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Avril 2017
I've been given a ICOM IC-R71E receiver that did not work and had been stored for a long time.
Symptom : no reception, no VFO or keypad action, no display.
RAM board
Symptom : no reception, no VFO or keypad action.
The Lithium battery on the RAM board which is plugged on the LOGIC board has been removed by the previous owner. The RAM board uses a static CMOS RAM uPD444C. When the backup battery is removed or flat, the datas stored in the RAM are lost.
The R71 has several parameters stored in this RAM, and when they are lost, the radio doesn't work anymore ! Some pretend that the processor is stored in this RAM. That's NOT THE CASE, it's stored in the processor ROM.
Only memory frequencies and mode shift are stored.
The cure is :
- send the radio back to Icom for repair (not sure if they still can do that after more than 30 years !)
- buy a third party RAM board, there are several on Internet. Look for IK2RND Roberto's offer.
- reprogram the board yourself !
Guess what ? I tried the last solution !
On Internet, i've found several infos about this problem and the easiest solution is the one offered by N2CBU. He has written a small software that can reprogram the RAM with the help of a simple programmer and file.
I quickly built this interface on a perf board. Durty but operational !
The main problem i had was to find a PC that was old enough to work under DOS at a relatively low speed and with a parallel port.
I had to try 2 different PCs before it worked. In the BIOS settings, i had to change the LPT mode to EPP. Once i did this, it worked at first try !
After this repair, i could store, clear the memories and the display worked normaly. The keypad worked again, but i still had other problems. The 2 digits on screen displaying the channel number had some strange behaviour and the receiver was still mute...
DC-DC converter DP-2
Symptom : The receiver did not give any sign of life in CW/SSB/RTTY mode. I had some sound in FM only.
The S-meter was stucked at middle scale.
It appeared that there was no voltage on -10V line coming out from the MATRIX board.
The small metal case marked DP-2 was very hot and lately i had the L2 coil that made a lot of smoke and the PSU made some mechanical hum... In short, i had a short circuit !!
I unsoldered this DP-2 module and opened it. I made some reverse ingeneering and tested all components.
Meanwhile, i found another ham making the same work and who published the DP2 internal diagram. I measured the small transformer and the secondary is 2mH and the primary is a center taped 300 uH. Another ham had to rewind the secondary that burned and counted 125 turns and 2 times 26 turns for the primary.
Finaly "only" the 2SD648C transistor was burned.
I didn't have any substitution for this later, and i tried several transistors i had before finding one that worked and did not heat too much or did not burn after a while. I used a BD139 for which i had to file the legs until they fitted in the board. The transistor case is higher than the original one, and the module cover does not completely close the case... But that's not a big deal.
After that i noticed that C13 (100uF/10V) on the -10V output on the MATRIX board was short ! This was probably the reason of all this mess ! After replacing it and the L2 coil, the radio came back to life !
Finaly, i had a rather clean -9.5V on the -10V line. I had noise on all modes, and the S-meter was at S0 level !
But still the channel number display problem...
PSU
The PSU is known to be very badly designed. It heats a LOT and has a lot of problems. It is strange that ICOM engineers who have designed such a good receiver could design such a bad power supply !
Mine had 17.4V output , no regulation and getting very hot, heating all the cabinet !
At least for all my tests i decided to supply the receiver with an external 13.5V power supply with current limiter. The receiver consumes 1.3 A @ 13.5 V
I finally decided to have a look at the PSU. I checked all components, printed board failures and wiring, but found nothing wrong or broken. I double checked again and replaced the transistors, just to be sure. Nope !! Still no regulation ...
Just to be sure, i simulated the circuit with help of LTSPICE, and guess what ? The predicted output was 17V !!
Using LTSPICE, i changed the R2 resistor from 56 to 560 Ohm (what i had) and BINGO ! i got 14V at the regulated output.
I confirmed this by changing this resistor on the PSU board, and i got a clean variable 13.8V !
Is this a design error or do i have a particular situation with my board ??
For those interested, here is the LTSPICE file.
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A friend of mine who bought a cheap Kenwood TL922 power amplifier asked me to repair it and to bring some modifications in order to improve the security. This is the fruit of my works...
So, before any tests i have made the following modifications :
- Step-start
- Filament transformer protection
- HV protection agiainst internal valve flash
- Zener diode substitution
- PTT circuit modification ofr low voltage switching
- RF relay substitution
- RF stability improvement
- Symetrical tube feeding
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- Hits: 36978
Here is a description of an audio frequency tone decoder build around a PIC 12F683.
For a cost not much higher than a basic NE567, you will have :
- A more efficient decoder
- Far better stabiliy
- A settable threshold with hystereis
- Possibility to tune from 100 to 2148 Hz or use a fixed frequency
- No exotic or particular component
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- Hits: 16450
Vous trouverez sur cette page quelques informations sur les câbles coaxiaux qui pourront vous être utiles.
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I'm not a knot specialist and don't have the claim to teach you how to make good knots... I should at first learn it myself !!
However, the few knots which follow are very usefull to me and will certainly be for you as well.
The reef knot.
Remarkably adapted for connecting two ropes of same diameter together.
CAUTION, do not use when the 2 ropes have a large diameter difference, it would not hold !
