Smoooth......

After much work, I finally get time to work on the 700ZXL again! After a quick check on the flywheels which are doing very well after their rust removal treatment, it is time to work on the rest of the transport. Today, I checked the bearings on which the capstan shafts run. These seem to be sintered bearings hence need to have their lubrication checked.

Sintered bearings behave much like a sponge by storing oil, and then releasing whenever it is needed. This happens when the joint starts to spin and causes heat. Heat causes the bearing to release oil and lubricate the running joint. A neat idea - until it is a quater of a centuary old!

The assembly consists of two sleeve bearings inserted at both ends of a cast metal holer. First the bearing is checked visually and everything is in good shape. Swabbing with cotton buds and alcohol does not show any dirty lubricant. The assembly is then inserted into a oven. Heat is then slowly and carefully applied to the joint to ensure that expansion is as linear as possible.

Our oven has a grill function will allows the heat to circulate. This ensures that the heat is even at all parts of the oven - useful!

After about 15 minutes at 250 degrees Celsius, thick , dark brown oil starts to drip out from the bearings! This is caused by the heat which causes expansion of the bearing which releases the oil.

The bearing is then slowly cooled down, then heated up again. This causes a small quantity of brown oil to be collected on the foil.

On the right, you can see the some of the dirty oil on a kitchen towel. (Thanks Wife for the oven and towel!)

Next the assembly is immersed in solvent (like common paint thinner in an open ceramic or glass bowl) and then set back into the over at a lower temperature of about 130~150 degrees Celsius.

This has to be done in a well ventilated area because we are dealing with heat and solvent. The bowl is then taken out and let to cool in outside air. Because the assembly is immersed, it will take some time to cool down. The assembly is then set back into the over for more heating. Doing this about twice turns the clear solvent into a brownish mixture which contains more used oil.

I then change the solvent and perform the heat and cool cycle until the solven runs near clear. Finally I see some clean oil which is the unused oil that was deep inside the bearings. The dirty oil would have clogged the pores and prevented the remainder of the clear oil from lubricating the bearings. On the picture on the right shows the solvent mixed with brown oil. Some of the clear oil is visible at the bottom of the bottle. The dirty oil comes out first and now the clear oil is able to exude from the bearing. However, now the bearing is void of oil and needs to be filled up with new and proper oil.

I will have to find out the best oil with the correct number for lubricating this grade of sintered bearings. Too viscous and not enough will enter the bearing. Too runny and the bearing will not soak and hold the oil.

Moving On...

I discovered some rust removal solution which was left over from a previous project. I tried applying a small amount on the surface to see how it reacts to the metal of the flywheel. After about 10 minutes, much of the rust dissolved, leaving very marks and a clean surface!

The flwheels were prepared for treatment by removing the oil retaining felt pads, and completely cleaned of all grease and oil. The grease between the back of the flywheel and thrust plate had hardened and stuck to the flywheel and had to be gently scrubbed away.

I next tried the solution on the belt riding surface and carefully monitored progress. After about 30 minutes, the rusted capstan flywheel turned out like this...

You can see the line where the flywheel was out of the solution and the difference prior to the treatment.

One member had posted about being careful about the diameter of the flywheel. This is very important because a changed dimension or flat spot can lead to poor tape handling.

Here is another picture of the flywheel showing clearly before and after treatment. Even with treatment, some deep pitting was still there. The rest of the smudge like traces are stains. The flywheel is much smoother now that the deep rust is all gone.

The other flywheel was more challanging because of the step. For this, a different vessel was used to give more exposure of the treatment fluid to the belt riding area.

After both flywheels were treated, the next step was to remove the remaining stains on the flywheel and make the belt riding surface as smooth as possible. This was done by gently buffing the surfacing with metal polish, by hand. After slowly polishiing away the stains, turning frequently and keeping the surfaces even, the following resulted:

The second flywheel was also cleaed and buffed. Both flywheels were checked carefully for any dings, scratches, marks or flat spots. Some pitting was still present but these will not affect the belt or performance and it is best to leave them as they are. The resulting surface is much smoother at has the right surface to give the driving belt a good grip.

The flywheels are ready to literally roll!






Now its time to move on to the rest of the transport...but first to get some sleep!

Rolling On..

While still looking for a solution to test the repaired board seperately, I move on with the other aspects of the Nakamichi. Today, I removed the transport. This involved removing some cable ties, and freeing four mounting screws that hold the transport to the main frame.

The transport used by Nakamichi in this period is truly a engineering marvel. It was a versatile transport that had been used as a basis to produce fully direct drive, semi-direct drive, belt drive, auto-reverse and a few other configurations.

