I need a replacement transformer

[mockba_the_borg]

Hi All,

I have a JP-8000 which is in great shape, and works absolutely fine.
However, as I leave it on for a few minutes, I start feeling a "smell" from the transformer.
The electronic guys will know what I am talking about, that smell of "transformer insulation".
I am afraid that this transformer may short at some point and fry my beloved JP-8000, so I want to preemptively replace it.
Can anyone point me to the correct replacement one? I am quite sure Roland won't source it anymore.
I even thought about replacing it by a small switching power supply, but I am not sure as it has separated Analog and Digital grounds.
So if anyone could give me some guiding light I would really grateful.

Thanks a lot!
Mockba the Borg.

[AncientGeek]

It seems that this transformer is prone to failure. You may find this thread from another forum helpful:

http://electro-music.com/forum/topic-59810.html

Good luck.

[mockba_the_borg]

Hi AncientGeek,

Thanks for the reply. One of the links on that forum led me to this one:

https://belfuse.com/product/part-details?partn=MT-8-15

Which is readily available at digi-key.
Looks to me that it is a good replacement (maybe some wiring will be required).
Maybe someone with more knowledge on electronics than me (which is pretty much anyone) can give some extra advice or recommendation here?

Thanks a lot!

[AncientGeek]

It looks like it has an adequate power rating. The physical dimensions are on the datasheet -- you'd have to check whether it would actually fit inside. Yes, some wiring would be required. The connections on the original transformer will very likely not match those on the new one. The most important ones to get right are the primary (mains input) ones, which *should* be relatively easy to identify. Get them wrong and it's game over. A multimeter set to AC volts will help to identify which terminal is which on the secondary side of the old transformer, but please be very careful when mains voltage is present. The datasheet of the new transformer can then be consulted to work out which wire goes where.

Please get help if you're not sure.

[mockba_the_borg]

No, that's fine, I am ok with the electronics, wiring, soldering, etc. etc.
Just wondering if there would be any special considerations for using a different transformer.

I have contacted the original manufacturer of the transformer used, but they are bound by contract with Roland to not provide me with any information ... :P

All things being equal, I think I will just check the dimensions. I will open the device to look at the actual dimensions for the original transformer.
Then I'll just order one of these and replace. I think it is a no-brainer, supposing it fits inside.

Fingers crossed ... :)

[AncientGeek]

Sounds good :) Let us all know how you get on. It seems that the original transformer is a bit underspecified, given the number of failures there seem to have been, so if you find a good replacement it would be good information to share.

[mockba_the_borg]

Hey guys,

The new transformer has arrived. I still need to check it for the right voltages and stuff, but it is a good chunk larger than the original.

20180920_145059_HDR.jpg (170.87 KiB) Viewed 7470 times

Maybe I should have ordered the MT-7-15 instead of the MT-8-15. However I am not sure if the 280ma on 15V the MT-7-15 has would be enough, probably leading to the same heating/smelling issues over time.
This little "beast" that the MT-8-15 is should be more than enough. And hopefully won't heat as much (the original transformer heats up to the point you cannot touch it).

20180920_145117_HDR.jpg (172.01 KiB) Viewed 7470 times

I am thinking about mounting it sideways, either attached to the side of the power supply body or to the bottom by using some 3D printed bracket.
I may need to remove its metal case so the body fits inside while still leaving space for isolating the connectors from the conductive bottom cover.
It would look something like this:

20180920_145152_HDR.jpg (183.52 KiB) Viewed 7470 times

So, I am open to ideas, comments, alerts, etc.. etc..

Cheers,
Mockba_the_borg

[mockba_the_borg]

All done ... replaced the transformer.
I had to remove its metal casing, so it could fit inside the transformer cavity.

20180921_171437_HDR.jpg (175.74 KiB) Viewed 7460 times

After soldering everything and making sure 300 times that nothing would touch or get loose or anything, I decided on a rough placement.

20180921_172408_HDR.jpg (182.08 KiB) Viewed 7460 times

This is how it looks like after snugging the transformer in with a plastic spacer and encasing everything (including the bottom) with a thick plastic insulation.

20180921_173743_HDR.jpg (166.38 KiB) Viewed 7460 times

Placing the cover back in holds everything firmly in place.
I know I didn't use any screws to attach the transformer, but I didn't care much about it as this thing sit on a stand and is never moved around.

So far no "hot transformer" smell, no burnt smell, no smoke, no fire, no smoke, no zombie apocalypse. (did I say no smoke twice?)

It may be a placebo effect, but I feel like the display looks bright now, not brighter than normal, but normal as it should be. (it was dim before)
And the sound seems to be better. Maybe the previous transformer was not feeding it enough?

Cheers,
Mockba the Borg.

[mockba_the_borg]

An update here.

I have noticed that the new transformer would still heat up a lot. Basically because, by just "floating" there, it didn't seem to have any way to dissipate its heat, so this is what I did:

Put a nice chunk of thermal paste between the transformer body and the bottom of the power supply case, which is basically a radiator for everything else.
Put a couple rubber feet between the transformer and the cover, so it presses the transformer against the aluminum case (and the thermal paste).
This seems to have solved the problem.
One thing that I noticed though, the linear regulator for 5V still put out a nice amount of heat. Nothing that looks like it would melt stuff, but still manages to keep the heatsink very hot to the touch.
I have these linear regulators. Anything above their output voltage turns into absolute heat.

So far no smoke, bright flashes or loud bangs. So I calling this one a win.

Cheers,
Mockba the Borg.

[AniaDeely]

Hi...Voltage ratings are critical to re-create the original operating voltages within the amplifier. On the other hand, as long as the new transformer can supply the required current, a higher than needed current rating is really a plus, as the transformer will then operate at a cooler temp than it would if providing it's full current output. The amplifier will only draw the current it needs. The fact that the transformer can supply more simply becomes a reserve of capability versus need. Since the Edcor transformer has a higher current HV secondary, it will likely be physically bigger as well. Be sure to check that it's dimensions and physical structure will work where the old transformer was mounted.

[mockba_the_borg]

A proof of concept I just implemented:

Got a piece of plexiglass I had lying around and made a bottom for the synth using the original bottom as reference.
Then made a hole on it and put a 12V fan running at 5V, so it runs silent. I am hoping that blowing cold air in will help with dissipating most of the heat ... let's see.

Cheers!