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EXACHRON DCF77 Time Pulse Receiver Repair

By on February 20, 2017
atlas dca75 tester










My friend Pro Watchmaker Charles requested me to have a look into his old EXACHRON DCF77 Time pulse receiver. DCF77 is the European standard time signal that is transmitted for synchronizing Radio controlled Clocks. Send from the neighbourhood of Frankfurt Germany, Mainflingen, which can be recieved over a distance of around 2000 KM. (Which is a distance from Ireland to the Polish border). This Receiver was build with mostly old TTL ICs and the manufacturer (in Braunschweig Germany, where also many Amiga 2000 Computers were assembled lateron in the 80- 90’s) apparently used the wrong Solder. And almost none of the many TTL ICs were AC decoupled on their Power lines.

And although it is in today standards far more efficient to make a DCF Atomic synchronized receiver with only a microcontroller it is a nice item to Display and Look at if all Display 7 segments work. (which I programmed and build around a small PIC microcontroller in 2007 which was Published In Elektor December of that year). Below the displays on the front.

time pulse machine repair

It also would consume far less energy too. Even a modern 16 x2 LC Display wouldn’t need this much current as the MAN 72 7-segment Displays used in this EXACHRON Time receiver. To see if the 7-segment displays or if the TTL driver ICs (7447 types) were defect I started by removing the 3th (green circle) display from the left. And I examined the Datasheet of these MAN72 displays and instead of connecting a DC voltage with a max limited current of 30 mA to the pins to see if the segment they represent did light up, I used another much better and quicker method.

I used my PEAK DCA75 Pro Tester to see if all segments were okay. Because this tester can’t damage the Leds, it also gives a oscillating signal so it doesn’t matter were we put the positive or negative sides of our DCA75 Test leads. It always works no matter how we connect 2 of the 3 Testlead Wires of our Tester!

atlas dc pro dca75

It turned out that the removed display was okay but the TTL 7447 driver wasn’t. So I replaced it by a good 7447.

ttl7447 ic

I first used my universal portable IC Tester (plus Zener, Opamp and Optocoupler etc. Tester). And to make sure the 7447 was indeed defect I also used my Elektor IC Tester that was published in 3/’98.

ttl ic tester

ttl ic circuit board

Last 2 photos showed how bad the Solder and the used PCBs were on the Display Solder side. The used flux was brownish and never properly cleaned. And the top photo of both showed the PCB with Display 3 from the left already removed.

After I had replaced the 3th 7447 Bad TTL from the Left next photo was the result:

fix time pulse machine

It clearly shows a ‘0’ (Zero) now. And before only segment F worked.

Sadly I only had one 7447 left that wasn’t defect because the 7 TTL ICs in the next photo all tested Bad! And the question is if we still can buy these old ICs? And we need 8 more to fix the other Displays too.

bad ttl ic

Next photos show more of this unique device:

time pulse circuit board

how to fix time pulse receiver

repair time pulse receiver

Previous photo showed the 3th 7-segment display that turned out to be okay.

And next follow some schematics of this receiver

Sadly the Display schematics are missing and maybe they turn up somewhere on the internet. Or maybe one of our Readers can help my good friend to complete his documentation? Anyway the following documentation also could help others.

time pulse receiver repair

time pulse receiver circuit

time pulse receiver board

Here is the complete schematic diagram of DCF receiver Tina V11  :

DCF reciever Charles V11


Until another interesting repair!

Albert van Bemmelen, Weert, The Netherlands.

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Note: You can read his previous repair article in the below link:




  1. moshe jacobson

    February 20, 2017 at 7:54 am

    Nice article Albert.
    Would the SN7447AN from TI work?

    • Albert van Bemmelen

      February 20, 2017 at 8:22 am

      It most certainly will Moshe! And probably also a 74ls47 or a 74HCT47 (CT means CMOS and TTL compatible). Although I didn't test with those last 2 versions. By the way : Both IC testers mentioned in the article had problems with this IC. Because they apparently also failed on good 7447 ICs. Following Universal Tester I also used afterwards gave much better results:
      And my TL866A universal Tester that can test and program over 13.000 different ICs isn't even capable to test this 7447 chip! And I can only check further after I have recieved 10 new ordered 7447 TTLs.

