Miracle Systems Floppy PSU

[bagpuss22]

Hi there,

I have a Miracle Systems Double Floppy with a built in PSU.

Looks like the PSU has gone, so my question is:

Does anyone have spares of this OR can I get it repaired?

Thanks

Russ

[skagon]

Without knowing the particulars of the unit, I'm quite confident it can be replaced with a modern switching-mode power supply that will also be more reliable, more stable, much cooler and probably weigh 1/10th of the original. You could even keep it outside the unit, if you'd prefer that.
A couple of pictures of the internals would be most enlightening, though.

[1024MAK]

I have a Miracle Systems Double Floppy with a built in PSU.

Looks like the PSU has gone, so my question is:

Does anyone have spares of this OR can I get it repaired?

Hi Russ

The PSU may well be repairable. It depends on the type and what has gone wrong. As Skagon says, we need pictures of the PSU. If possible, use macro mode on the camera. And take photos from different directions including overhead and if it uses a PCB, the underside / track side please.

Mark

[RWAP]

Quite often it is the capacitor which has failed but if you are unlucky, then you melt the copper windings around the transformer.

I have spares here from units where the disk drives have failed - and the PSU on its own (or maybe the case) would come in at under 2Kg, so postage would not be too bad if you need one.

THe one thing I never found was any plastic rivets large enough to put the case back together!

[bagpuss22]

Thanks for the replies gents.

I will get the item apart tonight and get some photo's.

I would prefer to repair, if I can, as I am one of those people who
like to keep things as genuine and possible. Call me sentimental!

If that does not work then I will go for a new PSU.

Cheers

Russ

[bagpuss22]

OK Gents,

I had a look around this tonight, unless I am just a useless software engineer, I would say that 1 of the primary winding has gone and 1 of the secondary as they appear to be open circuit.

240v AC going in, nothing out of the transformer. I am assuming it should be 18v, regulated down to 12v.

[skagon]

Yikes!
Transformer, rectifier bridge, shitty capacitors, 7812, no filtering?
Mate, do yourself a favour and get an SMPS unit to replace that thing... seriously.

P.S. Stupid question: you *have* checked the fuse, right?

[1024MAK]

Looks fixable to me (normal get out clause may apply )

With the unit unplugged you are looking to see low resistance readings (from zero ohms to about 10 ohms max) across the fuse, the primary windings and the secondary windings. Check to see if the board has been coated in a protective coating (as this will act as a layer of insulation)As per picture:

If you are getting open circuit (sometimes shown as O/L for over load on the meter) or you get very high readings, then the transformer has died. Although transformers (in general) are normally reliable.
Replacement transformers can be obtained, the only problem being the pins may be in different places.

If the transformer is okay, we can move on to the next step.

Mark

[1024MAK]

Yikes!
Transformer, rectifier bridge, shitty capacitors, 7812, no filtering?

Looks more like the rectified 9V ac from the transformer is smoothed by the large blue electrolytic capacitor, this the feeds the +12V dc supply to the FDD (but off load will be about 13V). Meanwhile this supply also feeds a 7805 voltage regulator, which in turn feeds a regulated +5V dc supply to the FDD.

State of the art, it is not, but it does the job.

Mark

PS - Russ, if you are going to measure the voltages with it live /switched on, remember to keep well away from the exposed tracks and connections that are connected (or indirectly connected) to the 230V mains.

[skagon]

Mark, I had a second look, I don't think you're right mate.
The only thing I was wrong was the 7812; it's probably a 7805. The output from the transformer goes through the bridge and then directly onto the 7805. The big ass capacitor is between ground and bridge positive, and the two smaller ones are between ground and 7805 in and out.
The drives are obviously +5V only models.
Does the job, sure but... designs like that I wouldn't really trust for anything important.