0

Locked LEDs lit on
Moderators: altitude, adafruit_support_bill, adafruit, phono, hamburgers

Please be positive and constructive with your questions and comments.

Locked LEDs lit on

by diplowave on Mon Mar 05, 2018 5:29 am

I've a problem, when power on, all the leds come on and stay locked. It's random sometimes power on, no leds do light up ... And x0x no run...

I've seen this on other x0xb0x's, usually it's dead quartz or dead microcontroller. I replaced the quartz and tried with another microcontroller, no change leds always blocked lit ... I tried with another board I / O, same problem.

On power up all the x0x do that, but after a few seconds the leds go off and we end up in play mode. What is LED lighting, when power on? Is it a reset? And what microcontroller pin manages that?


Image

diplowave
 
Posts: 95
Joined: Wed Aug 21, 2013 9:49 am
Location: France

Re: Locked LEDs lit on

by antto on Mon Mar 05, 2018 8:53 am

the LEDs are "driven" by "Serial-In/Parallel-Out" (SIPO) shift registers (74xx595)
each of those chips has 8 output pins, and 8 LEDs are wired to them, so 5 SIPOs -> 40 LEDs

initially, they don't have a "state", think of this as 8bits of SRAM, on power on - the states can vary, that's why SRAM is initially cleared shortly after power-on/reset typically
the SIPOs have a different mechanism for dealing with that - they have an OutputEnable(OE) input, which can be used to keep the 8 outputs in high-impedance state (sort of like almost disconnected) initially, untill an actual microcontroller wakes up, shifts proper data into them, and then enables their outputs

unfortunately, the OEs of the SIPOs are hard-wired in the PCB to "enabled" instead of going to a dedicated pin on the atmega (maybe there wasn't a spare pin for that), so this is not possible

now, you get those quasi-random LEDs when there's nothing to "shift" data into the SIPOs
shifting sane data into the SIPOs on the atmega162 only happens in the firmware, shortly after it starts (but it doesn't happen in the bootloader)
on the atmega2561, the bootloader does it

the actual LED states that you get (which i called quasi-random) can vary because the serial inputs on the SIPOs have a very big impedance since they are digital inputs, and while the atmega is in "reset" condition - its GPIO pins are also in high-impedance state, essentially "floating", and thus it's relatively easy for the voltage to vary there and sometimes happen to register as logic 1 or 0

antto
 
Posts: 1618
Joined: Thu Apr 15, 2010 3:21 pm
Location: 127.0.0.1

Re: Locked LEDs lit on

by diplowave on Tue Mar 06, 2018 6:21 am

Ok thank you, i understand a little better the operation of the leds and getting started. On the other hand, the x0x remains locked in reset state, it can't play, it remains frozen all leds lit; finally that i said it's random, other times it tests frozen with some leds lit or sometimes none is lit. Maybe the SRAM remains in cleared state when i power on the x0x?

diplowave
 
Posts: 95
Joined: Wed Aug 21, 2013 9:49 am
Location: France

Re: Locked LEDs lit on

by antto on Tue Mar 06, 2018 2:52 pm

i'm not fully sure i get the important symptoms, but here's some tips
- figure out if there is any sign that the firmware is there and works, at least from time to time (that's better than absolutely no sign of firmware, which cannot be cured with multimeters and soldering)
- if there is firmware, but it doesn't always boot - check the mcu's 5V supply (measure directly on the atmega pins) and also check the voltage on the RESET pin
- if the firmware works every time but there are just LED visualisation issues, then this could narrow the problem down significantly

antto
 
Posts: 1618
Joined: Thu Apr 15, 2010 3:21 pm
Location: 127.0.0.1

Re: Locked LEDs lit on

by diplowave on Thu Mar 08, 2018 5:42 am

Thank you for the explanations. In fact i have blown 2 microcontroler that remain blocked leds lit... I tried with another microcontroler that is new, the x0xb0x works, but not all the time, sometimes it stays leds frozen when powering on!
The only thing i did not replace is the 100n ceramic capacitors, can they be the cause of the problem? I do not think so but that's the only thing I did not replace... The x0xb0x also has a peculiarity, it has leds of all colors and therefore different kinds of resistances to obtain leds that all illuminate at the same instensity. Can this cause problems?
I have probed all IC have 5V, also the microcontroller, in 2 cases, x0xb0x working well or remaining frozen leds.

