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Old 10-22-2009, 09:28 AM
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Machineghost Machineghost is offline
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Tutorial: "Deep Cleaning" An Amplifier

Introduction - "Deep Cleaning" An Amplifier

I have thought that there will be members on the great forum that would appreciate this small tutorial that follows.

Not only do I appreciate vintage audio equipment but also service and repair a piece every now and then. I like to see vintage audio equipment being used and enjoyed by music lovers.

One of my favorite mottos goes: "When you do something, do it the best you can!"

When you are lucky you can find some nice vintage audio amplifiers on the cheap. If you are really lucky you can get your hands on equipment that is in truly mint condition. Most of us however need to spend some TLC on your thrift store finds.

What follows is an outline of my procedure on how to get a dusty and dirty amplifier shining again. Not just on the outside but on the inside as well.

Most of it has been self taught and some of it passed on by friends and a little bit borrowed from the internet.

This is however not the definitive way to clean amplifiers nor is it complete.

I supply this information only as a guide and cannot be held responsible for personal injury and/or damage to property resulting from the procedures described herein.

Follow these guidelines at your own discretion.


Last edited by Machineghost; 09-13-2013 at 05:36 PM.
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Old 10-22-2009, 09:45 AM
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Machineghost Machineghost is offline
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Part One

The overhauling of an audio amplifier


It is rare to find a piece of audio equipment that is in showroom condition. Most pre-owned equipment is in good physical condition but suffers from accumulated dust and dirt. This is usually caused by atomized oil particles (from kitchens, automobile exhaust gasses, tobacco smoke and other substances in the atmosphere) that bond with dust particles to for a layer of grime on and inside the audio equipment.

By normal dusting and compressed air one rarely is able to clean equipment that is badly soiled.

Let’s get wet!

Many people shudder at the thought of mixing electronics with water. Rarely do they know that one of the steps in the assembly of a PCB is washing. After the board has been soldered it goes through a stage were it is rinsed with chemicals to remove solder flux. After the rinse it is washed with a detergent to remove the chemical rinse.

In order to be able to wash an amplifier printed circuit board it needs to be disassembled.

Required Tools
• Set of good screw drivers
• Set of small crescent wrenches
• Fine wire cutters
• Long-nose pliers
• Round-nose pliers
• Pliers
• Soldering iron
• Solder
• Digital multi-meter
• Variac or “Series Light Bulb”
• Sturdy work bench
• Good light
• Few small containers with lids (like a Tupperware lunch box)

Other Stuff
• Biodegradable liquid detergent (i.e. Kleen Green)
• Bottle of turpentine
• Bottle of acetone
• Bottle of benzene
• Source of running water and good drainage
• 100 mm paint brush
• 30 mm paint brush
• Large pan (PCB must fit inside)
• Foam strip (with adhesive backing in various sizes)

Action Hint: Before you start
In order for the procedure to be a success you need to be well prepared.

Try to obtain a service manual (or at least a schematic diagram) of the amplifier you are going to clean up.

It is vital that you document, on a scribbling pad, the location of wires and connections as well as the location and orientation of various components (fuse holders, power outlet strips etc). Keep a digital camera handy and take photographs during disassembly to keep record of how the unit looked before you invaded. This might just be your saving grace in the instance you forgot where a certain thingamabob goes.

Work carefully and slowly. Do not rush the disassembly.

Ensure that your work area is tidy before you start. The will prevent disassembled parts from “disappearing” between other unassociated parts. Keep all screws and small fixtures in a dedicated plastic container with a lid.

Get cracking
The amplifier you are going to service needs to be carefully stripped down.

1. Unplug amplifier and allow capacitors to discharge.
2. Remove the top cover and place well out of harms way. Put screws in container.
3. Remove all knobs and toggles and put in a small container.

4. Carefully remove the amplifiers face-plate and place well out of harms way. Put screws in container. If you can, wrap it in a piece of cloth or bubble wrap.

5. At this stage it is best to remove the power transformer. This will greatly reduce the weight of the unit to aid disassembly. Put aside.
6. Disconnect wires and leads that links up to the devices on the rear panel (power sockets, binding posts, RCA connectors, fuse holders)

7. Remove the rear panel and put aside.

8. Remove all screws and nuts on the front panel of the potentiometers and switches. Be careful not to damage the potentiometers shafts.
9. Carefully remove any meters and/or indicators on the front panel and put out of harms way. Be very careful with Pioneer Fluroscan devices – they are rather delicate and irreplaceable.
10. Proceed to loosen all screws that hold the PCB(s) and heat-sink(s) in place.
11. Carefully lift the PCB and associated devices from the chassis. Put on the work bench and place chassis aside.

