Another Sansui AU-505 amplifier


Received a broken Sansui AU-505 in the mail today.

I had found the piece on eBay as a parts unit (US $28.77/Shipping: $32.61).
There was no description of issues other than 'no audio', and fuse holder issues.

I decided to take a chance. I had learned from working with my unit the switches oxidize and can cause all kinds of issues. Besides that, I specialized in power supplies and no audio, in either channel, hinted of power supply problems.

I opened the unit up and found a fuse holder had come loose and a couple of wires needed to be soldered to the loose fuse holder. After that, I fiddled around with the thing. I began to hear a faint signal from the outputs. I toggled a couple of switches and heard a popping noise. I closed in and vigorously toggled the Tape Monitor switch several times. I got some of the audio back. I push, moderately on that switch's paddle and toggled some more. I have gotten full audio back. The switch had become oxidized from disuse.

Done.

I now have two Sansui AU-505 amplifiers.
The first is still in repair.

I'll have need of both, I think. I purchased a used Pioneer Elite AV Surround receiver/amplifier. I may need more speakers and all my amplifiers. I don't know if the AV unit will be the best choice for my stereo setup. I'll have to wait and see.

ADDENDUM

There was something about the unit that caught my attention. The outside top cover has some white paint spatter. That could be removed or even painted over.
Inside the unit was where the surprise came from. The inside was clean as the proverbial whistle. Electronics, especialy high power elctronics, create electostatic fields. These fields, in my experience, attract dirt, dust and grime. Crud in general. A coating builds over time. This amp has little to none of it. The unit looks as though the owner had packed the amp away early and only recenty had someone tried to use the amp. Additionally, the serial number on my first AU-505 begins with '5'. The serial on the new unit begins with '0'. My first amp is more recent and I can see several design modifictions separating the two. The earlier model has a fuse/holder not present in the latter model. The latter model has a diode hand soldered in series with a small capacitor, one pair per channel. A plastic transistor in the newer model was initially a metal packaged transistor in the earlier model.
If I use the amp, I may consider making the changes to update the earlieer version. This could be tricky since a design change could involve parts value changes, whicich means I'll have to monitor parts values related to the basic modifications.

My guess is the amp sat unused for decades. Someone found the amp and tried to set it up.
The switches in that amp have contacts that oxidized over time and create problems with inconsistent symptoms. The most recent owner (an amateur) tried to troubleshoot the problem and ended up having to replace a fuse holder and in doing so, neglected to tighten the fuse holder and forgot to wire the fuse holders into the circuitry. I soldered one wire and added a short piec of wire, the effect of which was to re-connect the fuses to the circuitry. No wonder there was no audio. I found the same switch in this amp had caused problems in my first amp.
I vigorously toggled the switch a cople of dozen times. I sprayed the switch liberally with electronic contact cleaner and let the amp sit.

The amp's final test was to periodically turn the amp on and check for audio. I did this over a couple of days without problems. The amp is officially 'fixed'.


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