Technics RS-B665 Direct Drive Cassette Deck Service

The Technics RS-B665 is a direct-drive cassette deck and roughly the middle of its model range from 1989 to 1991. It was the higher end 2-head deck offered at the time, the 700-series and up were all three-heads and the 900 series got a dual-capstan mechanism. In truth the lower end 655 and 555 are better decks as they don’t have Panasonic’s proprietary PSX capacitors which degrade quickly with age – faster than most electrolytic capacitors do. PXS was Panasonic’s ‘audiophile-grade’ capacitor designed at a time when so-called ‘audiophile-grade’ electronics were in their infancy and snake oil was just starting to be bottled for mainstream sale.

Nevertheless this is a high-quality deck and is a low maintenance direct-drive design with solid drive gearing for the reels and only a single rubber part, the pinchroller, susceptible to failure with age. The capstan flywheel is integral to a three-phase brushless DC motor design that is essentially a smaller, high-speed derivative of Technics’ consumer turntable motor of the day. It is regulated by a quartz oscillator for extremely low wow and flutter especially from a single-capstan transport.

Generally these decks will run indefinitely without any maintenance besides cleaning the heads, pinchroller and capstan from time-to-time. They can benefit from a service however as the transport does become dry and noisy after 30 years of use or storage. No electronic device can be expected to perform at its best after decades spent sitting unused in a loft. I thought it would be interesting to crack this one open and show you what’s inside.

This is from a time when the electronics in a tape deck were being condensed into multiple integrated circuits, so besides the transport and the mainboard the chassis contains nothing but empty space. The board isn’t as sparse as the later Technics RS-AZ6 and RS-AZ7 however, and unlike those decks you do get a lot of calibration adjustments and test points for servicing. Also unlike those decks, disassembly of this one, the transport in particular, is relatively straight forward.

Providing, that is, you can avoid breaking the brittle connectors. Technics used 2 types of connector in this machine, both designed to accept a stripped and tinned ribbon cable. The larger connectors on the left are pressed to release their grasp on the cable, but the two smaller connectors powering the two motors must be lifted up to release them. Unfortunately they become brittle with age, and as happened in this case disintegrated immediately. You can’t buy the connectors in small quantities, so I took the easy way out – removed the mainboard and soldered the reel motor cable in place after removing the remains of its connector. The wire running to the motor is long enough that the mechanism can still be easily removed for servicing in future.

Four screws on the underside hold the front panel – three holding the panel itself and one into the underside of the mechanism. You’ll note the use of a TNRC (Technics non-resonant compound) base, a feature found in most Technics components from the mid ‘80s and beyond that helped dampen vibrations within the chassis and isolate the chassis from external vibration. It’s more useful on a turntable – but still, a nice touch.

The front panel pulls away, though this requires care. There are a series of connectors soldered to the front of the mainboard which mate with receiving sockets on the front-panel display and button boards. These aren’t particularly fragile but again they are framed in plastic, so ease the panel off by pulling evenly from either side.

The mechanism comes free with the removal of four screws, and in this and lower models the door must be open as the door latch is part of the mechanism. High-end models with the motorised doors are built slightly differently and the door mechanism is independent of the tape transport.

There are 4 screws on the back of the mechanism which remove the rear plate. The mechanism can then be folded open to reveal the gears and the components of the capstan motor within.

There are 3 components to the motor. The mainboard, controller and coils are mounted to the backplate. The coils are flat-wound around solid cores so it is not identical to the turntable motor design, but the principle is the same.

Beneath the flywheel, which is a permanent ring magnet slotted into its underside, is a board with a further set of flat coils printed onto it, which form the basis of the motor.

One set of coils produces a feedback pulse which is compared to the reference signal from the quartz oscillator. Thus the speed can be increased or reduced as needed.

The electronics make hundreds if not thousands of minute adjustments to the motor speed each second and, but like Technics’ direct-drive turntables there is some weight at the periphery of the flywheel to increase its inertial mass.

Many so-called ‘experts’ discredited Technics turntables due to a phenomenon called cogging. This is best described as a small bump, or just that is present as the poles of the magnet move past the stator coils. It was claimed that cogging was audible though measurements always proved otherwise. given that these tape decks use a much smaller flywheel running at a much higher speed, approximately 455 RPM, it could be argued that cogging would be a more prevalent issue with them.