      • Albert van Bemmelen

        February 22, 2017 at 6:35 pm

        Update! The in the article mentioned universal portable IC Tester (plus Zener, Opamp and Optocoupler etc. Tester) in the photo on the left disqualified all good 7447 TTLs in its 74LSxxx types test menu.
        But behold !! They tested fine in its 74HCxxx test menu !! My Elektor IC tester in the photo on the right never approved my good 7447 ICs. And it lacks the HC types anyhow. Not even my Genius G540 was able to test all of the good 7447 correctly! So next to being able to test Opamps, Zeners , Transistors, Optocouplers, FETs, Triacs, Diodes and several Amplifier chips, this portable tester is very usefull and as only one able to test were other testers fail!
        See here for this good universal tester:

        • Albert van Bemmelen

          February 22, 2017 at 8:44 pm

          In conclusion this means that both the in the article mentioned Universal Tester (on left photo)
          and the also very portable universal tester

          are capable to correctly test the 7447.

  2. Gerald Musy

    February 20, 2017 at 2:16 pm

    Hi Albert,

    My comment sent this morning seems to have disappeared in thin air...

    Yes you device is interesting, a trip into the past! You can also find those ICs at UTsource.


    • Albert van Bemmelen

      February 20, 2017 at 3:33 pm

      Hi Gerald, I guess that your comment was about the functioning of your CP2112 adapter that you had problems with concerning Laptop Batteries repair? The CP2112 never gave me any problem and still works everytime. But given they only cost about $24/23.93 euro, buying another one is still affordable? Buying the full version of the BE2WORKS software however is another matter. The free program version only reads Battery Packs which always should work. Of course only when I2C controller chips that the program is capable to reset are in your Packs.

      • Gerald Musy

        February 20, 2017 at 9:20 pm

        Not sure of what you are talking about? My comment was basically the same as the one above, informing you about the availability of those chips at Utsource... Regarding CP2112, I don't even know what this is. You must have confused me with someone else.

        • Albert van Bemmelen

          February 21, 2017 at 1:34 am

          Sorry Gerald, mea culpa! I had you confused with another Gerald. I now see that you always use a nice photo. (Which I also had tried to do too but never managed to accomplish)
          Thanks for your reply.

  3. Albert van Bemmelen

    February 20, 2017 at 4:42 pm

    By-the-way: The reason the 7447 ICs mentioned in the article were defect was most likely caused by a too high 5V supply voltage. TTL ICs are only safe within a voltage range of 5V + max 5% (+/- 250mV). But since the Supply output voltage exceeded this level being 5.49V ! it most likely had killed almost all 7447 and 7448 chips. Also because the Device was designed to operate on only 220V AC which now is about 230V AC today and could also have caused this too high 5V supply voltage. So I tuned one of the 2K5 Potentiometers (the top one with the large BU310 power transistor in it) to an exact 5.00 voltage. But not before I had disconnected the Supply voltage to all the boards first, not knowing if I would increase this voltage while turning on the potentiometer in the wrong direction. The other uA723 circuit under the top supply on that board gave a voltage of about 14.94V DC. Which also could have been 12V DC in the past? But without any original schematics it is always hard to tell.

  4. Anthony

    February 20, 2017 at 5:11 pm

    Hi Albert, that's some interesting equipment....something like Dr Brown from BTTF would build for his time
    travelling DeLorean vehicle. I found the IC still for sale on eBay...... luck resurrecting this device.

    Kind Regards

    • Albert van Bemmelen

      February 20, 2017 at 9:28 pm

      Hi Anthony. I did find them on (only logging to this site offers us in The Netherlands/Holland Ideal payments). And cheaper than those on eBay too!
      Speaking about Back to the future #1,#2 and #3. I recently saw a documentary that it already really is possible to hover above the ground in the air on a hoverboard like in those movies! It only involves a lot of Copper beneath the hoverboard. And an energy field. Thanks!

      • Anthony

        February 21, 2017 at 3:45 am

        Hi Albert, I'm glad you were able to source the parts cheaper than I was able to. I also saw that documentary
        on the hover board principle as they try to best replicate it from the movies.....I'll wait until they have it
        perfected as you see it on the big screen....though it's probably still a long way off.....I also wouldn't mind
        a real light sabre and a jet pack too ! Thanks for sharing your articles here Mr Albert which I always
        enjoy reading.

