Fresh Sansui au-317 owner looking for some restoration help

[Brekken]

Hi! So i recently bought a defective AU-317 that eats fuses. The story the last owner told me was it sat in storage for 5 years and was dead upon retrieval.

After some testing with my trusty multi meter i found one damaged diode in the small rectifier bridge and a pair of straight shorted output transistors (2sa745 & 2sc1403). Checked all the resistor fuses and they are OK. I have ordered up replacements for the trannys and both small and big rectifier bridge since i'm in there anyway.

Red areas are faults i found.
Altso is it fine if i power it up with the remaining channel in there and the faulty one removed, for testing?

Any tips for other things to check before powering it up after the parts arrive?
Thanks
-Ole

 

[slimecity]

Build a dim bulb tester - instructions are on this site for doing that - once you do your repairs - only power the amp up using that - it could save your bacon.

If it were me - I would just replace the fusistors as they tend to go bad anyway.

Im not familiar with this model but are there any VD1212 small blob-like diodes in this unit? If so, replace those too.

Otherwise - do your replacements, fire up, and see if the bulb glows bright once you do so.

 

[avionic]

Welcome to AK..Did you check your emitter resistors between those two outputs ?

 

[Brekken]

Build a dim bulb tester - instructions are on this site for doing that - once you do your repairs - only power the amp up using that - it could save your bacon.

If it were me - I would just replace the fusistors as they tend to go bad anyway.

Im not familiar with this model but are there any VD1212 small blob-like diodes in this unit? If so, replace those too.

Otherwise - do your replacements, fire up, and see if the bulb glows bright once you do so.

The VD1212's in this seems to have been swapped already, i cant see exactly what is in place of them but not blob style diodes. If i am mistaken i will change them for 2 x 1N4148 in series as this seems to be the standard fix.
Thank you for the great answer and i will definitively build a dim bulb tester!

 

[Brekken]

Welcome to AK..Did you check your emitter resistors between those two outputs ?

Thank you for the welcome, i have just been a lurker for 6 years.
I will make sure to check those, thank you.

 

[petehall347]

if its been worked on before do not trust previous work . make sure that is good first . unknown history is never that easy .

 

[Brekken]

if its been worked on before do not trust previous work . make sure that is good first . unknown history is never that easy .

Yes, i can at least see some proof of a previous recap (all glue broken around caps). It has a sticker from a local repair shop that closed its doors in 87, the previous owner bought it in 88 and has never had it in for repair so all work done on this is likely at least 30 years old. For the price i paid its fine though, i dont mind putting in the hours on this one for only ~20$. It will sing again!

 

[petehall347]

dont leave anything to chance .. check everything .like replacement semi conductors for correct installation

 

[Hyperion]

A check on the driver transistors would be a good idea on the channel with the blown OP transistors.