Intermission

The recent lack of progress has been fuelled by two parallel causes. Mr S, collegue and partner in crime, had to make a trip to Europe's mountains over a week. Also, central components for the Detectron computer, like the motherboard, are still being shipped (although probably by truck). While waiting, the current workspace was put to the test in restoring an old Sansui Stereo (1974), which is described in this post.

Although much of the hardware is still in transit, the tools, multimeters, and the phidget USB I/O cards have arrived. To complement the sterile, efficiency seeking table, a 60s string shelf has been filled with orchids, porcelain och cooking books. 

The Sansui Stereo receiver 771 was bought from ReHIFI a few years ago. It has a really warm and cozy sound that shines especially when playing classic and jazz. However, it did have problems with dropping one of the speakers every now and then, and making weird noises when turning the volume or equalizer knobs. The amateur diagnosis is that the potentiometers and inputs/outputs probably have become dirty during the last 40 years, and maybe a simple cleaning could fix things.

It turned out that one of the hardest parts in the restoration was to actually break into the stereo. After removing the wooden case with four simple screws, it took several hours to figure out that the front panel was actually attached behind the knobs, apart from the two screws on the top. Apparently the principle of single purpose does not apply to vintage stereos, and combining key structural support with sensitive input is not a problem. Behind the front panel could be seen the I/O circuit card that handled the knobs and buttons, along with the sought potentiometers. Unfortunately there was a lack of pictures taken of the inner workings, likely due to the excitement involved at this point combined with diverse family members requiring attention.

The insides of the stereo was first dusted using a vacuum cleaner and a paint brush (method taken from this post). There was surprisingly a lot of dust, although the domestic surroundings that are the stereos natural habitat are stringently clean... ahum. After this the potentiometers were cleaned with pressurized air, followed by a round of potentiometer cleaning spray. All inputs and outputs were similarly treated but using the regular contact cleaning spray.

Typically old stereos need a replacement of all old paper capacitors, since these loose their function with age. However, since the stereo has a very nice sound as it, it seems very likely that this was done at ReHIFI before the purchase. The capacitors also look newer that the rest of the electronics. Also take note of the highly analog (string-driven) radio tuner dial.

 

Before reassembly, a sort of successful attempt was made at replacing the old power cord with a new, grounded one. This did work out, but involved some very poor soldering, which is shown in a figure below to encourage any other enthusiasts. There was also an effort to replace the backlights for the tuner display into LEDs, but it turned out that they were operating on AC (multimeters are great!), which made the needed circuit construction and soldering a bit too scary compared to the small gains.

 

In conclusion, the issues experienced before restoration seem to have pretty much vanished. The stereo, now coupled to a Bluetooth receiver, played very diverse music flawlessly for four hours yesterday. The only thing that's still a nuisance is that one of the three pairs of speaker outputs still drops a speaker occasionally, but every old device needs it's own personality.