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Luxman C-5000A Preamplifier Repair & Restoration

A customer recently asked me to restore a gorgeous Luxman M-4000A power amplifier and a matching Luxman C-5000A preamplifier. In this article, we run through the C-5000A restoration.

You can read about my M-4000A restoration here. This post looks at the C-5000A, a rare and beautifully built preamplifier, from the somewhat enigmatic manufacturer, Luxman.

No Service Data

The Luxman C-5000A is so rare in fact that, despite searches and contact with the Luxman Yahoo group and the Luxman Vintage Audio website, there are no service manuals available for the ‘A’ series models. There is service data available for the M-4000 and C-5000, but these are quite different, so that data is not much help.

The only thing anyone found was a sketchy hand-drawn M-4000A schematic. Unfortunately, no information identifying the functions or settings of the various trimmers in either unit was ever located. Anyway, this meant I had to proceed blind with the Luxman C-5000A.

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Here she is, before attempting any work, with the wooden cover removed.
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Inside, you can see the labelled acrylic covers and modular construction. Notice anything else amiss at this stage…?

Someone had worked on both pieces previously, replacing various parts and creating the problem for me of not being sure the original parts were replaced with parts of the same spec. Experience tells me that in many cases like this, they are not.

Without factory service data, one can never really be sure that the replaced parts are of the correct values and I have found that often they are not. The other issue is that again, without factory service data, setting the equipment up correctly can be very difficult.

Modularity

The C-5000A is built in a way that most modern gear is not. The preamp is completely modular, with a chassis, in which the various modules reside, as plug in cards. This approach is more akin to that found in test and measurement gear and is only rarely found in consumer audio equipment.

Accuphase is one other such manufacturer which has always used this form of modular construction. This form of construction makes servicing and repairs both easy and hard – easy because the boards just unplug from the backplane inside the chassis; bad because you really need extender cards to allow you to make measurements and adjustments.

Restoration

This particular C-5000A was much like the M-4000A in that it was dirty, had poor quality replacement capacitors in places and really needed some TLC. The following images document my service and restoration of this lovely old piece of equipment. You can of course find more about the C-5000A at The Vintage Knob.

Cleaning
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Perhaps this makes it easier – I don’t think Luxman installed Chinese Suntan caps in this very awkward fashion..!
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Detail on the individual modules, a set for each channel.

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Here is one of those power supply modules removed. Not how the rubbish replacement parts are not the correct form factor and therefore do not fit into the modules correctly. Someone did this work, and thought it was good enough to reinstall into this customer’s equipment, that’s the part that bothers me.

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Detail of the toroidal transformer and plug-in chassis setup, before proper cleaning…
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And after – what a difference.
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Flux and dirt contaminated boards must also be cleaned…
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Chassis outside, for proper cleaning, with foaming cleanser, water and warm air and sunshine to dry her out.
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First stage of cleaning complete, the residue on these boards will be removed in stage two…
Refurbishment
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View of the amazing moving coil step-up transformer that plugs into the rear of the C-5000A. This is a brilliant way to do things because the transformer can be removed and exchanged for one of the other optional transformers, allowing the owner to choose the one best suited to his or her cartridge!
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Clean and dry C-5000A, ready now for further work. One must always start with clean gear, you can’t troubleshoot or repair problems in filthy gear.
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These awful ‘Suntan’ brand capacitors should never have been installed. Seriously, I can only hope that, due to the era, the technician was perhaps tripping or smoked a little too much during break…
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These Nippon Chemicon capacitors are very high quality, rated at 105 degrees celsius and feature the correct height and lead spacing. The only way to do a job like this is properly, the first time.

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Here they are, soldered in place.

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Several views of the finished, cleaned, repaired, de-fluxed and conformal coated power supply boards…

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Here they are, installed in the preamp for testing.
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Here is another board, buffer board this time, you can see the heavy flux contamination and dirt.
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Flux cleaning the board

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With everything back together, the next step is adjustments, after refurbishing the power supply boards.

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Almost back together, all acrylic panels back in place.

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No schematic perhaps, but at least we have a block diagram!

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Finally, ready to go back to her owner.

3 thoughts on “Luxman C-5000A Preamplifier Repair & Restoration”

  1. Hey, Mike, fascinating pics of your restoration process. What causes the flux contamination? Excessive heat build up overtime? Heavy dust and dirt probably interfere with heat dissipation.

    1. Hey Chris! Been meaning to send you a Christmas email, hope you received my last one OK 🙂

      The flux contamination is a result of the board preparation and assembly processes. Automated and manual soldering can leave flux residue on boards. The flux helps the solder ‘take’ to the metal components but can be corrosive and is rarely removed, except in the best audio and test gear. On its own, the flux is not necessarily an issue, but it is sticky and attracts dust, moisture and other contaminants, which can then cause corrosion and alter board resistance. This can be significant in high impedance circuits, so I always remove it from boards when I work on them.

  2. Nice description on your work. Attempting one of these as We speak The glue got to the components on the Regulator board and also failing caps. But one of the nices examples of a Preamp that I have had the joy of repairing

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