240V conversion

** Hi,

mainly due to the popularity of Ebay, electronic gear originally sold in the USA and Japanese markets is now regularly turning up in Australia. USA items are intended for a 120V, 60Hz supply while Japanese ones are for 100V,

50Hz.

Conversion to 240V mains operation involves internal inspection and modifications OR simply determining what VA rating step-down tranny will be suitable. The modifications involve removing or shifting PCB links, altering QC connectors or rewiring the supply side leads to the AC tranny - PLUS changing fuses and the AC plug to the Aussie version.

I had an EVENT active studio monitor (twin port model) in for such conversion this week and it looked easy. There is an IEC inlet on the back and markings that indicate the possibility of 120V and 230/240V operation.

The unit has a toroidal tranny fitted inside with four supply side wires, so it was of twin primary design allowing 120V and 240V operation. I reorganised the four QCs according to a pattern drawn on the PCB and used a variac to raise the voltage.

At about 30V, the ( T4A ) PCB fuse blew - indicating the two primaries were wired out of phase. No real harm done and a few minutes later I had the four wires the right way around.

Variaced the unit up again ( to about 130V ) and this time it started working, I verified the woofer and tweeter were both OK. Next I wound the variac up in gradual steps to 240V and suddenly and there was a very loud BANG !!

All sound stopped. WTF !!!

When I opened the unit again there was a smoke inside and black deposits visible on the PCB and the nearby acetate filling used in the box. The source was a 20mm varistor on the PCB that had exploded.

But why?

Markings on the part showed that it was rated for 270 volts ( 20K271) - but that is a DC voltage rating. So when exposed to a 240VAC supply with 340V peaks it was grossly overloaded.

The stupid " Ying Tongs " had fitted the WRONG varistor.

The correct part is a 430 volt rated varistor OR one marked as being 275VAC, as is the case with the class X2 cap wired in parallel.

.... Phil

Reply to
Phil Allison
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Just about every device I've ever hand my hands on that allowed such configuration had 2 MOV's, each rated for the lower voltage. When you properly configure the connections on the board for 200+ volts for example, the 2 MOV's end up in series, otherwise, they end up in parallel for low voltage configuration.

Maybe some one has serviced that unit in the past and replaced them incorrectly.

Jamie

Reply to
Jamie

"Jamie"

** There was ***ONE** only MOV wired across the pins of the IEC inlet.

Fuckhead.

.... Phil

Reply to
Phil Allison

the

items

be

altering

so

a

were

four

but

275VAC,

Ever come across Crate (not some mickey mouse operation) USA "made" amps , for export to 240V countries , with mains switches + neons? Neons glowing like lighthouses and melting all around, from the charring of the droppers which are set for 110V including stating so on the switch bodies

Reply to
N_Cook

Yesterday had a somewhat related 110/240V repair but this time not safety issue. Little PV practise amp , 20W, original PV , properly set up for 240V , mains fuse inside had "blown" at switch on.

1.25 inch F rated 250V 500mA . Maybe all right for 110V areas but repeatedly switching on with the random occassional 330V surges and it will fail mechanically (filament laying nicely diagonally in the barrel, fixed at one end only). T 500mA one went in there
Reply to
N_Cook

"Nutcase Kook"

** Surge and running currents are DOUBLED with 120V supplies.

The max peak ( switch on) surge can be estimated by measuring the resistance of the primary winding of the AC tranny and dividing that number into the supply voltage.

Eg:

The PV " Encore 65" tranny has a 7 ohm primary, the amp draws 0.25A rms at idle and 1A rms at full tilt. The max inrush surge is however over 30 mps - so the AC supply use needs to be rated at " T3A " merely to survive the surge.

In virtually essential to use a "delay" or " slo-blo" fuse with transformers and SMPS. Unfortunately, the fuckheads at PV and Fender do not comprehend the issue and refuse to be informed on the matter.

... Phil

Reply to
Phil Allison

I've noticed quite a bit of dubious pilot lamps on equipment that should allow 240volt export use. Luckily it's 120 here, so I've not have the pleasure of experiencing what really happens with those.

Reply to
Cydrome Leader

in

will

PLUS

back

operation.

wires,

used

the

loud

deposits

340V
,

of

Neoned rocker switches. After being on for ten minutes or more, the switch is too hot to keep a finger on it. The little neon is glowing as bright as a

1W filament lamp, and the lens over it has a brown patch. Go inside inside and melted plastic around the neon and the dropper which by now is a blackened cylinder with a helix, certainly no colour markings
Reply to
N_Cook

in

will

PLUS

back

operation.

wires,

used

the

loud

deposits

340V
,

of

Neoned rocker switches. After being on for ten minutes or more, the switch is too hot to keep a finger on it. The little neon is glowing as bright as a

1W filament lamp, and the lens over it has a brown patch. Go inside inside and melted plastic around the neon and the dropper which by now is a blackened cylinder with a helix, certainly no colour markings
Reply to
N_Cook

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