Thank you for doing this teardown video. I got one of these for free because it was intermittent, and as an older (old) retired tech I'm always a bit apprehensive opening up small equipment. With you leading the way it makes it very easy to get inside and fix the actual problem instead of creating new ones. Thanks.
Wow! That looks like the first digital meter that I bought back in 1990, it too was a Metex. I'll have to dig it out and see if it's the same model. I used it for about 20 years, and popped the fuse a few times.
Nice teardown :-D The version without the bargraph only has resistors in the oblong yellow box, no special thin film package, but the resistors were very accurate. I know this as i repaired one.
Wow. I am still using this M-4650 because the beeper for testing connections has no delay compared to my fluke 177 from today. My version seem not to have gold plated pcb for the big dial-switch so should say good bye to it after 30 years.
Metex made excellent dmm's in those days. Input protection from that era might not be up to modern professional standards, but the quality of the pcbs, components, switches etc was very good. Mine from the 80s still works and ut had a way harder life (workshop/mobile field use) than the one you have that is in excellent condition. I remember back in those days opening up the meter and was astouned with it's quality ( remeber in those days there were even new electronic devices sold that still had pertinax or worse pcbs..) Of course Fluke was also around in those days, and already had back then way better input protection, so those meters were truely top notch back then.
Although mine looks fine from the outside it also had a hard time. Fell on hard concrete floor a dozen times and (worst) I once had "overloaded" the precision input resistor-divider by applying more than 2000VDC to the inputs. But it survived and apparently kept the original accuracy :-)
I still have the Voltcraft M-4650B, which is a relabeled version of this one from Conrad Elektronik. Interesting video, even if it was not quite what I was looking for: Mine has never been re-calibrated in 25 years, so I'm looking for some documentation of what to adjust. Also have to get my hands on good references for calibration...
We will bring out references for calibration (U, R, I) in a few months in our shop or as a kickstarter project. Reference capacitors are already available: www.ak-modul-bus.de/stat/referenz_kondensatorn_reference_caps.html.
The calibration is pretty stable also in my unit. I just found calibration instructions in German on my HDD :-) If you are interested I can email them to you if you send me your email-adress to either info@ak-modul-bus.de or roger@kainkalabs.com. There is a little ten-turn trimmer VR1 inside for the basic DC voltage calibration of the ADC. This adjustment influences all other measurements directly and must be done first. The rest of the voltage, current and resistance accuracy depends then solely on the accuracy of the resistnace divider networks and the shunt-resistors. The other adjustments are for AC-to-DC conversion factor, capacitance, frequency and LCD-contrast.
That old Metex is quit impressive I think GDT and fuse and diode clamp better than and a precision divider network quite a bit better than any cheap meter you can buy now. Gold plated contacts and metal threaded inserts. It also had a bunch of NP0 capacitors by those hybrids so it must has some kinda precision oscillator in there so yeah looks very well made to me.
Yep. The accuracy is quite good compared to "modern" 4.5-digit multimeters. If you watched the series about "Selecting a better Mulltimeter" e.g. in Pt.5 or in the "Reference Capacitor Box"-video the capacitance-measurement feature is much better in the lower pF-range than the other "modern" multimeters. The resolution is 0.1pF and the accuracy is around 1%.
Your video is very interesting I have the same multimeter to which I performed a calibration but in the 2Volts scale (1.9999 counts) I could not align with the other scales. I downloaded the scheme from the web and the only trimmer on which I acted is the main critical on left side, all the other trimmer pots I do not know what they are for. Would you be so kind to tell me what mainly refers all VR trimmers specially what is immediately below the display. I thank you in advantage.
I´m afraid I can´t help you. A few years ago I tested the DVM against my Extech/Brymen wwhich had much better specs and the Metex was still well within it´s original specs. So I would never try re-calibrating a complex multimeter without the full calibrating instructions. You have to do the claibration in the right order of the trimmers because mostly one trimmer affects the measurements of some or all the other ranges/modes. In your case you probably adjusted the reference voltage and thus all other measurement modes and ranges were affected by the same relative change.
Can be seen in these videos:ruclips.net/video/r8vKN3jk_80h/видео.htmlttps://ruclips.net/video/twgDIcpgi1Ih/видео.htmlttps://ruclips.net/video/IcZS43CZ3oE/видео.html Steve Wozniak wears one too :-)
Strange. Here it works. Try right-clicking the link and then "...save target" because the link directly goes to/opens the zip-file Here again www.kainkalabs.com/upload/index.php?f=15b5a81d3244d5
Thank you for doing this teardown video. I got one of these for free because it was intermittent, and as an older (old) retired tech I'm always a bit apprehensive opening up small equipment. With you leading the way it makes it very easy to get inside and fix the actual problem instead of creating new ones. Thanks.
Wow! That looks like the first digital meter that I bought back in 1990, it too was a Metex. I'll have to dig it out and see if it's the same model. I used it for about 20 years, and popped the fuse a few times.
