Author Topic: EEVblog #710 - Intercom System Repair  (Read 21912 times)

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Offline ryanmoore

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Re: EEVblog #710 - Intercom System Repair
« Reply #25 on: February 01, 2015, 11:30:42 am »
The installation company is almost certainly full of shit when they say they can't get a replacement. 5 minutes on Google turned up a dozen places selling that module for about US$200.
 

Offline Muttley Snickers

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Re: EEVblog #710 - Intercom System Repair
« Reply #26 on: February 01, 2015, 11:36:30 am »
The installation company is almost certainly full of shit when they say they can't get a replacement. 5 minutes on Google turned up a dozen places selling that module for about US$200.

Agreed.

Muttley
 

Offline max_torque

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Re: EEVblog #710 - Intercom System Repair
« Reply #27 on: February 01, 2015, 12:33:11 pm »
Sorry, but for me, something still doesn't add up here!

If it were some issue with the micro, i don't think it would have changed by Dave poking round on the rest of the circuit (of course it could have done, i just think it unlikely)

Looking at pin outs for various SOT23-5 reset controllers, pin 4, the one with the 10K resistor and capacitor RC filter hanging off it, is quite often a manual reset (MR) or WatchDog Input (WDI) and the "RESET" pin is pin 1, over on the other corner of the device.

In this case, the 10K to the 5v rail would be forming an extra timedelay for the reset controller to be coming out of RESET after power up (we can assume it is the MR option not the WDI as that requires the pin to be toggled by the micro to kick the dog)

Possible??
 

Offline bktemp

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Re: EEVblog #710 - Intercom System Repair
« Reply #28 on: February 01, 2015, 01:28:35 pm »
Some points make no sense.
Using a RC filter at the output of a reset controller is unusal, but there are reset controllers with open collector outputs: The resistor is the pullup and the capacitor only serves for emi suppression.
But I have never seen a latchup of an input only pin without an increase in supply current. If a pin dies due to overvoltage it typically has a low impedance to gnd or vcc even without supply voltage. But this is not the case here.
The other strange thing is the higher LED brightness in latch-up state: The M16C series has week output drivers. It can not drive LEDs directly (at least not bright enough for use in daylight conditions). My guess would be a simple transistor to drive the LEDs, but then it would be impossible to increase the brightness.

A failed power supply because of a dead cap sounds plausible. It may have caused further faults due to spikes at the output voltage.
But there are a few things that are unusal:
The whole unit is powered by 24V dc. It only draws 70mA. Thats 1.7W. The power regulator has to dissipate max. 1.3W if everything runs at 5V. The area around the 5V regulator seems too small for this power level, therefore it does probably does not provide all the power, otherwise it would run quite hot. The board does not seem getting hot, at least I could not see any discolouration around the regulator. I would have expect a switching power supply, because 24V->5V gives otherwise a bad efficiency and those yellow/green backlights often take 50-200mA to get a decent brightness.
Why did the cap fail? There is basically no ripple on a linear regulated dc supply, therefore the cap is not stressed at all. Or is there a switching regulator hidden somewhere? The inductor looks like a common mode choke, but a switching regulator with failed caps could explain some of the problems.
 

Offline Solberg

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Re: EEVblog #710 - Intercom System Repair
« Reply #29 on: February 01, 2015, 01:56:33 pm »
I found the compatibility chart between the GF-GH-GT series.

http://www.aiphone.com/home/assets/GF-GH-GT-Compatibility-Chart.pdf

The compatibility looks pretty poor between the GF and the GT series.
 

Offline max666

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Re: EEVblog #710 - Intercom System Repair
« Reply #30 on: February 01, 2015, 02:06:58 pm »
If it latches up, does that mean the 5V rail would drop down to one diode drop (0.7V?)?
And if so, then the micro can't be driving the LED's directly, because then they wouldn't go bright on latchup, or am I missing something?

Also if a chip goes latchup, does that inevitably mean it's dead? Because if it works every 5th time or so, is that dead then?
 

Offline Muttley Snickers

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Re: EEVblog #710 - Intercom System Repair
« Reply #31 on: February 01, 2015, 02:07:55 pm »
I expect that Dave has already taken this into account but these door stations are not stand alone, they are wired back to a GFBC ( Bus Controller ) and room stations and relays for the gate or door strike are fed off the GFBC.

This unit may get a start/ poll pulse from the GFBC and could simply be offline through other factors, cabling etc, although this does not shed any light on the current draw issue.

Another door station on site would soon tell by swapping them around, we just don't know enough, did the company try this, I wonder.

