Sansui SC-1330

Cassette Deck

Maintenance/Servicing

Bought off ebay for little money, this was advertised as ´For Spares or Repair´. It was in good physical condition, and the heads had very little wear. The pinch roller looked aged, but after some cleaning with isopropyl alcohol, and later filtered water on a cotton bud, it is nearly as good as new!

So far I have replaced the old drive belt - a 72mm or less diameter is fine, 3.5mm width, although I have just ordered a 64mm diameter 6mm width belt, let us see how that works later when it arrives!?  

12/2/2020: The 64mm diameter, 0.7mm thickness, and 6mm wide belt was more difficult to fit. Overall, the tension was too high, due mainly to the thickness (0.7mm) of the belt. Also, this belt wouldn't always run well - not sure why!? So I reverted back to the 72mm belt.

I think a 68mm-70mm diameter, 3.5mm-5mm width belt would be optimal?

Replaced most electrolytic capacitors, and cleaned all potentiometers with Servisol. 

Rubber Renew

Bought 125ml of this toxic chemical, and so decided to use on my machines. It smells like rubber solution, only stronger! I decided to buy this stuff hoping that it would return the power and hence internal 'grip' for the tape rewind, fast forward, and the take-up spool during recording. It did the job, but I had already cleaned much of the idler gears with isopropyl alcohol, and diluted acetone anyway - I'm not sure if Rubber Renew is worth the money?

If you use Rubber Renew, be sure to follow the safety instructions.

Noisy ON/OFF switch 
The Sansui SC-1330 makes a small electrical arc when switching on or off. This interference can be clearly heard through both headphones and the loudspeakers. On investigate I saw that the internal mains switch does not have any form of arcing/noise suppression.

After studying the circuit, I decided to bridge the switching contacts with high voltage rating, ceramic capacitors - marked below in blue.

The diagram above was taken from the service manual. I also noted that only Japanese versions of the SC-1300 series had suppression support!?

I carefully soldered in some 3Kv (not 3.3Kv as suggested in diagram) rated capacitors - yes these are probably over-rated, but best to be safe than sorry?! These completely eliminated any sound blips due to on-off switch arcing issues. I didn't bother to add a small resistance in series with the capacitors - these limit the transient currents which only last for some micro-seconds anyway. This type of suppression circuit is know as an RC Snubber Circuit.

My alteration to the mains board is shown below.

Sansui SC-1330 Calibration
I have also calibrated the machine so that -

• Test Tape Input: 400Hz Dolby Level RefTape, gives Vout = 500mV (RMS)  or ∼1400mV p2p.
• Calibrated the peak level meters to read Dolby Level at RefTape Dolby Level input.
• Calibrated the internal Record Levels (for Maxell UR), this means .. record at 0VU, and achieve 0VU on playback etc.
• Bias adjustment: 1000Hz to 10,000Hz flat for Maxell UR tape. 
• Rec/Replay Head azimuth check with my ABEX 10Khz ref tape - the original setting was spot on!!!

21/02/2020

29/04/2020: I decided to give the shorter and stronger 64mm x 6mm belt another go. This time I had cleaned the pully wheel carefully, "roughing up" the surface for a better grip. I also allowed the flywheel to guide the line of the belt around the pulley - this was done by losening the pulley screws and turning the flywheel with my finger so that the belt would find a natural line, the pulley would then slide outward a little more. Finished this alignment by tightening the pulley grub screws.

Results: Both fast-forward (FF), and rewind (RW) are much better than before - no stalling!

So far, so good!