Nice teardown :-D
The version without the bargraph only has resistors in the oblong yellow box, no special thin film package, but the resistors were very accurate.
I know this as i repaired one.
Ich habe den Vorgänger ohne Bargraph. Bj ca. 1989.Er hat den schnellsten Durchgangsprüfer aller Zeiten.
Wow. I am still using this M-4650 because the beeper for testing connections has no delay compared to my fluke 177 from today. My version seem not to have gold plated pcb for the big dial-switch so should say good bye to it after 30 years.
Sir where from i download Uni-t M3900 digital multimeter circuit diagram
Metex made excellent dmm's in those days.
Input protection from that era might not be up to modern professional standards, but the quality of the pcbs, components, switches etc was very good.
Mine from the 80s still works and ut had a way harder life (workshop/mobile field use) than the one you have that is in excellent condition.
I remember back in those days opening up the meter and was astouned with it's quality ( remeber in those days there were even new electronic devices sold that still had pertinax or worse pcbs..)
Of course Fluke was also around in those days, and already had back then way better input protection, so those meters were truely top notch back then.
Although mine looks fine from the outside it also had a hard time. Fell on hard concrete floor a dozen times and (worst) I once had "overloaded" the precision input resistor-divider by applying more than 2000VDC to the inputs.
But it survived and apparently kept the original accuracy :-)
I used some bit older gray Metex long time ago. Only problem was selector broke from knob. Not found exact model, similar like METEX M-3610
I still have the Voltcraft M-4650B, which is a relabeled version of this one from Conrad Elektronik. Interesting video, even if it was not quite what I was looking for:
Mine has never been re-calibrated in 25 years, so I'm looking for some documentation of what to adjust. Also have to get my hands on good references for calibration...
We will bring out references for calibration (U, R, I) in a few months in our shop or as a kickstarter project. Reference capacitors are already available: www.ak-modul-bus.de/stat/referenz_kondensatorn_reference_caps.html.
The calibration is pretty stable also in my unit. I just found calibration instructions in German on my HDD :-) If you are interested I can email them to you if you send me your email-adress to either info@ak-modul-bus.de or roger@kainkalabs.com. There is a little ten-turn trimmer VR1 inside for the basic DC voltage calibration of the ADC. This adjustment influences all other measurements directly and must be done first. The rest of the voltage, current and resistance accuracy depends then solely on the accuracy of the resistnace divider networks and the shunt-resistors. The other adjustments are for AC-to-DC conversion factor, capacitance, frequency and LCD-contrast.
@@KainkaLabs Great and I'll send you my address, thanks in advance :)
That old Metex is quit impressive I think GDT and fuse and diode clamp better than and a precision divider network quite a bit better than any cheap meter you can buy now. Gold plated contacts and metal threaded inserts. It also had a bunch of NP0 capacitors by those hybrids so it must has some kinda precision oscillator in there so yeah looks very well made to me.
Yep. The accuracy is quite good compared to "modern" 4.5-digit multimeters. If you watched the series about "Selecting a better Mulltimeter" e.g. in Pt.5 or in the "Reference Capacitor Box"-video the capacitance-measurement feature is much better in the lower pF-range than the other "modern" multimeters. The resolution is 0.1pF and the accuracy is around 1%.
i still using 4560CR version, only problem is really big delay in continiuity test
121GW I like it ;-). Nice DMM from Dave Jonas. Became my daily drive besides Fluke and Brymen.
Your video is very interesting I have the same multimeter to which I performed a calibration but in the 2Volts scale (1.9999 counts) I could not align with the other scales.
I downloaded the scheme from the web and the only trimmer on which I acted is the main critical on left side, all the other trimmer pots I do not know what they are for.
Would you be so kind to tell me what mainly refers all VR trimmers specially what is immediately below the display.
I thank you in advantage.
I´m afraid I can´t help you. A few years ago I tested the DVM against my Extech/Brymen wwhich had much better specs and the Metex was still well within it´s original specs.
So I would never try re-calibrating a complex multimeter without the full calibrating instructions.
You have to do the claibration in the right order of the trimmers because mostly one trimmer affects the measurements of some or all the other ranges/modes.
In your case you probably adjusted the reference voltage and thus all other measurement modes and ranges were affected by the same relative change.
@@KainkaLabs Thank you for answer. 👍😏
Please can we see your watch in more detail?
Can be seen in these videos:ruclips.net/video/r8vKN3jk_80h/видео.htmlttps://ruclips.net/video/twgDIcpgi1Ih/видео.htmlttps://ruclips.net/video/IcZS43CZ3oE/видео.html
Steve Wozniak wears one too :-)
Hi, the link does not work, it comes up 404 not found
Link correctd. Reload this page and try again.
Still don't work
Strange. Here it works.
Try right-clicking the link and then "...save target" because the link directly goes to/opens the zip-file
Here again www.kainkalabs.com/upload/index.php?f=15b5a81d3244d5