Author Topic: Studio 5LX PSU  (Read 195 times)

Offline mmtuk

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Studio 5LX PSU
« on: September 07, 2017, 05:55:50 AM »
One of my two 5LX's is of the older type (much older than I thought!) and has all the power supply components as part of the main circuit board whereas the other has the PSU on a separate PCB mounted on stand-offs.

The older units transformer is buzzing audibly (albeit when you're close to the device) and I'm concerned that this might indicate inevitable failure at some point. What I'd like to do is remove the existing components and replace the entire PSU with an off the shelf switched mode PSU that supplies the right voltages at the required current level.

Interestingly, the later LX5 I bought from a USA based eBayer and when it eventually arrived in the U.K. the PSU assembly had broken loose and was floating around inside the case - I was really fortunate that the LX5 hadn't suffered catastrophic damage - it was completely unharmed!

I'm quite confident at hacking/modifying things so I'm not likely to be stressed by the tasked at hand. However, I'm not an electrical engineer and don't have the knowledge to work out the PSU requirements myself. If somebody has the info' and can pass it on, I'll happily go and source a PSU that meets or exceeds the required spec. and proceed with the 'mod'. I'm in the UK so 240v primary is a start!

If it's of any use I can simultaneously document/photograph the steps taken and post here as a project for others to follow (assuming I don't fry myself and/or the LX5!).

"What the mind of man can conceive, and truly believe, he will achieve" - Norman Vincent Peale

Offline Syn-Fi

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Re: Studio 5LX PSU
« Reply #1 on: October 30, 2017, 09:13:05 AM »
My LX has a switchmode inside.  In fact, i can't see that opcode would have used anything else but switchmode given the era.

Offline GaryN

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Re: Studio 5LX PSU
« Reply #2 on: October 30, 2017, 06:38:05 PM »
One of my two 5LX's is of the older type (much older than I thought!)
What this is is an original Studio 5 that was later modified into a 5lx with a firmware upgrade. The later ones gained the separate PSU board when somebody finally went "D-oh" and realized it was much easier and cheaper to build different units for worldwide distribution that way than to have different assembly runs for different countries. They probably outsourced the new PSU's already assembled from a supplier for the same reasons.
The older units transformer is buzzing audibly (albeit when you're close to the device) and I'm concerned that this might indicate inevitable failure at some point.
These types of transformers buzz because the enamel lamination surrounding the winding has cracked here and there and become a tiny bit loose. You're hearing a 120Hz buzz - the 1st harmonic of the 60Hz line frequency. This buzzing, albeit annoying, does not necessarily spell doom for the transformer. It can often work this way for the life of the unit without failure.
What I'd like to do is remove the existing components and replace the entire PSU with an off the shelf switched mode PSU that supplies the right voltages at the required current level.
The practical solution is to repair or replace the transformer only. Possible repair methods include, in this order, depending on the severity of the buzz, simply inserting rubber standoffs/grommets under the transformer, since the sound is being amplified by the vibration being transferred to the chassis. This often cures the symptom in 5 minutes or less. Since you say you have to be "close" to hear it, this will very likely do the trick. If the transformer isn't sealed in a metal can, you can attempt to drip a sealer into the windings to stop the noise. (Because the buzz is actually the overlapped windings of thin metal plates buzzing against each other as the magnetic flux varies with the AC) This can be an epoxy mixture, a superglue or even a basic wood varnish. The main requirement is that it be very low viscosity (thin) in order to be able to seep into the layers as far as possible before drying and reasonably heat-resistant, which most glues and such are.

Failing those, you might consider simply replacing the transformer with an equivalent. There's almost certainly a part # you can cross-reference. Plus, you know the primary is 240v and you can measure the secondary voltage with a multimeter. The current rating will be roughly 2/3-3/4 the internal fuse rating and you'll want something roughly the size of the one you're replacing. This is far, far simpler, safer and more practical than shotgunning the entire PSU.
I'm quite confident at hacking/modifying things so I'm not likely to be stressed by the tasked at hand. However, I'm not an electrical engineer and don't have the knowledge to work out the PSU requirements myself.
(assuming I don't fry myself and/or the LX5!).
I sure you wouldn't be so eager to hack on something you admit you're not qualified to if you only had one 5lx. While the reliability of these old beasts is generally very good, it really doesn't pay to risk "frying" one unnecessarily. Do you have so much MIDI that you need two units running simultaneously or is it just a spare? Try curing the buzz with the above steps first. If it doesn't work you can then resort to "hacking" more of it.