Author Topic: EEVblog #710 - Intercom System Repair  (Read 22058 times)

0 Members and 1 Guest are viewing this topic.

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
EEVblog #710 - Intercom System Repair
« on: January 31, 2015, 09:15:23 pm »
Join Dave step-by-step as he attempts to find the problem with a non-booting Aiphone GF NS building intercom system. Will a reset chip make a monkey out of him?
And as always, a trap for young players is explained.

Brochure:
http://www.zsing.com/download/aiphone/gf-k.pdf
Install Manual:
http://www.aiphone.net.au/media/GFNS_Install.pdf
Setup Manual: http://www.aiphone.com/home/assets/Uploads/downloads/documents/products/instructions/GF-NS%20Progr%20Instr.pdf

Datasheets:
Mitsubishi M16C: http://pdf.datasheetcatalog.com/datasheet/MitsubishiElectricCorporation/mXuuxwr.pdf
24LC128 EEPROM: http://ww1.microchip.com/downloads/en/DeviceDoc/21191s.pdf
RS232 driver: http://www.ti.com/lit/ds/symlink/ds14c232.pdf

 

Offline max_torque

  • Super Contributor
  • ***
  • Posts: 1169
  • Country: gb
    • bitdynamics
Re: EEVblog #710 - Intercom System Repair
« Reply #1 on: January 31, 2015, 10:13:55 pm »
Are you SURE the original 10K resistor is not to GROUND?

i.e. 10k keeps RESET low,  reset uC drives it high when 5v rail is above brown out voltage!

Hence, removed reset uC = RESET (cause 10k pulls reset low) and 100R mutimeter to 5v brings line high (Vreset is 5v * 9.9/10)

You swapped resistor to 1K, 100ohm still just enough to get out of reset (Vreset is 5V * 900/1000)

Then fitted 270ohm, now, of course your 100Ohm "mutimeter shunt" isn't enough, and you need 30Ohms!!


Check this!!!

PS, units current has gone up because you have a 270Ohm short to ground!
« Last Edit: January 31, 2015, 10:16:53 pm by max_torque »
 

Offline mux

  • Regular Contributor
  • *
  • Posts: 119
Re: EEVblog #710 - Intercom System Repair
« Reply #2 on: January 31, 2015, 10:24:57 pm »
As annotated in the video, this sounds like classic SCR latchup, especially with such a messy 5V rail. Older type chips (and I really mean type, this chip is probably made on absolutely ancient .35 or .25 straight CMOS) were very susceptible to damaging SCR latchup.

A great tool to see if this happens is getting out the thermal camera!

Anyway, SCR latchup is pretty much unfixable. The chip is functionally dead.
 

Offline DanielS

  • Frequent Contributor
  • **
  • Posts: 798
Re: EEVblog #710 - Intercom System Repair
« Reply #3 on: January 31, 2015, 10:30:14 pm »
Does the chip over-drive the LEDs while in reset state or only after coming out of it?

I'm thinking the voltage lock-out chip may have been there because the MCU had power-on reset issues and needed a cleaner reset source than an RC delay.

Since the MCU's reset pin was not drawing 90mA after getting lifted, I wonder where that current was going. Something else must be connected to that reset trace.
 

Offline Pentium100

  • Frequent Contributor
  • **
  • Posts: 258
  • Country: lt
Re: EEVblog #710 - Intercom System Repair
« Reply #4 on: January 31, 2015, 10:43:40 pm »
Since the MCU's reset pin was not drawing 90mA after getting lifted, I wonder where that current was going. Something else must be connected to that reset trace.

Also, that something should be getting pretty warm. Same for the 200mA input current - something should be heating up.

Anyway, it seems that the reset pin needs a delay or a clean signal, the way I would do this would be to use a bigger cap (to slow it down) and a Schmitt trigger.
 

Offline willis

  • Newbie
  • Posts: 2
Re: EEVblog #710 - Intercom System Repair
« Reply #5 on: January 31, 2015, 11:13:32 pm »
After one early attempt the entire debug was done with dip switch one set to the ON position. Can you tell if this is just digitally sampled to reset ID codes or is it also related to the reset circuit? Are you sure this was not holding the processor in reset and just being fought with the 30 ohm resistor (hence power consumption)?

