vintage BBC Digital Scope Multimeter M2050 teardown - Page 1
Forum section: electronics / testgear

author: maelli
author_rank: Contributor
timestamp: September 19, 2014, 06:08:27 pm
content: Found a Digital Scope Multimeter in the our company dumpster.A BBC Goerz Metrawatt M2050 DSM. What a strange device.Did not find much on the internet about this thing, except for this advertisement in"Radio Electronics" from December 1983.So that is a more than 30 years old, portable digital scope ;-)Could it be that this thing is the very first "scopemeter"?And it almost looks like a laptop computer, a fat one with a small display ;-)So let me play around with it, and see how this stands the test of time.There is a DC input jack, and a battery compartment for 4 C-cells. Inside the warning to onlyuse NiCd cells. Probably because of the internal charging circuit.Tried out with 4 alkaline cells, works fine. It draws 0.2Amps.Looks like it is fully working.The meter works as expected, even True RMS. Still within spec, DC and AC. Easy to readdisplay.The scope is awful, to say the least. 64x128 dots may have been state of the art backthen, but how could they have decided to make the screen display INVERTED?Maybe to imitate the looks of a real scope? Really hard to see anything.Sample frequency is 500kHz, single shot and repetitive.Yes it is possible to display a 20kHz sine wave. Above that it gets hairy.What is nice is that it can store a waveform. I keeps this waveform even when turnedoff. Not only one, but two waveforms!So let's crack it open and see what is inside.Two boards full of 4000 series CMOS 80ties porn.different datecodes, from 82 to 85.

author: P90
author_rank: Frequent Contributor
timestamp: September 19, 2014, 06:49:10 pm
content: that is really neat stuff!

author: coppice
author_rank: Super Contributor
timestamp: September 19, 2014, 07:24:27 pm
content: I don't remember that machine, but there were a few somewhat similar ones in the 80s.

author: Wh1sper
author_rank: Regular Contributor
timestamp: September 29, 2014, 03:22:46 pm
content: I do have such a Device in non working condition, displays some random line, DMM part seems better working but is unreadable after some seconds.Because I didn't find any documents, service manuals, Schematics I do not feeling any chance to repair.Maybe I reuse the case for something cool new stuff?I do have the Leather case also.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 29, 2014, 05:00:40 pm
content: Gotta love that look! Nice pics too!TC5514 ... wow 1Kx4 SRAM, just like in a VIC-20.

author: Lightages
author_rank: Unknown
timestamp: September 29, 2014, 05:32:40 pm
content: Why would anyone throw out something like that!!??!!Thanks for rescuing it and sharing with us.

author: Bored@Work
author_rank: Super Contributor
timestamp: September 29, 2014, 05:50:17 pm
content: Quote from: Wh1sper on September 29, 2014, 03:22:46 pmTry Gossen Metrawatt. BBC ended up as part of that company. Maybe they are willing to help.

author: Wh1sper
author_rank: Regular Contributor
timestamp: September 29, 2014, 06:13:26 pm
content: Quote from: Bored@Work on September 29, 2014, 05:50:17 pmI know.But this Company just ignore inquires

author: maelli
author_rank: Contributor
timestamp: September 29, 2014, 09:23:00 pm
content: Shame there is not much of documentation around in the net on this oldBBC, ABB, Metrawatt Gossen stuff....In the same dumpster I found two broken MA5D, managed to repair one withparts from the other one. Nice 30'000 count bench meter, mains/rechargeable.The manual of those is on BAMA, including schematics.b.t.w: Picture 8 shows the current drawn by a 8W compact fluorescent.9 days since my original post, I turned the meter on again and thewaveform is still there!

author: HighVoltage
author_rank: Super Contributor
timestamp: September 29, 2014, 10:04:22 pm
content: We had one of these in the university lab and I remember how smooth the switches turned.I still have two analog meters from the same time and they just work perfectly after so many years.Somehow BBC / Metrawatt knew what they were doing in those days.

author: bigsky
author_rank: Regular Contributor
timestamp: September 29, 2014, 10:27:48 pm
content: I do wonder whether, for example, a Scopemeter would still be working in 30 years time. And if it wasn't, could it be fixed? Same goes for my 87V compared to, say, an 8020A. Progress has its downside...

author: maelli
author_rank: Contributor
timestamp: October 05, 2014, 12:05:16 pm
content: update:Since the display is connected with a 16-pole ribbon cable, there must be more electronics on the display side ofthis thing. Two more screws to open, here we go:7136 for the 3.5 digit multimeter part2x H0438A serial LCD drivers (each for 32 segments or colums)Then I measured the current of the whole instrument when "off": around 0.5mA.Apparently for the "constant memory" functionality.So it will eventually drain the batteries over some weeks. Maybe that is why they stated "nicad only".

author: david77
author_rank: Frequent Contributor
timestamp: October 05, 2014, 12:21:17 pm
content: I remember these BBC meters from school, we had (probably still have) a whole bunch of them in our schools physics department, mostly the simpler analogue and 31/2 digit meters but I seem to remember this one as well. They were tough little meters, survived years of abuse by students and teachers.AFAIK the first proper hand-held scope was the Createc SC01, that must have been in the mid or late 80ies. It was a proper DSO with 10MHz bandwidth. Works reasonably well, only let down by the really crappy display technology of the day.