diplowave
 
Posts: 95
Joined: Wed Aug 21, 2013 9:49 am
Location: France

Re: Locked LEDs lit on

by redline7 on Sun Mar 11, 2018 6:51 am

This is basic stuff, but people sometimes forget about it.
Have you cleaned your board after soldering ?
You can soak the whole board in Isopropyl , brush it gently and then dry it properly.

I don't know your experience, but you should always start with the basic stuff :)

BR.

redline7
 
Posts: 4
Joined: Fri Mar 09, 2018 11:20 am

Re: Locked LEDs lit on

by diplowave on Tue Mar 13, 2018 5:28 am

Yes i had applied iso and cleaned with a toothbrush, then blown with compressed air. The annoying thing is that i used this x0xb0x for 1 year and suddenly it began to have problems at power up.

diplowave
 
Posts: 95
Joined: Wed Aug 21, 2013 9:49 am
Location: France

Re: Locked LEDs lit on

by diplowave on Sat Mar 24, 2018 11:29 am

I solved the problem, re-cleaning pcb with iso, and change most leds. It run. It's strange.

diplowave
 
Posts: 95
Joined: Wed Aug 21, 2013 9:49 am
Location: France

Re: Locked LEDs lit on

by diplowave on Wed Mar 28, 2018 8:46 am

I notice however that at power on, the leds remain in static state, longer than the other load x0xb0x. But x0x runs.
I wonder if the fact that there are several kinds of LEDs and several ohmic resistance values, will not be problematic. Especially for white LEDs there is resistance "strong enough", so as not to dazzle. Do you think Antto that this could create an erratic malfunction at power up? This means that the x0xb0x is working again and i have put more yellow LEDs and resistors of the same value, but it takes longer than normal to "load" at power up.

diplowave
 
Posts: 95
Joined: Wed Aug 21, 2013 9:49 am
Location: France

Re: Locked LEDs lit on

by antto on Wed Mar 28, 2018 12:56 pm

i don't know, what's the smallest value resistor you have for those LEDs?

if loading is *very* slow, you could try measuring the 5V voltage on the atmega with a multimeter
cheap multimeters usually sample the voltage slowly, but you might be able to still see the voltage slowly rising
otherwise probing the voltage with a scope would give you a better picture

also, the atmega's RESET pin is controlled externally by something like a "delayed start" circuit
this includes some logic element, and a capacitor, the idea is to keep the RESET signal logic-low for a given time untill the capacitor charges enough, then quickly and elegantly change the RESET signal to logic-high
the time is mostly determined by the capacitor value, and any current-limiting resistor onto it (so check if you've put wrong values there)
Note: this is probably not a very accurate explanation of how it works, so just check the schematic, IC1, C105, R200, and the two diodes there

it's possible that there's nothing wrong with the 5V supply, this delayed start circuit could be actually slowing down the start up of the atmega
you should be able to also measure the voltage on the RESET pin (or pin3 of IC1) with the multimeter.. 0V means "atmega is held frozen", 5V means "atmega should be working", a good transition from 0 to 5V causes the reset to happen (ram is cleared, program starts from the reset vector, etc..)

antto
 
Posts: 1618
Joined: Thu Apr 15, 2010 3:21 pm
Location: 127.0.0.1

Re: Locked LEDs lit on

by diplowave on Sun Apr 15, 2018 1:24 pm

Thanks, i repaired, but i admit, i did not really understand the cause of the failure. So after verifications with scope, had all the time 5V to atmega, even when the leds were blocked.
Without real certainty, i've replaced the 7805, the x0xb0x is run properly . It's ok.

diplowave
 
Posts: 95
Joined: Wed Aug 21, 2013 9:49 am
Location: France

Please be positive and constructive with your questions and comments.