It is a simple, but effective and very stable transport that has few problems. The tranport features two capstand that rotate at different speeds. This allows mechanical noise to be distributed and reduce flutter and modulation. The aluminum chassis of the transport is damped by plastic resins that absorbs vibration and inert. The transport does not use solenoids that give a 'thumping' noise on other decks. These wear out over time and induce mechanical shock. Nakamichi uses instead a near silent cam mechanism that operates the various modes.

Once the cable ties and screws are removed the transport is carefully removed from the main chassis. The transport is then inspected to asses its condition. From far, it looks not too bad, but a closer look reveals some issues. Some parts of the transport is covered with a layer of grime and dust.

The motor spindle which drives the idler is corroded! Some cleaning with solvent does not seem to help, so this needs to be fixed.

The classic transport uses a swinging idler wheel to drive the spindles. This is a very simple and reliable method. The idler wheel has a rubber 'tire' that needs to be changed althoug this is not often.

In this deck, the tire looks worn and cracked. It definitely needs to be changed.

The back of the drive consist of a back plate that mounts the capstan motor, thrust bearings for the capstan flywheels and the cam mechanism for overall transport control. Removing this, brings access to the capstan flywheels and cam mechanism.

The lubrication between the thrust bearing and flywheel is hard and almost dry. Small wonder for a deck of this age!

When turned by hand, the flywheel does not seem to be very smooth and some resistance is noted. The flywheels have to be removed.

The capstan drive belt, noted at the back on the left picture is quite slack and also needs to be changed.

Bad luck - the edges of the capstan are corroded! This edge comes into contact with the belt and they are rusted!

The other flywheel, visible slightly in this picture, also has the corrosion on the surface that contacts with the belt.

This is a majr problem and needs to be solved if this deck is every going to sing again!

A solution is required to remove the corrosion from the flywheel so that the surface does not damage the capstan driving belt.

Weaving a web

As the initial wiring worked well, I started wiring more larger sections of the board. The wiring seems to work well, although some wires have to be re-done so that they hold each other.

On the left you can see how some connections are used to hold the others down. Most of the connections closely follow the original circuit path.

The leaked acid also damaged the solder pad of most components, so m

uch of the soldering has to be done to the component legs. When I remove the original corroded solder, the solder par underneath was found to be corroded also as the chemicals have reach under the pad.

Here is more soldering with close components. The center row of components are transistors and heat is applied carefully to these.



This section shows soldering done underneath two ICs. The wiring was very close and have to be cleaned and checked.

The wiring was finally complete. No glue or solvent was used to hold the wires down. Now all that remains is to power up the board. However, before setting the board back inside the actually deck, I want to check the board seperately. What are the possible ways to make the board work seperately?

Getting the feet wet

The long holiday gave important time to look through the damage in great detail. The copper traces have all eroded away there are no connectivity between components. The only way forward is to perform point to point wiring to restore back the lost connectivity. After looking through various catalogues, I settled on 30AWG wire wrapping wire that gives the required stiffness, while being strong enough to withstand handling on the board. Thicker wires are not required here as the wires will be handling small signal levels.

First, all the corroded solder was removed and solder joints were repaired. Next I tried out some wiring and they seem to hold up well. The wires were routed as close to the original trace design as possible. Because the semi-conductors are not on sockets, there is a possibility of component damage if heat was applied too long.

I will be doing more of the wiring over the next few days and put up some pictures.

Looking Inside

Today I got the time to look into the 700ZXL to see what caused the problem. I was met with a deck packed with circuitry, all neatly organized and labelled. A quality machine indeed! Some screws were noted to be missing and some connectors were not correctly positioned.

Opening the back panel was easy. Releasing some screws allows the back panel to fan out. Bad corrosion was observed around the battery compartment.

Removing the auto-computing section brought more bad news. The corrosion had affected the bottom board and pieces of metal had falled on the components. The board has been badly damaged by leaking battery chemicals! This board controls all basic deck functions like play, record, rewind, forward and controls the cassette mechanisms.

The auto-computing board had not been spared as well. Leaked battery chemicals had spilled on the board and oxidized the board! Copper tracked had been eaten away and the board had been partially destroyed!

The opposite side of the board, the component side, seems to have been spared damage.

Upon closer inspection, the components seem to be in good condition. Only the printed board tracks seem to be damaged. The other board has not been damaged at all and looks to be in good condition. Over the week, I plan to explore different ways to repair the damaged sections. Looks like this lady is not going to be singing as soon as I expected.

The first meet...

The first glance upon this beauty shows a clean, zen-like design that blends in with today's modern minimalist looks. The left door opens up to reveal more controls. Powering her up only displays the lights. Nothing else seems to work. This deck had supposedly not worked for a long time and needs a complete work.