Quick GW Instek GDM-8341 bench DMM teardown / review - Page 1
Forum section: electronics / testgear

author: bd139
author_rank: Super Contributor
timestamp: October 13, 2017, 12:23:03 pm
content: This is a relatively cheap and average spec 4.5 digit bench DMM but it has three important things for me: a dual VFD display that I can actually see in my miserable little corner bench, a cal cert and USB data logging support. I picked it up for £320 from Amazon after losing way too many Fluke 45 auctions. Figured I'd just buy a new one, but you can't get them and I can't afford a decent Keysight or Fluke bench meter new!Notable good things:1. Fast read speed2. Input protection that isn't shit. Nice to see a decent quality HRC fuse and PTC in something from China.3. Dual display (current/voltage, voltage/frequency etc).4. VFD5. Nice and easy to use UI.6. Handle folds flush underneath it, not on top like some other kit.7. Feels pretty solid.8. No fan!9. AC bandwidth is flat to 180KHz which is way more than the quoted 100KHz total bandwidth.10. Relatively low burden11. Switchable impedance on low voltage range.CAT II rated and actually looks like it is.Notable bad things:1. The probes that come with it are crap! Chucked and replaced with some Pomona ones.2. No Kelvin / 4-wire resistance measurement (I don't need this anyway really)3. You have to manual range to use the 12A range. This confused the shit out of me for about 20 minutes.4. Crap electrolytic capacitors. I've added a calendar entry to replace these in about 5 yearsDesign notes:1. Lots of AD analogue switches and relays2. Couldn't find the ADC, not that I was particularly looking for that.3. Brains are in an Altera IC. Assume this is an FPGA, possibly with embedded core of some description.4. It has a JTAG port by the looks.5. USB controller is an SiLabs one. Will reverse engineer that from a host machine at some point.6. Nice design - you can access both sides of the board once you've slid it out of the chassis.Pictures:Input!Whole thingAnalogue switchingPower supplyFrontQuite happy with this

author: Specmaster
author_rank: Super Contributor
timestamp: October 13, 2017, 01:37:41 pm
content: Nice meter, HRC fuses are not uncommon on Chinese meters are they? I have them on my Iso-Tech bench meter too. i love that dual display as well, so handySent from my SM-J510FN using Tapatalk

author: bd139
author_rank: Super Contributor
timestamp: October 13, 2017, 01:41:02 pm
content: The lower end vendors tend not to bother with them. That's usually Uni-T and those awful yellow things that cost about a quidIso-Tech probably came from RS as that's one of their house brands so they have them built to a slightly better specification.

author: Specmaster
author_rank: Super Contributor
timestamp: October 13, 2017, 04:55:09 pm
content: Correct it did originate from RS, and like yours has the Bussman fuses fitted and considering what it looked like when I received it and how it looks now, combined with the price I paid, I'm well chuffed with it.Speaking of DMM's. the Fluke 8505A arrived today from, the USA, well packed but needing lots of work I'm thinking, DC volts does seem to be reliable, not auto ranging correctly and resistance range comes up with an error message. Hoping it just needs some slight TLC, factory resetting and calibration which according to the manual can be from a computer with the right interface or directly via the front panel. Huge manual, 315 pages long to read through to find the info on how to do it etc.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 13, 2017, 05:44:09 pm
content: Nice pictures; it is quite interesting to see GW Instek using the entire space of the enclosure - I confess I would have expected some more scantily filled product, similar toVC8145orUT804.It seems to me the main AD is a U303 (ADS1246) that is paired with the reference U302 (REF5025). A bit concerning that this section is so close to the beefy voltage regulators and that highway of TTL signals to the front panel...Also, my guess is the DMM's brain is the 80MHz Cortex M4 MCU (TM4C1236) and J400 is its JTAG connector - the Altera device seems too small to hold an embedded core.

author: wraper
author_rank: Unknown
timestamp: October 13, 2017, 06:01:19 pm
content: Quote from: bd139 on October 13, 2017, 12:23:03 pmCalling capacitors crap without knowing anything about them. Should be bottom of the barrel to be sold at Arrow and Distrelec/elfa. Every time I see someone calling them crap, that someone cannot explain why. And why would you need to replace them, there is no SMPS or heat to cause even cheap Chinese crap to fail. The only times I've seen them bulged was when general purpose series were put into SMPS or buck converter.

author: eeviking
author_rank: Regular Contributor
timestamp: October 13, 2017, 06:31:44 pm
content: I was about to comment on that also.Jamicon is a mid-range brand out of Taiwan. I would not call them crap. They are used by a lot of reputable manufacturers.If anyone have data to prove they are crap please share it.

author: bd139
author_rank: Super Contributor
timestamp: October 13, 2017, 06:58:39 pm
content: They are definitely shit. Notorious for Sound Blaster X-Fi failures. References via Google.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 13, 2017, 07:02:28 pm
content: In my experience I think Jamicon is quite alright as well. I have disassembled quite a number of products with Jamicon capacitors on them, the older being two 15+ year old Honeywell thermostats. All of the capacitors were still in quite good shape when tested with both my LCR meter and a compatible voltage leakage tester.

