Author Topic: C1-112A oscilloscope/multimeter - restoration  (Read 8478 times)

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Offline poorchava

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C1-112A oscilloscope/multimeter - restoration
« on: February 15, 2015, 08:30:43 pm »
I've scored a nice thing today at the flea market for about 20€:

It's a Soviet (actually Lithuanian) oscilloscope/meter combo. From what I've found it was made by company called 'Rimeda'. It's single channel, specced up to 10MHz, but reportedly working well up to 20MHz, which is not bad considering the overall technology level of this thing. The timebase goes from 50ms/div down to 50ns/div, vertical ranges are from 5V/div down to 5mV/div. It has an integrated 3.5 digit multimeter which displays digital measurement result using CRT. It has an external trigger input, altough it looks like a banana jack, not a BNC. It's a very small and compact device for an analog oscilloscope (it weighs about 3kg).

I bought it as supposedly working, but the guy didn't know much about the thing. It was pretty banged up (scratches and stuff, input BNC is damaged, intensity and contrast knobs are loose) but it turned out to be working quite well and the CRT seems to be in a very good shape. Originally, this unit came with a front cover, which also served as a storage compartment for probes, but this one came without the cover or the probes (which by the way were shitty, as I've read somewhere). My unit was made in 1991 and it's serial number 19833. The power cable had been replaced at some point, but the old one was just cut and an extension was added.

It appears, that it has never been opened before - seals which cover a screw on the bottom are still there:



After looking inside and briefly checking that there is no major damage inside I've powered it up and voila:





Some shots of the internals before disassembly:








I've found some schematics for the thing and I'll try to convert them to PDF at some point.

In general the scope is all-semiconductor. Vertical input amplifiers and and other related stuff are discrete analog, using soviet components. The digital parts (multimeter, some parts of timebase(?)) are built using soviet versions of 7400 logic (mainly K555LA3 which is an equivalent of 74LS00 quad NAND). There seems to be a lot of some white powdery residue on the internals and obviously shitload of dust and general dirt, but no signs of moisture ingress.

Stuff to do:
-clean everything
-replace the damaged BNC connector
-replace electrolytics
-sort out the power cable
-do something with the peculiar DMM probe connector. Either obtain an original probe or replace the connector with 4mm banana sockets (or 2mm if 4mm won't fit)
-clean potentiometers or replace them if possible (some fo them are quite unique mechanical contraptions)

Stay tuned :)
I love the smell of FR4 in the morning!
 
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Offline radhaz

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Re: C1-112A oscilloscope/multimeter - restoration
« Reply #1 on: February 15, 2015, 08:57:24 pm »
Very interesting device, thanks for letting us see the insides.
 

Offline electr_peter

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Re: C1-112A oscilloscope/multimeter - restoration
« Reply #2 on: February 15, 2015, 09:41:06 pm »
Neat scope. 20€ sounds like a good deal if you have extra space to keep it. It would be nice if it had two channels. Old 1-2ch CROs go for >100€ on used item sites in Lithuania.

Original scope probes are not worth to search for - they were pretty bad. Get any cheap (or expensive) >20 MHz probes - it will be much better. As for DMM, it used special connector - also not worth to search for it. Install some 4mm banana sockets (like these http://lemona.lt/index.php?page=item&i_id=44024).

How big is the screen? It seems smaller than other CRO's by looking at pictures.
 

Offline poorchava

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Re: C1-112A oscilloscope/multimeter - restoration
« Reply #3 on: February 15, 2015, 10:36:30 pm »
The screen is about 65mm by 45mm.

I've also learned a thing about the BNC connector - soviet BNC connectors were not completly compatible with western BNCs. From what I've read, standard BNC plugs will fit into soviet sockets, but not the other way around. I've plugged the from my Atten scope into this and it fit very tightly, but I assumed this was because of the dent on the socket. Seems like another good reason to replace that connector.

I will post some more detailed photos as I take the scope apart.

As for the DMM connector, the sockets that you have posted are way too large. I expect to have access to quite good machining equipment in near future, so perpahs I'm gonna try to fabricate some custom 4-way 4mm banana socket.
I love the smell of FR4 in the morning!
 

Offline tzok

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Re: C1-112A oscilloscope/multimeter - restoration
« Reply #4 on: March 08, 2015, 02:03:30 pm »
I have this scope, your unit, like mine, is actually a Soviet product. Later RIMEDA have sold it at Lithuania under their brand. Soviet instruments were never branded.
I have the German manual for it, English one also did existed for sure, but I can't find it anywhere. I've found it once, the guy have scanned a few pages for me, but then I've lost contact with him :(

http://www.elektroda.pl/rtvforum/topic2946383.html

Your scope for sure will require replacement of electrolytic capacitors, as well as most of the potentiometers, but be very cautious as the tracks easily peel of from the PCB. Also - not all pr are described in the manual, so try to measure/mark their position prior to removing them.

I've never used the integrated multimeter, but I have restored and calibrated it, and actually it's pretty accurate (but measures only DCV and Ohms). I also have the original probes.

The 2-channel version (w/o the multimeter) was called C1-118A.
« Last Edit: March 08, 2015, 02:12:43 pm by tzok »
 

Offline Martin.M

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Re: C1-112A oscilloscope/multimeter - restoration
« Reply #5 on: March 08, 2015, 07:30:57 pm »
nice the little russian.

There are 3 oldie scopes known who have on screen multimeters:

C1-112

Grundig GO15D

Tek, 213

greetings
Martin

 


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