Author Topic: EEVblog #482 - Retro Iskra Multimeter Teardown (Read 46749 times)

free_electron · « **Reply #25 on:** June 13, 2013, 03:59:35 pm »

A few words of additional information.

On the resistor drawings in the schematics with the diagonal lines and filled area's to denote the type:
This was very common in europe in the 70's and 80's before we had computerised cad. Schematics from renonownded tv beluiders like Barco Carad Philips Anex Grundig all used that system. I can't remeber if there was an official set of symbols. Like one diagonal line on sode meant 1/4 watt. Two was 1/2 watt one fat line was 1 watt. Two fat lines was 2 watt. On the other side of the rectangle they also filled in to denote metal film / carbon etc..

Most schematics had a legend showing what symbol meant what. There were even capacitor symbols.

Looking at the islra schematic it reminds me of the drawing style of siemens schematics. I had a collection of appnotes from siemens semiconductors . They were little red books . Exactly drawn in the same style.

The a/d converter is a dual slope convertor with residual compensation (autozrro). One chip (the socketed one) contains the integrator and comparator and switches. The white tubular capacitor next to it is a high quality, low soakage cap used as integrating cap. The reason this chip is most likely socketed is that it is the most expensive , and most prone to failure, in the entire meter. If a board was found to be non working (out of spec) they would try a different chip first.. If that didnt work it meand there was a problem with parts on the board. Chuck the board away, keep the chips.

The other chip on the dsiplay board is the runup/rundown controller..

Dd you noiuce the uA709 opamp in metalcan ? Thats a Bob Widlar design. The guru of all guru's.

http://en.wikipedia.org/wiki/Bob_Widlar

There is a couple of transistors in dometop. If you look just before the top digital board, on the board underneath there is a black transistor , round with a flat dide and a domed top. Those are pretty rare. That package was only used for fets.

There is also a different dometop with golden pins on the bottom board. Is suspect it is the reference diode.

Hydrawerk · « **Reply #26 on:** June 13, 2013, 04:01:10 pm »

A few of these multimeters are still used at my university. We have more modern equipment, too.

Hydrawerk · « **Reply #27 on:** June 13, 2013, 04:03:16 pm »

I don't know why they used LEDs. I have a HP calculator that went to market in 1979 and it has a LCD.

c4757p · « **Reply #28 on:** June 13, 2013, 04:05:08 pm »

I vastly prefer LEDs, VFDs - anything with active lighting - for bench use. LCDs are for the nanoamp pinchers.

Fryguy · « **Reply #29 on:** June 13, 2013, 04:11:14 pm »

I think this is a rare beauty and i love the LED display .

Please take good care of it !

By the way - why don't they use LED displays on new standard DMMs - the technology is so advanced these days - you can get a really bright display without killing the batteries in 5 minutes ! NO - DONT START

ABOUT OLED DISPLAYS - it's not the same !
LED displays would be great for service DMMs for example - they won't crack like LCDs on tough jobs . . .

Hydrawerk · « **Reply #30 on:** June 13, 2013, 04:21:11 pm »

How can you make this display with LEDs?? picture

Fryguy · « **Reply #31 on:** June 13, 2013, 04:27:17 pm »

EASY !

c4757p · « **Reply #32 on:** June 13, 2013, 04:30:37 pm »

You don't. LEDs aren't suitable for everything. That's not a multimeter, it's an LCR meter, and I wouldn't use an LED display for an LCR meter.

Alternately, you simplify it. You don't need to tell me what I'm measuring - if I don't know that, I probably don't know what an LCR meter is.... So ditch the units. Ditch the "analog" bar at the bottom - WTF does it even do on an LCR meter?? Replace the L/C/R s/p indicators with switches; the position of the switch indicates the mode. A few indicators can be replaced by individual LEDs behind text like on my analog scope. Get rid of the rest of the idiot indicators and all you need are the numbers.

But I'd still say that for the LCD. It's ridiculously cluttered. I don't need the damn thing to read me the user manual on the screen.

Fryguy · « **Reply #33 on:** June 13, 2013, 04:36:55 pm »

Units and other symbols are made just by using a mask in front of single LEDs - that and the numberblocks - done !

Yes it will be a bit bigger - who cares - small displays are not good anyway . . . you shouldn't have to use magnifying glasses on your equipment !

CodyShaw · « **Reply #34 on:** June 13, 2013, 04:50:12 pm »

Don't take that apart Dave! It's a museum piece for sure, I'd put it on a display shelf with its case off for visitors to see!

darko31 · « **Reply #35 on:** June 13, 2013, 05:14:56 pm »

We actually have at school Iskra's analog multimeter, it's similar design as this one, it has the same rotary switches, except, well its analog needle. I'll take a picture, but I'm not sure I can open it up without that special head screwdriver. I'll try to find an old flathead and grind away the middle of it.