Just a thought.    :-+


Muttley
« Last Edit: February 28, 2016, 01:50:28 am by Muttley Snickers »
 

Offline max666

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Re: EEVblog #710 - Intercom System Repair
« Reply #32 on: February 01, 2015, 02:26:00 pm »
Ohh I forgot! I love watching repair videos, even if they don't have a happy end, Dave.
Nice watching you brachiate through a circuit that isn't working. I think you can learn a lot by figuring out why something is not working.
 

Offline masshuu

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Re: EEVblog #710 - Intercom System Repair
« Reply #33 on: February 01, 2015, 06:54:46 pm »

So I am not the most knowledgeable with hardware but can somewhat understand the basics of what he talks about. Is there any reason to assume that the over current is not tied to an unrelated issue? An intermittent failure with a cap or other component causing a short somewhere? I suppose you would need to schematics to see where a short between 5v lines would cause that.

Or would be due to the failure of the reset mechanism in the chip causing the excess current draw.


PS Dave: First post! I've been watching your videos for like 3? years now and I love them. Feel like I learn quite a bit. Still don't understand it enough to read simple circuits and draw a graph like you did in the #708. I did buy a Hako 888D after remembering your recommendation(My $5 120v pen died after 5 years) and its night and day. I never realized solder work could be quick and easy like that.  Plz don't stop making videos, Even when your 95 years old on life support in a hospital. Well maybe...

PPS Dave: Video quality is fine but I'm an uneducated brute. Take that as you will.
 

Offline Richard Crowley

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Re: EEVblog #710 - Intercom System Repair
« Reply #34 on: February 01, 2015, 07:08:11 pm »
You can almost make a case for just doing away with that calling panel altogether.  Since practically everyone (including children) have cell phones, intercom systems like that are nearly extinct. Of course, you still need a way for the tenants to open the door when they get a call (cell or intercom) from a visitor.  But that could be as simple as a contact-closure.  And tenant entrance could be controlled with an RFID card, etc.
 

Offline Fungus

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Re: EEVblog #710 - Intercom System Repair
« Reply #35 on: February 01, 2015, 07:34:06 pm »
You can almost make a case for just doing away with that calling panel altogether.  Since practically everyone (including children) have cell phones, intercom systems like that are nearly extinct.

What about delivery guys, etc?

 

Offline Richard Crowley

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Re: EEVblog #710 - Intercom System Repair
« Reply #36 on: February 01, 2015, 07:38:14 pm »
Delivery people know who they are delivering to (name and phone number). 
If they DON'T know, then they might be a terrorist delivering a bomb and you probably shouldn't let them in.

And regular trades people would probably be issued an RFID card to open the gate for themselves.
 

Offline elgonzo

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Re: EEVblog #710 - Intercom System Repair
« Reply #37 on: February 01, 2015, 07:43:03 pm »
What about delivery guys, etc?

Well, if they don't have a cellphone, they can still shout. Or throw rocks at the windows...  :-DD

Delivery people know who they are delivering to (name and phone number). 
If they DON'T know, then they might be a terrorist delivering a bomb and you probably shouldn't let them in.

If you, your spouse and your children each have a cellphone, which one should the delivery guy call? Yours? What if you are not at home, but your spouse is? This is getting awfully complicated quickly...
« Last Edit: February 01, 2015, 08:16:05 pm by elgonzo »
 

Offline NickS

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Re: EEVblog #710 - Intercom System Repair
« Reply #38 on: February 01, 2015, 08:13:41 pm »
I'll stop trying to be helpful.
Off topic, but did you know your signature is wrong? It is kibibyte which is 1024.
https://en.wikipedia.org/wiki/Kibibyte
 

Offline Richard Crowley

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Re: EEVblog #710 - Intercom System Repair
« Reply #39 on: February 01, 2015, 08:17:03 pm »
If you, your spouse and your children each have a cellphone, which one should the delivery guy call? Yours? What if you are not at home, but your wife is? This is getting awfully complicated quickly...
I suspect most of us live in places where the delivery person can just knock on the front door or ring the door-bell.
If nobody answers at a business phone number, then nobody is there to receive the delivery anyway, so what's the issue?
 

Offline Stonent

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Re: EEVblog #710 - Intercom System Repair
« Reply #40 on: February 01, 2015, 08:21:18 pm »
The installation company is almost certainly full of shit when they say they can't get a replacement. 5 minutes on Google turned up a dozen places selling that module for about US$200.

Agreed.

Muttley

If they go that route you wouldn't even need it programmed by an installer. The micro is OTP probably for AIPhone. The dip eeprom would have thw install specific data in it and could be copied and flashed or swappes into the new unit.
The larger the government, the smaller the citizen.
 

