Audio level on a QCX+ #troubleshoot #troubleshooting #20m #audio
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I have had the big one and the mini for a couple of years and luv-em'.
Thing is, the audio on the mini is way better than its big brother. I know I can just use the mini, but I like to use them all. So, if someone can point me in the right direction to start sorting it out, I would be much obliged.
Thanks,
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Wayne S. KF7RCM |
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Hi Wayne. Since it¡¯s an audio issue you should start by measuring the bias on all the op amps. Look for 2.5v on pins 1,2,3,5,6&7 of ICs 5,6,7 and 8. Also on pins 5,6&7 of IC9. Also look for just under 5v on pins 1,2&3 of IC9 and just under half the input voltage on pins 1,2,3,5,6&7 of IC10.? Also, were you able to get good nulls on IQ balance, phase lo, and phase hi. And what level did you reach on the BPF adjustment??
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Here are the results:
IC-5: 1=2.8v, 2=2.5v, 3=2.55v, 5=2.56v, 6=2.5v, 7=2.46v
IC-6: 1=2.47v, 2=2.46v, 3=2.46v, 5=2.46, 6=2.46v, 7=2.46v
IC-7: 1=2.8v, 2=2.8v, 3=2.8v, 5=2.8v, 6=2.8v, 7=2.8v
IC-8: 1=2.6v, 2=2.6v, 3=2.6v, 5=2.6v, 6=2.6v, 7=2.6v
IC-9: 1=5v, 2=5v, 3=4.7v, 5=2.6v, 6=2.66v, 7=2.66v
IC-10: 1=6.5v, 2=6.5v, 3=6.5v, 5=6.5v, 6=6.5v, 7=6.5v
There seems to be some discrepancy with IC-5, pin 5 should be 2.28v instead of 2.56v. IC-6, pin 3 is 2.46v instead of 1.63v and pin 5 should be 1.55v instead of my 2.46v. IC-7, pin 3 should be 1.99 instead of 2.8v and pin should be 1.89v instead of 2.8v. IC-8, pin 3 should be 0.65v to my 2.6v and pin 5 should be 0.67v to my 2.6v. IC-9, pin 3 should be 0.65v to my 4.7v and pin 5 should be 0.67v to my 2.6v. IC-10, all the pins are 6.5 which doesn't match any of the values in the literature. I am thinking of doing another alignment from the ground up, but will hold off until I get your opinion.
Thanks, W.
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Wayne S. KF7RCM |
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Wayne, that difference is due to the fact that the chart on the manual was made using the internal voltmeter which has a very low impedance and loads down the test points. You obviously used a DVM with high impedance so it didn¡¯t load it. The voltages you reported are all very good.? It never hurts to do another alignment just to make sure all the nulls have been found. What was your reading on the bandpass filter alignment? Is it in the 8 range?? Ron
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Just to note, some months back I did a factory reset to resolve some issues, though I don't see how it would play into this. Did the alignment this evening, set the frequency to 14050. What is interesting is the nulls were significantly off. At 8.7, the peak was at 10, which is where it was from day one. The I-Q Balance was a little higher than I remember but Phase Low and High had alot of room for adjustment. I went back and forth several times to get the lowest values. I couldn't test it as the band went completely dead due to solar activity. Hopefully I will get a chance soon. I am toying with the idea of selling it. I really enjoy the mini you built for me and I don't need two. Flirting with the idea of a QMX+ KIT. Anyway, Thank you for your help, I will post a follow up asap.
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Wayne S. KF7RCM |
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That level 10 on the bpf adjustment is abnormally high. Did you have a dummy load attached when you did those adjustments?? It¡¯s usually a peak in the 8 range indicating normal sensitivity and will be higher without a dummy load. I was trying to ascertain whether you had the normal receiver sensitivity or not. Maybe one more time with a dummy load of not used previously??? Ron
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Wayne, are you getting any power output on transmit??
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OK Wayne. So the lowpass filter is fine and no bad connections between it and the BNC connector.? Also, since all the bias voltages look normal and you indicated the BPF and Phase and balance adjustments all worked normally, it means signals are getting at least all the way up to the input of IC10 section A. Do you have an oscilloscope available? You can put the radio in BPF test mode on menu 8.7 and trace the 700 Hz audio signal through that stage ... and previous stages if necessary. ALSO, you can use a small amplified speaker to trace back from the earphone jack and maybe find where the audio is disappearing. ... 73 .. Ron
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I don't have a scope, at least not yet. These are my further findings (all measured in receive: R38 is good at 120k. IC-10. Pin 4 is 0v. Q7 gate is 0v.?
The pot R-1 is doing interesting things but needs further testing before I post anything here. I will do the speaker tracing; I only wish I had thought of it before. My eyesight is not the best anymore, can you tell me where the volume pot in the schematic is? I must be looking right at it and not seeing it.
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Wayne S. KF7RCM |
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Pin 4 of all the op amp ICs is 0 volts. That¡¯s the ground pin for the chip. The volume pot schematic is on the separate front panel schematic page. Volume pot issues can be a damaged pot caused when bending the leads over for connection to the board. This was remedied in later kits by using wire cutoffs between the pot and board to avoid bending the leads.?
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I thought to include pin 4 for the record as I read about it being implicated in a similar issue. I will try walking the speaker and probably dismount the board to see if there is anything there. I probably forgot to mention this but I spent a good 15 minutes going back and forth tuning it. I can get a few signals but incredibly faint, using two different ear sets. Will let you know if/what I find.
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-- Wayne S. KF7RCM |
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OK, the finished mystery!
Using the DVM and checking continuity along the receive path it didn't take long to find the primary winding on T1 to not be soldered properly. They unit worked before but not like the 40-meter version I built. I assume that the "not so great" solder job had enough and decided to open the circuit. I resoldered the connections with plenty of heat to make sure any coating on the wire was burned off. Reassembled and hooked it up. Works absolutely great! Had to realign it, I found that the adjustments were a bit off after the repair. Thanks for all the helpful input I received.
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Wayne S. KF7RCM |
Ronald Taylor
Steve G4EDG