Rigol DM3068 teardown - Page 1
Forum section: electronics / testgear

author: wraper
author_rank: Unknown
timestamp: April 01, 2013, 08:08:35 pm
content: Hi, I teared down my new DM3068 as there was problem with intermittently changing button brightness and display contrast. Problem usually disappeared when multimeter warmed up. Sending back would take too long. There was a problem with 1117B-33 vreg ic, sometimes voltage shoot up to 3,7v on it for a short time. As it seems to be no info on the net about what's inside, decided to share my own. Here are some pics:https://plus.google.com/photos/117212633093763827202/albums/5861950419366571361. At first glance multimeter was well built with good parts, only bad thing was a flux residues on hand soldered connectors and relays. At start I didn't want to remove RF shield, but it was too interesting to look what's there so I gave up to my curiosity. And curiosity haven't disappointed me. There I found interesting bodge with 2 green wires. It seems that those wires are in parallel with existing traces (at least one, second trace is below IC so not sure). Don't know why Rigol done this, maybe for lower resistance... Also one IC is hand soldered, not sure if it is rework or done for other reasons.About parts used. All electrolytic caps are nichicon. In digital part there are blackfin DSP, some strange ISP13628D chip, hynix RAM, spansion flash, one Altera MAX CPLD and one MAXII. Davicom DM9000 ethernet controller. Isolation made with AD ADUM 1301 and 1401 digital isolators for data and one PC817 optocoupler for powering on input part. On measuring part there are Ti ADS1256 24 bit ADC, Vref is LM399H from Linear Tech, biggest chip as some others is with marking laser burned off. There also are caddock 1776-C6715 precision resistor divider, meder BE05 reed relay, 3 Matsushita relays and one small axicom relay. Two current sensing SMD resistors are 4 wire and both are hand soldered. Input seems to be well protected, 2 big MOVs and 2 powerful 1400V ceramic spark gaps there.Greetings from Latvia

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: April 02, 2013, 04:56:39 am
content: Hello Aleksander from Latvia and welcome to the forum. Thank you for the tear down picturesThis forum has members who are very knowledgable about bench DMM's, but sadly I am not one of them. Very interested in finding out Rigol is using a TI delta-sigma instead of dual./multi-slope like the others. That they use Blackfin not so surprising as they seem to really like these, but is still a somewhat strange choice for a multimeter. I guess they get a volume discount.Actually I think Mrflibble and Stoney are on a better chip selection path to achieve a 6.5 digit meter -on the open source multimeter thread.

author: KedasProbe
author_rank: Frequent Contributor
timestamp: July 15, 2013, 09:15:50 am
content: Thanks for sharing. (I expect my new DM3068 to arrive somewhere next week)In case you want to improve on your Chinese:Contains powerpoint/PDF that Rigol made to present their DMM (some time ago).http://www.docin.com/p-389396256.html(you have to pay to download it)

author: poorchava
author_rank: Super Contributor
timestamp: July 15, 2013, 12:01:17 pm
content: Blackfin seems to be a serious overkill. I mean what sort of DSP do you have to do in such a meter? Most of the filtering is done in analog domain. Frequency counter would be easier with some programmable logic (which is also there on the photos), True-RMS is easier and probably better done with dedicated hardware chip from AD or TI.And the rest can be implemented in something much smaller, like for example AVR, MSP430, some Arm Cortex from NXP/ST/Freescale/TI or even utter shit like PIC.I don't really understand this...