And yeah, Iskra (translation is Spark) is now divided in bunch of smaller divisions and isn't the giant that it just to be. It must have been quite of sight using them and other famous company "products" around Yugoslavia. Well I can't really call those things products, everything from cars to electronics was made in Yugoslavia, and the industry was considered a national pride. Cars were national symbols, and the products of electrical and electronic companies were also considered similarly.

Honorable mentions include Sever, they mostly made electromotors and they still exist today, owned by Austrians (not Australians

), and EI Niš (pronounced Nish), they were also prominent electronics company, and they still exist today, one of the few remaining companies that still make vacuum tubes.

I'm one of those post war, younger generations, so I can't remember the life in Yugoslavia, but I've heard a lot of stories of people missing the old times.

There are still a lot of remains here of the things these factories produced, we used the other day an Iskra's relay timer, I've opened it up to see what's inside, and of course there was a 555 timer.

Thanks for the video Dave!

txescientist · « **Reply #36 on:** June 13, 2013, 05:21:16 pm »

Hi Dave,
here are pictures of two multimeters that we still use in physics laboratory at my University of Physics. Very reliable instruments...
Best regards from Serbia!
Milos

Hydrawerk · « **Reply #37 on:** June 13, 2013, 05:53:26 pm »

Three Digimers in action... And in late 1980s, the Metra PU510 digital multimeters were produced in Czech Republic. They have a Lecroy-black design.
/Picture of PU510 was not taken by me!/

JoannaK · « **Reply #38 on:** June 13, 2013, 07:06:20 pm »

Hydrawerk: love that Lab picture. So neat mishmach of technology from las 50 (or more) years.

Dave, please try to fix that meter. IMHO it's too good to be thrown away..

Dajgoro · « **Reply #39 on:** June 13, 2013, 07:06:59 pm »

I still use the analog version (Unimer). I had lots of those Chinese multimeters, and all of them died, and the only thing left working in the end was the old Unimer (along with another vintage digital multimeter).

Btw: One of the cans was marked RIZ, which is also a local manufacturer.

BillyD · « **Reply #40 on:** June 13, 2013, 09:07:08 pm »

Hmm, seems to have been a certain amount of sneering in that vid.

But it's 33 years old and is still very close to working order. Easy to laugh at it now, but in its day and in its location it would have taken a lot of ingenuity to produce and personally I admire that.

Glad you didn't tear it down.

qno · « **Reply #41 on:** June 13, 2013, 10:00:09 pm »

The analog meters look like Goertz meters . They where made in Austria (not Australia) which are practically neighbors.

Goertz has been bought by Gossen Metrawatt.

txescientist · « **Reply #42 on:** June 13, 2013, 10:14:42 pm »

This is Iskra mains frequency meter

txescientist · « **Reply #43 on:** June 13, 2013, 10:27:27 pm »

and some more...

Hydrawerk · « **Reply #44 on:** June 13, 2013, 11:00:23 pm »

How old are these instruments?

WattSekunde · « **Reply #45 on:** June 13, 2013, 11:32:54 pm »

Quote from: Hydrawerk on June 13, 2013, 04:21:11 pm

How can you make this display with LEDs?? picture

With such a smart dot matrix led display like this for the character display part: Osram ISD2353 for example
http://catalog.osram-os.com/catalogue/catalogue.do?favOid=000000010000021600020023&act=showBookmark

... and some others:
http://www.digikey.de/scripts/dksearch/dksus.dll?pv320=1&FV=fff40008%2Cfff80031&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Crockett · « **Reply #46 on:** June 14, 2013, 02:14:02 am »

Quote from: fridrik on June 13, 2013, 07:41:20 am

Beautiful meter Dave, thanks to the guy who sent it in!
please don't ruin it. I would very much enjoy seeing you use it in your (fundamental Friday) videos!

(maybe fix the current range?)

Thanks for the video.

I second the motion, here! Aye, aye!!

gnif · « **Reply #47 on:** June 14, 2013, 02:21:26 am »

I would tear it down just to repair it and then put it to work, I love retro stuff, the LED readout is classic! I remember my dad had an old Casio calculator with a LED display, I wish I knew what happened to it.

BeanerSA · « **Reply #48 on:** June 14, 2013, 03:03:10 am »

A thing of beauty IMO.

ron · « **Reply #49 on:** June 14, 2013, 03:40:25 am »

This is an interesting meter but it is not "retro". It is an old original. The new BMW Mini's are retro. The original Coopers are just old and some would say classic.


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Author Topic: EEVblog #482 - Retro Iskra Multimeter Teardown (Read 46749 times)

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