Sansui AU-719 Complete Rebuild Project

[Jamaica1985]

Hey guys!

Not long ago I posted pictures of my new (obviously used ) Sansui AU-719 which probably sat for a long time without any use in some place however with time it did develop some issues that were not discovered until a few weeks I had it running . After some time of light use it started to develop a light hiss on the background from both speakers, the balance pot started to produce some cracking noises out of the speakers when turning both directions and not being bothered by it too much I just kept on using it… Well, that’s where I should´ve stopped because not long after both of my tweeters made a horrible burning noise and they were gone… literally before I could turn of my amplifier I saw the magic white smoke being released from the area where the power amps are located, giving me little tears in my eyes, and no this was not because of the smoke…

I opened the device up and what first caught my eye is that 2 of 5 fuses were blown, but it looked like, since the rest were glass fuses, the ones that broke were those slow blowing versions with white powder in it, making me think that this amplifier had problems before they sold it to me and they simply put in some slow blowing fuses to keep it working...

Now, after reviewing the device further I noticed the famous Sansui glue literally almost rotted through a couple of resistors and diodes and even a jumper cable making me wanting instead of troubleshooting all that could be wrong, simple replace everything, and by everything I mean literally everything that is possible to be replaced.

Now then again I do not know if this is a wise solution because I´m sure some of the components are just fine, but since I will likely be removing everything from the boards anyway to give the boards a proper cleaning and tin job I might as well put in new components given that this will likely be a multiple month job anyway.

Some of the things that I will have to do first is:

- Completely disassemble the device. Done
- Buy a better Multi-meter since my crappy 5 dollar one probably is not gonna cut it
- Buy a soldering device, whether it is a station or one of those simple suckers, I don´t mind
- Considering an oscilloscope however I´m not in the mood to spend hundreds of dollars at this point
- Buy all if not most of the replacement components on Mouser

Some of my initial questions I have so far are:
- I really don´t know the wattage of these old resistors, would that be a 1/4 Watt for the yellow ones, 1/2 Watt for the green and blue ones and 1 Watt for the large blue ones?
- Hoping that a good multi-meter can check the functionality of the power amp components, what other can I do to check if they still function? Can you simply do Ohm readings between BCE? If they are shorted, is there any suitable replacement for these?

Lastly I want to thank user jeromach for providing me a component list with a lot of information on it. This has helped me a lot to identify most of the components.

Again, this project will likely turn into months, but any progress will be posted in this thread for sure. The problem I have, as with most people I assume... is money and time, where money is always the biggest issue

And since , I am attaching the disappointing pictures below...

 

[AUD101]

 

[Jamaica1985]

Already starting to identify every single component and the respective replacements for them. So far so good. Only some semiconductors and those weird minuscule capacitors are hard to find for a decent price

 

[rasenthiran]

Agree, the price is a bit more expensive, lucky i reconditioned my AU 719 five years ago.

 

[Hyperion]

Only some semiconductors and those weird minuscule capacitors are hard to find for a decent price

In my opinion you don't need to change all the semiconductors, and certainly not all the capacitors - all the electrolytics need to go, and the 'Black Flags' in the phono EQ (if found) need to be replaced. May I suggest you have a read of some documented restores on AK for similar models, to gain an idea of exactly what needs to be replaced. (The ones by Leestereo are the best IMO, try looking at his one for the AU-717 )

However, the title of this thread is 'Complete Rebuild' in which case - carry on

 

[Jamaica1985]

Agree, the price is a bit more expensive, lucky i reconditioned my AU 719 five years ago.

Did you only perform a recap or did you replace other components as well?

In my opinion you don't need to change all the semiconductors, and certainly not all the capacitors - all the electrolytics need to go, and the 'Black Flags' in the phono EQ (if found) need to be replaced. May I suggest you have a read of some documented restores on AK for similar models, to gain an idea of exactly what needs to be replaced. (The ones by Leestereo are the best IMO, try looking at his one for the AU-717 )

However, the title of this thread is 'Complete Rebuild' in which case - carry on

Yeah, so I do have some sort of limit on money, and I really don't want to source components of ebay. As long as I can get things for a somewhat decent price on Mouser, DigiKey or AG Electrónica locally here in México I'm ok...

Another question. I am able to get for a very decent price all of the electrolytic caps from the brand TEAPO. All 105 degrees Celsius ones. I have usted them on a rebuild of my Harman Kardon HK6600 amp without issues. Do you guys have any experience with that brand?

 

[Karl vd Berg]

I would avoid the Teapo's electrolytic caps, to be honest.

Any Nichicon's PW series can do much better than the original caps, same for Panasonic's FR or FC series. Hyperion is right: if you follow Leestereo's AU-717 rebuild you'll find a lot of good info on proper capacitor replacement.

And for the bookmark, you may take a look at this thread: http://audiokarma.org/forums/index.php?threads/once-more-sansui-transistor-substitutions.583009/

 

[LBPete]

I don't know them but a quick google search for Teapo found this. They appear to be a legitimate supplier. Keep in mind that Sansui and the rest of the Japanese audio manufactures at the time used ordinary general purpose electrolytic caps. Almost any quality modern cap will be better than what was used originally.

Please post the serial number for the database. Click on the link in my signature block.

- Pete

 

[Jamaica1985]

I would avoid the Teapo's electrolytic caps, to be honest.

Any Nichicon's PW series can do much better than the original caps, same for Panasonic's FR or FC series. Hyperion is right: if you follow Leestereo's AU-717 rebuild you'll find a lot of good info on proper capacitor replacement.

And for the bookmark, you may take a look at this thread: http://audiokarma.org/forums/index.php?threads/once-more-sansui-transistor-substitutions.583009/

Great stuff Karl, thank you very much for the insights and I will definitely review these sources. Depending if cost/worthiness makes sense I would go for Nichicon, I´d like to read a lot of sources before making my final decision.

I don't know them but a quick google search for Teapo found this. They appear to be a legitimate supplier. Keep in mind that Sansui and the rest of the Japanese audio manufactures at the time used ordinary general purpose electrolytic caps. Almost any quality modern cap will be better than what was used originally.

Please post the serial number for the database. Click on the link in my signature block.

- Pete

Thanks so much, yes I noted that as well. Most of the caps in the current amp seemed no-named, found a couple of ELNA´s and that is it really. I´m going to dive deeper.

 

[LBPete]

The Japanese manufactures of the era would have purchase orders with all the major Japanese capacitor manufactures to ensure a constant supply to meet production demand. Aside from the orange "low noise" capacitors, there was no effort made to place a particular brand of cap in a particular application. It's whatever was in the hopper during that day's production. If you look at the boards in several of the same units you will see all the capacitor brand variations.

As a follow up to my earlier comment on Teapo caps, I should have said they wouldn't be my first choice if I had the option of selecting from all name brands of caps but I wouldn't hesitate to use them if the brand choice was limited.

- Pete

 

[Jamaica1985]

The Japanese manufactures of the era would have purchase orders with all the major Japanese capacitor manufactures to ensure a constant supply to meet production demand. Aside from the orange "low noise" capacitors, there was no effort made to place a particular brand of cap in a particular application. It's whatever was in the hopper during that day's production. If you look at the boards in several of the same units you will see all the capacitor brand variations.

As a follow up to my earlier comment on Teapo caps, I should have said they wouldn't be my first choice if I had the option of selecting from all name brands of caps but I wouldn't hesitate to use them if the brand choice was limited.

- Pete

Hi Pete, thanks for the comments and it does make sense, my amp has 2 different brand caps, even different with the same values. Either way, I am starting to replace the corroded resistors and two zeners and for now did choose to buy the cheap TEAPO´s I really couldn´t leave them for the price... And in the future a proper recap won´t take too much time really. What I´ve also started working on is to replace the variable resistors and changed the power transistors that due to the issue described earlier were shorted out... I have managed to obtain new old stock for a very nice price for those. I have also desoldered everything on each board and resoldered everything. Still missing two boards but almost there. Hopefully this weekend I can make a first test run without the case. Below some pictures, more to come! By the way, I am only doing the highly needed fixes on all boards, I want this amp up and running quick, and due to the cost of replacing all components it would take me months to complete. I will get there, just bit by bit, board by board.

 

[Overundr1]

Looking good so far
-Lee

 

[Hyperion]

Looking very promising - thanks for posting the pictures.

 

[Blue Shadow]

As a follow up to my earlier comment on Teapo caps, I should have said they wouldn't be my first choice if I had the option of selecting from all name brands of caps but I wouldn't hesitate to use them if the brand choice was limited.

- Pete

Glad you softened the comments on the Teapo caps. It does not look like a BAD Cap brand but maybe there are better choices if there are choices.

 

[LBPete]

We are spoiled here in the US by the range of options available to us. That's not the case in many parts of the world due to poor distribution networks and/or the cost of directly importing stuff. One of the great things about AudioKarma is it's truly worldwide membership and the ability to have open discussion with people everywhere.

- Pete

 

[Jamaica1985]

Hey guys,

I got the amp back together all resoldered and even with a 100 Watt light bulb in series it looks like that on board F-3101, resistor R621 with 100Ohm keeps getting up in smoke and the amp won´t go out of protection mode.

I desoldered the resistor and the amp stays in protection mode but is stable. No burning nothing. So I removed the 100 Watt light bulb and all stays stable. Now I did some measurements and when disconecting the resistor that is connected to the transistor base, the base is getting 52 volts... this is AT the base, versus ground. This doesn´t make sense to me.

Would transistor TR610 be fried from the previous problem I had as shown in the initial forum post? When I turn the amp on and I do some voltage readings without the resistor connected I´m reading 52 volts on base, collector and emitter of the transistor, this can´t be right?

 

[Leestereo]

According to the schematic, TR610 is a 2SA726. This transistor is known to be failure-prone, remove from board and test with DMM to confirm failure. A good replacement is KSA992 (also replace TR611 which is also a 2SA726).

 

[Jamaica1985]

According to the schematic, TR610 is a 2SA726. This transistor is known to be failure-prone, remove from board and test with DMM to confirm failure. A good replacement is KSA992 (also replace TR611 which is also a 2SA726).

Thanks, that will probably the next thing I will do. I have rechecked the cabling of the PSU board and the Protector part three times over now, everything has been connected alright. The only thing I changed are the electrolytic caps, some resistors that were completely rotted by the glue and that´s it. Right now I have only this board connected. All other boards are disconnected but still the same thing. Funny thing I noted is that the power led is blinking but in a irregular fashion after a couple of seconds... First it starts flashing as usual, after a few seconds it becomes like a patter of 3 times normal speed after that 3 time super fast. Anything else you guys think I should review?

 

[Hyperion]

Anything else you guys think I should review?

There is an incorrect 'silk screen' polarity mark for a capacitor on the PSU/Protector PCB, if you have changed these capacitors, providing you took pictures to refer to, and installed the replacement (for the incorrectly marked one) exactly as it was previously installed you should be fine. (I think you will find that it is C615 located on F-3101 PCB on the output of the negative regulator). If it is installed as per the silk screen markings it will be back to front, the '+' of the capacitor should go to a ground trace.

http://audiokarma.org/forums/index.php?threads/au-719-capacitor-of-the-exploding-kind.598174/

 

[Jamaica1985]

Hi Hyperion, yep I was aware of that one actually, I reviewed this information earlier as the silk screen didn´t make much sense to me. Installed the new caps as the old ones were installed.
I just finished checking all the diodes and they check out fine. All resistors but the burned on are fine too. Now onto checking the Transistors...
.