Sansui AU-317 MK2 Repair/Restoration.

Sagitta

New Member
Hey fellas, a little cut and paste from another forum.

I've had this amp which I bought at the tip shop for just $10 collecting dust for the last 4 years.
Twice in that time I pulled it out, pulled the covers off, had a look and put it in the "too hard basket" after remembering why I put it away the previous time.
It was labeled as "not working" but was hopeful it'd be a simple fix, especially when lifting the cover and seeing the date and bias voltage on the shield dating to just a year prior.

But alas, it had many problems, a simple fuse was not one.
I posted up on an existing AU-317 restoration thread, where I had attempted to diagnose the issues but quickly found I was getting in too deep for my knowledge and confidence.
I also considered sending it off for repairs, which I never really followed through with.
This time however, I'm wanting to actually get this amp going and wanting to do the work myself, and put in some time to learn the hows and whys, for most of my electrical knowledge is with much simpler workings and most of that I've forgotten.

I'm hoping it'll take the place of my Monarch Series 8 Model 88 amp which is in the middle of a Rega RP1 with a Nagaoka MP110 and a pair of Acoustic Research TSW 210 speakers.

I've also found a service manual and several pages of others restoring/repairing this particular amp which so far has proven helpful, I'm also hoping to lean on the knowledge of a few on this forum who know their stuff to help get me by.



During the service before my ownership it seems a few capacitors were replaced with Hitano branded and another brand that I've yet to identify (haven't removed them from circuit, tested fine in-circuit).
There was also quite a few poor looking solder joints too.

I'd like to replace as many as I can while I'm at it anyway.

I'm only looking at the power amp at the moment too, haven't looked at the other boards yet, only going to go board by board, I'll get this working first then move on.


I found a combination of of Panasonic FR and Nichicon PW/HE caps to replace all of the electrolytics, I tried to keep them all one brand and series but easier said than done it seems, at least keeping the same capacitance and voltage anyway.
Aside from the 2x 10000uf 56v filter caps, not sure what to replace those with yet.

I'm also replacing the following transistors.
2SB 527 with MJE 15031G
2SD 357 with MJE 15028G
2SC 2261 with MJ 21194G (or MJ 15015G ?)
2SA 981 with MJ 21193G (or MJ 15016G ?)
2SC 1951 with ZTX 694B
2SC1313 with KSC1845FTA

Any idea if they will be suitable replacements?
I found most of those suggestions on other forums.
Can't remember where I found the 2nd option for the outputs, but looking at the spec sheet, they didn't seem too far off ?

From the info I've read so far, the KSC1845FTA has opposite pin layout, the 2SC1313 mounts in place where the flats on them are on the heatsink with paste.
The replacements won't, will they still be ok for this use?

Is it worth replacing the bias pots?
If so, what could I replace them with?

I've now checked half the resistors and 18 of them are out of spec or faulty.
About to get started on the rest of it.


Also, what can I use to clean up the PCB from flux and the glue?
I've used some iso alcohol and a "circuit board cleaner" neither really seem to help at all.

Can I substitute R609, R617, R608 and R618, the 2.2k ohm 1/2 w resistors (where the common "burn mark" is) with higher wattage/larger resistors, will that help with the heat?
 
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Perhaps you already finished this repair.. if not, here you go:
Have you tested the output transistors? If they are the original Sankens, why replacing them?. If you need to replace them use the ON MJ21193/4 pair. Good replacements for the 2sc1313 are 2sc1815, 2sc2785, 2sc3331. Check the pinout. If the new transistor is smaller you may need to suplement the gap between the board and the transistor with a soft elastomer to ensure a good thermal contact against the heat sink. This transistor is there for tracking the temperature change of the output transistors to keep the bias current constant.

Cleaning the PCB glue is simple, use q-tips to apply acetone (or nail polish remover if you do not have acetone) then use wood chopstick sanded at the ti to have a chisel shape. Do not use metallic spatulas or screwdrivers, you can damage the screen print. You may need to remove some components to make way for the wood chisel to scrape the glue. It is slow it may take a couple of hours of work to do this right.
Clean the legs of any component that has glue.

In this amplifiers, watch out for the ribbon cables, and also the joints may be dry, and cracked, so they may work fine before you work on the unit, but they give you surprises after you finish (unit does not work, you get crackling noise or interrupting sound).

Clean all the connectors with deoxit or similar contact cleaner.
 
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