Amprobe AM-220 undocumented feature

[ivan747]

I don't really know if this can be modded to support this interface. When you power up the AM-220 all the LCD segments turn on. You can see RS232 at the top. I always thought they did this to save some money by having the same LCD on many models.

BUT if you press the REL? button (relative mode) as you normally press the backlight button to turn the backlight on (for 2 seconds) you can bring the RS232 segment on. I still have to investigate more on this. Does Amprobe carry a model with an RS232 interface and a display like this?

By the way, I just blew the 500mA fuse on the meter. What blow speed do you recommend for multimeters? My Extech's manual recommends fast blow fuses. Also, searching around the Internet I couldn't find any good reason for a 500mA fuse to be ceramic, like the ones included in the Amprobe. (Found it, thanks to "Uncle Vernon"). I will try to find the proper ceramic fuse on the local market, but I think I might only find glass ones.

Ivan

[Uncle Vernon]

Also, searching around the Internet I couldn't find any good reason for a 500mA fuse to be ceramic

Search around the Internet for HRC to explain why. (hint: -Honda Racing Company -Hilary Rodham Clinton , try High Rupture Capacity)

[EEVblog]

It is common for the chipsets used to have RS232 capability, and many epople have modded meters like this to give them RS232 output.
It is very likely the chip actually is now outputting RS232 reading data on it's (unconnected) RS232 pins.

Dave.

[ivan747]

It is common for the chipsets used to have RS232 capability, and many epople have modded meters like this to give them RS232 output.
It is very likely the chip actually is now outputting RS-232 reading data on it's (unconnected) RS232 pins.

Dave.

Let's see... I will hook up my oscilloscope tomorrow and see if there's any kind of waveform that looks like RS232. Now, I must search for some RS-232 waveforms so I can identify it.

UPDATE: it is a silicon chip soldered directly on the PCB with one of those huge black blobs and no QFP footprint on the edges.  Unless the designers wanted us to discover the feature, it is probably hidden behind the nasty blob. Management could have forced to remove the RS-232 interface to match the price range or something.

[ipman]

Maybe there are traces left unconnected or missing chips, look for that.

[FenderBender]

I just noticed the same thing on mine yesterday. I don't think I saw any jumpers inside that would do that...

[ivan747]

I just noticed the same thing on mine yesterday. I don't think I saw any jumpers inside that would do that...

Can you post photos of the inside of your multimeter please? In case they want to void you warranty just tell them you where inspecting the fuses!  Serial number would be good for comparison.

[FenderBender]

Nah it's okay. Amprobe was dumb enough not to put a battery compartment on this meter, so every time I want to change the batteries I see the PCB and everything on it. I will surely take a picture. One second please. 

[FenderBender]

Here we are. I uploaded the full hi-res pictures just in case anyone wanted to really zoom in....usually I would upload a smaller file, but the big ones might be more helpful here.

I'd suggest right clicking and opening in new tab or window, because the forum probably won't be able to display the whole picture.

[ivan747]

Mine is lacking some soldermask in some areas, I could find a serial port or something.