Czechoslovakian measure equipment collection

[MetraCollector]

Hello gentlemen

Let me introduce myself. I am Andrej, I am 20 years old and I am from Slovakia. (please, NOT Slovenia like Tekfan  )
I study Microelectronics and Electrotechnologies at Brno University of Technology in Czech Republic. I currently occupy this country.

I have been interested in electronics and similar domains for about 3-4 years and finally I have found myself in measuring devices.
I collect test vintage equipment from czechoslovakian national company Metra Blansko and Tesla Brno.

These national concerns were monopoly manufacturers of majority of measure devices in Czechoslovakia till 1989 when Soviet Union fell.
Although a quite good measure attributes of devices made in Metra/Tesla, these are well known for their unreliability and non-stability and what is more, they are known for their extreme backwardness.
Czcechoslovakian electronic industry was backward and non-inovative since politic plot in 1968. (5 year semiconductor delay in this era)
However, I found interesting collecting these devices, perhaps the main argument is I can get them for free from closed laboratories or like a junk or I can buy them for symoblic prices on auctions.

A little overview I store them at my home.

[MetraCollector]

MT100 - Metra Blansko

MT100 is a precious DC voltmeter made in years 1970-1980 in Metra Blansko. It has evolved of series of NRxx devices and this electronic unit is named NR60.
The first A/D converter unit made in Metra Blansko ever is NR10 and it consists of germanium transtistors with vacuum tube comparators and amplifiers. This was in year 1967. The first evolution of it is NR20 and I own it. I will take photos of NR20 later, because I store it in basement and its weight is about 30kg.
Voltmeter uses 2-stage integration and it is controlled by TTL logic. It is concipated as grounded non-floating section and floating unit with Guard shield. Comunication of them are provided by ferrite transformers.
Range is 15mV – 1.5kV.



Aluminium skelet with boards off.
These gold-plated connectors were made in good quallity.


Data communication ferrite transformers.


On the left: KN – Calibration supply and reference voltage supply.
On the right: AZ +/- 15V power supply and zero setting divider.


Up: IK – The integrator with switches, comparators and reference voltage switchers.
Down: LO  +5V power supply, limit comparator and some logic circuits.


OZ – Input amplifier and limiter


CP – This is the logic board, here is memory of received data and all necessary control circuits.


LP – Range control circuits, oscillator bounded on 50Hz network and star/stop impulse circuits.


ZL – power supplies of +/-15V, +5V and +200V for nixies.


ID – Range switching board and external communication unit with floating point switcher.


This is interesting. Metra didn’t use in these years tin or silver plating. They just used flux laquer and all of boards were soldered manually in the manufactory.


All boards and floating section cover installed.


This unit works properly, perhaps it was never used. I bought it on international radio-meeting in Holice in Czech Republic. Including manual and schematics.

[firewalker]

Nice!!!

Alexander.

[MetraCollector]

M1T 290

M1T290 multimeter is evolved of older voltmeter MT100. They have very similar topology.
This machine is real proof of czechoslovakian backwardness in elektrotechnic industry because it was made since 1984 to 1987 and technology used in is typical for early and mid 70th.
However, this years let engineers from Metra improove and troubleshoot all points of its construction using classic TTL logic and precious measurment methods.
Despite its huge mass and great dimensions, it is a very precious and what is more, a quite reliable multimeter. It is much more reliable than more advanced M1T380 which crash without an obvious reason very often.

Multimeter provides AC and DC voltage measurments in range of 20mV – 2kV, current measurment of 2uA – 2A and also a 4wire resistance measurment method.
It is possible to include this device in IMS2 measure system with special modul. (IMS2 is Eastern Europe GPIB equivalent)



Lets look what is inside.

Typical floating section with Guard shield on the left and digital section on the right.
Data communication are provided by ferrite transformers.


After dissasembling all of boards. A great opportunity to clean it of dust.


All of the boards located inside.


Backsides of the boards. Some of them are made of very poor material and laqued with unsolderable laquer. Repair of boards made of this material is very painfull proces. The main use was for digital board which supposed not to be repaired, in my opinion.


Floating section

D462 – Average AC value converter and effective value converter.
This is not a True RMS voltmeter.


D463 – Input AC amplifier, relay control circuits and current shunts.


D464 – Input DC amplifier, resistance divider for 20mV and 200mV.


D465 – power amplifier of input amplifier, invertor, resistance divider for 20V and 2kV and relay control circuits.


D466 – Set of accurate resistors for resistance and current measuring, current shunts for 200mA and 2A, relay control circuits.


