Friday, November 27, 2020

Tecsun PL880 Repair

 


 I was fortunate to pick up a broken Tecsun PL-880 for almost nothing. Here is the story and result.

 

Back Story

The radio was owned by a ham radio operator who used it as a bedside companion. He said that it fell off the nightstand one day and crashed on the floor. There was a Tecsun AN-48X antenna connected at the time and the crash damaged the connector. The owner attempted to repair the antenna jack using a home brew method. He said the radio never worked right afterwards. AM and Shortwave band reception was flaky and the tuning encoder wasn't working well either.

Here are some screen caps of a video he made about the repair.





 


Diagnosis/Repair

The radio arrived a week later and I put a fresh 18650 in. Powered up and tuned FM stations just fine. Switched to AM and shortwave - it was completely deaf. Normally the strongest AM station in town is able to come through on a crystal radio set, but not the Tecsun. The tuning knob was erratic and seemed to jump two steps or not do anything at all while tuning. Touching the tuning knob increased static to the radio.

A few ideas crossed my mind at this point. The radio suffered cracked solder joints or misalignment occurred from the crash. The front end transistors were blown or the repair failed.

 My first look inside the radio. Notice the compressed brown wire next to the screw hole. There was a nick in the insulation from the screw. (The back of the radio case has a metal shield and pad to ground the radio to the PCB shield.) Also noticed several missing screws.


 I removed the home brew connection and the broken  antenna connector, then installed a temporary jumper across the external antenna switch pads. Also cleaned up the solder flux and excess solder. I wanted to see if this was a simple fix.


I powered up the radio and it was still deaf on AM and shortwave bands, but the tuning encoder works great now (suspect ground short from previous owner's repair).

Time to figure out the radio circuitry and trace/test components. I used my DMM, signal generator, and scope to make my way through the receiver. Immediately, I found a cracked diode in the protection circuit next to the antenna jack, I replaced it with a 1N4148.

 


No other broken traces or failed transistors in the front end until I made my way to the mixer circuit and the signal died. I found a broken inductor on the board at L9. L9 is a .47uH fixed inductor that couples L6 to the mixer input for AM/SW. I cannibalized another receiver and replaced the component. Now the signal tracer was making it to Q7 and Q8!

I powered up the radio and tuned WWVH on shortwave. The radio came alive! Tested AM and it was very weak. Time to go back to the AM input circuit. Q26 tested fine, but the ferrite antenna leads needed to be reflowed as well as a broken wire repair at AM1.



Tested the radio and AM came back to life! Now on to the external antenna jack. I ordered replacement jacks and soldered one in.



Now the radio is as good as new! External and internal antennas work. I did not need to perform an alignment on the radio (The RF shields need to be desoldered).




73,

W9JES


Saturday, November 14, 2020

New Radio?

 Coming soon to the blog! We will perform some repairs and enhancements on this radio.. Stay tuned for more updates.




Friday, September 25, 2020

Live Shortwave Radio Chat on Zello

Remember the good old days of the IRC chatroom on SWL'ing Post? Well now there is a new way to network and discuss all thing shortwave!

Visit the SHORTWAVE AM LW channel on Zello.

 

Thursday, September 17, 2020

Radio Shack/Sangean Replacement Speakers Available

 Hello folks. Those of you who want to revive your radio's sound can purchase a replacement speaker for $26. Shipping in the US is free.

 


 Speakers available for:

  • ATS-909
  • DX-398
  • DX-399
  • ATS-505
  • DX-402
  • 20-629

The speaker requires replacement if the volume of your receiver is low and the audio distorted with a crackling or buzzing sound. Radio Shack no longer carries this specific replacement anymore, but I have a limited quantity of replacement speakers from a different source.

Here is a bad speaker and the sound on a DX398.



These speakers are manufactured by a different company with the same dimensions and audio characteristics of the original speaker. They are a direct replacement and fit inside the radio without modification or damage.



