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N1NKM

Radio Shack Travel Radio Model #2000125

This is a very nice little AM/FM/SW radio.
It tunes the standard, analog AM and FM bands,
and SW from 2.3 MHz to 26.1 Mhz, continuously.

Radio and manual
headphone amp module

As Radio Shack was going out of business, :'( my local store was selling these nifty little radios at half-price. I bought seven of them at $17 each. They use three "AA" batteries, and they really do work very nicely! They have excellent sensitivity and selectivity on all three bands.

Taking the radio apart
Removing the back cover

This is the "back" circuit board, where the actual RADIO circuitry is located. The "front" circuit board is the CPU, buttons, and display, which are UNDER this one as shown in this pic.

My original plan was to modify some of these, putting them into bigger cabinets with a bigger speaker & power supply, essentially converting them into "Table Radios". So, I cut the wire to the whip antenna, to make it easier to work on without having the back dangling from the wire. Instead, I should have de-soldered it, but I digress. ;)

I soon found out that my idea to modify this radio wouldn't be possible. :(

Taking the radio further apart
CPU, control, and display board

This is the "FRONT" circuit board of the radio. The "brain" of the radio is a chip that is under that black blob. The way the radio is made, there are FIVE SCREWS holding this board to the front panel, around the LCD display... this is where I realized that modifying this thing just wasn't going to happen. :( The LCD is held in place by the precision-molded case, using one of those rubberized conductors from the board to the conductive paths on the glass. In other words, it's EXTREMELY FUSSY and PRECISE. The slightest mis-alignment, means digits segments don't work... so, no joy there. :(

The large, gray ribbon cable to the right, connects this board to the "back" board.

I put the thing back together, praying that I didn't ruin it. Thankfully, it still worked fine... WHEW! I am concerned that it will STAY WORKING... only time will tell.

I did discover that I could make ONE small modification, which made a nice improvement to AM reception. That will be shown, further down. :)

To the heart of the matter
The chip that IS the radio

This tiny little chip (little black square in the center of this pic) is the HEART of the whole radio! There are no adjustments, no ceramic filters, nothing... the antenna connections just go to this chip, and everything happens within! The external parts provide the display and keyboard control, as well as the audio amp, volume, band switch, and power control. (A button turns the radio on/off electronically.) I cannot find *ANY* data on this chip, either! (I tried!) So, the workings of it remain mostly a mystery, as do the functions of the pins that aren't obvious.

The obvious pins are the AM antenna coil, whch is at the top, connected by two thin wires. You can also see where the SW/FM whip antenna connects, with a thicker white wire coming off the left in this pic.

With my oscilloscope, I figured out where the audio came out, and a master clock signal went in. (Likely coming from the CPU in the front half of the radio.) There are other signals, like frequency data for the display, as well as signals to "tell" this chip what frequency to use. (Probably serial data streams.) Other pins control the mode, AM/FM/SW, and RF sensitivity. I didn't bother to trace those out, since there wasn't anything more I could do with them, anyway. :(

Improving AM reception
Modifying the AM antenna ferrite core

Since I had the thing apart, I decided to investigate the AM antenna loopstick. Sure enough, the alignment was *NOT* optimal! However, there wasn't enough room in the case to move the coil off the end of the ferrite rod... so the only thing I could do was remove about 1/4" of the rod.

This required carefully scoring the ferrite with my Dremel tool and cutting wheel. Since ferrite is ceramic, it is VERY hard, and thus also brittle. Once I cut a 1/32" deep (approx) ring around the end, I clamped it carefully in the vice, and snapped that 1/4" piece off the end.

The next step involved positioning the coil on the rod at just the right point to get the best reception at the low end of the band, then putting it all back together in that position.

Putting the radio back together
Putting the radio back together

Here the AM antenna can be seen "dangling" by its wires, as I prepare to put the radio back together.

Putting the AM antenna back
Modified AM loopstick back in place

They used a double-sticky pad to hold this in, so removing it was tricky... but thankfully, the pad wasn't too badly damaged, and I could re-use it to put the AM antenna back into the case, and hold the coil in the correct position on the ferrite rod. The improvement to AM reception was definitely noticable! It was GOOD before... now, it is GREAT! :)

You can see that there is a small gap at each end of the antenna... where before, the ferrite rod was solidly touching the plastic "stops" at each end. Hopefully, it won't move from this position. The adhesive is pretty strong, so it SHOULD stay put. I am seriously considering trying this with my other radios... now that I know just what I need to do, and how. :)

Unfortunately, this appears to be the *ONLY* mod that can be done with these radios. They are NOT "tinker-friendly".

"Stay Tuned!" ;)
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