D467 – Calibration voltage reference and integration voltage reference, current power supply for resistance measurment and some relay control circuit.


D468 – Impedance separator, the integrator, comparator and FET control curcuits.


D469 – time pulse supply, comparative level memory, overflow detector, integrator switches control.


D470 – reversible counter, control oscillator bounded to frequency (50Hz), control circuits and up and down range impulse supply.


D471 – Data multiplexer and demultiplexer providing communication of floating and-non floating part of multimeter. Here is also the memory of maximum and minimum for range switching.


D472 – Floating power supply providing +/- 15V, -20V and +5V for logic circuits.


Non-floating section

D473 – Data memory,  LED display multiplexer and floating point control unit.


D474 – Floating and non-floating section communication circuits, measuring cycle start circuits.


D475 – I am not sure about this board, because I am missing this part of the manual, but this is propably button set control unit.


It is difficult to recognize it, but these are ferrite transformers providing galvanic seperation of floating and non-floating section. However, these transformers are very noisy and the machine during its duty is really anoying. It is hard to believe that Metra didn’t use optocouplers despite they were already avialable in these years. Perhaps political reasons.


I had an issue about display, sometimes it was blinking or didn’t show the value. I dissassembled it and discovered that it is absolutely OK. The only problem was connector on the board. All in all, I already know how it looks like inside the display unit.


Front panel and top cover off.


Just testing resistance measurment.


Many of these multimeters were made and there are still few calibration laboratory providing calibration of these machines. However, this process cost more than all this machine itself. The price of M1T290 was 75 000 kc in 1985. This price equals value of smaller car thatyear or 3000€ nowadays without calculated inflation and real money value.
You can buy it for 50€ nowadays in auction or bazaar.

[MetraCollector]

M1T 380

M1T380 is the most advanced and one of the last multimeters made in Metra Blansko in years 1987 – 1991.
It is a precious programmable multimeter for measuring DC voltages and currents, AC measuring using True RMS methodic and resistance measuring including 4-wires method. It also provides many programmable mathematic and statistic calculations. Device is able to be connected in IMS-2 system. (IMS-2 is Eastern Europe equivalent of GPIB, except the LPT connector it is the same).



The device is known as a very accurate providing very comfortable and inuitive user interface. It is controlled by 8bit 8080A system.
However, multimeter is also known for his extremme unreliability about typical freezing, restarting without obvious reason or giving ERROR report on display in the better case. In worse, multimeter shut down with no warning and then you have to find the failure at your own. There are few typical reasons for it.
Metra Blansko made this multimeter in 1987, but technology used in is typical for late 70th  (early 80th ?) compared to the Western world.
Great pain of the multimeter are parts used in.
There are typical tantalum capacitors which explode without warning. In better case, they just make short circuit.
There are typical flat cable connector which increase their resistance with age or lose contact. Solution is recutting them.
There are TTL chips which are unreliable, after 30 years they just don’t work or behaves strange.
There are chips in ceramic package. National company Tesla made these chips, but after years they do not seal and they let moisture into package.

M1T380 with top cover off.


8080A computer on the left.
TRMS converter, input voltage dividers+shunts on the right. Power supplies are aback.


Overview of the M1T380 from the bottom.


Display, keyboard and their multiplex controllers.


This is the A/D converter board. It uses 8748 microcontroller.
On the down-left there are protect relays.
On the up-left there is a precious input amplifier, however, schematic is not avialable and I don’t want to break its package.
On the right there is the microcontroller with optocoupler interface which send and receive data from 8080A computer. Optocouplers make active measure circuits floating and isolated of the rest of the device.

(There is a controversy about this microcontroller, because Tesla made some processors and many other chips copying and reverse engineering Intel originals without license. They had to aditionally buy it. Nowadays it is impossible to discover which chips vere copied and which were made in license.)


Close up of input circuits.


Czechoslovakian variant of 8748 called MHB8748C, made in Tesla Pieš?any. Nowadays there are ON Semiconductor offices and technical support. No production 


These are input circuits consisting of switches, input dividers and current shunts.


True RMS / DC converter. I am not sure how exactly it works, but manufacturer statement in manual is about operational rectifier and non-linear exponential characteristic of base-emitor junction.


Floating power supply +/- 15V


Floating power supply for additional voltages. Nottice the 7805, this Tesla copy is known for its high quallity, better than original, holds much  more current and overload.


IMS-2 interface equalls GPIB interface in Western World. It is supposed to have the same parameters except the connector, Eastern countries used LPT connector from Western world.


