Trying to bring Sansui AU-517 back to life

[Hyperion]

Interesting, thank you, it looks like the 2 larger white cement resistors are 330Ω - ('330R') and should be 0.33Ω - if I am right this would entirely explain your protection issues.

Would you please check this and confirm?

This statement in your first post really surprised me.

Changed out some shorted resistors.

I thought to myself 'WHAT'!!? - but passed over the remark.

 

[Dahond]

Haha this is stupid.
You're right. they are 330 ohm.
I'm quite ashamed not seeing this.

Not sure about the R47. I didn't change them and the schematic says 2.2 ohm.
I wil solder them out and check again.

 

[Hyperion]

schematic says 2.2 ohm.

You are correct - I was (briefly) mistaking the 2.2K 2W standard resistor (R04) for the 2.2Ω cement resistor (R47) - which should be 2.2Ω. - my apologies.

Oh, and if you change those 330Ω resistors for the correct value, be careful of the bias setting, be sure to turn it right down before powering on again. Or start up on DBT just to be safe.

I'll be interested to see what you find.

 

[Dahond]

IT'S ALIVE
Oh man this is great! No more protection problems.
Thank you this is really amazing.
SO stupid I didn't check the resistors well enough @kevzep
Thank you so much @Hyperion for taking a look.
I'm quite happy right now
My wife's going to be disappointed the big sansui SP3500 speakers have a reason to stay in the room now

 

[Hyperion]

Yay ! - Well Done !! - very happy for you

But one question, are the zener voltages OK now?

 

[Dahond]

Zener voltages:
Right:
ZD01 22.55
ZD02 -23.11

Left
ZD01 21.93
ZD02 -23.30

Seems like they are only off by 0.6v max
-> 0.8v on the left ZD02

 

[Hyperion]

Well, assuming 5% tolerance components originally, both ZD02's are out of spec' but only just... - you can now properly enjoy your AU-517 but personally I like to see these voltages closer together. Perhaps consider buying some replacement zeners when it is convenient, no hurry, just something to consider.

 

[Dahond]

I'm going to reassemble it for now and enjoy for a while.

I've recapped the powerboard with some cheap caps at first to try and figure out the problem.
I'll be ordering some decent replacement caps, new zeners,1N4148's, maybe recap the preamp and EQ too in the near future.
This whole adventure made me realize it would be such a shame to loose the amp but now that I know it's not lost, I can take my time and make sure I get it right.

Any other things I should do to it to make it live forever? Maybe swap the relay?

 

[Hyperion]

Maybe swap the relay?

Yes, good idea - all proper reconditioning should include this.

Have a look around here on AK at what other AK members have done with their AU-517 /717 reconditioning - especially the excellent 'Leestereo' thread(s) - there is one of his for the AU-717 which you can use as a guide for doing your AU-517 as they are nearly identical.

There are plenty of others.

In addition, reading the other threads will teach you a lot, there is so much knowledge and experience in those threads.

 

[Dswankey]

@Dahond

I'm glad the resident Sansui experts were able to help you out. Congrats! on getting her back up and running.

 

[Dahond]

Leestereo's work looks very nice.
I will certainly check his threads.
Here's the assembled 517 with his partners. Thank you very much again.

 

[Leestereo]

@Hyperion is correct, the AU-517 and AU-717 are very similar, in fact they share the same service manual.

Here are some pictures of a restored/upgraded AU-517:

 

[Dahond]

Looks amazing @Leestereo
Why did you increase capacitance in the AU 717?

 

[Leestereo]

The goal of increasing the values of the local filtering capacitors is primarily to enhance/maximize the performance of the circuit. Generally, there is no problem increasing the capacitance rating of the local decoupling/filtering capacitor (especially for small values less than 1000µF). IMO, a 2X-3X increase is acceptable for most small capacity capacitors whose function is DC filtering.

Why increase the capacity of a power supply? It has been argued that a power supply is essentially in series with the stage's output (hence in the signal path), and as such does impact the sound of an amplifier. Nelson Pass uses the analogy of a water reservoir as the power supply and the output stage as the valve that controls the flow of the water: https://www.passdiy.com/project/articles/power-supplies. If you have a poor and/or inadequate supply, the quality and/or the quantity of water is affected. For an amplifier, a poor/failing power supply capacitor (e.g., low capacity, high ESR) may not be able to supply the voltage/current that the output stage is "asking" for. IMO, this is primarily why improving the power supply (e.g., increasing capacity, lowering impedance/ESR) often does impact/improve the sound of an amplifier.