real dumb question

thanks again guys. Right off to argos for me then, and I'll get some pictures up once I've done the testing.
Thanks for the support.

 

Well I got the multimeter and did some testing.

The motherboard seems to be split into two identicle channels with a fuse seperting the transformer and each channel. (Both fuses blow when power is connected!)

Everything the amp side of the fuses seems to be fine and offers a resistance across it.

There is one Black and two red cables coming form the transformer and conneted to the fuse holders. Testing resistance across either combination results in a 0 reading so looks like the transformer is dead!

Anyone know where I can get a new Rotel transformer (and its rateing) from and roughly the cost?

If I have to keep the amp (ie my mate doesn't want it back!) i will probably just replace it with a maplins transformer. Is it worth getting a better spec one?
Thanks again all. I can post pictures tonight if wanted but it seems the transformer is the problem

 

That's an easy one...

I highly doubt that the transformer is dead. What actually happens is that a transformer appears to offer no DC resistance (and thus seems a short to the diode test mode of the multimeter), but it's an AC device (simple explanation).

If the output devices are checking out ok then it's hard to say what the problem might be without getting hold of the amp.

 

Thanks Isaac, I do hope its not the transformer! However I wasn't using the diode test to test the transformer. I was using the Maximum (2000k)setting of the resistance (ohm) section. As I understand it this passes a current through the tested componet and if the reading is zero then it denotes a short! Is this incorrect?

Is there a definitive way of thesting the transformer?
Cheers

 

Resistance testing does indeed measure the current that passes for an applied voltage, but this is done with DC.

The only way to easily test a transformer is to check that there's no short between the primary and the secondary windings (DC is fine for this), and then apply an AC voltage to the primary, and measure the output of the secondaries (you'll need the multimeter on VAC for this, but ideally use an oscilloscope...)

 

A transformer will have a low dc resistance, use the lowest setting on your meter rather than the highest.

A transformer fault would blow fuses on its input, not its output.

IIRC you shorted the output, this has probably destroyed the output transistors. Photos would be interesting.

Paul

 

Well if anyone is still interested. The cost of labour and parts to repair would have come to over £100 pounds to fix (from Rotel! but fortunatly it wasn't the transformer that died) so Im not going to get it repaired. But of course i had to pay my friend for it . So I am the owner of a poorly power amp.

Warren M if you are interested in it drop me a line.
Otherwise any ideas as to where I could sell it as is (ebay?). I'm sure some one can make good use of it. It would be a shame to see what is a good amp with mostly working parts get binned.

Thanks agian all:

 

Welcome to the club. I have an Arcam Alpha 8P which was fed a dose of dodgy mains by our friends at SWEB and now distorts badly on one channel. The cost of shipping it in two directions plus the likely cost of repair basically make it questionable as to whether it's actually worth repairing

 

Chris
yopu can claim from SWEB aslong as you know the time/date it happened (i think).
Just remind them of when they blasted redland in bristol and paid out

 

It was a almost a year ago now!

 

oops!

 

You can take the amp to any competant tv repair shop, they're really very simple devices, most technicians won't even need a circuit diagram to diagnose them. It won't cost much to repair.

Its very unlikely you've blown your transformer, they're not really devices that can go faulty unless a very high amperage passes through them. Its more likely that the output transistors have gone, from shorting the output terminals of the amp. They should be pretty cheap to replace.

Shorting left and right pairs of input cables doesn't do any damage, if you look inside the device you'll see that most inputs/outputs share a common ground anyway. Naim, and other manufacturers who use XLR connections, do not suffer from this problem, provided you keep the earth balanced throughout (usually means buying their kit )

 

Hi Tom Thanks for the advice. Thats exactly what I did. An d the cost of the replacement parts (from Rotel) and labour was going to be more than a £100 so It isn't really worth repairing it. Shame really.
So looks like it only good for a project or spare parts. Anybody want it for a small sum then drop me a line.

 

What parts were they asking for? I can't imagine Rotel are using anything other than stock components.

 

Now that I'll find out tomorrow.
I also found it hard to believe that the grand total cost of parts in the whole amp cost the £137 asking price, let alone for the few parts required.
I'm picking it up tomorrow and will post when I know.
I agree with you that it probably is just a few transistors. I gave it a good look over and there were no scorch marks or any visible damage at all except for the blown fuses!