AU-717 the LeeStereo way

Overundr1

Overundr1

AK Subscriber
Subscriber
Decided to start another thread chronicling an AU-717 using all the information from the most excellent LeeStereo AU-717 upgrade thread so as to not clutter up that relevant build.
Anyways, took in a 717 in trade that had known issues for my own collection. Once on the bench I was surprised to find the power supply voltages right on spec, the rest of the amp was in serious trouble including no left channel except for looks where she gets a 10 including rack handles.
So, backwards to the way I normally redo a 717 I started with the amplifier cards. Offset was way off and no bias at all Out came the cards, talk about glue damage egads what a mess. Also worth noting the glue did contaminate surrounding components requiring even more fiddling about and the fuse resistors were off the charts most measuring in the 500k range vrs 150ohm
IMG_1584.JPG
 
I used the components suggested, increasing capacitance values, 1% 22v zeners, film resistors only deviating in the trim pots since I have lots of 25 turn Bournes on hand. I also pulled the original outputs which had hfe values from 460-515 and saved them replacing them with modern Onsemi equivalents and new mica insulators. Brought the cards up to voltage and offset and bias were easily set and as stable over time as any 717 I have had across the bench. I rate this section a win :)
Next up will be that pesky tone board, losing the signal somewhere through the board, its not the 2SA726's which I replaced with KSA992's so its scope time tomorrow.
Here is one of the output cards all clean and ready for another 40 years for your viewing pleasure.

IMG_1586.JPG
 
First an observation, LeeStereo's changing of the two sets of back to back caps to non polarized 1/2 value single cap mod is brilliant and not sure why I never saw this possibility before. Will be on the lookout in the future throughout my restorations for other amps and locations where this works :)
Anyways, sharp eyes will note the two sets of polarized coupling caps still on the board, my error in not having enough es series muse caps in stock so for the moment I used Nichicon fine gold instead. Otherwise I pretty much followed his lead throughout the board, only real change was replacing all of the signal transistors with low noise modern equivelents 2sa726 and 750 to kas992's and 2SC1400's to KSC1845 and the four fuse-able resistors with metal film 1% versions.
Immediate improvement noted in both low and high frequency accuracy, both channels now working correctly. So--- on to the power supply.
-Lee

IMG_1589.JPG
 
Last edited:
Power supply part 1
For those who wonder why we sputter about corrosive glue these next two pictures tell the tale. Quite amazed this old gal still putting out the volts :)
I have found the only way to properly deal with the 717 supply is to remove it completely from the chassis, those that have not worked on this series take note of the mayhem getting it out creates.
IMG_1591.JPG

And what I will be dealing with over the next couple of hours, sigh.

IMG_1592.JPG
 
Last edited:
One side cleaned, what a mess. 4 resistors, 4 diodes, and one zener eaten away not counting the caps. Pays to have the schematic handy and be able to follow it if you are going to strip all the components at once. 1st side now completed with new 105c caps, new 1n4004 diodes, a 1.3w 13v zener and either 1% or 5% resistors depending on where they were located. Enough for now, the other side awaits. I have a pin drill that is just slightly larger than the original through holes that I run through the spots that had corrosive glue contamination to ensure that none will be in contact with the new parts.

IMG_1595.JPG
 
Last edited:
Yeah, they have very minor surface rusting, when I get to those transistors to pull and grease will hit the heatsinks lightly with 1000grit wet/dry paper. In past builds that really shines them up. Rest of the amp is blemish free.
 
In good hands! Glad to see you bringing her back to better than new Lee. I will have to venture down to hear it sometime in person as a vid or soundclip isn't gonna cut it.
 
Now the other side. I included a picture to show why you have to take out everything the glue contacts, even those components mounted with standoffs. Also note the glue damage under the component through holes. That has to come off or the same issue will again plague the board.

IMG_1596.JPG

Yuck :(

IMG_1597.JPG

Ready to load with new components.

IMG_1599.JPG
 
Those running glue infested Sansui's should take a long look at the middle picture above, an example of what some of your components look like - now!
 
Last edited:
"This is your sansui on DRUGS!! just say NO" Good Job on the 717, I'll be doing a G-801 soon and am in planning stage for the recap doing a leestereo job too If I can help it
 
The G8000 I rebuilt a while back also benefits from mods within the power supply to reduce the heating of a couple of power resistors, I forget which two I changed out but the power supply runs much cooler now. When you start the thread I will see if I can find my notes.
-Lee
 
Yes, noticeable improvement in under hood temps. It took hours to pull and clean those switches, in fact I broke one of the thin plastic links on one of them (forget which one) and was able to get a replacement switch from a fellow tech on the forum. Several revered techs have posted the details on doing this and member Kale is the master at it but be warned it is not for the faint of heart. The 9000 has been singing ever since in my shop rack and not intimidated one bit by the sx-1980 below it. One of my favorite monsters, we shall see when I get a Rotel R-1603 restored where IT fits in the monster pecking order.
Now, back on the 717 restoration, I ran into a small snag I might pass along. When you upgrade those power supply 800uf 63v caps be sure and order the short fat ones not the tall skinny ones. I will provide the part# of the ones I use once I verify fitment. On most units not a problem however the 717 is so tight between the transformers and the support rail for the output blocks being tall and skinny works about as well as an NBA star trying to get into a vintage Volkswagen beetle :)
 
Last edited:
Yep, there are often 2 or even 3 sizes of some values of electrolytics in the same manufacturer's range. Tall and thin, short and fat, and one somewhere in between.
 
Overundr1 said:
Now, back on the 717 restoration, I ran into a small snag I might pass along. When you upgrade those power supply 800uf 63v caps be sure and order the short fat ones not the tall skinny ones. I will provide the part# of the ones I use once I verify fitment. On most units not a problem however the 717 is so tight between the transformers and the support rail for the output blocks being tall and skinny works about as well as an NBA star trying to get into a vintage Volkswagen beetle :)
Click to expand...

Yes, the devil is in the details; when searching on Mouser or Digi-Key, one can filter for diameter and/or lead spacing. The SFF (Short Form Factor) capacitors are a good fit in vintage restorations; my preferred technical term for them is "Short Fat Fanny" types.
 
You must log in or register to reply here.

Similar threads

dolamike
Me and the Dog are Restoring an AU-717
3 4 5
Replies
91
Views
2K
lbcgav
lbcgav
HPower
My Leestereo AU-717
Replies
14
Views
676
HPower
HPower
P
My first ever restauration of my good old Sansui AU-717.
2
Replies
37
Views
2K
PoorEars
P
Leestereo
Leestereo's Restoration/Upgrade Of A Sansui AU-717
25 26 27
Replies
534
Views
127K
Aircooled
A
AmbientNoise
Hanging by a thread, aka restoring a Sansui AU-717 the Leestereo way!
2
Replies
29
Views
2K
AmbientNoise
AmbientNoise
Back
Top Bottom