        Kind Regards

  5. suraga Electronics

    February 20, 2017 at 7:54 pm

    Hi.. Mr- Hi Albert.
    Wow... Nice and good Informative Article.
    Thanks !

    • Albert van Bemmelen

      February 20, 2017 at 9:50 pm

      Thanks Suranga, I always hope to give some interesting information that makes it worthwhile.

  6. George Persico

    February 21, 2017 at 3:07 pm

    Albert, you can usually source 74xx series IC and many more parts from BG Micro Garland TX USA

  7. Albert van Bemmelen

    February 22, 2017 at 3:41 am

    Thank you George. I do not live in the USA but in Europe which would mean extra high VAT and import costs. Buying outside of the EU is expensive. Even when ordered through (China?). Last month I bought a very small S805 Android TV Player for 28 euro plus 10 euro Shipping costs. But I had to pay an extra 20.95 euro for VAT and Handling right at delivery by our PostNL. Having paid 68.95 euro for a product costing only 28 euro is nothing more than a big scam! Every product outside Europe above 22 euro is charged this way! (;)

  8. Albert van Bemmelen

    February 22, 2017 at 3:45 am

    Oops: Paying almost 60 euros at a price of 58.95 (and not 68.95) is still not worth it!

  9. Ulises Aguilar Pazzani

    February 22, 2017 at 11:56 am

    Mr van Bemmelen ,great repair Sir very professional no words for it

    • Albert van Bemmelen

      February 22, 2017 at 11:05 pm

      Thank you Ulises. After all 7447 TTLs are replaced the displays certainly will work. However since the DCF Pulse Time Reciever Antenna Amplifier still is missing just as the matching schematics, I am now building a DCF Transmitter to be able to completely test the Receiver. This way I do not need an Antenna Amplifier to be able to tell if it needs further fixing/adjustments.
      See Dutch Elektor Jan/Feb 2015 on DCF Test transmitter.

  10. Albert van Bemmelen

    February 23, 2017 at 7:02 am

    Just finished building and adjusting the mentioned Elektor DCF transmitter tester. Works great up to a distance of about 10 meters! And I used my TL866A to program the ATtiny 48 with. Although the programmeren programs perfectly AVR and other chips, it is not compatible with BascomAVR in which the AVR was written. But if we adjust its configuration 'fuses' it will work just fine!

  11. Albert van Bemmelen

    February 23, 2017 at 4:38 pm

    PS: my smartphone editor is not that smart and it keeps interfering by changing my original intended text. Although I had switched it off!
    See above Post where "Programmeren" was originally typed in as Programmer!

  12. Albert van Bemmelen

    March 1, 2017 at 4:03 pm

    Addendum: After examining the circuit of the Exachron Time pulse reciever and creating it (reverse technology) in Tina design suite 11, I noticed that the 7447 and 7448 7-segment-decoder/drivers have a LT pin 3 function.

    By connecting pin 3 to gnd (low level activated), all segments (being an 8) will light up as test function for the displays.
    It showed that probably of the too high 5V supply some of the 7-segment leds already failed giving any light.
    The simulation in Tina however runs even on my quad core PC too slow (factor 100 to 1000 slower than in real-time) compared to the Device. Which runs on 77.5 KHz. Also because there are 4 retriggable monovibrators used in the circuit with several capacitors that all limit simulation speed.

  13. Robert Calk

    March 4, 2017 at 6:55 am

    Good job, Albert.

    • Albert van Bemmelen

      March 13, 2017 at 4:33 pm

      Thanks Robert!
      PS: if you look at the in Tina 10 made circuit attached to this article there is a small but significant error around transistor BC237B. The emitter needs to be connected too, and the ground symbol shorts one of the wires unintensional.
      I corrected the circuit lateron but it was already published. Therefore if anyone needs it to repair his Exachron device he can ask me or Jestine for the corrected schematic.

  14. Albert van Bemmelen

    May 8, 2017 at 4:05 pm

    I found a missing connection from /CLR_74164s to both U16_7400 1Y and U17_7404 2A. Now corrected in new send circuit!