Non floating power supply +5V, +12V for digital board. +5V is switched and I had an issue about this board. Nottice the 1R0 resistor above the trimmers and some MKT capacitors.
This M1T380 sometimes suddenly restarted and was producing a lot of noise. I believed in capacitors failure, but it was not the problem. Then I notticed something suspicious about the ferrite core of the inductor. I dissassembled it and then the ferrite core pour out to my hand smashed into uncountable pieces. Well, I installed a new ferrite core and finally M1T380 do not freeze, do not restart and it is quiet now. Unluckily I didn’t take a photo of cracked ferrite.


8bit control computer. A very problematic board.
Printed board is made of material of very poor quallity from slovakian Gumon factory in 80th.
It is ussual that copper trace unstick from laminate and it is not possible to use classic solder tip for desoldering parts. Well, it is not possible to dissassemble the board at all. The only way to replace parts is to cut off their pins and solder new parts on the remainig pins.
What is more, chips made in Tesla love suddenly not to work and that is a problem.
I had an issue about this board too. Multimeter sometimes shut down and I was discovering the problem. I found cracked tantalum capacitor near by the inductor (down-left).


Pattiently cut off this controversial tantalum capacitor and leave only pins.


Solder new parts on remaining pins.


Just for be sure, I replaced all of them. The one on the upper left went gone with smoke effect.


Despite of poor quallity of used material is M1T380 a very good measure device. In moments it works properly, it provides you a 6 ½ measuring with comfortable user interface.


Measuring Vishay Dale 0,1ohm resistor using 4wires method.

[firewalker]

90 degrees tracks!!! 

Alexander.

[Kibi]

Welcome to the forum. 
Thank you very much for sharing. These are most interesting pieces of kit.

[wkb]

Welcome Andrej!  Thanks for this fascinating view into the world of old Eastern-block electronics.

I remember we had exchange students over from Czechoslovakia in +- 1985 (I think it was).  They brought money
to bring home to their university the meanest clone PC we had on sale here in NL.  Lots of puzzled looks when they found out
the range of choice.

I gave them a box of surplus TTL and CMOS chips to take home.  Very happy faces 

The world has changed quite a bit in the past decades!

[MetraCollector]

I am pleased, thank you

There are many opinions and observations around our sk/cz forums of people were students thatyears or years before.
Some people love that era, some people hate.

It is funny to read stories, that someone get an important task to buy Intel components in Western World and then smuggle it to the CSSR. Instantly, other person write it is an absolutely lie.

Then it is quite difficult to find as most objective statement as possible.
I obtained some docummentary movie from Piestany electrotechnology high school made in 198x and there are some funny hints that Tesla invented the 8048 processor by themself and many others.

[bsgd]

A-M-A-Z-I-N-G Pictures! Thank you very much.

I had never seen vintage instruments from that area of the world and this post is just great. Thanks for sharing those nice pics.

[Blue]

Welcome to the forum. 

It is nice to see all those pictures of your treasures.

What happened with the Tesla company?

[David Aurora]

Very cool stuff there! 

[Drirr]

What happened with the Tesla company?

After revolution a lot of Tesla companies were not able to keep up because the market was opened to foreign companies.

Some of them survived..
http://www.tesla-blatna.cz/en/
http://www.electron-tubes.cz/about-the-company-tesla-electrontubes-s-r-o/

[EEVblog]

Awesome photos, thanks for sharing!

Dave.

[saturation]

Great photos, and thanks for sharing.  I've never seen devices from the 'Eastern' block; its interesting in so much is familiar yet different.  The dominant Tesla brand for components is one, which I've heard of but never seen.

[nukie]

Very nice, thank you much for the write up. I enjoy it very much. I see some of the construction similar to Fluke earlier devices.

[smackaay]

Thanks for posting these, I love old stuff like this. Gotta love those weird headers.

[jnd]

Very nice write up. I like these Tesla/Metra instruments even if some people complain it's old, bulky, unreliable etc., guess I'm into the retro stuff Recently I acquired two M1T 330 from local auctions, each for about $40 (still less than shipping for any decent bench meter on eBay). The first I got just before Christmas and it included the whole documentation and original case. It's working well, still in the tight specs +-0.01% from range and +-0.01% from value for 30000 count Voltmeter. So then I caught another one which was more used and it's pretty much spot on. One of them I'd like to reverse engineer the 8080 firmware and possibly mod a bit in the digital section, just for fun. I'll add some photos and description here when I have time.

