can I solder an extra length of wire of similar thickness to the tail in order to reattach to the pins.

That depends on your manual skills.
This connection was a copper wire to a solder pin the day it was born. Now you want to know if you can connect a copper wire to a solder pin. What's the difference? A couple of millimeters of copper wire attached to the end of dozens of feet of copper wire? Will your kitchen faucet stop working if the water pipe is 1/8th of an inch longer?

Will this impact the performance of the transformer in any way?

Yes. It might change the probability of a long life. Any sort of repair is difficult to do to the highest possible standards unless you're good at it. I could do that. Can you?

You have three options: Try to fix it, buy a new transformer (and attach it properly so it doesn't get jerked off the board when people drop it), or give up and throw it all in the trash bin. Pick one.

 

So can I solder an extra length of wire of similar thickness to the tail in order to reattach to the pins.

Note that the thin wire is coated magnet wire, not bare copper. You may need to use some fine sandpaper to take off the insulation in order to get the solder to tin the end of the wire. Then the challenge is to make a mechanical repair in addition to the electrical connection. That wire is too thin to take any stress, so figure out a way to hold it – and whatever you solder to it – steadily supported. I like using hot glue for such things but I'm not sure if that transformer might get hot enough to melt the glue when you get it running. Maybe some epoxy would be better.

 

Note that the thin wire is coated magnet wire, not bare copper. You may need to use some fine sandpaper to take off the insulation in order to get the solder to tin the end of the wire. Then the challenge is to make a mechanical repair in addition to the electrical connection. That wire is too thin to take any stress, so figure out a way to hold it – and whatever you solder to it – steadily supported. I like using hot glue for such things but I'm not sure if that transformer might get hot enough to melt the glue when you get it running. Maybe some epoxy would be better.

Thank you for the advice. I will try to repair this but based on the cost of a replacement I would prefer to purchase a new transformer but haven't have been able to find a suitable replacement. I see from the attached manual that the primary is 780 omhs and the secondary winding is 2-3 omhs. Based on the figures on the rectifier the and the input voltage could you recommend a suitable replacement?

 

That depends on your manual skills.
This connection was a copper wire to a solder pin the day it was born. Now you want to know if you can connect a copper wire to a solder pin. What's the difference? A couple of millimeters of copper wire attached to the end of dozens of feet of copper wire? Will your kitchen faucet stop working if the water pipe is 1/8th of an inch longer?

Yes. It might change the probability of a long life. Any sort of repair is difficult to do to the highest possible standards unless you're good at it. I could do that. Can you?

You have three options: Try to fix it, buy a new transformer (and attach it properly so it doesn't get jerked off the board when people drop it), or give up and throw it all in the trash bin. Pick one.

Thank you but you are stating the obvious and not too much technical advice which I require. I can work out all of the above but what I want is the spec of a suitable replacement. The transformer is damaged and the cost of a replacement is relatively small. Once I have a spec to work off I can source an appropriate one. Can you help based on the information I have provided?

 

what I want is the spec of a suitable replacement.

I told you in post #12 that I can't name that transformer. I have no numbers for voltage, current, or the space between the solder holes. Most likely you will have to ask the manufacturer.

 

The transformer is damaged and the cost of a replacement is relatively small.

I think the collective wisdom you'll find around here is that it's virtually impossible to find replacement transformers. I still look once in a while but I can't think of a single success in many years of repairs. The best you can hope for is knowledge of the input and output requirements so you can find a similar transformer. The DC resistance of the two sides is not enough. If you could determine the wire gauge of both sides, you could get closer. What you really need is the turns ratio, which gives the voltage ratio.

It's odd that this transformer does not appear in the schematics. I wonder if its function is simply to adapt 120V to 220V or vice versa.

 

It's odd that this transformer does not appear in the schematics. I wonder if its function is simply to adapt 120V to 220V or vice versa.

This would make sense as the input is a single IEC female connector that can accept US or European voltage 110v/220v. Dependent on the input voltage the wiring sequence from this relay board to the main Toroidal transformer is changed.

To keep things a simple as possible for us let us say I will never use 110V so that the input votage is 250v AC as this is the input voltage to the rectifier and the output is 12v DC. However, there is also a 30V DC on the rectifier dependent on whether a switch is open or closed. Could you explain these figures please?

The max power stated on the back of the unit is 1100VA. So I would guess I would need a transformer that had an input of 250v AC and an output of 12V DC rated at 6A. Is that an accurate guess?

