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 Post subject: Tecsun 2P3 troubleshooting
PostPosted: Jun Wed 17, 2020 3:52 pm 
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Joined: Jun Wed 17, 2020 3:27 pm
Posts: 3
I recently built the Tecsun 2P3 (Amazon) and made the mistake of reversing all of my zener diodes. Before I fixed the diodes I only heard pre-amp hiss from the speaker. After fixing the zener diodes polarity, I still only hear pre-amp hiss from the speaker. I get no AM/VHf audio from the tuner. I don't know if reversing the zener diodes fried my IC chip (CD7368CS). Included with the kit is a full schematic, with basic install instructions but no troubleshooting. I know this is a basic AM radio kit with 3 transistors, so the diagnostic should be fairly simple. Can anyone look at the attached schematic and suggest a place to start my troubleshooting. Thank you in advance, Ohiotech.

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Tecsun 2P3 Schematic.jpg
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 Post subject: Re: Tecsun 2P3 troubleshooting
PostPosted: Jun Wed 17, 2020 7:41 pm 
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Joined: Jul Sun 07, 2013 1:42 am
Posts: 31
I recently built the same radio, it's quite a good kit. but I don't recall there being a single zener diode in the set. there are three 1n4148 as a voltage dropper and a single 1n60 as a detector, make sure you installed the 1n60 detector in the right spot as it's important. the CD7368 is designed to run on 3 volts so i doubt you fried it. there are so many things that would keep your set from working so i can only suggest you go over your work and follow the schematic. my oscillator coil and IF transformers were already set nearly perfect from the factory but you may need to adjust them, as well as the tuning on the varicap. good luck with your radio, once I took the time to calibrate mine it became a very sensitive radio.


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 Post subject: Re: Tecsun 2P3 troubleshooting
PostPosted: Jun Wed 17, 2020 9:31 pm 
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Joined: Jun Wed 17, 2020 3:27 pm
Posts: 3
You are correct in the supplied diodes. And the 1n60 was in the right place but also reversed as the were all three of the 1n4148 diodes. I will go through my work flow with measurements as best that I can. In the mean-time if anyone can think of why the oscillator is not giving output and what I can specifically test for that, I'm all ears. Thanks


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 Post subject: Re: Tecsun 2P3 troubleshooting
PostPosted: Jun Wed 17, 2020 11:18 pm 
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Joined: Jul Sun 07, 2013 1:42 am
Posts: 31
one thing i forgot to mention, there are 3 current measuring test points on the circuit board that need to be bridged with solder before the radio will work. labeled IC1,2,3 on the drawing.


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 Post subject: Re: Tecsun 2P3 troubleshooting
PostPosted: Jul Mon 06, 2020 8:38 pm 
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Joined: Jun Wed 17, 2020 3:27 pm
Posts: 3
I finally got some time to get back to troubleshooting. I had no DC Milliamp voltage at any of points A, B, or C. I decided to follow The Jerry Davis review ( This is the best AM radio kit available today) from Amazon of his purchase of the 2P3 (Cudos to Jerry for the detailed analysis). Jerry has an alternative test for each stage. The 2nd IF Amplifier (jumper pad C ) needed the resistor changed from 150 to 120K to get the voltage up across resister R10 by replacing R8 with 120K down from 150K. The first IF Amplifier (jumper pad B ) voltage was then too high 2.7 when it was recommended .6 to 1.2 volts at R6. The recommended resister was changing R5 to 22k from 18K, but the kit did not have any spare and I also did not have any spare. I decided to close jumper pad A and see if it works. Horay! It works. I have many steps to finish like check the tuning (first I need to build my loop antenna) and adjust the antenna coils for permanent position. (youtube video for that: Tecsun 2P3 Retro Radio Kit Build DIY) Thank you all for your support and I hope this helps someone else for getting their 2P3 working.


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