I would put everything back and check that dip switch is not faulty!
« Last Edit: January 31, 2015, 11:41:50 pm by willis »
 

Offline max_torque

  • Super Contributor
  • ***
  • Posts: 1169
  • Country: gb
    • bitdynamics
Re: EEVblog #710 - Intercom System Repair
« Reply #6 on: January 31, 2015, 11:36:24 pm »
Dave measured the RESET line at 12K to ground iirc
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
Re: EEVblog #710 - Intercom System Repair
« Reply #7 on: February 01, 2015, 12:14:22 am »
Are you SURE the original 10K resistor is not to GROUND?

Yes, I'm sure. You can see the traces, and I measured it.

Quote
PS, units current has gone up because you have a 270Ohm short to ground!

No, the current goes up all on it's own!
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
Re: EEVblog #710 - Intercom System Repair
« Reply #8 on: February 01, 2015, 12:14:56 am »
Anyway, SCR latchup is pretty much unfixable. The chip is functionally dead.

Yep, that's what I suspect.
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
Re: EEVblog #710 - Intercom System Repair
« Reply #9 on: February 01, 2015, 12:17:27 am »
For some reason this one is the worst one so far for video quality  :-(

Oh FFS, are you still on about this?
You are comparing video quality on what youtube is producing using whatever codec it want's this week, on your connection and machine which as has been demonstrated has an issue that is degrading quality.
The problem is not the video quality I am uploading!
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
Re: EEVblog #710 - Intercom System Repair
« Reply #10 on: February 01, 2015, 12:19:09 am »
After one early attempt the entire debug was done with dip switch one set to the ON position. Can you tell if this is just digitally sampled to reset ID codes or is it also related to the reset circuit? Are you sure this was not holding the processor in reset and just being fought with the 30 ohm resistor (hence power consumption)?

Yes, I am sure. If another person comments on this on Youtube I'll scream!
The DIP switch goes to an I/O pin, nothing to with the reset line at all, it's a software function.
And yes, I have tested with the DIp switch off, makes absolutely no difference to anything.
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
Re: EEVblog #710 - Intercom System Repair
« Reply #11 on: February 01, 2015, 12:22:20 am »
Does the chip over-drive the LEDs while in reset state or only after coming out of it?
I'm thinking the voltage lock-out chip may have been there because the MCU had power-on reset issues and needed a cleaner reset source than an RC delay.

Yes, but that's not the real issue, the real issue is the excess current.
If there was no excess current issue then I would have solved the reset problem one way or another.

Quote
Since the MCU's reset pin was not drawing 90mA after getting lifted, I wonder where that current was going. Something else must be connected to that reset trace.

It's most likely SCR latchup, the chip has been damaged.
 

Offline cmpxchg

  • Contributor
  • Posts: 12
  • Country: de
Re: EEVblog #710 - Intercom System Repair
« Reply #12 on: February 01, 2015, 12:27:05 am »
After one early attempt the entire debug was done with dip switch one set to the ON position. Can you tell if this is just digitally sampled to reset ID codes or is it also related to the reset circuit? Are you sure this was not holding the processor in reset and just being fought with the 30 ohm resistor (hence power consumption)?

I would put everything back and check that dip switch is not faulty!

It's a DIP switch to erase the configuration, that has nothing to do with the reset line of a processor. Otherwise this would be a design where every powerup has the configuration erased.
 

Offline willis

  • Newbie
  • Posts: 2
Re: EEVblog #710 - Intercom System Repair
« Reply #13 on: February 01, 2015, 12:31:39 am »
Ahh - armchair remote debugging - gotta love it!
 

Offline Agent24

  • Regular Contributor
  • *
  • Posts: 103
  • Country: nz
Re: EEVblog #710 - Intercom System Repair
« Reply #14 on: February 01, 2015, 01:42:48 am »
It's most likely SCR latchup, the chip has been damaged.

