Here is the article is like a man tinkering with the radio:
That allowance, on which I remade, because there is clearly written that can be distributed freely on the territory of Russia, etc. publish the name of the author, but my amendment, which was skated on the 2 copies DRH9255, so that they consider the regularity and advise you to use!
Inaccuracies in the article, and add / correct a signed text of the valves, so you must first COMPLETELY Read the full article, get to the core and get down to business!
As I rewrote the tuner in the DRX9255. Reporting manual.
(C) Docent 3D
Andrew, Peter
The following information is a summary of my research on "Remaking FM-tuner Addzest DRX9255 on the European frequency range," and allowed to free spread throughout Russia, CIS countries, as well as Europe, America and others ....
To start a small introduction. The basis for the alteration of operations was the information kindly provided by Alexander Yureninym (Alex), as well as material from the book by Anatoly Shishatova (ZHSH) "at the Concert Hall koloesah." Ea is a special thank you to them.
A bit of theory to help understand the process of remaking. FM tuner with DRX9255 built under the scheme with the local oscillator and frequency synthesizer. The idea of ??this design is that the LO signal is divided by frequency and compared with the reference signal frequency and phase. The reference signal is generated separately, in the management of the scheme and the step is in the relevant frequency range. In our case it is 0.05 MHz. After comparison, the control signal is generated LO frequency, which changes the latter so that it was equal to the net step frequencies multiplied by a factor of division. Thus, fine tuning is achieved to the desired frequency oscillator. LO frequency control, and other tunable LC-circuits arranged with varicaps included in this circuit.
Now, how and what was done, and how can you do if you decide to rework.
The stage of disassembly.
- Take out Addzest RDX9255 of the car.
- Remove the top cover.
- Remove the bottom cover.
- Remove the front panel.
- Turn off and remove the vehicles.
- Turn off and put off to the side of her hair off RCA-plugs.
- Unscrew all the screws that hold the rear wall of the housing unit with everything else.
- Unsolder the wall from the board (two points) and remove it.
- Carefully remove the lid-screen tuner. It is attached to the snap-ledges. Two left and right.
Stage alteration management system
- Put the unit upside down and "face" of his own. In the upper right corner of the board we find two pairs of pads, next to which it is written «Japan» and «USA». SMD-resistor is zero resistance to solder a pair of contacts «Japan» a couple of «USA». Everything. Now, the control system switched to the Euro-American bands. This means that the display will reflect the figures familiar to us from 87.5 to 108MHz, and the frequency synthesizer is to compare the frequency of oscillator, taking into account the fact that the oscillator has been tuned to other frequencies (for our range).
- To change the pitch of the tuner of American 200kHz to 50kHz for our holding down the «BAND» double-click on the "<<"
- Switch to manual / automatic setting by pressing and holding the button «BAND»
Stage of alteration itself tuner.
- If you look at the back of the unit, we will see a lot of on-board tuner coils and other detalyushek Lilliputian size. As it is not terrible, but some of them we have to vypayat and subjected to modification. To do this, always need a low-power (preferably not on the 220, but with the step-down transformer), a small soldering iron, a magnifying glass and good light source.
- So, we place the device flat on the main board down. We are looking at him from behind. Standing vertically on board tuner, we are interested in three coils (TOP - BLACK, WHITE MEDIUM, LOWER GREEN BEZKARKASNAYA (looks like a very large, spiral).
They are strictly on a vertical axis passing through the center of the board tuner. The first coil on top - odnoobmotochnaya. This oscillator circuit coil. Under it a trimmer toli, toli trimmer capacitor - to us he was not interested. Another double-wound coil is below - it's interstage transformer with tunable LC-circuit at one of its windings. Still lower is a frameless coil of the input circuit of the tunable radio frequency FM tuner.
Alteration of LO.
- Put a muzzle device in place and turn it. In Tuner mode are connecting a voltmeter to the 15th pin connector tuner, designated VT. According to it, the tuner receives the signal tuning circuits with a frequency synthesizer circuit. Regardless of the selected frequency in this output will be about 7volt. Though when all is well, there must be a minimum of 2.1 (87.5 MHz) to 6Volt (108MHz). But we switched to a different synth mode, and the oscillator is still running in the old format and can not be reconstructed. Accordingly, the frequency synthesizer provides the best possible control signal to the LC-circuits varicaps tuner. In order to outline the LO can be reconstructed at high frequencies, it is necessary to reduce the inductance of the coil. Fed to it. It turns 4.5. Wind off one or two turns (do not cut off the excess wire!!!) And solder the coil on the back of the card. So convenient to adjust. In the tuner is turned expose the frequency of 87.50 MHz and a control voltage at the VT. It should be 2.1 V. If you close, you can try a miniature ferrite rod otvertochkoy twist in the coil and adjust the voltage of 2.1 V. If the voltage is always greater than necessary, it is necessary to further reduce the number of turns in the coil. If the voltage at the point of VT markedly less than 2.1 volts, you overdid it and you want to turn back into place. I have the grace came when I removed about a half turn (unfortunately tuning inductance with the ferrite core has a very small range of adjustment). When you tune into the very same 2.1 V, then try to go to 108MHz. At the point of VT should be about 6Volt. I was a little less by the way, but it is IMHO not a crime. Now you can finally cut off the excess wire and solder the coil in its place. Radio has already PLAY. Bad, but it should!
So, in practice, turned the voltage at the point at 87.5 MHz, VT 3 volts!, ??With the core of the Black coil should be in the middle position and have the freedom to adjust!!
More to break and remake does not have to!!!
Crank radio, first known to be a good tune on the wave, take a mini otvertochku, such as for hours, and begin to customize the second coil (which is white), twisting back and forth achieve the best result, and then adjusts the first coil (black, although a full chocolate I had a at 3 volts! at the point of VT) and least adjusts the last coil (green) by gentle moving apart / moving the turns and get pleasure from the work done!
Unfortunately, pictures do not, disassemble the new no mood and time, if someone does not understand - please send photos of the tuner-tknu what and where to do it!
Reconfiguring the remaining circuits.
- It is necessary to reconfigure the input LC-circuit. Fed to the appropriate coil and remove one turn. Solder back. The reception quality must now be considerably higher. Moving / pushing the turns of the circuit configuration can be changed and therefore the quality of reception. In fact, the input circuit is a bandpass filter with all the considerations and consequences.
-Next. Tune in a station manually with the naiotvratitelneyshim reception. And start to turn the ferrite rod coil-winding. According to the ideology of the reception should be improved by reducing the effect of iron on the winding. Yes there seems, in practice, the way it is! I do my best result was achieved with a fully torn off from the coil core. With this experience with the removal of a single turn coil which is built LC-circuit was not very successful. The inductance of the coil was too small and even a ferrite rod was not able to raise it to the required level. While this may be a feature of a particular instance and no more. In any case, I will describe how and what to do. In this case we are interested in is the winding, which is connected to the board with two pins varicap (This is a three-legged SMD-bony plates on the back side of the board). I have been a top coil on coil and its conclusions have been soldered to the board of the oscillator coil. Fed to the coil and the wind off a round with that winding. Then solder it back and donastraivaem ferrite rod ..
- Putting it all in reverse order, and .........
....... listen to the radio in the usual range
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