repair

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Ik heb een probleem (mede-)ontdekt met de RC522 rfid kaartlezer modules die op ebay / aliexpress en dergelijk aangeboden worden: ze lezen sommige kaarten niet. In deze blogpost wil ik uitleggen wat het probleem is, en hoe het opgelost kan worden, in de hoop dat mensen die hetzelfde probleem tegenkomen daar wat aan hebben.

rfidadvertentiefoto
RC522 module (foto uit advertentie van verkoper)

En omdat het anders een erg droog stuk tekst wordt, schrijf ik halverwege een stuk onzin over een zomerjurk. (Want dit is mijn blog, en niet mijn scriptie :P)

Kieskeurige kaartlezers

Laat ik bij het begin beginnen:
Bij MakerSpace Leiden worden deze RFID-RC522 kaartlezers gebruikt om toegangskaarten te lezen in het deursysteem en bij de zwaardere machines waarvoor training nodig is. Deelnemers van de MakerSpace kunnen daarbij hun OV-chipkaart (Of een andere 13,56Mhz RFID kaart die ze al hebben) gebruiken. Ze kunnen dan deze kaart gebruiken om toegang te krijgen tot de MakerSpace, of om b.v.  (na relevante training en goedkeuring) de cirkelzaagtafel in te kunnen schakelen.

Het probleem dat daarbij boven water kwam, is dat sommige RC522 kaartlezers sommige kaarten niet lezen. (Wat voor de (on)nodige frustratie zorgt als het toevallig je eigen kaart is bij de lezer van de deur waar je door wilt… Of het is de kaartlezer van het project waar je mee bezig bent…)

I did not know this was possible.

The hollow core motors of a Cheerson CX-10 can actually be opened, and a new wire can be soldered to the brushes when the original one broke of.

IMG_7643_holowcoremotor

This started as a challenge, me stating it was impossible to open these motors without damaging them beyond repair and my father insisting it is possible. So don’t ask me how to open them, I still think it is impossible. I only soldered the wire and closed it again. (Make a hole for the new wire by removing all residue of the old wire, remove part of the glue over the brushes, tin the new wire, then very quickly solder it, as to not overheat the plastic. Carefully press the back back on the motor again, making sure the brushes don’t bend in ways they are not supposed to)

IMG_7642_holowcoremotor

And now my CX-10 is flying again. With a battery that’s slightly to large, a half-painted side to help orientation (Does not actually help), and rubber bands instead of screws holding it together. Also, half its props are pink because those where the last ones I had around. So its almost as ugly as possible, but it’s flying again. And that’s kind of crazy.

cx10

(And yes, I bought new motors just in case, and I still think this repair should be above my fine motor skills (pun intended) as everything is way to tiny and way to melt-able, but apparently its less impossible then I thought.)

Because there is no big news yet, some short updates.

– Claude Schwarz pointed me to the Yahoo user group “Lecroy Owners group”, they have design files for a HHZ406 replacement. (Made by Dieter Frieauff). So maybe the ext. trigger input can be repaired as well.

– A service manual for this ‘scope (And others) can be found there as well, or alternatively here: http://www.ko4bb.com/manuals/index.php?dir=LeCroy (Or on elektrotanya.com – but that site is full of ads)

– NoTMS was caused by a missing “Vct”, I accidentally scratched trough this trace while placing the bottom cover. Took quite some time to find, then just a little wire to fix.

9450_scratchedVCT 9450_scratchedVCTFixed

– Thanks to Claude Schwarz (Again), I now have a third ADC card. So I now have spareparts, and if I get one of the 2 broken cards working again, a working 2ch 350Mhz / 400Ms/s (10Gs/s)  DSO. (Or rather: the Leidse Makerspace then has a 2ch 350Mhz DSO). The 3 ADC cards will hereafter be named “9450_3A Claude”, “9450_3A LMS-Broken” and “9450_3A LMS-Working”. (order shown in the picture, ltr: broken, Claude, working )

9450_3A ADCs

– I measured the power supplies on “9450_3A LMS-broken”. All are present. (-5V, -12V, 5V and +12V). Next up: reference voltages and tracing the signal path.

– Some more pictures:

lecroy_patchedOn some of the ADC boards, a 5V regulator is placed where others have just a cap.

lecroy_patched_2

This is another original patch (-5V regulator), both on “9450_3A LMS broken”. This board has no LeCroy repair stickers (shown below), but those patches were there when I got the ‘scope so I assume they are original.

Bot these 2 regulators and the -12V and 12V ones have the correct output voltages.

lecroy_repair

Lecroy Repair stickers on the timebase board. (This board is working fine) There are more of those stickers in the scope on other boards.

9450_errorlog

And the last one for today: The calibration error log. Chan2 has “9450_3A Claude” in this picture, but “9450_3A LMS broken” gives similar results. If I exchange the cards between the channels, ch1 gets the errors and ch2 is error-free. (The error-free channel has “9450_3A LMS working” in both cases).

‘ll keep you posted!

EDIT 2-7-2014:
“Next up: reference voltages and tracing the signal path.”

Measured on HMS403, seems to be OK. Also none of the ADC’s have stuck bits (did not log what bit connected to what line of the LA, but with no input all are 0, as long as there is no selftest / calibration running.)

Please note if you connect a logic analyser to these circuits they are negative logic (“1” is – 5V, “0” = 0V). As the 0V is connected to chassis ground, and your LA’s ground might also be (through the powersuply’s both connected to earth ground), use caution!

The scope does not do a memory test on boot up. I carefully removed one of the RAM IC’s to test this, and the scope does still show “ADC/TMS state working”.

So there might be something wrong with the memory. Fortunately this is normal TTL logic again.

EDIT 8-Aug-2014:
On slower sample rates this scope only uses 1 of its 4 ADC’s (per channel). On slower sample rates, the problem stays, 1 out of 4 points on the display (Maybe 1 out of 4 samples?) is out of line. So it’s not 1 of the 4 adc’s that’s broken (because it only uses one at that sample rate), but something in the memory or further in the data pad. The memory is also divided in 4 parts/banks, so it could just be… But for now I’m going to work on other projects for a while.

Please comment if you have any questions or suggestions!