author: bd139
author_rank: Super Contributor
timestamp: October 13, 2017, 07:16:00 pm
content: One of the caps blew up in my Honeywell thermostat and sprayed electrolyte all over the membrane key switches and wrecked them! Didn’t check the vendor though at the time. Got replaced by a Honeywell remote one.I usually only use Vishay(BC/Sprague)/Rubycon/Epcos myself.

author: wraper
author_rank: Unknown
timestamp: October 13, 2017, 07:39:57 pm
content: Quote from: bd139 on October 13, 2017, 06:58:39 pmWay overblown to call that notorious. One out of a very few mentions of Jamicon failing. And it's a single 220uF (isn't this too low for the purpose?) LOW ESR cap working in buck converter in between of the hot heatsink (main chip) and hot linear regulators around. Put that near to the graphics card and you have a very nice deathtrap. X-Fi has tens of other Jamicons around and not a single of them failing. I've seen 20x more faulty Nichicon (hello HN and HM series) and Nippon Chemi-con (KZG, KZJ) than Jamicon. Jamicon LOW ESR caps are not that common, to be fair. I have a few LCD monitors at my work which failed just after 2 year warranty ended and they are still going strong for 6 years after recapped with Jamicon WL.

author: wraper
author_rank: Unknown
timestamp: October 13, 2017, 08:09:03 pm
content: Quote from: bd139 on October 13, 2017, 07:16:00 pm

author: nctnico
author_rank: Super Contributor
timestamp: October 13, 2017, 08:41:13 pm
content: Quote from: wraper on October 13, 2017, 06:01:19 pmI agree. Electrolytic capacitors in a linear PSU without a heatsource nearby can last for decades!

author: wraper
author_rank: Unknown
timestamp: October 13, 2017, 09:04:20 pm
content: Quote from: Specmaster on October 13, 2017, 01:37:41 pmGW instek is not Chinese, it's a Taiwanese company and most of it's gear is made in Taiwan as well.

author: bd139
author_rank: Super Contributor
timestamp: October 13, 2017, 09:05:23 pm
content: That’ll be why it has decent protection then!I concede on the capacitors

author: nanofrog
author_rank: Super Contributor
timestamp: October 14, 2017, 01:44:26 am
content: Quote from: wraper on October 13, 2017, 09:04:20 pmFWIW, I picked up a couple of pieces of GW Instek gear from all the ITT surplus that hit eBay,and both were made in Taiwan. Build quality is decent IME.Even if it wasn't wonderful, I wouldn't be disappointed given what I paid for both units.Edit: I screwed up on COO...FWIW:GW InstekGDM-8251Awas made in TaiwanGW InstekGPC-3020was made in Malaysia (uses analog meters vs. 7-segment displays)GDM-8251AGPC-3020

author: Dwaine
author_rank: Frequent Contributor
timestamp: October 14, 2017, 02:23:55 am
content: Ground is done Right,

author: Inflex
author_rank: Regular Contributor
timestamp: December 05, 2020, 06:13:07 am
content: Apologies for reviving an old thread.What's the continuity and diode mode speed like? I'm looking to purchase this meter but if the continuity speed is slow (ie, more than "near instant") it might not be viable.

author: bd139
author_rank: Super Contributor
timestamp: December 05, 2020, 09:30:02 am
content: Couldn’t answer that for you. I don’t own it any more.In fact I’d recommend avoiding the meter at this point. It’s nearly impossible to find someone who can calibrate it.

author: Inflex
author_rank: Regular Contributor
timestamp: December 05, 2020, 09:45:18 am
content: Hello @BD139,Thanks for the quick reply. More and more looking like it'll be back to the VC8145C for the job it'll be used for ( board repairs, not precision work ).

author: HKJ
author_rank: Super Contributor
timestamp: December 05, 2020, 09:51:06 am
content: Quote from: Inflex on December 05, 2020, 09:45:18 amYou can compare a couple of bench meters here:https://lygte-info.dk/info/DMMReviews.htmlClick on the "Type" column for sorting.

author: bd139
author_rank: Super Contributor
timestamp: December 05, 2020, 09:59:20 am
content: Just a few!I wouldn’t bother with a bench DMM now. Invest in a Fluke 87V or Brymen BM867s and job done.

author: Inflex
author_rank: Regular Contributor
timestamp: December 05, 2020, 10:02:46 am
content: Quote from: bd139 on December 05, 2020, 09:59:20 amI genuinely prefer bench meters. Gone through enough hand-held units and still have a few as a fallback, but bench meters stay out of my way, don't turn off, have decent data connectivity and I can program them to switch modes from my software.

author: Inflex
author_rank: Regular Contributor
timestamp: December 05, 2020, 10:05:12 am
content: Quote from: HKJ on December 05, 2020, 09:51:06 amUnfortunately there's no spec on how quickly the continuity mode works. Some meters, you encounter a short (say, below 20R) and they'll near instantly beep; others, seem to go out for a cup of coffee, mull over the crossword in the latest newspaper and eventually get back to you with a "Oh yes, that might be a short".VC8145, BSIDE ADM20, B&K 390A seem to be fast enough but it would appear some of the better meters seem to go slower than anticipated with continuity.