At this point you can carefully study the PCB assembly(ies) for defects and/or damage. Do not attempt to fix any problems at this stage. Just make a note of the damage(s).

If you have access to a large basin in a washroom at home you are lucky. If you have limited resources you can wash the PCB assembly in a large pan.

1. Fill the pan with an inch of undiluted detergent liquid.
2. Carefully place the PCB assembly in the pan.

3. Carefully begin too flood the PCB with the detergent using the brushes.
4. Using the brushes carefully scrub the board and components. Never use force or speed as this will result in damaged or broken components (upright capacitors are vulnerable).
5. Scrub well around potentiometers and switches to ensure that the solution penetrates.
6. Scrub the underside of the board.
7. Scrub the heat-sink(s) to remove dust and fluff.
8. Rinse the board and associated devices under lukewarm water until all detergent is washed away.
9. At this stage you can use compressed air to blast away water from the board and components. A powerful hairdryer, such as the ETI Professional types, can be used.
10. Place board in direct sunlight to dry properly.

11. If sunlight is lacking you can place the PCB upright in front of a fan heater on “low” setting or simply blow-dry with a powerful hairdryer or compressed air.
12. It is vital to get the board dry. Experiences persons might want to place the PCB in an oven at 80 degrees Celsius to aid the drying process.

Repeat steps 1 – 4 and 8 – 11 with the other parts and devices of the amplifier. Take care not to damage paper stickers and/or decals. Remove damaged and perished foam strips.

Some parts, such as panel meters, cannot be washed as per the above instructions. Care must be taken to gently wipe the devices with a damp cloth and some mineral turpentine.

Whilst the parts are drying you can take some time to clean up your work bench and sweep the scattered dust away. It is always a joy to work in a tidy workshop.

Never submerge transformers and/or chokes in water and/or any liquid. Transformers should be wiped with a damp cloth to remove dust and dirt. A paper towel soaked in turpentine can be used to clean up grime from such units.

Action Hint
Some manufacturers do not rinse their PC boards to remove solder flux. You can do this by rinsing the board with a solution of 50% Benzene & 50% Acetone. The boards should be re-washed immediately after this chemical rinse. Work in a well ventilated room or preferably outside. Fumes are flammable and care should be taken to prevent personal injury (inhalation and/or fire).

Some TLC
Some TLC (Tender Loving Care) can commence after the PCB and parts are dry.

Check for dry solder joints. Replace bad components.

At this stage some persons might be tempted to replace capacitors and wiring with “something better”. No problem with that. Poke around the board to look for capacitors that NEED to be replaced. Work carefully not to damage the PCB tracks.

Clean solder flux with a cotton bud soaked in acetone. Remember to keep painted parts well away from acetone. Take extra care when working with flammable liquid – do not smoke or operate high heat devices (such as soldering irons and lighters). Always provide adequate ventilation in your workplace.

Some PCB(s) might develop white blemishes on the solder mask (usually the underside). Remove this by gently brushing the white blemishes with a brush soaked in turpentine. Do this over a piece of news paper. Discard the news paper afterwards.

Make it tidy
Manufacturers producing amplifiers by the thousands do cut some corners when it comes to tidiness inside the unit. Wires run loose from point A to point B etc.

Take some time to arrange wires neatly by carefully twisting them together. By twisting wires an “unshielded twisted pair/bundle” is created. This aids in the preservation of delicate signals and reduction of interference.

Many Japanese amplifiers used a wire wrap connection system on the PCB(s) (consisting of a tinned pin, soldered onto the PCB and the wire conductor twisted around it in a tight fashion). This system usually oxides over the years and makes for intermitted or bad electrical connections. These connections can be “reestablished” by simply flowing a bit of solder over the wire and pin.

Alternatively the pin can be de-soldered from the PCB and the wire can be soldered directly into the circuit.

Fuse holders, voltage selectors and power outlets also employ this wire wrap system. Here an alternative and necessary solution has to be applied.

The pins cannot be removed and has to be reshaped to be used effectively.

Using round-nose pliers carefully shape the pins into small loops. These loops can be tinned with solder. Wire and cable can then be soldered easily to the devices.

Some people would want to do some electrical alterations at this stage as well. The rear panel can be prepared to accept better binding posts, rca sockets and even an IEC power inlet plug (if the rear panel layout and internal space will allow).

If the cut-outs are too big for new binding posts simply make a filler panel from a thin piece of aluminum sheet. Drill the holes for the plugs and sockets in the filler panel and fix the filler panel, from the back side of the rear panel.