[ronwoch]

Awesome! Love the VFD's! Much better use of them than a mere clock, though I still lust after several nixie-clock kits. 
Thanks for sharing!

[MetraCollector]

I am very pleased for positive response, thank you

What is that reverse engineering about ? Reading EPROMs, or deeper analyse ?
Usually that is no problem about reading EPROMs in M1T330, because there are in sockets, however, one of my two 330s have GPIB software EPROM soldered in PCB.
If you have a problem with EPROM, do not hesitate to write me, my friend has read all EPROM of all his 330s.

What is more, I think it is a little bit funny that Metra used Texas Instruments EPROMs and in newer M1T380 there are Tesla EPROM.


//one more thing. Please, do you have any experience with M1T380 computer ? I have two of this device, one is functional after repairs and the second one do not work. I bought it for few €uros with ERROR14, I thought it is about lithium backup battery and lost calibration, so I replaced the battery and then started to calibrate, but after few minutes it freezed. When I tried to switch CAL jumper it turn display off and freezed. So I replaced SRAM chip with no effect. Then I resoldered pins but it went worse, when I turn on M1T380, it only blinks chaotic.

My question is about reading EPROMs wich are soldered. Do you have an experience about it ?
I am confined about remaking board computer because I have an opportunity to make PCB with through holes.
Thank you.

[Mashpriborintorg]

Hello Metracollector, as a big fanatic of eastern electronics (I have a huuuuge collection of soviet electronics) I must thank you for these photos, and hope you will post more. Let me share here a wonderfull link from a russian forum, were lots of instruments are taken appart: http://offtop.ru/dustyattic/v1_700390_1.php . For whoever is interested in easten devices, this link is somewhat awesome. I have a big soviet C1-99 o'scope in the attic, I may post a teardown here sometime soon, together with other ones.

[wkb]

Hello Metracollector, as a big fanatic of eastern electronics (I have a huuuuge collection of soviet electronics) I must thank you for these photos, and hope you will post more. Let me share here a wonderfull link from a russian forum, were lots of instruments are taken appart: http://offtop.ru/dustyattic/v1_700390_1.php . For whoever is interested in easten devices, this link is somewhat awesome. I have a big soviet C1-99 o'scope in the attic, I may post a teardown here sometime soon, together with other ones.

Fascinating stuff, thanks for posting! 

[SgtRock]

Dear Andrej:

--Lovingly made, lovingly photographed. Thank you very much.

--A friend of mine once told me that "There are Czechs and there are Slovaks but there are no Czechoslovakians.

"A thing of beauty is a joy for ever:
Its loveliness increases"
John Keats 1795 -1821

Best Regards
Clear Ether

[vk6zgo]

Hello Metracollector, as a big fanatic of eastern electronics (I have a huuuuge collection of soviet electronics) I must thank you for these photos, and hope you will post more. Let me share here a wonderfull link from a russian forum, were lots of instruments are taken appart: http://offtop.ru/dustyattic/v1_700390_1.php . For whoever is interested in easten devices, this link is somewhat awesome. I have a big soviet C1-99 o'scope in the attic, I may post a teardown here sometime soon, together with other ones.

Very interesting stuff,though the naked ladies which one poster has around the periphery are a bit distracting!

[MetraCollector]

M1T 330

Greetings.

I would like to show you another czech test instrument
It is a precious, hi-stable 4.5 digit voltmeter made in Czechoslovakia in years 1984-1987.
There are few manners of this device, it is extremly unreliable, tantalum capacitors explode without warning and flat cables loose their connectivity with age. And many other failures but inspite of them, it is a good voltmeter which is possible to control from computer using IMS2 which is eastern equivalent of GPIB

Overal view:


Modular design - voltmeter itself + power supplies.




Power supply. Thin wires love to fall apart. So when you loose -5V connectivity, you can replace EPROMs If you have backup of them.




Digital board. 8080 system. The GPIB is controlled by computer too so it is much more reliable than TTL controlled GPIB in M1T380 which loves to fail.


This is not TESLA made. It is rebranded hungarian Tungsram 8080 clone.


Schematic updates during manufacturing


Analog.


Here was an old relay with rusty/green contacts. Had to be replaced.


Year of production is 1984 and optocouplers were available, but economic leaders said NO to them.


Hybrid A/D converter. When it fails you can replace it easily because many of them have been produced.


And some overall.


I was told that every czechoslovakian test instrument was a clone of some western with 10 year delay. Could you please someone write here WHICH is M1T330 clone of ?

Thank you and regards Ondrej