Sansui 551

[Carlosraj]

Dear Everyone,

I am working on a Sansui 551 Stereo Receiver belonging to a friend. Its left channel was dead. One output transisitor (2SD315) and One Driver (2SA697) were shorted. I replaced both the parts but within seconds they blew up again. One further checking, I realised that a Diode mounted on the heatsink has open. From the schematic, I realised that the diode part number is SV-03F. I cannot get the datasheet for this part as it is obselete. I guess it is a NTC diode to increase the resistance and control the current as the heatsink heats up. I cannot get this part from any electronic parts dealers locally. Can someone advice me on a replacement part number or how to modify this circuit and the actual function of this part. Please help as I am still a junior as far as repairing is concerned.

Thank you


Carlosraj

 

[pauls86ed]

Better late than never, The SV-03F in the Sansui 551 can be replaced by a temperature compensated voltage multiplier. I have a 551 and will post my results. Initial tests will be done with the BC556B with a 1N4148 in series with its base to a pair of 1K's as a bias network to the pot. The collector of the BC556B goes to the base of the pnp driver transistor, or the shorted side of the pot on the Sansui 551. LTSPICE simulations show very good results. I have a feeling this network performs better than any SV-03F.

 

[Ian Finch]

That seems like a reasonable plan with adjustment too. It's simpler and fiddle-proof though (for repairers) to just fit a set of 3 x 1N4150 diodes in series but Z-folded to keep it compact. These are similar but apparently tougher diodes than than the originals inside the SV-02,3,4 diode series arrays which proved vulnerable in several 1970's Japanese brands/models.
SV03 & SV04 diode replacement | Audiokarma Home Audio Stereo Discussion Forums

 

[wiseoldtech]

To refrence the OP:
It's been stated in numerous service manuals through th decades - when replacing outputs, even is one is defective - BOTH should be replaced with a matched pair.
This goes for that Sansui too.
This has been part of any technician's library of training since forever.


Anything less is half-baked and lazy.

 

[pauls86ed]

That seems like a reasonable plan with adjustment too. It's simpler and fiddle-proof though (for repairers) to just fit a set of 3 x 1N4150 diodes in series but Z-folded to keep it compact. These are similar but apparently tougher diodes than than the originals inside the SV-02,3,4 diode series arrays which proved vulnerable in several 1970's Japanese brands/models.
SV03 & SV04 diode replacement | Audiokarma Home Audio Stereo Discussion Forums

Thanks, Ran a pair of 1N4150's with a pair of SD103B's in series with the pot in the sansui 551 amp with ltspice. Looks like the ticket, simpler too. This sansui 551, or scare face will incur great abuse at the lake. Scare face sounds great and benefits by being too ugly to steal. The TO-66 outputs have long since been replaced with TO-220 MJE15028's so I figure I should make sure bias current doesn't run away with heat.