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- Hits: 40259
Like me, you probably often needed to calculate a gain, loss or SWR when measuring powers or working on antennas. And when you are on the field, you never have the right calculator or forgot the right formula !
It's a long time i wanted to make a chart that could make me the life easier. I was thinking about a circular chart, but i never found the right tool with which i could do it easily. Until i found the GALVA software written by F5BU.
The result of my thoughts is presented below. This tool can calculate gain, loss, SWR and return loss in a second with enough precision for most amateur works.
The principle is simple, the powers are on 4 decade logarithmic scales, for a 40 dB range. The gain and return loss use the same 40 graduations linear scale and the SWR is a special scale responding to the SWR vs power formula.
To use the chart, you only have to align the 2 powers on 2 concentric disks and you read the result in a small window. There is a short explanation on the disk itself.
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In our hobby, we sometimes use silver plated parts for their excellent characteristics in HF circuits. Higher Q and better electrical contacts.
One drawback of silver, is that it is corroding, and getting black. This black color is mainly due to the silver sulfid (Ag2S). Silver sulfid is a much worse conductor than silver and giving a ugly look.
For one of my recent projects (VHF tube amplifier) i used an old socket which had all pin contacts very corroded. I looked for a simple and safe way to clean them.
The following method is the result of my experiences and works perfectly with things that can be found in any kitchen !
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It sometimes happens that while repairing old antennas or searching for an antenna fault, the question of connections between tube or in traps arises. A few tenths of Ohm in traps or in between tubes can already be a problem and lead to high losses.
Measuring very low resistances is not easy with common multimeters, and if you have them it's sometimes difficult or risky to carry them on field. Often, we are in situations where we need to measure low resistances without any special equipement.(contests, fieldday, etc...)
Even the lowest range of a digital multimeter is of no help to measure resistance under a few Ohms.
The following method described here allows to measure very low resistances, in particular contact resistances between tubes or any other metallic parts.
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If, like me, you sometimes want to use old used capacitors, what follows might interest you !
Why ?
When an aluminium capacitor is produced, it can't be used immediately. It must pass thru a generating process. This process consists in charging the capacitor with a very low current until it reaches its nominal voltage.
During this charging, a certain quantity of aluminium is teared off from the electrods and is deposited on the dielectric in the form of aluminium oxyd. This oxyd is an insulator that protects the dielectric up to a voltage at which it has been formed.
This oxyd layer is maintained and regenerated each time the capacitor is used by a small amount of current, called leakage current. The serious manufacterer are giving a maximum value for this leakage current.
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Unsoldering SMD components can be very frustrating, time consuming and a disaster. Here is a trick i've found in a electronic magazine of which i forgot the name.
All you need is a piece of enameled copper wire of about 0.2 to 0.3 mm in diameter.
Take a length of this wire and slide it under the pins of the circuit you want to unsolder. Attach one end firmly,( because you will have to pull on it ) in soldering it on a large pad close to the circuit.
Pull firmly on the free end of the wire so it leants again the first pin of the circuit. Do that while keeping the wire as close as possible to the printed board.
Heat the first pin, the enamelled wire should slip under the pin and raise it from the board.
Repeat this procedure for each pin, taking care not to break them. Double your attention for the last one, the wire being stopped by nothing.
Make some tests on a defective board before applying this method to a board you want to repair.
The smallest SMD components can't be unsoldered this way, you can't even slide a wire under the pins !
Let me know if this could help you and/or if you have a better method.
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Ilt is sometimes necessary to split the output of one transmitter in order to drive 2 amplifiers or 2 antennas. There are several ways to do that, but an elegant one is to use this splitter.
The following description is the fruit of my own experience and works perfectly.
This splitter is composed of 4 lengths of 75 Ohm coaxial cable.
During normal operation, the injected power in the input IN and split in 2 equal levels on outputs OUT1 and OUT2.
No power should be present on the 50 Ohm dummy load.
The signal available on ouput OUT2 (via a Λ/4 line) has a -90° phase, the one on OUT1 (via the 3Λ/4 line) has a phase of -270°. The signal arriving into the dummy load (via the 3Λ/4 + Λ/4 and Λ/4 +Λ/4 lines) has a phase of 180°, so is cancelled !
One advantage of this splitter is that the 2 outputs are insulated one from the other !
In case of a mismatch on one of the outputs, the other output is not (or very slightly ) affected. All the power normaly present into the output is dissipated into the dummy load. This later one should be able to safely handle half the input power.
This circuit can be used on any frequency, you only need to cut the lines to the right length.
CAUTION, the lines have to be made in 75 Ohm coaxial cable !!. Don't forget to apply the velocity factor (depends of the isolating material) when you cut your lines !
This circuit can be used in a reversed manner, for example when you want to couple 2 amplifiers into one output. In this case, the splitter is used in a reversed manner, OUT1 and OUT2 are respectively IN1 and IN2, and the output is on IN.
CONS
Works only on one frequency/band...
A bit large, coaxial lines can be long...
I hope this can be useful for you ...
Subcategories
Test equipements Article Count: 5
Antennas Article Count: 8
TS850 Article Count: 4
TS590 Article Count: 3
Cartes Article Count: 2
Radiosondes Article Count: 1
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