According to that schematic you should also change from a 1/4 amp fuse to a 1/8 amp when running at 220.

 

Looks like what might be a slight miss-application of that transformer as it would appear it was originally intended for 110/220 with primaries either series or parallel.
Which is more commonly seen now.
Also must be an old unit as N.A. power is 120/240 for many years now.
Max.

Thanks Max, yes I believe it’s from the 80s

 

According to that schematic you should also change from a 1/4 amp fuse to a 1/8 amp when running at 220.

Thanks Electric, the fuse inside the unit is rated at 1A250v.

 

According to that schematic you should also change from a 1/4 amp fuse to a 1/8 amp when running at 220.

Well spotted Eletric, I will change the fuse and give it a try. Cheers

 

If a quarter amp fuse blew then an eighth amp fuse should blow even faster.

We all make mistakes. Are you adding the jumper and not removing the original or are you moving the original from one position to the other? The jumper should go to one OR the other setting. Not both. I don't know that you made that mistake or not - I just know it's the sort of thing I might have done. So don't do as I might have; do as I should have. And make sure there are no solder bridges.

Also, it's hard to tell, but I'm assuming the two black wires are the 220 primary of the transformer and the white is likely the center tap. I'm wondering if those three wires are correctly positioned on the board. If not - that may be the reason for the fuse blowing.

 

Also...and this is important. Make sure that the transformer is also rated for 50 Hz operation.

220VAC is also used in North America, but equipment rated for that voltage are rated for 60 Hz.

 

@schmitt trigger Not certain on this but I believe back in the 80's those transformers were rated for 50/60Hz. But would a transformer solely rated for 60Hz cause a fuse to blow if it were run at 50Hz? (or vice versa)

 

If a quarter amp fuse blew then an eighth amp fuse should blow even faster.

We all make mistakes. Are you adding the jumper and not removing the original or are you moving the original from one position to the other? The jumper should go to one OR the other setting. Not both. I don't know that you made that mistake or not - I just know it's the sort of thing I might have done. So don't do as I might have; do as I should have. And make sure there are no solder bridges.

Also, it's hard to tell, but I'm assuming the two black wires are the 220 primary of the transformer and the white is likely the center tap. I'm wondering if those three wires are correctly positioned on the board. If not - that may be the reason for the fuse blowing.

Thanks Tony, great advices.

I first removed the jumper from J3 to J2 and when I applied the 240vac the 3amp fuse on my power cord blew up however the 1A250v fuse on the unit itself was intact. So I solder it back to the original position to test it if it’s still working with 110v, and it works fine.

 

OK, STOP! With no connections NOTHING should be blowing up.

You removed the jumper. Pay close attention to the words I used - you removed the jumper. NOT "Moved" the jumper, "Removed" it. Sorry if it feels like I'm talking down to you - I'm definitely not. I just want to be sure I know exactly what you've done. If you've removed the jumper - according to the schematic no fuses should be blowing. NONE. So something is way way wrong here. Unless I'm missing something (not the first time for sure).

Completely remove the jumper. No fuse should blow. Incidentally, the schematic only shows a single fuse. If you're talking about a fuse on a power strip or something - then there's definitely something wrong and we need to get to the bottom of it. And don't be replacing fuses with higher values. ONLY use the correct fuse that belongs there. Higher rated fuses can cause fires.

 

The unit was switched off when I plugged it to 240v but as soon as I inserted the plug into the socket I got the plug fuse to blowup. I just couldn’t figure it out but there’s most be a reason for to blow.

 

Re-read my last comment. I did some editing.

And if it's "OFF" and blowing fuses then something is shorted. It might be advisable to take the board to someone who knows more about electronics than you do. Just don't burn down the house - or shock the heck out of yourself. We'd hate to lose you.

 

OK, STOP! With no connections NOTHING should be blowing up.

You removed the jumper. Pay close attention to the words I used - you removed the jumper. NOT "Moved" the jumper, "Removed" it. Sorry if it feels like I'm talking down to you - I'm definitely not. I just want to be sure I know exactly what you've done. If you've removed the jumper - according to the schematic no fuses should be blowing. NONE. So something is way way wrong here. Unless I'm missing something (not the first time for sure).

Completely remove the jumper. No fuse should blow. Incidentally, the schematic only shows a single fuse. If you're talking about a fuse on a power strip or something - then there's definitely something wrong and we need to get to the bottom of it. And don't be replacing fuses with higher values. ONLY use the correct fuse that belongs there. Higher rated fuses can cause fires.

No worries Tony. I have to learn it the hard way

 

Success, I’ve tried again and this time no fuse was blown.
I appreciate all your valuable reply‘s I learned a lot add to that I’m still alive.

The unit is now running at 240v

 

The unit was switched off when I plugged it to 240v but as soon as I inserted the plug into the socket I got the plug fuse to blowup.

The links are after the switch so with the switch off the links can make no difference.

Now can somebody from US land explain the difference between the two voltages.
Is 110V a live and a neutral, whereas 220V is two lives?
In that case maybe there is a short between one power input and chassis earth and that should definitely be sorted out even it works OK.

 

Please forgive me I don’t understand what is MOV ! Yes it works fine with 110v

MOV = Metal Oxide Varistor, which is a component that is supposed to change from a very high resistance value to a very much lower resistance value when the voltage across it exceeds some value. These are used for protection against excessive voltage spikes. On many occasions they do not return to the high resistance mode after a voltage pulse.

 

In the UK you have 230v which is derived from a 3phase transformer, 1 phase and a Grounded star neutral.
In N.A. you have a single phase transformer with a centre tap secondary 120-0-120, the 0 point being earth grounded neutral.
AKA split-phase.
A residence uses 120 & N for low wattage items and 240 for higher current appliances.
N.A. has been 120/240 for decades now, old system 110/220v.
Max.

 

The links are after the switch so with the switch off the links can make no difference.

Now can somebody from US land explain the difference between the two voltages.
Is 110V a live and a neutral, whereas 220V is two lives?
In that case maybe there is a short between one power input and chassis earth and that should definitely be sorted out even it works OK.

220V in the UK is a line and a neutral, while in the USA 220/230/240 volts is two live wires. The two systems are different.

 

So on the 120V supply if the neutral was shorted to earth nothing bad would happen?
On 240V both inputs are live so that short would blow the fuse?

 

Any low impedance path to GND on a N.A. 240v supply will cause a high current, i,e. short circuit.
Both jurisdiction use a grounded neutral system so very little difference.
Max.

 

Any low impedance path to GND on a N.A. 240v supply will cause a high current, i,e. short circuit.
Both jurisdiction use a grounded neutral system so very little difference.
Max.

So there is a short on the wiring between the power socket and switch which needs fixing.

Then it will work, with the appropeiate link, on 240V painlessly