Leestereo's Restoration/Upgrade Of A Sansui AU-717

Indeed, there is much useful information in this thread, and in LeeStereo's other threads. But when you want to see the fit of components described, there ain't nothing like a photo. The more common refrain seen in these hallowed pages is this:worthless27.jpg

Too bad the photos are trapped in Photobucket and can no longer be seen. Can this be fixed?
 
Can this be fixed?

That would be up to Leestereo, he still has access to the pictures, and could potentially move them to another hosting site - but it is a lot of work and I am sure he has other calls on his time.
 
A very nice Sansui AU-717 was on the workbench for a complete restoration and upgrade.

The restoration/upgrade plan included the following:
1. Replace all power supply electrolytic capacitors with low ESR types (increasing capacity where appropriate and physically possible).
2. Replace all of the signal path electrolytic capacitors with either "audio grade"/bi-polar electrolytic types or film types (whenever possible).
3. Upgrade original polyester film capacitors to polypropylene film types (as appropriate).
4. Replace signal path ceramic capacitors with film or C0G types.
5. Replace fuse resistors with metal film types.
6. Replace VD1212 (dual diodes) with pair of 1N4148 diodes (in series).
7. Replace any components damaged by the infamous corrosive board glue.

Although cosmetically near mint, there was a noticeable "hum/buzzing" noise on both channels (independent of the input source and the volume control setting). Further investigation revealed that the noise originated from the preamplifer stage; specifically, failing capacitors in the regulated 35V power supply for the preamplifier. Accordingly, the first board to be restored/upgraded was the power supply board.


Part 1: Regulated Power Supply & Protector Circuit Board (F-2663)

The F-2663 board contains 2 independent regulated 35V power supplies (one for each channel). Unlike the main amplifier power supply, the regulated power supply uses rather modestly sized capacitors; this is one of the few weak spots in this otherwise excellent design. Fortunately, since modern electrolytic capacitors are physically smaller than their vintage counterparts, the capacitance reserve can be significantly increased with the replacement capacitors.



Capacitors C05, C06, C07 and C08 filter the raw DC from a diode bridge, and were originally rated at 220µF/63V; the replacements were low ESR types rated at 820µF/63V. Similarly, capacitors C09, C10, C11 and C12 were originally rated at 100µF/63V and the replacements were low ESR types rated at 330µF/63V. Capacitors C17 and C18 which shunt the 13V zeners were originally rated at 470µF/16V and were replaced with low ESR types rated at 470µF/25V. The small value (0.47µF) low leakage capacitors, C19, C20, C21 and C22, were replaced with 0.47µF stacked film types. The final filtering capacitors in the regulated supply, C23, C24, C25 and C26 were originally rated at 100µF/35V and the replacements were low ESR types rated at 220µF/50V. Note that the voltage rating of these capacitors must be increased to 50V from the original 35V since these capacitors are subject to ~35V. The VD1212 double diode was replaced with a pair of 1N4148 diodes in series. Also, since the integrity of a number of solder joints appeared suspect, in particular the ones for the regulator transistors (TR01-TR04), these were re-flowed/renewed.





Due to the cramped installation of the components on this board and the location of the board within the amplifier, this circuit runs rather warm. In order to improve the air cooling of this circuit, most of the replacement capacitors were selected to be physically smaller than the originals, except for C23-C26 which were the same size as the originals.

A number of components had to be replaced due to damage from the corrosive glue used to secure the larger capacitors on this board. The damaged diodes, ZD01 and ZD02, were replaced with precision (2%) 13V BZX55B13 zeners. Similarly, the glue damaged 10kohm resistors (R7-R14) and the 22kohm resistors (R33, R34) were replaced with same value metal film types. Note that all remnants of the corrosive glue was removed from the board prior to the installation of the new components.



The measurements of the restored/upgraded regulated circuit confirmed very stable ±35V rails, with no measurable AC ripple. Also, a quick listening test confirmed that the "hum/buzzing" noise was completely eradicated.
 
I must add my signature to the petition as my own rebuild is on the horizon and was so looking forward to working off Leestereos notes AND pictures! This photobucket situation is a mess.. I cant believe how many great threads have been destroyed :(
 
I have prints of most of Lee's pics from the 717 restore. I can scan and put them up. Here is a sample.
This is the power supply,before pic.
717 ps.jpg
 
Very kind of you, Fhamre. Now if someone could do the other Leestereo threads, like the AU-9500, etc.
 
Yes, thank you. Pictures always help. I am near the end of a 717 restoration now and just having the pictures confirms things. :beerchug:
 
Thanks, Leestereo! I used to live in Ottawa, MerryChristmas to you (and all AK, as well)!
 
The embedded Photobucket pictures can be viewed with a Chrome Extensiion or a Firefox Add-on.

I have noticed that at different times one or the other workaround will stop working; currently, at the time of writing, both workarounds allow the pictures to be viewed within the thread.

And they're back! Thanks Leestereo.. feel a little silly that I didnt figure that out thanks again for the effort you made.. so valuable to refer to this!
 
Greetings. This information is very helpful to me as I am restoring an AU717. Have you had an issues with inrush via the increased capacitance?

Kind regards.
 
Have you had an issues with inrush via the increased capacitance?

I am not aware of any issues wrt the inrush current following the restoration/upgrade described herein (and this particular AU-717 has seen regular use in the >3 years since the work was completed). Also, to my knowledge, no issues have been reported by other techs that have emulated this thread in restoring a AU-717; note that the increase in capacitance (~5,000µF) is less than 10% of the total capacitance of the main capacitors (60,000µF). HTH.
 
Re the tone board.
With the subsonic filter engaged, the signal additionally passes through a pair of polarized 4.7µF/50V capacitors in series (forms a "bi-polar" capacitor) for each channel (C33/C35 and C34/C36). Each original capacitor pair was replaced with a single 2.2µF/50V stacked film capacitor. Also, the film by-pass capacitors for subsonic filter, C31 and C32, were removed.
Just finishing up a AU-717 and would like a little clarity regarding the placement of the single 2.2uf once C33/C35 or C34/C35 are being replaced. Can't quite make it out in the pics provided.
Do you install the 2.2uf BP in the place of say C33 and jumper C35? Or?
 
Yes, you can install the 2.2µF capacitor to replace either C33 or C35 and install a jumper in the other. In this particular case, the width of the Panasonic 2.2µF capacitor allowed it to be installed with one leg in C33 and the other in C35 (the trace between C33 and C35 is not used).
 
Thx Lee. Now I have to figure out why the right channel has less volume than the left.
Was fine until I did the tone board.
 
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