Many vintage Japanese equipment use fiber board panels with RCA and other connectors affixed. Improved panels can be made as described above.
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Old 10-22-2009, 09:48 AM
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Machineghost Machineghost is offline
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Part Two

Get back
Now you can start to assemble the amplifier.

The procedure is basically the reverse of the disassembly procedure.

1. Place a clean chassis on the workbench.
2. Replace any perished foam strips with new stock.

3. Re-install the PCB assembly (ies).

4. Re-install meters and associated devices.
5. Fasten the nuts can screws to hold the switches and potentiometers in place. Take care not to over tighten.
6. Secure the PCB to the chassis (usually the heat-sink is fastened to the chassis at a few points)
7. Put chassis aside and get the rear panel ready.
8. Affix all parts to the rear panel and do as much wiring as possible. Such as installing the power cord.
9. Attach the rear panel to the main chassis.
10. Reattach speaker and other wires.

11. Get the transformer and install.
12. Connect transformer wires to associated parts and devices.

Take some time to arrange the wires in a tidy fashion.

Use cable ties and heat-shrink tubing to keep the wires in neat bundles.

You are now basically complete with the amplifier.

All that is left is to reattach the faceplate.

Make sure that the faceplate’s glass/plastic apertures are good and clean (remove finger marks from behind using a soft rag soaked in turpentine) before fitting.

Do not energize the amplifier from a mains outlet at this stage.

Carefully energize the amplifier using a variac or light bulb in series.

Monitor all voltages using a multi-meter. Turn power off IMMEDIATELY if you notice any anomalies.

Allow the amplifier to gradually warm up and stabilize.

Check bias and adjust if necessary.

Do an audio sweep and check output potential.

Replace top and bottom cover.

Replace knobs, buttons and toggles.


Final notes

Be careful when working with electrical appliances. ELECTRICITY KILLS!

Do not soak printed circuit boards for long periods in liquid. Some types of boards absorb moisture. Keep the wash and rinse "cycles" short.

Ensure that all parts are DRY before commencing with assembly.

If you are not comfortable with this type of work it is better left to a professional.

I cannot be held responsible for any damages and/or personal injury that might result from the described procedures.

Use this tutorial as a guide only.
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Old 10-22-2009, 09:53 AM
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Machineghost Machineghost is offline
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I use the word "CAREFULLY" often with reason. If you are not careful you will suffer damage on the unit you are working on.
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Old 10-22-2009, 11:36 AM
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Great post!. I have learned a lot from this and will definately use this for my next project. Thanks
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Old 10-22-2009, 12:00 PM
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Where are the tubes?
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Old 10-22-2009, 12:20 PM
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Thanks for the excellent tutorial! This thread should be stickied.
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Old 10-22-2009, 01:09 PM
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Excellent post!
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Old 10-22-2009, 01:46 PM
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MoreBeer MoreBeer is offline
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I also agree, nice post and quite informative. Maybe I'll try this on an old integrated amp that I could care less about and see if I destroy it or not!

I wouldn't recommend doing something like this as your first DIY project on a piece of gear you really like. Apparently, the OP really knows what he's doing. A noob would probably wreck the amp. I'm sure I will! Just my puny thoughts on it.
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Old 10-22-2009, 02:16 PM
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Outstanding tutorial! Is it advisable to keep the PCB cleaning solution out of the potentiometers? I'd say that this is an advanced tutorial, removing the power transformer and such isn't for the audio gear newbie. I'm going to try it, I have a nasty little Marantz 2220.
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Old 10-22-2009, 03:26 PM
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Very nice and detailed tutorial! many thanks for the sharing...
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Old 10-22-2009, 04:57 PM
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How about adding a caution to test the acetone, benzene, or any other solvent on a non-critical area of the pcb. The solvent may remove the PCB silk-screened lettering.
Boards with flat pack ICs, and especially microprocessors shout be sprayed with Deoxit before drying, and the residual soaked up with a towel. Closely spaced leads hold water and are easily corroded.
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Old 10-22-2009, 07:59 PM
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Originally Posted by Redboy View Post
Thanks for the excellent tutorial! This thread should be stickied.
Sticky +1...

Thanks! Education is always a good thing...
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Old 10-22-2009, 09:17 PM
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Great job on the tutorial...very well written and clear. I always wondered how the cleaning was done .

I spend most of my pay on Bozak speakers, a fast car, faster women and beer...I just waste the rest!
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Old 10-22-2009, 09:23 PM
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Great information for those of us buying up old & crusty gear!
Magnestand MMG's. Crown XLS-1500 amp. Acoustat RP 2 pre amp. Sansui SR 717 with Denon DL 110. Technics SL-Q2 with Ortofon 2M Blue cart. Oppo DV 980H for CD playback.
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