So, the 5v rail capacitor went out, too much ripple caused a latch-up issue that wrecked the chip? Even though you fixed the capacitor problem, the chip is still dead... ?

POR IC and circuit was probably fine... ?
 

Offline barnacle2k

  • Regular Contributor
  • *
  • Posts: 53
  • Country: de
Re: EEVblog #710 - Intercom System Repair
« Reply #15 on: February 01, 2015, 02:50:35 am »
#1:
Couldn't the not properly reset micro result in the excess current draw? - since it doesn't happen all the time.
Maybe if test that reset chip still works, it might. (just whack 5V on it and check the output)

#2:
power up ramp being too slow due to current limit causing a brown out and latch-up behavior.
I know one can cause latch ups by say putting current into an IO pin of a Micro before the supply rail of said micro is up.
Its powered by 24V, so there might be some pin that is connected to 24V through a voltage divider to an IO and the 5V rail now takes too long to get up.
 

Offline Co6aka

  • Supporter
  • ****
  • Posts: 255
  • Country: us
Re: EEVblog #710 - Intercom System Repair
« Reply #16 on: February 01, 2015, 03:55:09 am »
Looks like only the two center (yellow?) LEDs go "hi-brite," is that right? (If so, why only those two?) How are the LED driven; what's the current path? I'd expect a current-limit resistor and LED in series, with a uC pin pulling it low to light it, so how could it possibly go "hi-brite?"Anyway... First thought that's popped into my sleepy mind is a "ground fault" somewhere around the uC; probe voltage between supply ground and ground traces/points on the PCB . But I'm also curious about the 5.2V on the 5V rail; have you taken a look at the Vreg circuit; what does it look like it should be; maybe 5.2V is a symptom of something, even if it's still in spec; maybe the uC doesn't like 5.2V. Also, when the LEDs are "hi-brite" what is the 5V rail at?

 :=\
Co6aka says, "BARK! and you have no idea how humans will respond."
 

Offline nitro2k01

  • Frequent Contributor
  • **
  • Posts: 844
  • Country: 00
Re: EEVblog #710 - Intercom System Repair
« Reply #17 on: February 01, 2015, 04:12:11 am »
I'd expect a current-limit resistor and LED in series, with a uC pin pulling it low to light it, so how could it possibly go "hi-brite?"
Maybe a PWM with a higher current to increase the apparent brightness, that sometimes fails and goes 100% on when the CPU crashes.
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Offline djdelorie

  • Newbie
  • Posts: 1
Re: EEVblog #710 - Intercom System Repair
« Reply #18 on: February 01, 2015, 04:57:34 am »
The MCU is a16-bit  M16C/62, now owned by Renesas, and they have lots of info on that series.  They can be factory programmed (hence the laser engraving) and, at the customer's choice, made so that the firmware is neither readable nor changable.  Note: you can still buy them at Digikey, and they're supported by GCC.
 

Offline Stonent

  • Super Contributor
  • ***
  • Posts: 3824
  • Country: us
Re: EEVblog #710 - Intercom System Repair
« Reply #19 on: February 01, 2015, 06:06:12 am »
I found something on latchup here:
http://documentation.renesas.com/doc/products/mpumcu/rej09b0167_m16c62ano.pdf

Quote
When different power supplied to the system as shown in figure 1, and input voltage of unused
dedicated input pin is larger than voltage of VCC pin, do not connect dedicated input pin and
power supply directly. Connect to VCC via resistor (approximately 1kohm) as shown in figure
2. This note is also applicable when VINPUT exceeds VCC during power-up.
3. Cause
When dedicated input pin voltage is larger than VCC pin voltage, latch up occurs.

So it will latch up if VINPUT exceeds VCC during power up, which might explain why it's intermittent. Maybe a voltage spike of some kind, perhaps if the regulator kicks a bit too high during start up and there's somehow a lower impedance path to a VINPUT pin so VINPUT exceeds VCC.    Maybe singleshot the 5v line and input pins during a non-boot mode and a boot mode

From another document: http://www.cucat.org/general_accessibility/accessibility/colour-sensor/M16c%20Tools/M16Umanual.pdf

On P. 179 it mentions that noise can cause a latchup and to put in a .1uF cap between VSS and VCC.  It also mentions using a 5K resistor on VPP, though I'm not sure if that matters after it has been programmed as it is an OTP.