    And I also managed to make a working subcircuit of the Exachron timepulse reciever in Tina to examine and the 4 retriggerable monopuls flipflops in both 74123 ICs.
    Because adjusting 4 analogue 10k potentiometers correctly without information is close to impossible! And after replacing all bad components I managed to get the Exachron synchronizing with date, time and seconds correctly running, but sadly it still was frequently wrong after switching on. So it must be a calibrating thing with the analogue 10k potmeters. And there are 7 of them on reciever and decoder boards. (plus one on the little sound board, but that one works ok). Although I checked the monopuls flipflop outputs on my oscilloscopes, it still was very difficult to know how to correctly adjust them. Also because of the very low frequencies of around 1Hz.

  15. Albert van Bemmelen

    May 8, 2017 at 4:33 pm

    And I recently also tested the Antenna Amplifier circuit as was given in the article. I had quickly build on a experimenter's board to be able to tell if it helped by further fixing/adjusting the reciever board. It worked great on the 15V from the reciever antenna input cable. However made no difference by tests in combination with the also special DCF Time pulse tranmitter I had build.
    So both mentioned antenna amplifier, and the DCF time pulse transmitter worked great! The only chips on the Exachron I still had not tested or replaced were the 6 pins TBA861A and 8 pins 1458. Also because the reciever's board output was a correct DCF 200mS/100mS timepulse.

  16. taco roos

    October 1, 2017 at 1:27 am

    beste, ik heb de hele ontvanger na gebouwd aan de hand van de tina schema's en de foto's heb nu alleen een probleem kan niet goed zien wat de kleur codes zijn van de 8 weerstanden bij de 74123 ic en de 2 gele condensator cq dioden ook bij de 74123 zou u mij die kunnen door geven heb de ontvanger opgang werkt naar behoren maar net niet geod genoeg als ik de weerstanden goed heb en de 2 dioden of condensator de gele die tussen de 22uf en 100uf in ziten dan kan ik verder bvd
    Dear, I've built the whole receiver based on the tina schemas and the pictures have just a problem, but I can not easily see what the color codes are for the 8 resistors at the 74123c and the 2 yellow capacitors or diodes also the 74123 would you be able to give me those who are able to pass through the receiver upwards properly but just not geod enough if I have the resistors good and the 2 diode or capacitor the yellow that between the 22uf and 100uf in seats then I can continue to bvd

  17. Albert

    October 12, 2017 at 3:25 pm

    Hi Taco. I'm impressed that you were able to build the entire reciever from my Tina schematic. Although the DCF reciever of my friend did occasionally work as expected it most of the time didn't. So the repair was not entirely successful, mainly because I couldn't find any defect components on both decoder and display boards.
    Therefore it still could be because of deviations on the reciever board with the 77.5 KHz Quartz on it. Or just the calibration thing with the 4 potentiometers on the right decoder board. And because no calibration procedures exist after all those years it is very hard to find the cause. After I had replaced and checked all defect TTL chips and had made all photos and finally the schematic I gave all back to my pro watchmaker friend Charles.
    Anyhow I am almost sure that the diodes are just simple (silicium) diodes and not zeners and I will have to look back into my notes if there are any photos or notes of the project left to answer your capacitor, resistor question. I will try to answer them lateron. Maybe this even helps to find out what exactly might still be wrong with my friend's device.

    • Albert van Bemmelen

      October 24, 2017 at 4:31 am

      Thanks for your terrific contribution to find out how to calibrate the Exachron Taco! You are a real pro and I was astonished that you took the time to almost build the entire Exachron circuit on a big experimenter's board (or maybe two?) and managed to calibrate it with the four mentioned 10K 74123 potentiometers. And your tip to use a High Precision 25MHz MHS-5200a 12-bit 200Ms dds signal generator frequency counter timer (with Arbitrary Waveform function) definitely will make a big difference and is THE solution to adjust the correct length (in milliSeconds) of the time pulses! Thanks to the integrated precision Timer Counter in the MHS-2500A (Be aware that there exist an older model and an upgraded newer real 12-bit version). It probably is the easiest way to do, because it is something that was very difficult to check and adjust on my scopes. If my Pro watchmaker friend brings his old device a second time I hope to be able to make a decent calibration procedure manual for it, and maybe a third Final Exachron article that will be of great help to other Exachron owners too. It is not often that we find someone who went into such great length to contribute to a difficult problem. Again thanks Taco. I'll let you know how it goes if I know more!


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