Technics RS-673 Cassette Deck
I saw this on ebay very recently, and I was hooked. This is a quite a rare machine, but before I bought it, I just wanted to be sure it was repairable as I mulled over all the pictures, and the description of this 1978 machine.
Original Advert
Before continuing, the reader might wish to know that there is no obvious or available service manual to the RS-673 as far as I am aware. If you know where I can find a service manual to this machine, then please do help, thank you.
Another Technics RS-671 has an available service manual, and much of what is in there applies to this RS-673 model, except for the fluorescent metering.
Initial Testing
I could see that the deck was 'basically' operational, but it would not Play, nor rewind (RW), nor fast forward (FF).
The transport mechanism has seized up - decades of 'dry' lubricants, a fine layer of dust, and enough oxidation to grind things to a halt stopped the deck from making any sound.
Before any other work was done, the transport had to be working, and so the top side of the transport was cleaned carefully.
The tape supply hub/spindle has seized completely, so much so that I could hardly move it with my hand! This was the reason why the auto-stop kicked into action once Play was pressed.
However, after injecting some OB41 freeing-oil down the spindle of the hubs and 'working' the spool a little with my hand, free movement was restored to this and the take up hub. The remainder of this side of the transport was taken apart and cleaned with a mixture of detergent/water, switch cleaner, IPA, and acetone. Note - take care when using acetone on plastics, there will be a chemical reaction with regard to some plastics and this will ruin the 'look' of the said plastic. Please check online for more details.
Later, all idler tyres were removed, cleaned, carefully 'roughed up', and with Rubber Renue applied, returned to their original postions.
Other concealed but essential sliding mechanisms had to be cleaned and lubricated too - 'renewing' the idler tyres was simply not enough to cure the problem of zero RW and FF!
Later, the pinch roller was carefully 'sanded', cleaned, and Rubber Renue applied, and then allowed to dry. Associated mechanisms were removed, and cleaned to allow free movement of the pinch roller.
Earlier on, both heads were cleaned with acetone, with special attention applied to the record/play head. There is obviously some wear, and as a result I am aware that this could impact on performance, possibly more in the right-channel (innermost track) more than the left-channel (outer track)? The capstan and heads were also de-magnetised.
The flywheel was taken out for inspection, lubricated then returned and cleaned again as the oils ran into the sintered bearings and would probably transfer on to the pinch roller if I didn't clean this again!
Drive Belt
Estimating for now, the main drive belt is about 130mm in diameter, and about 5mm wide - this seems to have been replaced in 1996 and/or 1999? The belt will be replaced later, but at this moment it's fully operational and stable.
Basic Calibration
With already some 6 hours into this restoration project some basic calibration work was performed.
Before that could be done, all potentiometers, and switches were 'switch cleaned'.
Also, the bias traps were re-set to maximize rejection of the bias frequency 'carrier' - there are calibration points marked to do this.
After basic calibrations: Bias Trap, Azimuth, PB Levels, PB EQ, Record Levels etc, the machine at this moment is returning the following figures ...
Wow/Flutter: < 0.11% WRMS (more often under 0.10% wrms).
Speed Stability: WRT a 3150Hz ABEX reference tape, it is good at approximately ±2Hz after 10 minutes.
Frequency response: 35Hz ... 14,500Hz -3dB for Type I 'Normal' tapes.
THD: At +2dB or slightly greater above Dolby Level, it is approximately 1.5% at 1Khz.
Recording Level Instability
A small, almost un-trackable variation in recording level in one channel was sometimes experienced. This was seemingly fixed when associated electrolytic capacitors, and 2SC828 NPN transistors were removed and replaced. Possibly pre-emphasis was affected in a small way?
So far, the Technics RS-673 is running very well.
This Blogger article is unfinished, and will be subject to corrections, additions etc without notice. [15th November 2024]
