EEVblog #710 - Intercom System Repair

Показать описание

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:
Install Manual:

Datasheets:

Support the EEVblog through Patreon!

EEVblog Amazon Store (Dave gets a cut):
Donations:
Projects:
Electronics Info Wiki:

Рекомендации по теме

Комментарии

i like the repair more then the normal tear down, where tear down is a blast thru and this is way easier to follow and more understandable also for people not really into electronics

mclaarson

I don't see a diode in the RC reset circuit you put in. The data sheet shows that there is one there to bypass the resistor to let the cap discharge quicker. When you turn it off and then on so quickly, could that be causing the latch up since the cap isn't discharged below 0.2v before the power is restored?

That reset chip (5-pin SOT package) must have been monitoring the power rail for stable power and with the bad cap in the power rail it never became stable and so it never brought the controller out of reset. I think if there were maybe a smaller cap and a diode across the resistor to discharge the cap quicker the thing would boot every time with no over-current.

The datasheet for the controller says the reset should be held below 0.8v for at least 20 cycles. At 4MHz that wouldn't be very long at all but no harm in having it low for longer. The cap just needs to get below 0.2v before power is restored after power off. A power on reset chip can hold the reset low for as long as 250ms, so I think this reset circuit is now the trouble here.

rsn

Please Dave, don't leave one of your most exciting episodes without a sequel!

cvt

Hi Dave. Thanks for the awesome videos. I had the same experience troubleshooting a treadmill motor board just month ago.I found the faulty components and replaced them right way. The micro-controller on board was just working ok. After a short break and back to troubleshooting i powered the board up and guess what! chip never booted-up. Next step was to check 5v rails and all was just fine. I changed the crystal just to be sure it dum works.but i had no luck. After getting the data sheet for the micro i started with the reset pin and traced on the PCB, the voltage on reset pin was just 1.3v and normally it should be around 5v, down the line it was hooked to the collector ofA337 transistor that has to pull the pin high (5v)with a resistor divider on base and the emitter to 5v. I decided to add a 10ohm resistor on base pin (A733)to 5v, to allow 5v flow from emitter pin to collector to reset, and wow the A733 started heating up really hot due to high current flowing to reset pin. I got the micro out of PCB and did a standalone test on solder-less test board and also added logic components that a micro needs to boot. Lastly i measured how much current the reset pin was consuming and wow 250mah! Really!The chip never booted but was getting kinda warm. Hmm

led-matrix-au

thanks Dave, same unit, similar black LCD line, swapped both caps for 5v reg, and lifted reset pin which was grounded, voila it boots, made an rs232 lead for 2.5mm jack and I'm happy it's worked. Thanks for the insight, appreciate it.
Dave DPS

dpstek

Check the processor data sheet for the spec of the reset signal, it might have a maximum rise time which is why the simple R-C circuit won't cut it. I've had fun and games with them not resetting properly before now.

alancordwell

Jolly good show. I learn no matter what the end result, so keep them coming Dave. I would hate to think this footage would be dumped because the device was 'unrepairable'.

DavidConnollyvolthaus

Dave - I enjoy your repair videos, regardless of success. The process for troubleshooting and isolating issues is the fascinating bit.

slothjr

When I have power going 'somewhere' due to suspected low resistance or short (like when you had 90mA+ during the direct pull-up through the meter) I just shine the thermal camera at the board and see who's holding the line down (or up).

Has saved me some serious pain :-)

brandonm.

I love this type of investigative troubleshooting even if the end result is not what you want, it still makes a very interesting video.
Most people who commented spotted the same things that I was wondering about but very few people had any useful suggestions especially concerning the high current draw. It seems to me that the current is finding a path that should not be open which points to some other component going bad somewhere else, could be a whole string of faults in there.

ian-c.

It's like watching an electronic version of House xD

olivor_h

You’re still a rockstar Dave! Never would’ve gotten to the resistor pull-up/pull down whatever it was.

markragus

There are so many good sound clips that can be taken out of context for great comedy. i.e. 41:39 "If you bend that, you can snap it off." Sounds like a great line for an anti-masturbation PSA. LOL :)

sbrazenor

Even when the task is not successful you can still learn lots from it.

TheEPROM

If you're struggling to read part numbers that are waterproof coated, like in the video, try using light of just a single wavelength. You can pick up red, green, blue laser pointers, and so IR bulbs and UV lights can be used. Just trial and error, but it's handy to have at least one of each in your workshop. They are really cheap and can be extremely handy in reading difficult things. You'll be amazed how some things look like they have no writing on but under the correct sort of light appear crystal clear.

Cobalt-Jester