 If you don't feel comfortable opening your radio and using soldering tools, then let me do it for you for $35 plus shipping.

Feel free to contact me for details.


Thursday, May 21, 2020

Radio Shack DX-398 / Sangean ATS-909 Mods Part 4 - IF Out Panadapter

This modification is similar to the DX390 panadapter tutorial that I posted HERE. I encourage you to check it out for more detailed information on panadapters, software, SDR dongles, and configuration.


What You Need

  • SDR


  • Female MCX bulkhead connector



  •  MCX male to SMA female cable
  • 24ga insulated copper wire
  • Additional cables or adapters to connect the SDR to your radio available on Amazon.
  • 1k ohm, 5 watt resistor
  • 1 nf to 2.2 nf non-polarized capacitor (I used a 2.2nf film capacitor)
  • Drill bits. Cordless drill
  • Soldering iron. Heat shrink tubing
  • SDR software
  • Drivers for your RTL-SDR

  

The Radio


The DX-398/ATS-909 is a dual conversion, superhetrodyne receiver.. The first IF is 55.845 MHz and the second IF is 450 kHz. We want to use the 1st IF stage for our panadapter for maximum bandwidth.


Connecting your SDR directly to the radio could alter the signal of the IF stages and cause poor reception. It could also transfer unwanted DC voltage between the radio and your SDR. We will use a small value capacitor for blocking spurious voltage and resistor to prevent receiver sensitivity drain. Connect them in series to your radio.


Identifying the correct tap point for a strong IF signal in this radio is fairly simple. We could tap between Q3 and Q4 near the filters. The Sangean service manual indicates TP11 is used to measure the 1st IF frequency. We can use this for our panadapter.



 

Connecting the Cable to the Radio

Disassemble the receiver case and remove the large circuit board. It is much easier to remove the speaker and control pcb before drilling holes and soldering. 

Drill your holes in the plastic case near the external antenna jack. Watch out for the two inductors. You can gently separate the rear pcb from the plastic housing to prevent damage to the components.

Make your cable assembly and add heat shrink.


 

Secure the cable assembly with the connector nut.




 Route the wire through the top hole and solder to TP11.


 

 Reassemble the radio and test.




73,

W9JES

Monday, May 4, 2020

Radio Shack DX-398 / Sangean ATS-909 Mods Part 3 - Tuning Knob

The next part of this series covers the rotary tuning knob. The DX-398 has a good tuning knob, but it has an unwanted feature causing it to stop or "click" in small increments. It is hard to spin the dial freely while tuning for DX. This is due to the plastic notches or detents in the tning shaft that mate up with a half-circle in the metal retainer/spring assembly.

Arthur Hollingsworth  created a video on how to perform this mod - You can view it here https://youtu.be/53VKmO8mqTc?t=1172



Steps

  • Locate 6 solder pads on the circuit board near the LCD display light
  • Remove the solder from the 6 pad connections
  • Remove the tuning control from the board


  • Gently pry up the 4 metal tabs on the back of the tuning control with a small, flat bade screwdriver. Use a pair of needle nose pliers to remove any bends
    Copyright Arthur Hollingsworth
  • Gently separate the metal case and plastic control housing.



  • Remove the copper section from the 4 plastic retaining posts

  • Using needle nose pliers, gently flatten the notch that sticks up on one side of the ring.

  •  
  • Reassemble the tuning knob in reverse order noting correct orientation (note the "detent" is now removed, but is shown here for reassembly reasons)
  • After the control has been put back together gently flatten the 4 tabs back into place using the needle nose pliers
  • Resolder the control into place on the PCB
  • Check your work and power up the radio
  • You should now be able to tune much easier now


73,
Jesse W9JES

Radio Shack DX-398 / Sangean ATS-909 Mods Part 2 - LED Replacement

This is one of the easiest mods you can do to a 909. Replace those dim, lime green LEDs with white ones!

All you need to do is desolder the old ones and replace them. Be sure to note polarity as seen on the PCB.






73,
Jesse W9JES