What breaks on a Sansui 5000A, and what to check first
Sansui is the brand where the single most consequential bench fact in vintage audio was documented: the corrosive glue used to hold capacitors down eats through component legs, and it is the reason a Sansui that worked last year will not come out of protection this year. Beyond that, the 5000A's service manual publishes the protector threshold adjustment and the output stage bias procedure, which most owners have never had set.
The glue, before anything else
It will not come out of protection, and nothing looks failed
Suspect the polychloroprene glue first. It eats through the tin-plated copper legs of components near it. The documented treatment: scrape the hard crumbly glue off with a flat blade screwdriver, soften the pliable glue with acetone, then replace every lead that looks doubtful. Damage can be severe enough that components fall off the board when touched, so inspect the whole board before powering anything up.
One channel goes intermittent for no obvious reason
The same glue, acting on a component leg somewhere in the signal path. Same treatment: remove the glue, inspect the affected leads, replace any that are doubtful.
A related shape on early 1970s Sansui gear: a channel that crackles violently after a few minutes of playback, sometimes starting with a loud bang, is a small-signal transistor breaking down once warm. The XA495 flying saucer and 2SC458 types are the suspects. Split pre and power at the back panel to localize the fault, then replace the noisy device.
The 5000A's own procedures, from the manual
The protector trips too early, or will not trip when it should
The threshold is adjustable. Remove the wiring from T901 and T902, feed 6 V rms at 1 kHz into T901 and adjust VR901 until the protector lamp glows, then do the same into T902 with VR902, then reconnect the wiring exactly as it was.
Bias current cannot be set
MAIN VOL to minimum, a 10 ohm 1 W resistor across each speaker output, remove the quick-acting fuse from its holder and put an ammeter of about 100 mA range in its place, adjust the trimmer on the F-1040 board for 23 mA, then remove the ammeter and refit the fuse.
Stereo separation is poor, or the decoder will not align
Multiplex alignment needs instruments a small bench may not own: a stereo generator, an oscilloscope, an AC VTVM and an audio oscillator. The 67 kHz and 71 kHz traps are adjusted for minimum through TP404, the 19 kHz and 38 kHz transformers for maximum, and separation is set with the output meter at TP403.
Questions people ask
Why did my Sansui die sitting still?
The glue keeps working after the set is switched off. A unit that worked last year and will not come out of protection this year is the classic presentation; the glue has been eating a component leg the whole time.
Is the 5000A hard to align?
The protector and bias procedures above need a multimeter, resistors and an ammeter. The multiplex alignment is the one that needs a real bench: four instruments, and the order matters.
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Sources
Sansui 5000A service manual (via ManualsLib, manualslib.com/manual/4119013) for the protector, bias and multiplex procedures; liquidaudio.com.au's documented corrosive-glue treatment for the protection and intermittence rows. Confidence on each row is carried in the knowledge base itself.