Another AU-919

Not counting disassembly antics and diagnostics for those reading along that equates to 262 desolder and 262 install solder points, (cut you a break on three legged critters), add in time to remove glue and measure and you will start to understand why there are not many of us that go through the full restore boogie anymore. 10 component changes per hour times 131 components equates to 13 hours bench time not counting aggravation time chasing down those critters and screws that mysteriously disappear right when you need them most. Nice write up John.
 
I greatly appreciate the tremendous skill and dedication that John is applying to the task.

I'm not sure I've done enough good in life to deserve the pleasure that the results will give. But let there be no doubt that I will enjoy! :)
 
Another 2 zener diodes changed, making it 133 changed parts, the F-2835 is about 80% finished - I have run out of steam for now, maybe pictures tomorrow. ;)

(Our central heating has been offline since last Wednesday :( - so it's a bit cold in the workshop - hence the above comment :) )
 
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Here is the completed F-2835 MM Head Amp Board - minus the input selector switch.

IMG_2189a.jpg

But something I noticed - look down there in the bottom right hand corner - ringed in red.
IMG_2189b.jpg

I didn't remove that resistor - and the solder pads underneath are soldered over like it has never been there. It's friends R52, R54, and R51 are all present - but not R53 ! :)

There are a few other 'missing' resistors - like R99 and R100 - but they are supposed to be missing, I think R53 should be there. :thumbsup:

I have just been checking the 'With glue' (before) picture in post #83 - and R53 isn't there. :bye:
 
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I'll be remounting the input selector switch next, then reassembling the MM Head Amp assembly into the chassis. I will then be able to get a proper look at the MC Head Amp, the Protection Board, and anything on the rear panel - like the connected separated switch.

I don't have the correct value for the missing R53, and there are one or two other items I have discovered I need, so once I get a look at the last boards, to check for any 'surprises', I'll place a final (v.small) parts order.

Now rapidly moving towards the end game...:smoke:
 
Yep, those resistors (R52, R54 & R51, R53) are all 39K ohms, I don't know why I don't have any - but I don't :)
 
Input selector switch remounted, MM Head Amp track side cleaned and now remounted in the chassis.

Rear panel off - work now proceeding on the F-2833 MC Head Amp.
 
Here is the F-2833 MC Head Amp board completed

IMG_2191a.jpg

I have also done the Connected /Separated PCB, switch removed, dismantled, cleaned, reassembled, capacitors changed.

So that leaves:
Fitting that missing resistor to the MM Head Amp. (I'll change the one in the same position in the other channel)
And the Protection PCB.

Then reassembly, and settings, then a listen. ;)
 
John - As I've gushed before, I'm highly impressed with your skills and methodical procedure. I've very fortunate to be at the receiving end. Thank you so much!

Lee - Judging from the list of music you used to test the AU-919 you restored earlier, we have very similar tastes. I'm looking forward in particular to a Wynton Marsalis session, not only his jazz pieces but also a couple of his superb classical renditions.
 
Great. Will you ever use the MC section? If you put in 68 Kohm resistors in R39 & R40 then you will be set up to use the low output Grado wood-body cartridges. FYI
 
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The owner of the amp will be using the MC section, those resistors have been changed to 180 ohm. (10 times the cartridge impedance).

Unfortunately I can't do an MC listening test as I don't own an MC cartridge... yet :naughty:

I think I am finished changing components now.

Total removed parts count now: 162 - comprising
95 Electrolytic capacitors
4 Film capacitors
14 Trimmers
10 Zener diodes
6 Resistors
32 Black Flags.
1 Transistor.
 
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I'm sure John won't mind me expanding on his reply by relating the history behind the change...

I found the AU-919’s MC input impedance to be incompatible with my Signet MK111 cartridge when I bought them (from different retailers) in 1980. I corresponded with Sansui on the problem and they eventually conceded the mismatch and advised me to try other makes/models of cartridge until I found one that worked with their amplifier!

I didn't want to move from the (very expensive but evidently superb) Signet, so for the intervening 36 years I've been feeding its signal via a step-up transformer Into the MM input.

John and I discussed the mismatch and he kindly offered to increase the amplifier's MC impedance from its incredibly low value of (IIRC) 10 ohms to 180 or 240 ohms to suit the Signet's 18 ohms. I believe that many (most/all?) other low-output MC cartridges would also need the increased input impedance.

One of my first actions after firing up the rebuilt amplifier will be to carry out listening tests between the modified MC input and the transformer-into-MM input. Nothing of significance will be lost if I need to stay with the latter, however I'm reasonably confident that John will have cured the MC incompatibility problem.
 
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