Since you said it may work one out of five times,  maybe set up a small 555 timer chip circuit that keeps pulsing the reset line until there is some sign of life in the processor. Just crazy idea.

If you do ever get this thing working, you should definitely read the EEPROM and hex edit in a new name in there like "Fixed by Dave Jones"

EDIT: Ok I started watching the EEVBlog scr latchup video and you've basically explained that overdriving an input is a common cause of SCR latchup, so I may not have said anything up there that helped.  But still curious of that's somehow happening.
« Last Edit: February 01, 2015, 06:30:41 am by Stonent »
The larger the government, the smaller the citizen.
 

Offline Pentium100

  • Frequent Contributor
  • **
  • Posts: 258
  • Country: lt
Re: EEVblog #710 - Intercom System Repair
« Reply #20 on: February 01, 2015, 06:17:32 am »
I'd expect a current-limit resistor and LED in series, with a uC pin pulling it low to light it, so how could it possibly go "hi-brite?"
Maybe a PWM with a higher current to increase the apparent brightness, that sometimes fails and goes 100% on when the CPU crashes.

Except that most of the time the CPU is in reset mode (until Dave found that it was in reset mode) and the LEDs light up normally. I doubt that the MCU in reset mode was outputting any kind of PWM...
 

Offline TheRevva

  • Regular Contributor
  • *
  • Posts: 87
Re: EEVblog #710 - Intercom System Repair
« Reply #21 on: February 01, 2015, 07:49:21 am »
Personally, I suspect that Stoneent might be on to something...
The actual SCR latchup may well be caused by the residual charge left on the !RESET capacitor in the RC reset circuit.  This can easily be proven by simply connecting a diode (preferably a 0.3V Schottky) from the RC network to the 5V rail so that the reset cap will quickly discharge into the 5V rail and thus eliminate the potential latchup if the system is re-powered too soon.
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
Re: EEVblog #710 - Intercom System Repair
« Reply #22 on: February 01, 2015, 09:28:13 am »
Personally, I suspect that Stoneent might be on to something...
The actual SCR latchup may well be caused by the residual charge left on the !RESET capacitor in the RC reset circuit.

I recall it doing this without a cap at one point.
 

Online EEVblog

  • Administrator
  • *****
  • Posts: 32171
  • Country: au
    • EEVblog
Re: EEVblog #710 - Intercom System Repair
« Reply #23 on: February 01, 2015, 11:09:22 am »
Previously you were uploading at 25 fps and YouTube is fine with that, it doesn't re-encode it for the 1080p stream.

Youtube always re-encodes video!

Quote
If you are not interested in improving it that's of course fine, no need to bite my head off.

Sorry, but I've just seen this multiple times from you now, it had gotten rather monotonous.
I proved in the last conversation about this that there is no loss of detail in the 50fps video. So any perceived quality must be at your end in some way shape or form. And someone alluded that there are different ways youtube delivers it depending upon your configuration.

Quote
I thought you were genuinely interested in the subject since you made a number of comparison videos and asked for comments on the subject.

I am, but I think it's done and dusted. I've proven there is no loss of detail in the 50fps video as you claimed.
You keep claiming it's horrible, worst ever, or whatever. Why is noone else complaining? I can only presume it's something at your end.
 

Offline Muttley Snickers

  • Supporter
  • ****
  • Posts: 2116
  • Country: au
Re: EEVblog #710 - Intercom System Repair
« Reply #24 on: February 01, 2015, 11:16:36 am »
I thought it was rather funny when Dave called bullshit in regards to the installation company indicating that the unit has passed it's use by date.

Then he said that it should display their name if working and then I thought shit, hope it doesn't come back to life and shortly after it did.

  :bullshit:    :-DD    :scared:


Muttley
« Last Edit: February 28, 2016, 01:51:59 am by Muttley Snickers »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf