Sansui AU-666 repair and restore thread

stopkidding

Well-Known Member
Thanks to a kind AKer, I got tipped off on a local 666 that was on sale. The amp was being sold off in an estate sale of a recently deceased (RIP).

The external condition is extremely good, the front face is flawless, the wood cabinet is in perfect condition. Opening the interior, there was some dust, but still really good for it's age.

I reluctantly and curiously turned it on and seems like one channel is out. Now begins the quest to repair and restore this almost 50year beauty.

I will start with cleaning the switches and pots with deoxit to troubleshoot, followed by a full restore to the best of my amateur ability. I would appreciate any help and guidance from you fine people here.
 
Hi
Sounds like a really nice score, would have made it excellent it was fully working!
After the fuse check you can also remove the 2 metal jumpers for the pre out/main in and use rca cables to to determine if its an issue coming form one channel or the other and which section too.
 
Looks like one of the four fuses fuse is blown. Now it won't power on. I am thinking I might find a local repair guy to bring it up to basic running condition before proceeding further. While I am handy trouble shooting, I am afraid I might do more damage than it's worth. Time to down load the schematics and take a look.

In the picture below it's the fuse furthest away from the transformer that's blown. I didn't check if it was blown before hand or it just happened when I powered it on.
 

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I think that they are 3.5 amp fast blow fuses.
Also check the fuses on the back if the unit, sometimes they just need to be wriggled again and tightened up. And check that your wall plug has a firm grip of the wires..
Do you have a multimeter?
 
Ok right speaker fuse was blown, which explains so the single channel. Now the main power fuse is blown too.

So right now the following fuses are blown
F004
Right Speaker fuse
Main power fuse.

I have multi meter and a soldering station. I have recapped and aligned an AU-7500 before. And recapped half of the AU D11 II. I am fairly handy, but not adept enough to trace the signal on the schematics to find the problems. Willing to learn :)
 
Sounds like you're all over it, just fuses and a service to get it playing again would be a nice fix. Good luck :)
 
@AnalogueBen - copying from your thread, your choice of transistor replacements. I am going to update the small signal transistors with the same. But what was your reason for replacing the output transistors? were yours fried or did you do it for other reasons?

Output Transistors~
Original - NEC 2SD188 NPN
Replacement - OnSemi MJ21194G NPN
Original - NEC 2SA627 PNP
Replacement - OnSemi MJ21193G

Remaining transistors ~
Original - CDC8002
Replacement - ZTX694B
Original - CDC9002
Replacement - ZTX795A
Original - XA495
Replacement -ZTX795A
Original - 2SC871R (E,F), (F)
Replacement - KSC1845
 
:lurk:

Here is my thread for interest which does spell out a couple of the basic mods with some images/instructions (but note that the AU-666 does not require the extensive mods that the AU-999 does and if anything, the goal with modding AU-999 would be to make it sounds like an AU-666/888, not vice versa), but beware it was my first forum posting and I was a bit of a novice so likely said some incorrect things...
 
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:lurk:

Here is my thread for interest which does spell out a couple of the basic mods with some images/instructions (but note that the AU-666 does not require the extensive mods that the AU-999 does and if anything, the goal with modding AU-999 would be to make it sounds like an AU-666/888, not vice versa), but beware it was my first forum posting and I was a bit of a novice so likely said some incorrect things...

Thanks! Will review that thread, especially for the speaker protection board mod.
 
Thanks! Will review that thread, especially for the speaker protection board mod.

The filter gave me good results when removed, but the speaker protection removal is one you should consider further. People seem hate this protection setup from a sonic point of view, but I didn't notice any sonic difference with it in/out, so if doing over again I would actually give some serious thought to leaving it in. Basically what it does is, if you have sufficient DC on the outputs the DC switches a transistor on, opening up a easy way for the outputs to blow the speaker fuse and protect your speaker from DC faults.
 
Yes, sadly a pair of outputs got fired when I didn't follow instructions the proper way..lesson learned. They are the correct small signal replacements you've selected, although I'd also look at the ztx694b or BC550C (both different pinout) for a 2sc871 replacement, I actually left mine in as they are quiet.
 
Btw, those Zetex are all over the place when it comes to finding matching pairs, and at nearly a buck each its not a cheap exercise. They are of high quality however but if $ is a more important factor then I'm almost certain that you can use all Fairfield subs.
 
Btw, those Zetex are all over the place when it comes to finding matching pairs, and at nearly a buck each its not a cheap exercise. They are of high quality however but if $ is a more important factor then I'm almost certain that you can use all Fairfield subs.

What is the process for matching transistor pairs? what tool do you need for it? I have a few digital multi-meters that have diode testers built-in, but don't have a transistor tester.

I saw the recommendation in your thread to use the Zetex alternatives.
CDC 8002 → KSC2690
CDC 9002 → KSA1220

But the KSA1220 is not in stock in mouser as of today.
 
What is the process for matching transistor pairs? what tool do you need for it? I have a few digital multi-meters that have diode testers built-in, but don't have a transistor tester.

I saw the recommendation in your thread to use the Zetex alternatives.
CDC 8002 → KSC2690
CDC 9002 → KSA1220

But the KSA1220 is not in stock in mouser as of today.
Those sound right, that's what I used.

I completely restored a AU-666 last summer and love it. Mine had a blown bridge rectifier, so check that. Lots of 2SC871's that have to go to.
 
Some multimeters have slots where you can insert small transistors for hFe testing (matching) they can be had for cheap just about anywhere online or at local hardware stores etc. Or you can buy a cheap component tester that tests transistors and also will read ESR of capacitors, which is very handy and used by many throughout AK.
In your situation now, I'd order a nice cheap component tester, put in you fuses and dial in you bias and dc.. put on your favorite music and leaver her be. I'm doing the same with a 5000x, only replacing what is needed while I enjoy its original vintage flavor. Hope that I'm helping and not steering you away from work you may want to do right now. ;)
 
What is the process for matching transistor pairs? what tool do you need for it? I have a few digital multi-meters that have diode testers built-in, but don't have a transistor tester.

I saw the recommendation in your thread to use the Zetex alternatives.
CDC 8002 → KSC2690
CDC 9002 → KSA1220

But the KSA1220 is not in stock in mouser as of today.

Buy a cheap transistor tester on amazon - it might not be exact but it will be exact relative to the pairs your are measuring hfe on. I bought this - although I had to get a replacement, it works really well and does capacitance and ESR too.

Yes the KSA1220 are sold out, but I found a reputable source here - they have been around for a long time, based in Florida, but do sell through their ebay store where you can make an offer. I got them as drivers for my 800, and used them as pre-drivers in my 999 rebuild. I don't see any pre-drivers in the 666 schematic, but they would be really good for the driver position TR811/813. Then for the differential pair TR801/803 you can either use MATCHED zetex 795A or KSA1015 (according to Smurfer77, the KSA1015's are a lot better matched right off the bat). If you replace the 2sc281, then a great match is ksc1815 (but I'd keep em if they are in a sleeve on the heat sink and working and are working). Then for the TR805/807 you could use KSC2690 since the original rating of CDC8002 are 1 A - now this would be the standard operating procedure as to stay with the same or higher than original spec's current rating. HOWEVER - I used ZETEX 694B at 0.5 A in those positions in the 999 and so have others with no issues. In fact I think Sansui got rid of them in later production run and I would be surprised if they replaced with a 1 amp transistor - I think these UFO's just happened to be brutes.
 
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Thanks @stereofun and @AnalogueBen. I bought one from amazon. I am waiting for the new fuses to arrive. In the meantime, I lubed the pots and switch contacts and took these pictures.

Just love how easily accessible all the boards are. Amazing design for serviceability...
 

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Hi,

BC639 and BC640 are a match to the CDC8002 and CDC9002 spec wise (and were a recommmeded replacement back in the 90's). I have used them with good results on a range of Sansui's (alhough they are getting harder to get hold of lately).

Cheers

John
 
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