Yet their speed stability even in the low-end single-capstan mechanisms is better than 0.05%, and the dual-capstan mechanisms a mere 0.03% which is almost equal to direct-drive turntables of the day. Frankly nobody can reliably claim to have heard a deficiency in the sound of a Technics direct-drive turntable that can be directly attributed to cogging, and as far as I know it is never discussed in relation to their cassette decks because it isn’t an issue and never was.

The rest of the mechanism is driven by a solenoid and a cam driven by the capstan, which is always rotating when the deck has power. The cam is responsible for lifting the heads into position, and can drop them slightly into a position where there is less pressure on the tape, used when finding tracks with the automatic music scan feature. This is to avoid premature head wear, as fast-winding a tape across a head with the head applying a normal pressure would quickly wear the head surface, and cause excessive heat to build in the tape which could in turn separate the layers of base material or degrade the magnetic coating on the tape.

Some have questioned the noise these decks make in operation. Technics direct-drive turntables are, for all intents and purposes, silent when they’re spinning, but these cassette decks do emit a low growling noise when their capstans are spinning. This is perfectly normal and correct lubrication will make it almost inaudible. The direct-drive turntables are based around a massive bearing and are positioned horizontally, not vertically. The capstan motor is also spinning at more than ten times the speed of a turntable motor, there is more friction and thus more noise generated by the bearing, and the thrust bearing is a small plastic pad. THey’ll never be completely silent, but you can’t hear them over the gentle hissing sound of a tape moving through the machine.

There’s little else you can say about this mechanism. The reels are gear-driven by the small DC motor at the top, which has a slightly longer than normal shaft (approx 20 mm) and a higher than normal DC resistance (more than 40Ω). I always remove these motors and apply a drop of synthetic oil to the top bearing. They’re not easy to disassemble and the bottom bearing doesn’t get noisy with age so I’ve never tried to open one for a complete lubrication. I also apply a general-purpose silicone grease to the reel gears and to the gears mounted to the top of the motor itself, as well as both beneath and around the head cam. The capstan shaft gets a few drops of synthetic bearing oil, and a blob of silicone grease on the rear thrust bearing.

Putting the deck back together is the reverse of the disassembly procedure. There are a couple of additional things to tackle. I always take the time to spray the switches on the top board with some contact cleaner. These press against the tape and are there to determine whether there is a tape present, the tape type, and whether or not the record protection tabs are in place.

Another common issue these decks suffer is failure of the front pushbuttons. The tactile switches behind oxidise and their function becomes intermittent. They work in a resistor ladder formation whereby they’re wired in series with a number of resistors, and the microcontroller determines the desired function by sensing the resistance to ground when the button is pressed. It’s a common way for manufactures to implement a large number of pushbuttons using only a single input pin on a microcontroller, but it does present issues if the buttons fail.

Common symptoms are the deck performing erratic functions, or some buttons triggering functions other than those which they are supposed to. For example if you press play and the deck goes into rewind, or if the deck stops playing or winding at random, or if functions turn themselves on or off without your input, you likely have this problem. It’s not limited to this series of cassette decks either. It’s a problem most machines from Technics will suffer eventually, and other brands too.

There are two ways to solve it. Both require you remove the screws securing the button and display boards to the front panel. They’re usually layered, with two boards interconnected by more connectors. Once you have the boards removed you’ll see the tactile buttons as small square components with rounded button tops. Unfortunately there is no easy way to get this open. You can either replace them all with brand new equivalents, or you can hose them down with contact cleaner, let it soak in and clean up any residue with isopropyl alcohol. It’s also a good idea to clean the display and the back of the front display window while you’re at it.

And there we have it, another one saved from landfill. I checked over the electronics which all remained perfectly calibrated, checked the speed which was within 5Hz using a 3kHz test tape, and set the azimuth as I’ve described in several prior articles.

The heads of this particular machine were in mint condition as if it hadn’t seen a single tape since it left the factory, and those pesky PXS capacitors were still in perfect condition and measured well within spec. Consequently the deck sounds crisp and clean. It’s a very neutral sound as is common for Technics components produced since the early ‘80s, though it’s not the quietest performer as the single-chip preamplifiers Technics used in all but the highest-end models weren’t the finest. Nevertheless a good performer and a fuss-free, maintenance-free cassette player.