Sansui AU-919 Restoration

[Aud10file]

F2841- Flat Amp

This one slowed me down some.

The board in this unit had some screen-printing that was slightly different from my service manual. On the board (rev Ⓐ), there were four 3pF black flags labeled C35-C38. The positions correspond to C31-C34 which are labeled 5pF in the service manual. It seems like Sansui changed the capacitor values and the part numbers at some point during production. They did provide the new part numbers and values on the layout for F-2841 in the service manual. It was an interesting revision involving the black flags.

Service Manual:




Board before:
R21 looks discolored in the picture but that’s only a shadow cast by the transistor.




There was a bit of the infamous glue holding C17-C22. C17 and C18 were replaced with .33uF polypropelene. C19-C22 were replaced with 100uF/63V.

Before glue removal:




After glue removal:




The zener diodes, ZD01-ZD04, were replaced with new 2% tolerance diodes. The two 470 Ω trimmers, VR01 and VR02, were replaced with 500 Ω mutiturn trimmers. I offset C13 slightly, to allow easy access to VR02 for adjustments.


Completed board:




The only board remaining is F-2835 Equalizer board. This one had some interesting challenges, which will be detailed in my next post.

 

[Aud10file]

The final board left to restore was the Equalizer Board.

F-2835 Equalizer Amp

This one proved to be the most challenging, only because the conductor side layout for the board in the service manual was somewhat different from the actual board in my unit. Much of my time was spent referring to this board and the schematic to doublecheck connections.

This board is marked with a screen printed Ⓐ.


Picture of layout:





Actual board:




This board has two ribbon cables soldered in and connected to F-2834 Terminal Input Board. I removed both boards from the unit for better access, and to prevent extra stress on the ribbon cables.




This board was densely populated on the equalizer half of the board. The half with regulated 10V supply has plenty of breathing room around components.

Both VR01 and VR02 were 330Ω on my board, and they looked to be factory original. The service manual showed these as 220 Ω.

There was a bit of glue around C47-C50 that had to be cleaned. Also, there were twelve black flag capacitors on this board which were replaced with COG type.

All the heatsinked transistors had the compound removed and new thermal compound was applied.


Before picture:




After picture:




All the settings on the amplifier dialed in perfectly and testing showed stable and even signal on both channels. but the original outputs still need to be installed. I had to put the unit back on the shelf for a bit, in order to take care of a few customer units that were dropped off for repair. One is a Pioneer SX-980, which was a relatively simple fix and the other is a Sansui CA-3000 preamp, which may have a bad connection or a pass-through issue, due to the symptom described.

I think I’ll get the 919 buttoned up and installed in my listening station this weekend, before I tackle the CA-3000.

Left to do: I still have to refinish the cover which had a few scratches. Also, the four oval 15000uF filter caps measured between 12060uF and 12500uF with an ESR between .06Ω and .09Ω. This is just above the low end of acceptable, so I will listen to the amp for a while, and defer the oval cap rebuild for when I have some spare time. I am definitely planning to re-stuff the ovals, but I need to whittle down the growing backlog first. Parts are already on order.

I will post some final pictures in a separate thread.

 

[ghamilton]

F2841- Flat Amp

This one slowed me down some.

The board in this unit had some screen-printing that was slightly different from my service manual. On the board (rev Ⓐ), there were four 3pF black flags labeled C35-C38. The positions correspond to C31-C34 which are labeled 5pF in the service manual. It seems like Sansui changed the capacitor values and the part numbers at some point during production. They did provide the new part numbers and values on the layout for F-2841 in the service manual. It was an interesting revision involving the black flags.

Service Manual:

View attachment 2614409


Board before:
R21 looks discolored in the picture but that’s only a shadow cast by the transistor.

View attachment 2614413


There was a bit of the infamous glue holding C17-C22. C17 and C18 were replaced with .33uF polypropelene. C19-C22 were replaced with 100uF/63V.

Before glue removal:

View attachment 2614415


After glue removal:

View attachment 2614427


The zener diodes, ZD01-ZD04, were replaced with new 2% tolerance diodes. The two 470 Ω trimmers, VR01 and VR02, were replaced with 500 Ω mutiturn trimmers. I offset C13 slightly, to allow easy access to VR02 for adjustments.


Completed board:

View attachment 2614428


The only board remaining is F-2835 Equalizer board. This one had some interesting challenges, which will be detailed in my next post.

Why didn't you put a single bipolar cap in the place of the 2 polar caps in C 19 20 21 22? The only reason that the factory didn't do it (according to Dorian) is because they couldn't at that time due to parts availability?

 

[Aud10file]

Why didn't you put a single bipolar cap in the place of the 2 polar caps in C 19 20 21 22? The only reason that the factory didn't do it (according to Dorian) is because they couldn't at that time due to parts availability?

Reason was stated in post #1:
“My plan for this unit was to restore it to the original as-designed state without any value modifications, if I could help it.”

Also, in post #13:
“Keep the unit true to the original design”


Note: This does not mean that I disagree with the substitution of a BP for two polarized capacitors in certain situations.

 

[ghamilton]

I understand that, but the only reason that they (the designers) did it this way is because they had to at that time due to lack of the better cap selection (according to Dorian).
I guess the owner wanted it done the way you did it.
I understand.

 

[Aud10file]

The remaining work is almost finished. The original Sanken outputs were installed, along with new mica and thermal compound. The amplifier has been completely reassembled, save for the cover refinish, which needs to be completed.

Here are some more pictures.

Original Sanken outputs installed:





Numerous parts were replaced in this restoration:






The cover had some scratches and missing paint and needed some work. I had prepped it for paint, but the weather has been very humid outside today and definitely not good conditions for applying paint. So, I’ll add the ‘After refinish’ picture in the next few days.

The cover before refinishing:




Prepped for paint:




After refinishing:




Final assembled:












I hope to do some power testing and post some pictures next.

 

[Vintagear]

The remaining work is almost finished. The original Sanken outputs were installed, along with new mica and thermal compound. The amplifier has been completely reassembled, save for the cover refinish, which needs to be completed.

Here are some more pictures.

Original Sanken outputs installed:


View attachment 2618857


Numerous parts were replaced in this restoration:



View attachment 2618859


The cover had some scratches and missing paint and needed some work. I had prepped it for paint, but the weather has been very humid outside today and definitely not good conditions for applying paint. So, I’ll add the ‘After refinish’ picture in the next few days.

The cover before refinishing:

View attachment 2618861


Prepped for paint:

View attachment 2618863


After refinishing:

[picture placeholder]


Final assembled:

[picture placeholder]


I hope to do some power testing and post some pictures next.

 

[Aud10file]

Just an FYI: Post #26 edited to add final pictures.

 

[ghamilton]

Great job! Beautiful!

 

[Vintagear]

I got a chance to audition this specific unit last week in @Aud10file's shop playing through the Philharmonic Audio New AA monitors he has in there. Dennis Murphy used an even higher grade Morel tweeter than usual when he sent these to @Aud10file. Incidentally, I had New AA monitors a few years ago and these sound much better.

This is the first 919 I've ever laid ears on and I was not disappointed. The presentation was clean, clear and open. The soundstage was pinpoint accurate in the listening space of his shop. I've heard various units in that room and the 919 was definitely one of the best. We also listened to some MM & MC and both were excellent. @Aud10file did a great job restoring this unit. Fantastic!