Offline firewalker

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Re: EEVblog #710 - Intercom System Repair
« Reply #41 on: February 01, 2015, 08:31:38 pm »
If you, your spouse and your children each have a cellphone, which one should the delivery guy call? Yours? What if you are not at home, but your wife is? This is getting awfully complicated quickly...
I suspect most of us live in places where the delivery person can just knock on the front door or ring the door-bell.
If nobody answers at a business phone number, then nobody is there to receive the delivery anyway, so what's the issue?

This is the reason those system are found on apartment buildings without a doorman. You can't just open the door to a ring, without knowing hwo is ringing the door bell. Even if you are expecting the pizza guy.
Become a realist, stay a dreamer.

 

Offline Fungus

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Re: EEVblog #710 - Intercom System Repair
« Reply #42 on: February 01, 2015, 08:39:55 pm »
I suspect most of us live in places where the delivery person can just knock on the front door or ring the door-bell.

Nope.
 

Offline Flump

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Re: EEVblog #710 - Intercom System Repair
« Reply #43 on: February 01, 2015, 11:56:08 pm »
Great video, I was glued to it all the way through.
And you are right Dave it's not so much the final result but the process you follow.

I want to blow some shit up and send it to you for more repair videos  :scared:
 

Offline masshuu

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Re: EEVblog #710 - Intercom System Repair
« Reply #44 on: February 02, 2015, 12:12:50 am »
So I am not the most knowledgeable with hardware but can somewhat understand the basics of what he talks about. Is there any reason to assume that the over current is not tied to an unrelated issue? An intermittent failure with a cap or other component causing a short somewhere? I suppose you would need to schematics to see where a short between 5v lines would cause that.

That's actually a really good point. Although it does appear to be a classic latch-up, sometimes you can get things like half-on transistors or floating pins that cause high currents when the micro isn't running properly. Sometimes the firmware engineers don't properly account for the start-up sequence and don't notice the problem because the micro is running a few milliseconds after everything powers up and it comes out of reset.

Yay I said something smart.
 

Offline EEVblog

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Re: EEVblog #710 - Intercom System Repair
« Reply #45 on: February 02, 2015, 12:46:11 am »
Is there any reason to assume that the over current is not tied to an unrelated issue? An intermittent failure with a cap or other component causing a short somewhere? I suppose you would need to schematics to see where a short between 5v lines would cause that.
Or would be due to the failure of the reset mechanism in the chip causing the excess current draw.

The overcurrent could very well be unreleated to the reset issue, but it's most likely they were both caused by the fault.
The most likely scenario we have evidence for so far is that something took out some aspect of the reset circuit. Might have been the failed 5V rail cap failing causing over voltage.
SCR latchup is a strong possibility. Once again, might not be, but you won't know unless you spend more time tracing the circuit and troubleshooting. Could be many many hours of dicking around, only to eventually come to the conclusion that it probably is SCR latchup. or you could hit a winner, but you don't know unless you put the hours into it.
It's unlikely you'd get another programmed chip, and you wouldn't risk putting back into a service a device with potential SCR latchup issues.
This one is just way too big of gamble.

And some people have complained that I didn't fix it and I wasn't creative enough etc.
At some point in cases like this it comes down to how bad you want/need to repair it.
Well, for me, this is not my fight, I don't care enough to trace it further, and I have a strong hunch it's SCR latchup. That's good enough for me to call it quits on this one knowing the odds of success from this point on.
I'm very confident I'm not going to crack it with another 30 minutes of work.
It is highly likely this thing is screwed and I will have wasted a lot of time for nothing.
 

Offline EEVblog

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Re: EEVblog #710 - Intercom System Repair
« Reply #46 on: February 02, 2015, 12:46:57 am »
Great video Dave, not sure if you saw my YouTube comment but have you tried to contact AIPHONE (not the contractor) to find out if the new models are interchangeable.

Someone on twitter pointed out their product page that very specifically states the GT is not backward compatible with the GF.
 

Offline parbro

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Re: EEVblog #710 - Intercom System Repair
« Reply #47 on: February 02, 2015, 12:50:07 am »
I did not understand how connecting the current meter acting as 100 ohm resistor to the reset line would pull the line high. Doesn't that reset chip work by pulling the reset line to ground? Anyone catch how that was supposed to work?
 

Offline EEVblog

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Re: EEVblog #710 - Intercom System Repair
« Reply #48 on: February 02, 2015, 12:54:59 am »
I did not understand how connecting the current meter acting as 100 ohm resistor to the reset line would pull the line high. Doesn't that reset chip work by pulling the reset line to ground? Anyone catch how that was supposed to work?

i was putting the 100ohm across the 10K pullup.
 

Offline gnif

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Re: EEVblog #710 - Intercom System Repair
« Reply #49 on: February 02, 2015, 05:27:11 am »
Could it be that the traces that power the MCU are faulty in some way and the MCU is actually getting powered via the RESET pin?
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