Mhz crystal was checked with a portable receiver and is oscillating.
    Having read in several notes about the test pins contributing to inadvertent shorts during testing, alignment , or repair, I elected to leave those out for the time being, but all other components are       present and appear to be the proper items.

The big discrepancy on IC2 is pin 12, which should read around 1.9 volts and shows an voltage oscillating between about 2 and about 3.5 volts - with a regular period of about 140 cycles per minute.  Also, pin 13, which should show "0" shows a voltage of 4.92 volts. I have been over the schematic and the PCB chart but am not that adept at following it after a certain point and have not been able to resolve this. The problem does seem to involve the rotor switch.

I do not have or have access to an oscilloscope, and have no experience using one.

So I am at an impasse and would appreciate any guidance.  I'm a surgeon with limited background in electronics, and most of my kitbuilding was in the vacuum tube era, although it was accomplished successfully.  I'm a bit rusty, but do have some soldering experience, albeit limited experience with PCB construction.

Vy 73,

Don Lynch W4ZYT
Don Lynch MD W4ZYT 
Virginia Beach, Virginia
Donald F. Lynch, Jr., MD, FACS



 Hi Ron-

Per your guidance, I went back through and re-soldered all possibly questionable joints with special attention to - as you suggested - IC 2 and the rotary encoder switch.  I then rechecked voltages and the continuity between the rotary switch and pins 12 and 13 of IC 2.  When I applied power, I could turn the rotary switch counter clockwise and was able to advance the alignment process to "1. Preset"  at which point it would go no further.  Nothing happens when I turn the switch in a clockwise direction. I feel like I am moving ahead by baby steps :o), but at least it's forward movement.

In checking continuity from the rotary switch to ground and to IC 2, continuity between the center (ground) tab and ground was present.  Continuity between the left tab and pins 12 and 13 of IC 2 was also intact, however there was no continuity between the right tab and IC2.  As you suggested, the switch itself seems fine.

I broke out my old surgical magnifying loupes, and with that magnification, traced the PCB markings on the bottom of the PCB relative to the right sided rotary switch tab..  Referring to the chart, there is a very short blue trace which goes to the middle lower of the six diagnostic pins to the right of the switch - that was, no surprise, intact.  When one looks at the diagram of the right tab on the rotary switch, there is a second red trace (top of PCB) which extends immediately due north from the right tab to a blue trace which then goes to IC2.  With the switch installed, that top trace is under the switch and can't be accessed.  There is one of the tiny apertures at the north end of that red trace which is at the south end of a blue trace going to IC 2. This aperture would admit the tip of my VOM, and continuity between that end of the (blue) trace and pins 12 and 13 is present.  So it appears that there is a break in that (red) trace such that the right tab of the switch does not connect with the trace to IC2. 

I have limited experience with modern PCBs such as this one, and no experience with their repair.  If the problem is as the diagram suggests, how would one repair that bridge or test the connection to see if that resolves the problem I'm having? The rotary switch covers the section of the top of the board involved, so short of removing the switch a topside approach seems precluded.  Is there an acceptable "work-around/"  I guess one could run a wire along the bottom side of the board between the right side tab and (it looks like) pin 2 of IC 2 which connects with the appropriate other pins.  Or possibly install a very small calibre jumper wire between the right tab and the small aperture due north of the right tab on the bottom of the board.  I haven't tried either of these; just trying to reason this through.

What should my next step be?  I'm going to research postage to Izmir, just in case :o)

I am very grateful for your interest and help with this.  I will copy Hans as well.

Best regards,

Don Lynch W4ZYT

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