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120V to 240V internally
120V to 240V internally
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Old 7th December 2017, 03:29 AM   #1
armarra1 is offline armarra1  Australia
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Red face 120V to 240V internally

Hi,
I apologise if this is in the wrong section , however I am trying to modify a 110v USA cassette deck to run on Australian 240v main input.

I've paid to download the service manual which includes the 'instructions' for changing voltage.

well.. the instructions are not that clear in identifying the pins to reconnect but it does mention the primary pins soley.

what makes me worried is that the secondary has 250v glass fuses and clearly labeled 250v on its circuit board that's straight onto the secondary pins.

if this is step up, then what happens if I put 240volts across its primary ?

I am assuming that by changing the primary to be across the two live pins instead of a live and neutral, that I get well.... 220v and that this goes to 250v at the secondary also.

as the voltages are high and I don't want to bugger the electronics can anyone suggest a course of action.

attached(at least I think so) is the downloaded pdf service manual. I refer to page 22 for relevant schematics. note.

holes 3 , 5 and 6 on the circuit board are the only ones that have terminals with pins on the transformer beneath and that pins 3 and 5 are connected to 120v plug and labelled live and neutral respectively.

Last edited by armarra1; 7th December 2017 at 03:32 AM.
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Old 7th December 2017, 04:26 AM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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Usually in 110v the windings are in parallel.
For 240v the windings are in series.
You should be able to work out wiring from that.
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Old 7th December 2017, 04:30 AM   #3
armarra1 is offline armarra1  Australia
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Quote:
Originally Posted by nigelwright7557 View Post
Usually in 110v the windings are in parallel.
For 240v the windings are in series.
You should be able to work out wiring from that.
thanks for the quick reply. It appears to be a solid state transformer. the internals are not visible, just a gold mesh of copper wire.

can you elaborate ?

I'm talking of the transformer itself.
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Old 7th December 2017, 04:39 AM   #4
nigelwright7557 is offline nigelwright7557  United Kingdom
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What are the connections to it ?
When you say solid state do you mean a switch mode power supply ?
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Old 7th December 2017, 04:47 AM   #5
armarra1 is offline armarra1  Australia
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Quote:
Originally Posted by nigelwright7557 View Post
What are the connections to it ?
When you say solid state do you mean a switch mode power supply ?
Its a transformer coil/unit within a domestic device.

so.. it have primary and secondary terminals.

curiously the secondary has two 250v glass fuses on the circuit board that's attached to the terminals.

I'd include a picture if this site would let me attach one.
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Old 7th December 2017, 05:14 AM   #6
leadbelly is offline leadbelly  Canada
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120V to 240V internally
1) if the service manual describes rewiring the primary side for 240 and leaving the secondary alone, that is perfectly correct

2) 250VAC is one of the standard voltages for fuse ratings, it does not mean the secondary voltage is 250V
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Old 7th December 2017, 06:20 AM   #7
armarra1 is offline armarra1  Australia
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Originally Posted by leadbelly View Post
1) if the service manual describes rewiring the primary side for 240 and leaving the secondary alone, that is perfectly correct

2) 250VAC is one of the standard voltages for fuse ratings, it does not mean the secondary voltage is 250V

thanks..

its just that the pin numbers on the schematic don't match the pin numbers on the primary board of the transformer connection.

there are only three terminals and two are connected for 120v. I presume switch over the neutral to the other and assume its a 'live' connection for 240.

perhaps I'm being too careful, the fuses ought to blow if there's any power problems and the house 'safety' switches should throw if its a short.
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Old 7th December 2017, 06:22 AM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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If you measure primary impedance for 110v then it will be right when it is connected to give twice that impedance for 240v.

If its wrong it will likely destroy the electronics.
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Old 7th December 2017, 06:32 AM   #9
armarra1 is offline armarra1  Australia
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Quote:
Originally Posted by nigelwright7557 View Post
If you measure primary impedance for 110v then it will be right when it is connected to give twice that impedance for 240v.

If its wrong it will likely destroy the electronics.
Well I definitely don't want to destroy the electronics.. So at least my caution and protracted enquiries is warranted.

the schematic has the numbers 2, 3 and 5 next to the lines that represent the primary yet the actual circuit board have 3 and 5 as connected but 2 isn't connected nor is there a pin there and 6 is connected to the primary but nothing to the mains power wires.

the schematic isn't matching the circuit board on the unit via pin numbers, hence my caution. I figure there are only three terminals on the primary. two are connected, surely the solution is a specific permutation of 2 out of the 3 possibilities(excluding the current one).
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Old 7th December 2017, 07:11 AM   #10
multi is offline multi  Australia
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You could always use a 120 volt step down. I have ordered Tube amps from China and they tell you are 240 volts but I never trust them so use a step down to check. I always use a 240 volt 60 watt globe old type not a led in series with the amp with a switch, just to make sure after changing the wiring. If the wiring is correct the light globe will only light up a little if wrong very bright. Never tried it with transistor equipment.
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