MEOPTA 87328 16mm projector supply

Description: A 1200 VA transformer-based power supply.
Manufacturer: MEOPTA
Made in year(s): 1965 mine model
Country of origin: Czechoslovakia
Status: Working

The MEOPTA No. 87328 was an optional power supply designed for the 16mm sound film projector named Meoclub Automatic 16, also made by MEOPTA. Because the projector itself was powered from a 220V mains and used a 220V halogen lamp too, this enabled the usage of 75V/375W and 110-120V/1000W projector lamps, and also made it possible to power the projector from a 127V mains. In addition, an analog illuminated AC voltmeter and a huge 10-positional rotary switch have been implemented to manually compensate for incidental mains voltage drops and to ensure the correct voltage is applied to the lamp, so it’s additionally some kind of a manual stabilization supply.

MEOPTA 87328 transformer BackBack view

Except for the transformer and all the mechanical selectors, there are no other electronic parts in the cage – not even a fuse. 🙂
If there’s 220 volts AC supplied (or 127V AC, if switched properly) and the switch is at the “minimum” setting, all output voltages are nominal, i.e. same as the transformer itself is rated for. For verification, the AC voltmeter is connected to the 220 volt secondary and has a red marker on its scale, indicating nominal voltages on all outputs.

MEOPTA 87328 transformer, guts1200 VA transformer with a sticker in Slovak

Should the input mains voltage be lower than nominal, the voltmeter goes below the red “220V” marker and the rotary switch is used to short-circuit the tapped primary by a few tens of turns, basically, yielding an increase of all secondary voltages as a compensation. Doing such tapping on a today’s 230-240V mains supply – if stable – can lead to destruction, as it will oversaturate the transformer and is going to cause, along with a violent growl, some unpleasant smell; so it mustn’t be done unless there’s some mains dropout.

MEOPTA 87328 transformer, voltage selectorsInput-output voltage selectors

Since the primary had been constructed for a 220V input which was used back in communist Czechoslovakia and neighboring countries, operating this supply nowadays on 230/240 volts is going to yield slightly higher voltages than the rated nominals. Because it does not allow dimming (going lower than the nominal input) I’d have to rewind the primary to solve this 🙂

MEOPTA 87328 transformer, big switchThis scary switch sparks nicely inside!

Overall, it weighs around 13 kg, with at least 6 kg being the copper windings in the transformer. (The good old days when electronic things were actually built to work properly…) Finally, some reverse-engineered schematic of the guts, for those interested. I’ve originally done it in Slovak, but hopefully it shouldn’t be that hard to understand.

6 Replies to “MEOPTA 87328 16mm projector supply”

    1. Podľa mňa schéma zapojenia nesedí s reálom.. podľa zapojenia to skôr vyzerá ako autotransformator.

    2. Možné je to, že som ten stroj dostal už upravený (viď tá zásuvka na zadnom paneli). Ale už ho nemám, takže ak máš schému pôvodného zapojenia, prilož a zavesím ju na stránku.

  1. Hallo Jozef, erst einmal dickes Lob für Deine vielen äußerst interessanten Beiträgen, besonders Deine Beiträge zu Computernetzteilen haben mir sehr gefallen und so einige Anregungen werde ich ganz sicher mit nehmen.
    Nun zu diesen Trafo : ich habe das gleiche Model erwerben können, weil ich eigentlich einen Trenntrafo gesucht habe. Ich habe dieses Netzteil fast vollständig zerlegt und mußte mit Entsetzen feststellen, daß der verwendete Transformator KEIN Trenntrafo ist !!! Ich wollte vollkommen sicher gehen und hatte bereits bei der ersten Vorprüfung Unstimmigkeiten feststellen müssen, auch bin ich über den selben Umstand der zu hohen Netzspannung “gestolpert”, wie Du, deshalb die Zerlegung. Also es ist zunächst erst einmal so, daß der Trafo mit sehr hoher Wahrscheinlichkeit kein Trenntrafo ist und in der verbauten Schaltung definitiv nicht ! Leider sind sowohl die Wicklungen als auch die herausgeführten Anschlüsse mit einem Harz ähnlichen Kleister zu geschmiert – möglicherweise könnte man durch Trennen der Anschlüsse doch noch einen Trenntrafo draus machen, aber so, wie der Trafo verbaut ist, ist bei diesem Trafo eine Sparschaltung verwendet worden und das würde dann einen Trenntrafo ausschließen. Wie sieht es aus ? – hast Du schon mal den Trafo bzw. das Netzteil näher untersucht ? Würde mich echt über Deine Erkenntnisse freuen – vielleicht liege ich ja mit meinen Erkenntnissen völlig daneben oder ich habe eine andere Modelvariante ?! …
    Liebe Grüße aus Dessau, die Bauhaus- und Gropiusstadt im Dessau-Wörlitzer Gartenreich im Bundesland Sachsen-Anhalt; Deutschland

    1. Hi Ronald,

      consider yourself lucky – I’ve managed to fish out your comment from all the others marked as ‘Spam’ by WordPress’ Akismet engine, destined for deletion. Perhaps one of the characteristics of the German language, the famous long compound words, have triggered it to mark it as such. But I have no knowledge over the internal workings of the algorithm that decides so.

      As for the power supply: yes, as per the schematic that can be viewed above, the output is galvanically connected with mains. As such, in no case it can be considered as an isolated power supply by design. (Remember that the purpose of this thing was to compensate for lower-than-nominal mains voltage situations that affected the projector lamp; or to permit usage of 75 and 120 volt projector lamps. The projector itself was still being supplied with 220V~). On the other hand, the “9WN 663” series of transformers made by ZVS DUBNICA were all typized mains-voltage transformers by design, so if I remember correctly, you should be technically able to just disconnect one of the input mains wires out from the secondary winding. But without a datasheet and a test of the insulation breakdown voltage between pri./sec., you should not consider it as a safe replacement and conformant to the norms – I think this was the reason they connected it like that. Feel free to experiment!

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