Another AU-919 recon

Hyperion I can't seem to find the oval capacitors thread >.<

Here it is
http://www.audiokarma.org/forums/showthread.php?t=561441&highlight=Oval+Capacitors

Also will you be changing the JFETs in this one - the 2SK129 package? If so what would be good substitutes ?

No, why? there is no need, regarding substitutes I would have to research the availability of originals or suitable discrete JFET's to use instead.

Also I read somewhere that some 919s (depending on their vintage) have different cap values - just wondering what caps values are in this new one you're doing and if they do in fact deviate from the service manual values? This is quite confusing wouldn't the right thing to do is to always follow the sm?
Or did Sansui print two of these sm's?

See the page towards the end of the recon thread for my AU-919 for a list of differences I found, I expect this one to be no different. See my note in the first post of this thread where I make a commitment to note any additional differences or other peculiarities, should I find any.

Also 'rule of thumb' is to trust the component values/voltages that are in the amp NOW - and not rely on the SM & schematic of which there are only one of each as far as I know. This is why it is SUCH a disaster when someone has been into an amplifier changing things around without knowing what they are doing - it gives you no point of reference.

Ohhhhhh dirty pictures..... droool

More to droool over later on Mike :)
 
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The parts order has arrived, and I have begun removing components, and cleaning the 'glue' - 38 components removed from the driver board alone so far.

Some things discovered along the way:

Mains switch is stiff - action is not as free as I would like.
Speaker select switch - likewise stiff.
Balance control is definitely dirty.
Broken speaker terminal - Sansui Parts Shop has them in stock !

On this one I will be replacing the 'black flags' with Ceramic NP0/C0G capacitors. :yes:

EDIT:
Got to 'lift' a few components to get under them for the last of the glue... :dammit:

More later.
 
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At some point in production, Sansui switched from spring clips to binding posts on this model. I have an earlier one with spring clips.

- Pete
 
I now have the driver board very nearly finished. (just 4 capacitors to be installed).

The main PSU is now getting the 'treatment', it is stripped of capacitors and I have been removing the 'glue' :sigh:

After this is done, I'll probably put it back together for a brief test before continuing.

More later.
 
Careful, you might NOT have as brief of a test turning intothe endless test drive.... like I'm having with the BA/CA combo...
 
OK, latest is:-

Driver board finished, both PSU's finished, all reassembled, Bias and DC offset are set - no issues.

This AU-919 sounds beautiful - might even be nicer than my own :)

MM Head Amp and input selector switch next, closely followed by MC Head Amp, Protection Board, Pre-Main Board, Speaker terminals and mains cable.
 
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I spent the afternoon removing 28 components ready for installing new, and lifting another 12 or so to get at the glue which, I am pleased to say is now gone from the F-2835 MM Head Amp board. I'll be removing the input selector switch for cleaning next.
 
Thanks Guys,

Switch is out and cleaned, I won't be remounting the switch until the board is repopulated with components, it's easier that way.

No more until tomorrow.
 
F-2835 board fully repopulated with components, flux cleaned, input selector switch (already cleaned) re-mounted onto the PCB.

Tape select switches removed, cleaned and replaced. Rear panel removed, Protection PCB re-capped and relay drive transistor changed. Pre-main PCB re-capped.

More parts arriving in a couple of days.
The speaker terminals have been ordered, and I need 2 trimmers, :dammit: I thought I had some but they were the wrong adjustment orientation. :sigh:
 
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Update
2 trimmers arrived and have been fitted to F-2835 Equaliser/MM Head Amp board.
Mains cable has been changed
Replacement speaker terminals arrived and have been fitted.
F-2833 MC Head Amp Board recapped, trimmers replaced.
Rear panel cleaned and re-assembled.
Chassis re-assembled in preparation for dropping the front panel to deal with switch and control cleaning, and recapping the F-2841 Flat Amp board.
 
Questions- at the bottom of the power board there are some 10 ohm resistors. Can you tell what the factory used? Do any show evidence of being wire-wound, or are they big metal films?

Also, I don't know about power in the UK. Is there such a thing as a 2-wire cord, or are all cords 3-wire? What did the unit have from the factory and what did you use to replace it?
 
Questions- at the bottom of the power board there are some 10 ohm resistors. Can you tell what the factory used? Do any show evidence of being wire-wound, or are they big metal films?

Do you mean the main PSU = F-2845? - or do you mean on the underside of that board? I do remember seeing 10Ω resistors (on the topside) - these are the standard grey bodied type so commonly seen in Sansui amplifiers.

Also, I don't know about power in the UK. Is there such a thing as a 2-wire cord, or are all cords 3-wire? What did the unit have from the factory and what did you use to replace it?

It depends on the appliance, but yes we do have 2 wire power cords, although they are less common these days. My AU-717 had a 2 wire power cord for example, I changed it for a 3 wire - but did not connect the earth (third) core.

Interestingly, this AU-919 has a 3 wire power cord (as did my own AU-919), and the earth IS connected to the chassis. This is unique in my recollection, I do not remember seeing another Sansui amplifier with the power cable earth connected. I used a standard 'moulded plug' fused power cord, with 3 cores, the existing cable was quite short - and had no plug.

BTW:
Conrad, I am using C0G/NP0 Ceramic MLCC capacitors instead of Mica on this one. I have done a listening test part way through the recondition - it sounds fabulous. ;) no different in fact from the one with the Mica capacitors.

And I can confirm that my one (and this one) do not sound flat with the tone controls engaged but set to 'flat' - which is in line with your findings.

Update:
I have removed the Flat Amp board - it is now receiving 'the treatment' :)
 
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Sorry for my sloppy language, I meant the power amp board. I think the resistors are the typical HF loading resistors near the coils. I've got a unit with a mixed collection of films, wire wounds and mystery resistors. It goes just out of spec on THD at 20 kHz and I'm wondering if having a wire wound on the output has anything to do with it. I need to just buy some and replace them all.

Sansui actually touches on grounding in the service manual, and that it can cause oscillation, so it's interesting they supplied a grounded mains cord on some units.

I wouldn't expect anything but great sound from C0G/NP0 or silver mica. Some have questioned the reliability of silver mica, but I've never seen a modern one fail. They certainly have gotten expensive, especially the larger ones.
 
John, nice job sir~

Thanks Mike :thmbsp:

I have now changed all the components I intend to change, it is back together again - except the covers.

I powered it up, first time on the DBT - all good - (except one small thing... :headscrat )

So, I connected it to full mains and it comes out of protection in 8 seconds with a nice sharp 'ping' from the relay. But the 'small thing' was that the protection light would flash very fast until relay engagement... it was quite normal before I recapped the protection board. I had used a couple of very plain-Jane 4.7µF capacitors on the board, and thought they must be faulty or mislabelled. Off with the rear panel again, and a look at the capacitors in the multivibrator confirmed that one of them was a 4.7µF as it should be, but looking at its companion, physically identical, it was a 0.47µF ! - I changed them both - now perfect again.

I have adjusted the voltages, offsets and bias, all nice and stable - with the right channel showing a very slight tendency to have drifty DC offset in the sub 20mV zone, nothing to worry about I think.

More checking/testing and then listening tests :)
 
Interesting aout the PLAIN JANE being THAT far off….
On my BA-3K ( US version ) IF I set the DC .000X on left it wiggles about, BUT If I set +/- .00X it's rock steady… The right doesn't seem to care.. ODD!
 
The cap was marked as 0.47µF - but because it 'looked' so identical to the 4.7µF - same voltage, same size, same colour sleeve and markings - I thought they were the same, just me not checking properly ;)
 
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