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pjh
August 25th, 2015, 08:45 PM
Recently, among several floppy read failures, I began to notice an acrid smell coming from my 8 inch floppy disk enclosure. I opened the enclosure and saw that the source of the smell was the floppy power supply transformer which was now discolored and misshapen. Wondering if I had a shorted component on the circuit board, I tested and found that the board itself was OK. The transformer had just decided to short out on me. In looking around for a replacement transformer, I came across pictures of my power supply in an XOR system. I will try to upload pictures of the power supply and schematic with this thread.

Does anyone know how to locate a suitable transformer that has these two secondaries. When I have tried to search for a match, I end up on some trasformer website and then immediately get lost in the forest of transformer options before finding anything that is even remotely close to what I need.

Any help would be greatly appreciated.

Phillip

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Chuck(G)
August 25th, 2015, 10:57 PM
Phillip, switching PSUs have pretty much obsoleted the linear ones. Your best bet is to replace that single transformer with two separate ones, which will allow you to keep your current PCBs. You didn't state if you were in a 120VAC or a 240VAC mains country--your current PSU can be wired for either voltage. You could also find a couple of switching supplies to give you similar output.

Take a look at Jameco.com.

retrogear
August 26th, 2015, 02:06 AM
>I began to notice an acrid smell coming from my 8 inch floppy disk enclosure.
>I opened the enclosure and saw that the source of the smell was the floppy power supply transformer which was now discolored and misshapen.

Philip, if you are using 120VAC I noticed in your schematic the primaries are switched in parallel. If that has a switch, you might want to check that switch with an ohmmeter to make
sure it does indeed add them in parallel. Parallel windings provide more current capability. If it's been running on one primary due to a defective switch or in
my case the switch mounting screws had come loose, the functioning primary has to provide twice the current and will run warm and discolor over time. If the switch
was wrong, you could try running it again with them connected properly in parallel. AC line transformers are very durable and forgiving. However, yours might
have gone beyond that point.

Larry G

pjh
August 26th, 2015, 02:18 PM
Thank you for the replies.

Chuck, I am in the USA so the supply is wired 120vac. I will probably go to a switching supply. I had hoped to find a similar transformer for originality, but by the time I find two seperate transformers, I will probably end up spending nearly as much as a new switching supply will cost. I have found a supply on eBay that provides all of the voltages at sufficient amperage for 39.99, so I will go ahead and get that.

Larry,

Thanks for your input too. The configuration of my supply was hard wired with no option switch. There are two black and two red wires on the primary side and the supply was wired from one red and black pair. I stripped the shrink wrap tubing off of the other red and black pair and tried them but the heat damage to the transformer was too extensive. The transformer simply began to overheat on the second primary winding as well.

Thanks again to you both.
Phillip

gekaufman
August 26th, 2015, 02:33 PM
It pays to mention that transformers rarely fail without something causing excessive current draw, often the filter caps drying out and shorting.

It your case it sounds like it was never wired correctly in the first place, with only one primary hooked up.

A switcher is a good solution, but if you're looking to preserve a vintage piece their are many folks who will rewind or "clone" vintage transformers. I've used Heyboyer (Michigan, USA) in the past for some vintage vacuum tube gear. It's a more expensive option.

- Gary

Chuck(G)
August 26th, 2015, 03:16 PM
Transformers that are subjected to temperature extremes can often develop shorts in the windings. Like anything electronic, it pays in the long run to keep everything cool. Your choice of a switcher will greatly reduce the heat in the enclosure.

retrogear
August 26th, 2015, 03:19 PM
>There are two black and two red wires on the primary side and the supply was wired from one red and black pair. I stripped the shrink wrap tubing off of the other red and black pair and tried them but the heat damage to the transformer was >too extensive. The transformer simply began to overheat on the second primary winding as well.

Just to clarify, the red wires should be tied together and the black wires together and AC applied to both primaries together. One primary by itself will overheat. The current is split in half when paralleled together and the output power is doubled with less drop across the transformer from primary to secondary which generates the heat.

Larry G

Chuck(G)
August 26th, 2015, 03:33 PM
If you disconnect the secondaries from the power supply board and apply line voltage to the transformer--regardless of how the primaries are set up--and it heats up, it's toast. A transformer with no load should not heat noticeably at all.

If it heats up only when connected to the power supply PCB, then your problem is in the power supply itself, not the transformer.

retrogear
August 26th, 2015, 05:27 PM
>If you disconnect the secondaries from the power supply board and apply line voltage to the transformer--regardless of how the primaries are set up--and it heats up, it's toast. A transformer with no load should not heat noticeably at all.
>If it heats up only when connected to the power supply PCB, then your problem is in the power supply itself, not the transformer.

Yes I agree totally with that test. It's a shame if it burned up because only one primary was being used improperly wired alll these years. The schematic shows it should have had both primaries in parallel.

Larry G