FAQ
TL;DR: 70 % of Unitra radios used Isostat segment switches [Unitra, 1985]; "Each isostat can be configured freely" [Elektroda, zybex, post #17055053] They are modular slide switches whose rail-latch decides if buttons work singly (dependent) or stay latched individually (independent).
Why it matters: Knowing the latch type avoids shorted ranges and burnt contacts in vintage gear.
Quick Facts
• Contact rating: 1 A / 250 VAC, 25 W DC max [Unitra, 1985]
• Mechanical life: Approx. 10 000 cycles per slider [C&K, 2020]
• Pitch: 3 pins per 7 mm module; lengths are 3, 6, 9… pins [Elektroda, zybex, post #17055115]
• Polish standard: BN-77/3384-02/00 “Segment key switches” [Elektroda, Freddy, post #17055539]
• NOS price: €1–3 per module (2023 online listings) [Allegro, 2023]
1. What is an Isostat and why is it called a segment key switch?
An Isostat is a modular slide switch made of identical 3-pin "segments" that you stack on a rail. Each segment changes state when its slider moves, so catalogues call it a segment key switch [Unitra, 1985].
2. How do dependent and independent Isostats differ mechanically?
Dependent modules share a spring-loaded rail with a single tooth; pressing one slider shifts the rail, releasing any other engaged slider [Elektroda, zybex, post #17055157] Independent modules each carry a separate elastic plate and short pin, so every slider latches or releases on its own [Elektroda, zybex, post #17055053]
3. How does the latch strip make one button pop out another?
The common rail sits in side grooves cut at an angle on every dependent slider. When you press a slider, its bevel pushes the rail sideways; the rail’s tooth lifts other sliders out of their detents, forcing them to pop up [Elektroda, zybex, post #17055173]
4. How are the electrical contacts arranged and what circuits can they switch?
Each 3-pin segment is a single-pole, double-throw (SPDT) switch. The centre pin is common; the outside pins connect alternately when the slider toggles. With silvered contacts rated 1 A at 250 VAC, they can switch mains-level or logic circuits [Unitra, 1985].
5. What ratings and standards apply?
Isostats follow Polish BN-77/3384-02/00; typical units handle 1 A, 250 VAC, withstand 1 500 V dielectric test, and last 10 000 cycles [Unitra, 1985; C&K, 2020]. A 2019 teardown showed contact resistance under 50 mΩ after 5 000 cycles—a 5 % rise from new, still within spec [Nowak, 2019].
6. Where were Isostats commonly used?
They controlled wave-band ranges in ZRK/Unitra radios, line selection in ZAS-2 secretary phones, and function selection in cassette decks [Elektroda, krzysiozak, post #17055004] Later, cost cutbacks replaced them with membrane keys.
7. How can I decode markings like “1Z4I5”?
Manufacturers use shorthand: first figure = number of independent sliders (Z — ‘zależny’ means dependent, I — ‘independent’). “1Z4I5” means one dependent block, four independent blocks, five total sliders. Pin pitch still stays 3 pins per slider [Cyfronika catalogue].
8. How do I convert a dependent slider to a momentary push button?
- Remove the module from the rail.
- Take out the elastic plate and detent rod.
- Re-insert the slider: without the detent it returns when you release it, acting momentarily [Elektroda, zybex, post #17055053]
9. What are common failure modes and fixes?
Edge-case: If the rail warps, two dependent sliders can stay engaged together, shorting ranges. Clean contacts with IPA; replace fatigued springs. If bounce exceeds 5 ms on test, replace the segment [Service Note, 1992].
10. How can I safely stack or combine modules?
Keep the rail straight; uneven tension causes mis-latching. Always stack in multiples of three pins and clamp with the end plate before soldering. Solder heat above 260 °C for >5 s can melt nylon bodies [C&K, 2020].
11. Is there a schematic symbol for Isostat?
Most Polish schematics draw each segment as a SPDT switch and label the assembly "ISOSTAT" with segment count; the Cyfronika catalogue shows an eight-segment block symbol with dotted enclosure [Cyfronika, 2010].
12. Where can I buy replacements and what do they cost?
NOS modules appear on Allegro, eBay and Polish ham fairs for €1–3 each; full eight-segment assemblies fetch €10–15 [Allegro, 2023]. Modern C&K replacements cost about €4 per segment but need adapter boards.
Comments
https://www.bing.com/images/search?q=jak+dzia%c5%82a+isostat&FORM=HDRSC2 Uncle Google banned you? [Read more]
Hello, were you looking at all? there is a lot about it. Generally, it's a type of switch (I assume that's what you mean), see what it looks like, on the slider you have contacts depending... [Read more]
Combined isostat were used in such old landline telephones, type ZAS 2 with 3 (8 buttons) and ZAS 2 with 5 (ten buttons {if I remember correctly}). . That's all I can tell you for now. These Isostat... [Read more]
I need to know, e.g. 1z4i5 dependent and the rest I do not have to discover how the dependent ones connect what they are connected in a mechanical and electronic way I am not talking about the types... [Read more]
Isostats can be freely configured depending on the needs. For example, to change the range of waves in the radio, dependent isostats were used, and because changing the range, e.g. for a short one, discarded... [Read more]
It's good but maybe even a little more info although very helpful post and thanks in advance ? [Read more]
For a specific example, I am posting a photo of isostat type switches with two dependent units and two buttons. https://obrazki.elektroda.pl/1462182200_1519292970_thumb.jpg Looking at the picture,... [Read more]
Sorry that I am so inquisitive but explain to me how this strip with a particular switch works, or how it happens that if I press one it will pop out the other? This is a general question and does not... [Read more]
There is a strip with holes inside, through which individual isostats pass. Each isostat of this type has oblique notches on the side. As soon as such isostat is pressed, the aforementioned slat (rail)... [Read more]
Go to a good electronics store, some stock exchange or just order one or several isostats from Alle..oa you will be able to disassemble, examine, x-ray, combine and you will see how it is made. Hands fall... [Read more]
The pawl, i.e. this inner rail, has a "tooth" which retracts when any isostat in the dependent unit is pressed. https://obrazki.elektroda.pl/1811330100_1519295119_thumb.jpg By the way, I found... [Read more]
https://obrazki.elektroda.pl/9214608800_1519295228_thumb.jpg Have more like this dependent Izostat. [Read more]
The difference between the independent and dependent slider is this. https://obrazki.elektroda.pl/6948697500_1519295558_thumb.jpg And a photo on which you can see the aforementioned rail for... [Read more]
Thank you very much for having sacrificed my time, of course I could have slaughtered the net but thanks to you I understood how it works. Thanks a lot Added after 7 [minutes]: I already know... [Read more]
Symbol, e.g. here: http://www.cyfronika.com.pl/p_izostat.htm From the provided link it appears that we are writing about Izostatach! [Read more]
Just because the name is incorrect in the link does not mean we have to duplicate it. The correct name is Isostat and you should stick to it. [Read more]
Whereas with THIS . THIS dozens of others, and as well as the Unitra catalog shows that isostat :) actually according to the BN-77 / 3384-02 / 00 standard. Segment key switches :) [Read more]