author: bd139
author_rank: Super Contributor
timestamp: December 05, 2020, 10:16:26 am
content: Quote from: Inflex on December 05, 2020, 10:02:46 amHP 34401A then

author: Inflex
author_rank: Regular Contributor
timestamp: December 05, 2020, 10:21:45 am
content: Quote from: bd139 on December 05, 2020, 10:16:26 amAye, have been looking at those as an option, at least they seem mildly available on the second hand market.

author: bd139
author_rank: Super Contributor
timestamp: December 05, 2020, 10:24:04 am
content: Yeah there are plenty on the market. Do some research though (plenty of threads on here) and avoid the early ones as they have unreliable display modules. If it’s Agilent branded it’ll be good.

author: AVGresponding
author_rank: Super Contributor
timestamp: December 05, 2020, 10:31:20 am
content: Quote from: bd139 on December 05, 2020, 10:16:26 amOr a used Keithley 2000

author: bd139
author_rank: Super Contributor
timestamp: December 05, 2020, 10:34:19 am
content: That too!

author: Inflex
author_rank: Regular Contributor
timestamp: December 29, 2020, 05:52:48 am
content: Ended up with the GDM-8341. Continuity response is quick. VFD is nice. Actually has a manual that lists all the SCPI commands.Only complaint so far, the buzzer (for continuity) is weak, may not hear it over the fume extractor.

author: Inflex
author_rank: Regular Contributor
timestamp: December 30, 2020, 12:00:38 am
content: Two issues to add;1) On linux, you will have to (currently) modify the cp210x module to add in the VID:PID pair along with all the other victims of this USB bridge chip, and recompile so you have a module that will setup the /dev/ttyUSBx deviceCode:{ USB_DEVICE(0x2184, 0x0030) }, /* GwInstek GDM-843x */2) While you're communicating with the meter, the front panel is disabled, this is a real pain. I know why it's being done but it'd be nice if there was an option to at least read the various values without it doing this. Working on a work-around in my software but not sure if I'll be able to tolerate it... time will tell.

author: bd139
author_rank: Super Contributor
timestamp: December 30, 2020, 10:16:14 am
content: Ah that really pisses me off that they give different vendor IDs and stuff out for one chipset. Doing that on macOS is nigh on impossible due to the signing process. TTi are the same. Supposedly *ID via SCPI should be enough to determine what device is what but nope, no one understands the difference between protocol and transport

author: Inflex
author_rank: Regular Contributor
timestamp: December 30, 2020, 10:36:41 am
content: Yes, when I plugged it in and Linux saw all the information... but wouldn't assign a tty device to it, I wasThankfully at least the cp210x is so commonly modified because of this that it wasn't a major task. Will be 2 years before we see an update in the linux kernel in a mainstream distro though.New software is athttps://github.com/inflex/gdm-8341, still early days, still doing major edits, but it's working for my job and I can do mode changes with keyboard combos even when not focused on the app.Hoping GwInstek comes though though and provides a way to enable the front panel even while connected/communication (ie, a SCPI command like SYST:ENablePAnel etc )

author: Kean
author_rank: Unknown
timestamp: December 30, 2020, 11:16:25 am
content: Quote from: bd139 on December 30, 2020, 10:16:14 amWell actually I think this is exactly how it was intended that the VID & PID should be used. The problem is more in the way serial drivers for most if not all operating system are hard coded for a fixed list of VID/PIDs when the major USB serial chip vendors clearly allowed and intended customisation. Signed drivers requirements now make it just that much harder for the end product manufacturers and support organisations.It would have been really great if the USB device class, subclass, and protocol descriptors had been defined better early on and were used to identify beyond just being a serial device and indicating support for specific protocols like NMEA, SCPI, etc. USBTMC was defined this way. Then leave the VID/PID as per the chip vendor for driver support, and just adjust the other string descriptors to match the end product info.I'm not an expert on USB protocols, but I'm surprised those implementing equipment haven't done more on this beyond basic USBTMC support, but I guess they have little incentive. OSHW products need to lead the way. USB serial was probably only ever intended as a stop-gap, with more specific/proprietary USB protocols expected to take over. Thankfully I think the use of common USB serial interfaces have helped to keep things more open for end users.

author: Inflex
author_rank: Regular Contributor
timestamp: December 30, 2020, 12:09:20 pm
content: Drifting OT of course; but certainly I feel the creation of USB-serial bridge chips allayed a lot of concerns for both manufacturers and developers. No way I wanted to be dealing with a full USB stack for a simple blinky-blinky device I wanted to connect up. A dedicated HID/similar standard would have been nice, though I suppose we have defacto's somewhat now.Always felt it was a glaring oversight that we cleared away dedicated serial and replaced it with system with magnitudes more complexity to do even the simplest of things, and no fallback to *serial* or degenerate mode.