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Advantest R6871E-DC 6.5digit DMM Overview/Teardown
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ve7xen:
I've had this for a while and have wanted to do a teardown for some time since there's little information out there on this model. It's a 6.5 digit meter as far as its accuracy and stability is concerned, but can display 7.5 digits. This particular model (-DC) only does VDC and 2W/4W R, the non -DC version also does VAC and IDC/IAC. From the board markings, the design is from the early 1990s, and almost everything in the meter is made in Japan.

First post will be basic information, second post will have the teardown.

If you like videos, I did a overview / basic operation video:



The operation manual (if anyone has a service manual I'd appreciate it, I couldn't find one, this was hard enough to find) is here.

This is a pretty good meter. The specs are fairly comparable with a modern 6.5 digit, it's got a nice display and a fair amount of functionality for an older device, with math, storage, GPIB and so on. After using it for a few months and keeping it on a reference it seems very stable as well. They occasionally pop up on eBay for very enticing prices, which is why I bought mine despite not being able to find much information on it. Hopefully this post will encourage some others to get in on the action ;).
ve7xen:
I spent a lot of time on the teardown video going through most of the meter in a bit of detail, so I won't waste a ton of space on words here, if you're interested in my thoughts, watch the video:

Full gallery of photos is here, all pictures below link to full (ie. huge) images.

Any thoughts on why there's a backup battery in here? There are at least two separate EEPROMs in the meter visible in this shot.


High impedance madness! Is that the reference in the machined can? If you look closely at the full-res shot, you can even see a resistor crammed in directly between the pin and the board. What are those black bricks (there are 3 that look similar around the meter)?


Hang on a second... what on Earth is going on with those ceramic things? The curlies had me confused for a while, but they must be for strain / vibration tolerance - not sure what these things are doing though, they don't seem to have any components on them.


Some interesting ceramic transistor carriers.


Haven't seen this sort of isolation before, but they use a copy of it on each board (digital and analog). I suppose they're isolating the same lines on both boards - either that or there are actually 6 lines, with 3 isolated on each board. Also wondering what the paper-like flat part is, marked M003 in this shot, there are a few similar devices scattered in this section.


Can anyone tell me what's up with the capacitor top right (potted looking black thing beside the big hybrid)? Never seen a capacitor potted like that before, what's the dielectric? It's 33nF, IIRC 50V.


These 5x7 dot matrix LED arrays used for units display are fantastic looking, and I didn't know about them before. Very tiny LED dies too. Interesting.


And we'll end with an action shot.


A neat meter and fun to look at inside.
alm:

--- Quote from: ve7xen on September 26, 2013, 09:28:15 am ---Any thoughts on why there's a backup battery in here? There are at least two separate EEPROMs in the meter visible in this shot.

--- End quote ---
To store calibration data most likely.


--- Quote from: ve7xen on September 26, 2013, 09:28:15 am ---Hang on a second... what on Earth is going on with those ceramic things?

--- End quote ---
You mean the ceramic PCB inserts? For isolation, FR4, especially if dirty, is kind of low impedance compared to the > 10 GOhm input impedance it probably has.


--- Quote from: ve7xen on September 26, 2013, 09:28:15 am ---Also wondering what the paper-like flat part is, marked M003 in this shot, there are a few similar devices scattered in this section.

--- End quote ---
Resistor networks.


--- Quote from: ve7xen on September 26, 2013, 09:28:15 am ---Can anyone tell me what's up with the capacitor top right (potted looking black thing beside the big hybrid)? Never seen a capacitor potted like that before, what's the dielectric? It's 33nF, IIRC 50V.

--- End quote ---
Looks like a film cap to me, especially given the 50 V rating.
ve7xen:

--- Quote from: alm on September 26, 2013, 10:27:05 am ---To store calibration data most likely.
--- End quote ---
Perhaps my question could be better phrased as "why have battery-backed SRAM and EEPROM on the same memory bus?". Speed, maybe?


--- Quote from: alm on September 26, 2013, 10:27:05 am ---You mean the ceramic PCB inserts? For isolation, FR4, especially if dirty, is kind of low impedance compared to the > 10 GOhm input impedance it probably has.
--- End quote ---
Yeah, I'm thinking of the 3-terminal looking ceramic substrates. I do assume they have to do with the ultra high impedance input, but I don't know what their purpose is. It's hard to tell for sure but they don't seem to have any components on them, and just connect the air wires to the teflon solder pot things.


--- Quote from: alm on September 26, 2013, 10:27:05 am ---Resistor networks.
--- End quote ---
Thanks, that's what I was thinking but the construction seemed odd.
Vgkid:
The high impedance section is very interesting, can I get some of the component ID's if you have them. I'cant tell if the to-72 packages are fets/bjts.
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