Repair and restoration of an Sansui AU 417 for my

[GrisPato]

Bought this one a few months ago with right channel not working, to repair for my son's first stereo.
Disassembled it and then got caught up in some other projects. Luckely it came with all the connectors intact.
Did some cleaning of chassis and PCB's when I had 30 minutes here and there. Don't like to start on component replacement if I don't have sufficient time to finish at least one board.
Was full with a black greasy film everywhere. Guess it spend most of his live in a garage.
Made time in the last week to work on it several days for 1-2 hours a day.



Power supply board had some capacitors replaced already with unknown to me Chinese brands.
Glue not removed.

 

[GrisPato]

Started last week with the driver boards F-2721 and F-2722. Yes they are the same as in the au517/au717!
But with a more simple circuit.
Was a little confusing because the service manual shows the same board image as for the au 517 but on the schematic components are missing and others added.


I am considering to upgrade the driver boards later to au517 specs but first I'll keep it as is.
Ofcourse glue!











Always a pain. The dried out parts are easy but the gummy parts are more work intensive. If you start to early with dissolvents ( isopropanol ) you are in for some work.
On the second board I used a little stick of bamboo and have to say worked perfect. After 5 minutes it looked like this:



Another 5 minutes with isopropanol and it's done.



Measured the fuse resistors:



Almost 69k,up from 150 ohm. So let's hope that's the repair part

 

[GrisPato]

Components replaced on driver boards:
C2,4 shunting zenerdiodes from 33uF-25V to 100uF-50V, UCC EKY.
C 11,14 local filter, decoupling capacitors from 470uF-63V to 820uF-63V United ChemiCon EKY.
C13, from collector to emitter on bias transistor ( honestly, still have no idea why it's there ) from 1uF-50V, same value.
Just 5 electrolytics on these board.
Then ofcourse the zenerdiodes to Vishay BZX55B22 500mW 2%, and the fuse resistors with metal film ½ watt from Yageo.
And for the first time I replaced the mox base resistors from the output transistors also with metal film.





Replaced the diode D2 full with glue naturally also.

 

[GrisPato]

Next is the control board, F-2673. Just a few electrolytic capacitors here.
C11,12 10uF-25V low leakage replaced with 10uF-50V Nichicon UKL.
C31,32 4,7uF-25 bipolar replaced with Nichicon UES 4,7uF-35V.
I found these weird local rail decoupling ceramics C27,29 from 47nF. Replaced them with UCC EKY 22uF-50V. Considering to put a small 22nF in parallel but am not sure if that is useful.



Still have to reassemble the volumepot meter that I took apart learning how to clean them. Have to get some equipment first to unrivet it and close it up again.







Was/is really dirty.

 

[GrisPato]

Than the powersupply / protection board F-3043. This one is unique for the AU 417. Logical,because just one transformer and no dual mono configuration here in the powersupply.
I removed the already changed out capacitors for some UCC EKY.
C3,4 originally 220 uF-63V upgraded to 680uF-80V.
C5-8 from 100uF-35 to 220uF-50V.
Capacitors in the protection circuit where changed for same value and type except the two 4,7uF's, did not have them anymore.





The main filter capacitors will stay for now. I want to change them for 2x2 parallel 8200uF capacitors to lower the esr. These are 35mm in diameter and stupidly I ordered 35mm mounting clamps that won't fit on the chassis. So have to think that over first.

 

[GrisPato]

Was just cleaning the driver boards a little more after seeing that they where still a little dusty.
Felt that one of the 2sa899's moved a little.



Still have to learn: always check the solderjoints.
I assume this is from the heat so considering to make a little steel plate heatsink for them.

 

[rasenthiran]

Nice

 

[GrisPato]

The last if the boards is the head-amp/ equilizer board F-2723, the same board as in the AU517/717.
Interesting differences. First because there is no dual mono power supply they did not filter the rail for the right channel. I am going to put them in and upgrade from 10uF to effectively 660 uF with four Panasonic FC 330uF-35V. I am assuming that it can't hurt?!
The other difference is the input coupling capacitors.
On the 517 Sansui used an 0.047 uF film with in parallel an 1 uF low leakage, on the 417 they used an 1uF film ( same as 717) but changed the series resistors from 1k and 22 ohm to 220 and 22. Anyone who can tell me why they could lower the value of the resistor??
The output coupling capacitor C41,42 is upgraded to a PP Panasonic ECW 4,7uF
( could you get away with a lower value here, they are crazy big?)
C19,20 the "speedup" capacitor (learned that from Leestereo's thread about his restoration from an AU 717 which I used as reference for this restoration) was replaced with Panasonic FC 10uF-25V. The low end roll off capacitors for the riaa equalisation C5,6 also according Leestereo's example upgraded from polar 220uF to bipolar UES 470 uF-25V.
Ofcourse also replaced the fuse resistors R47-50 with metal film same value.
I am still considering if I am going to change the MV12 diodes or do that only when necessary.

 

[GrisPato]

That one is ready. In the end still a softer leftchannel. Only thing I can find is the volume pot. Cleaned it for another 3 times. Is still there but almost undetectable now, has to do for now.
Sound is really good, powerful.
My son is really happy. Purchased a Sansui rack with some cheap Sansui cdplayer and cassette deck for him to play with.