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BPF Peak Issue / Question

 

Hello everyone

I am quite a novice at electronics but have built the 20m QCX mini. All looks to be working ok however with the BPF peak I cannot get above 6 and the capaictor blob is towards the right indicating I need more turns on L1. I put 5 more and then another 5 and yet the position still remains very similat if not the same.

I continued and followed the other steps. I checked power out and initially I had 1w but expaning the wire on L2 and then squeezing toegher on L1 I now have 5w out.

I have checked continuity on the inductors and all seems well. Any tips for what else I should check?

Thanks a lot in advance

My concern is that something else is wrong.?
 

This is a very low reading. The first thing you should now do is the bias voltage measurements on the Op Amp ICs, IC5-10. With your external DVM, look for 2.5 v on pins 1 & 7 of ICs 5, 6, 7 & 8, as well as pin 7 of IC9. Also look for 4.8 v on pin 1 of IC9 and half the input voltage on pins 1 & 7 of IC10. You didn't indicate whether you were able to do any of the other adjustments of the IQ balance and Lo and Hi phase null steps. Just curious if you did and how those came out??

73 .. Ron
 

Ronald, I think I might be having a similar problem. I'm not able to get the BPF to peak at more than 3.

I ran these voltage checks you suggested and I only have 0.8 v on pins 1 & 7 of ICs 5, 6, 7 & 8. I have a solid 5 v (not 4.8 v) on pin 1 of IC9.?

Any help is appreciated! 73
Levi
 

Hi Levi. The 5v on pin1 of IC9 is fine. The other voltages indicate a problem though.?

Please check the voltage at points 5,6,7&8 on T1. Refer to the manual to find these point numbers. They aren't labeled on the board. You should see 2.5v there. If you see 0.8 there as well, first check and maybe re-heat those 4 connections. If that doesn't solve it, examine resistors?R1 and R2 which should both?be 10K and should be soldered well in place and have no shorts. If all that looks good, lift the wires at points 5 & 8 and see if the voltage goes up to the expected 2.5 on those two wires as well as points 6&7 on T1. If it does go up to normal at that point there could be an issue with IC4. Before replacing that, though, please check for shorts at C43,44,45&46 A well as R5,6,8&9.?

73 ... Ron

On Sun, Feb 5, 2023 at 1:11 AM Levi ¨C K6LCM <lcm@...> wrote:
Ronald, I think I might be having a similar problem. I'm not able to get the BPF to peak at more than 3.

I ran these voltage checks you suggested and I only have 0.8 v on pins 1 & 7 of ICs 5, 6, 7 & 8. I have a solid 5 v (not 4.8 v) on pin 1 of IC9.?

Any help is appreciated! 73
Levi

 

Thank you, Ron. I checked all of those voltages and saw that 5, 6 and 8 were measuring 0.9 v. All of the wires on the T50-2 toroid had continuity but one or more must have had some amount of excessive resistance from incomplete enamel removal. I reheated these toroid wires once again and the voltages popped up to 2.5v and the BPF amplitude scaling factor jumped up to 08-09.

I think I am all set. Thank you!
 

Nice job Levi. Glad you found it.?

73¡­¸é´Ç²Ô

On Sun, Feb 5, 2023 at 23:20 Levi ¨C K6LCM <lcm@...> wrote:
Thank you, Ron. I checked all of those voltages and saw that 5, 6 and 8 were measuring 0.9 v. All of the wires on the T50-2 toroid had continuity but one or more must have had some amount of excessive resistance from incomplete enamel removal. I reheated these toroid wires once again and the voltages popped up to 2.5v and the BPF amplitude scaling factor jumped up to 08-09.

I think I am all set. Thank you!

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