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How to find a drop in replacement for this transformer?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author How to find a drop in replacement for this transformer?
tioJim
It's started buzzing like a mad thing!

CMOSCrash
Having trouble viewing the picture. Try to re-upload.

Transformers are pretty easy to substitute, in my opinion. All you need to know is the primary and secondary voltage, and the full-load current drawn by the load. If it's a center-tapped transformer, that's important to know, as well.

I'll assume the transformer in question is a "step-down" transformer - meaning it steps the high "primary" voltage down from something like 120V AC to a lower "secondary" voltage, like 12V AC. Then find your "turns ratio", R, by dividing the primary voltage by the secondary voltage.

A 120V to 12V transformer has a turns ratio of 10:1

Once you have identified the primary and secondary voltages, and turns ratio, you'll need to figure out how much current the load would ever possibly draw on the secondary side of the transformer. This is your "full-load curent" or FLC. If you re-upload the picture, I can try to help you figure that out. For a safety factor, I'd multiply the full load current by 125%. We'll call that A.

1.25 x FLC = A

Then multiply A by the secondary voltage. This will tell you what size transformer you need. Transformers are rated in volt-amperes, or VA.

Then all you need to do is search for a transformer that is rated for at least the calculated VA and at least the voltages on the primary and secondary coils.

Let's say you've done your calculations and found you need a 42VA transformer to step 120V down to 24V. Your turns ratio is 5:1. Say you find a 5:1 transformer rated at 60VA and rated for 240V on the primary. That would be more than adequate in most cases. Again, without knowing the exact application, I can't say for sure.

Lastly, use extreme caution if either primary and/or secondary voltage of your transformer is greater than 50 volts. Do not mess with mains voltage unless you have the skills and knowledge to do so safely. In a fight between you and the power grid, I'm betting on the grid every time.

Best of luck!
tioJim
CMOSCrash wrote:
Having trouble viewing the picture. Try to re-upload.

Transformers are ...


High. thanks so much!

There were no replies for a few days so I assumed the thread had disappeared beneath the page break.

Here's some other pics

http://www.makermobile.co.uk/shared/pic1.jpg
http://www.makermobile.co.uk/shared/pic2.jpg
http://www.makermobile.co.uk/shared/pic3.jpg
http://www.makermobile.co.uk/shared/pic4.jpg
http://www.makermobile.co.uk/shared/pic5.jpg

There are two coils so presumably two secondary voltages?
Rowan
Why don't you contact MOTU or their UK distributor, MusicTrack (the markings on the PCB indicate this is a MOTU Midi Time Peice AV)

http://musictrack.co.uk/repairs/service-and-support.html

They may be able to provide you with a replacement transformer or at least give you enough information to source a replacement.
tioJim
Rowan wrote:
Why don't you contact MOTU or their UK distributor, MusicTrack (the markings on the PCB indicate this is a MOTU Midi Time Peice AV)

http://musictrack.co.uk/repairs/service-and-support.html

They may be able to provide you with a replacement transformer or at least give you enough information to source a replacement.


I tried MOTU. They stared at me blankly. I said "Schematics?" They said "Sch-what-ics?"

I'll try Musictrack though they do warn on their website

Quote:
Unfortunately, due to the unavailability of parts certain older MOTU products are proving uneconomical to repair. For that reason we are no longer able to accept the following MOTU units for repair ... MTP AV (Serial)


But they might just mean the digital bits not something simple like a transformer

Jim
wavydave
Mercury Magnetics/Mercury Vintageā„¢ Transformer Restoration Service restores guitar transformers. I have bought their chokes before. The parts are top notch and they are always helpful with questions.

They even make keyboard x-formers (OB-Xa, Rhodes, Wurlis).

So the question would be how much are you willing to pay?

https://www.mercurymagnetics.com/pages/mainframe.htm
tioJim
wavydave wrote:
Mercury Magnetics/Mercury Vintageā„¢ Transformer Restoration Service restores guitar transformers. I have bought their chokes before. The parts are top notch and they are always helpful with questions.

They even make keyboard x-formers (OB-Xa, Rhodes, Wurlis).

So the question would be how much are you willing to pay?

https://www.mercurymagnetics.com/pages/mainframe.htm


Thanks Dave

Well I'm in the UK so let's add international postage on top!

The modern equivalents from MOTU are quite pricey so I'd pay more than you might expect! I could wait for another used one to pop up on eBay but that could have a noisy transformer too.
Graham Hinton
tioJim wrote:
It's started buzzing like a mad thing!


That is not surprising since it is burnt out at the lower right corner. The question you should be asking is what burned it out? It is quite likely that a faulty bridge or capacitor caused the transformer to overheat in which case a replacement transformer would suffer the same fate.

Is the LM340 the only regulator or are there more? An MTP is probably 5V only which would need a 9Vac transformer, the mains side fuse tells you it will be less than 30VA and the lack of a heatsink on the LM340 less than that. If you can separate the circuitry from the regulator(s) and run it from a bench PSU you can determine a PSU spec and work backwards.
Rex Coil 7
tioJim wrote:
It's started buzzing like a mad thing! ...
lol lol that thing is so roasted .... lol

Y'best work out ~why~ it roached ... the new one could very likely turn to yet more stinky lacquer if you don't give everything attached to that side of the trxfrmr a good looking over.

tioJim
lol @ the meme!

The bizarre thing is, it still works. I mean the unit powers up and behaves as it should.

The noise has become quite terrifying now. Like there's a swarm of angry bees trapped in it lol

I've given up and found another one on eBay
Rex Coil 7
tioJim wrote:
lol @ the meme!

The bizarre thing is, it still works. I mean the unit powers up and behaves as it should.

The noise has become quite terrifying now. Like there's a swarm of angry bees trapped in it lol

I've given up and found another one on eBay
Well at least you have a parts whore on hand now.

thumbs up
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