I am uncertain of how to determine the resistance values influence? Would it be enough to get a resistance rating equal, higher or lower? Or how does this value matter?

 

So I would guess I would need a transformer that had an input of 250v AC and an output of 12V DC rated at 6A. Is that an accurate guess?

I can't comment on much here, but I'm confidant that is not a 6A transformer! More like 0.6A or less. I guess that rules out my theory that it's a voltage step-up or down for the mains power.

 

I have contacted the manufacturer's authorised repair agents and one of the guys told me that he has had the same problem more than once. Probably not enough glue (my opinion not his). He says the purpose of the transformer is for a Low Voltage startup. I presume this is some sort of soft start so that the current is controlled and there is reduced risk of current surge which could damage delicate components or speakers.

More importantly he says he cannot even get the parts so looks like I am back to trying a repair. Something to look forward to this weekend.

 

You were lucky to get a hold of someone that knows something. That's a challenge these days.

By "low voltage startup", does that mean it's essentially a wall wart to supply a small voltage for a few components related to starting up the main power? That might be fairly easy to reproduce if you know the output voltage. Maybe you can probe those broken wires and see what's there. Be careful, of course, if you power up that board.

 

You were lucky to get a hold of someone that knows something. That's a challenge these days.

By "low voltage startup", does that mean it's essentially a wall wart to supply a small voltage for a few components related to starting up the main power? That might be fairly easy to reproduce if you know the output voltage. Maybe you can probe those broken wires and see what's there. Be careful, of course, if you power up that board.

Yes it delays the current inrush. It's to do the way toroidal transformers draw current when powered up.

After doing some research I found this:

Taken from http://sound.whsites.net/project39.htm

When your monster (or not so monster) power amplifier is switched on, the initial current drawn from the mains is many times that even at full power. There are two main reasons for this, as follows ...

• Transformers will draw a very heavy current at switch on, until the magnetic flux has stabilised. The effect is worst when power is applied as the AC voltage passes through zero, and is minimised if power is applied at the peak of the AC waveform. This is exactly the opposite to what you might expect
• At power on, the filter capacitors are completely discharged, and act as a short circuit for a brief (but possibly destructive) period

These phenomena are well known to manufacturers of very high power amps used in PA and industrial applications, but 'soft start' circuits are not commonly used in consumer equipment. Anyone who has a large power amp - especially one that uses a toroidal transformer - will have noticed a momentary dimming of the lights when the amp is powered up. The current drawn is so high that other equipment is affected.

This high inrush current (as it is known) is stressful on many components in your amp, especially ...

• Fuses - these must be slow-blow, or nuisance fuse blowing will be common
• Transformer - the massive current stresses the windings mechanically and electrically. It is not uncommon to hear a diminishing mechanical buzz as the chassis and transformer react to the magnetic stress
• Bridge rectifier - this must handle an initial current way beyond the normal, because it is forced to charge empty filter capacitors - these look like a short circuit until a respectable voltage has been reached
• Capacitors - the inrush current is many times the ripple current rating of the caps, and stresses the internal electrical connections

It should come as no surprise to learn that a significant number of amplifier failures (especially PSU related faults) occur at power on (unless the operator does something foolish). This is exactly the same problem that causes your lights at home to 'blow' as you turn on the light switch. You rarely see a light bulb fail while you are quietly sitting there reading, it almost always happens at the moment that power is applied. It is exactly the same with power amplifiers.

There are also some formulae on this page which may help work out the rating of this transformer. I think the black plastic box may actually be a thermistor and not a rectifier as I previously thought.

 

The transformer is a step-down transformer providing AC voltage to the Protect / Safety circuit. It was added in a later revision of the PX-612. It is not related to the audio. The circuit is in charge of providing the mains ac to the BIG transformer.

 

Have a look at C4 1000uF electrolytic, what is the voltage rating of it, that will give you an idea...

 

Have a look at C4 1000uF electrolytic, what is the voltage rating of it, that will give you an idea...

Did a search for C4 1000uF electrolytic and it brings up a lot of 10uF and alot of capacitors but no transformers?
The PCB function is to act a low voltage regulator. The transformer output is 12VAC rated at 1.5-2VA similar to this one:
http://www.maplin.co.uk/p/2x12v-6va-chassis-mounting-mains-transformer-a80qj