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Orange Cap replacement procedure (by Kannan S)

It is observed that large number of Nakamichi cassette decks start behaving strangely after years of use or storage (with very limited use) mainly due to certain make of capacitors losing their properties.

Engineers call this "Aging failure". Fortunately the failures are noticed only on Orange colored Polyester (or Mylar) Capacitors. This Document is meant to help DIY Nak users who want to replace these Caps and restore their Naks to fine working condition.

Warning

It is assumed that these interested Nak enthusiasts understand basic electronic schematics and understand the component parts. Also it is assumed that they are capable of soldering and de-solder Electronic components like Capacitors, resistors, diodes, Transistors and Integrated circuits (or at least passive components like Resistor / Capacitors) without damaging the Printed circuit board, components or wires/ cables on them.
It is expected that all who attempt to carry out these modifications know that the power input wires / switch and certain PCB parts on Nak decks carry lethal 220V or 110V AC voltages. They are warned to remove the power connection before opening the top / bottom covers to do these modifications. They should take adequate precautions to avoid touching parts carrying live AC if they do not remove the power chord to these decks.

Capacitor types

There are different types capacitors available. We better get to know the types before we start our work.

Electrolytic (Polarized) capacitors

These capacitors have positive and negative leads. Generally they are marked on the negative lead. (Generally Negative mark printed on the casing next to the negative lead).
Caution - If you apply DC voltage exactly opposite of what is indicated as positive / negative, the Capacitor will blow. So the PCB is marked with which polarity of the leads to be soldered on that particular location. Soldering of Electrolytic caps with wrong polarity can cause failure of this Cap! These Caps are called polarized Electrolytic caps.
Also note all Capacitors are clearly meant to work within certain voltages called ratings. The applied voltage should not exceed these voltage ratings. Check the service manual for correct voltage rating of these Capacitors.
You get non-polarized electrolytic caps without positive or negative leads. They are expansive and are used in limited applications like Speaker crossover etc. The values of Electrolytic Caps start around 1uF (micro-farad or one millionth of a Farad value).
Since 1 Farad is a huge value and such value Caps are used only as power supply back up Capacitors on Computers. The usable value of Electrolytic caps can go up to 10,000's uF

Plastic film type

Mylar / Polyuestrene / Polypropylene / - they have values from pF (Pico Farad or one millionth of micro farad) to few Micro Farads. No polarity.

Mica

Values pF range. Silvered Mica are expansive Capacitors used in RF (Radio Frequency) Circuits. No polarity. You can use them where you may have to replace pF range Orange caps if you do not mind the price!

Ceramic

Used only for Decoupling Power Supply of IC's and are not suitable for Audio work. They are available in pF range.

Others types are

Teflon / Paper in Oil/ Ceramic Chip / SMD capacitors, we will not bother about them here.

Replace these Orange caps with Mylar/ Polyester variety mostly. You are welcome to use expansive MIT Film caps but that may be an overkill in Bias Oscillator circuit.

Step 1 Identifying the Orange Cap

Look at the Picture. It shows failed Orange caps removed from my Nak 480 circuit board. The picture after next shows CR7's inside with large number of Orange caps among brown Polyester and other Electrolytic caps. To replace all of them with reliable plastic film types note the part numbers printed next to them on the PCB and use the service manual to identify the part and their values.
These notorious Orange Caps are of this color and look similar to the ones in this picture. They contain no marking of the manufacturer.

Step 2 Acceptable replacement

Select the replacement caps with same values. Select 5% tolerance caps if possible, as they are more reliable than 10% or 20% tolerance ones. If you have a Digital multi meter with Capacitor measuring facility, it is better to check the values before selecting them for replacement. Say you need 3300 pF or 3.3nF ( Nano Farad) or 0.0033uF, you can select 3.0nF to 3.6nF ( 10% tolerance ) to replace them but see that the two capacitors going in to left / right channels are similar in values ( as all playback / record circuit in your beloved Nak contain two sets of same circuit for left / right channel).
The following picture shows Capacitors in different shapes / colors as well as marking of their values. Some contain manufacturer� marking like "WIMA". The wider Orange Cap is in fact of Philips make and a good substitute.

Step 3 Select the method to remove the Caps

De-soldering requires patience and care to avoid damage to nearby components as well as circuit board.
You can use de-soldering wick (of good quality) or de-soldering gun.
See the following CR7 board containing many Orange Caps. Also note blue/ Green colored Electrolytic caps as well as Brown colored Mylar caps.
Remove the Orange capacitors one by one carefully. Generally Nak boards have component identity printed on both the sides of PCB. This will help you identify the correct value of the component.

Step4 Insert the replacement Caps

after verifying that they are the correct ones and solder them on the circuit board.

Step 5 Solder the Caps in Place

Recheck that you have replaced the correct value caps on the locations before powering up the circuit.

Next we look in to how to solve Bias Oscillator problem common to 480/582/ZX 7/ZX9 series Decks caused by the Orange Cap failure.

The picture shows the Nak 480 Bias Oscillator Schematics.
C301, C302 and C303 all are Orange caps. The failure of C302 and C303 (4700 Pico Farad or 0.0047 uF) caused failure of Q302 as well as R310 in my 480. I observed similar transistor failure on my 582 as well. So incase of Bias Oscillator problem, check this Transistor, Q302 and Q303 as well. Remove the failed components and replace them for restoring recording/erasing functions. Following page has the photo of my 480 where the green caps marked with red arrows are the replaced good caps. Also note the transistor as well as the resistors were replaced.� You can clearly see the Orange caps next to Dolby chip (part of Dolby circuit) � a possible failure area.

You can obtain these necessary parts from many electronic component suppliers like MCM electronics or RS components in Europe/UK.

Good luck in replacing these Orange Caps in your Nak!

Another view. The recently replaced green caps and other Orange caps nearby can be clearly seen. Also note the component numbers marked like VR105.

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