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Space invaders TOEI MUSEN chassis GM 120 - 140


baz
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Am working on a black and white toei chassis gm120 for a space invaders.

am trying to understand the chassis power brick.

100 volt goes into a transformer....  in the brick is a bridge rectrifier , two transistors both with caps and one large 300uf cap.

16 volts comes out of that transformer.

the output to the chassis is 100 volt.

what exactly is the entire purpose then ? couldnt i just bypass this stupid brick which keeps blowing the 1.5 amp fuse and just wire 100 volt straight to the chassis and tie a fuse on the neutral line anyway ?

its AC going into to the power brick.. and AC to the chassis.

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Hi, here's a bit of background which may also be of help to anyone with a similar question.

The purpose of running the 100V monitor supply through a 1:1 transformer is usually to achieve electrical isolation between the monitors 'live'  chassis and the mains and other machine electronics. This allows a video signal from the game PCB whose ground is at '0 Volt' which is usually tied back to mains earth at some point to be directly connected to the 'ground' level on the crt chassis pcb. Without isolation those two points would have a damaging or even dangerous Voltage between them and could not be safely connected.

If the transformer is frequently blowing the correctly rated fuse then either one of the loads on its secondary windings is higher than expected (the monitor itself or whatever is connected to the 16V winding) or possibly the transformer itself could be faulty. A shorted turn in its windings could cause excessive current even without any external loads connected,

This can occur if the enamel on the internal windings wears away over time allowing adjacent wires to make contact. Although a transformer has no moving parts, windings which are not perfectly packed can vibrate causing an audible hum and possibly eventual wear of their enamel insulation.

Most machines which are set up for 240V originally use a stepdown transformer for the 100V or 110V monitor which also provides the required isolation but machines which were manufactured for Japan or the US still usually need an isolation transformer for the monitor even if the Voltage is 1:1.

Some newer monitors do not require external isolation, mostly multi Voltage types which incorporate some sort of switchmode power supply on the chassis PCB. Although the switching transformer on a switchmode supply is smaller than a conventional 50Hz or 60Hz transformer (being switched at a high frequency allows for a smaller core to be used) there can still be isolation between its primary and secondary windings which would allow the chassis ground to connect directly to the other machine electronics.

In summary most machines especially older ones do require an isolation transformer with appropriate Voltage for the supply and monitor so always check this important detail, especially if replacing a monitor with a different type or converting a machine imported from overseas.

Hope this helps, (no offense intended to anyone who already knows this stuff)

Regards John

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14 hours ago, baz said:

Am working on a black and white toei chassis gm120 for a space invaders.

am trying to understand the chassis power brick.

100 volt goes into a transformer....  in the brick is a bridge rectrifier , two transistors both with caps and one large 300uf cap.

16 volts comes out of that transformer.

the output to the chassis is 100 volt.

what exactly is the entire purpose then ? couldnt i just bypass this stupid brick which keeps blowing the 1.5 amp fuse and just wire 100 volt straight to the chassis and tie a fuse on the neutral line anyway ?

its AC going into to the power brick.. and AC to the chassis.

You can replace the 100-100 transformer with a 240-100 transformer, commonly found in AUS built LAI machines, this would achieve the same outcome

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you people are a wealth of information and its people like you who help to keep this hobby alive , many would be lost.

Transformer is fine , the moment i disconnect the transformers output 16 volt to the bridge rectifier it stops blowing the fuse.

but of course , the bridge rectifier could be fine too , i have to check the two transistors.. the main issue is trying to get these damn rusted nut and bolts undone holding the transistors lol

might be easier if i just unsolder the suckers and just run my multi meter into them.

Edited by baz
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