• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Sansui AU-517 DC-offset problem

In preparation,
I think I am missing something here,

HansVenlo said:
went the full monty for the power supply: replaced all big rectifiers and other small diodes and replaced TR01/02 with KSC1845 matched!
Click to expand...

You are talking about the powersupply, which Tr-01/02 did you replace with matched c1845? I am assuming you're talking about the differential pairs Tr-01/03 Tr-02/04 on F-2673!
 
I only did TR01 and TR02. You see I am a novice.
Maybe I introduced the problem myself. I’ll check this evening and report!
 
Last edited:
I checked what I did in the PS. Sorry I was unclear.
When I mentioned TR01 and TR02 I forgot to tell their location. That were the 2SC1400 transistors on both driver boards, since they are notoriously bad when coming at age.

On the Power supply I changed TR01 and 02 for SC2690A and their complementary transistors TR03 an 04 for SA1220A. but that did not help so I put the old ones back in place since I thought the new ones might be to heavy. But the old ones have no good matching hfe.

Yesterday I checked Bass and Treble Control resistors. They were all in spec! Cleaned switches and bass and treble pots.
On the Tone control board I checked all orientations of transistors and new caps. All OK.
 
Last Thursday Grispato visited us to help find the problem. We set up the system first on DBT, No signs of problems. The cleaning of the bass and treble pots and the switches of the tone control board seemed to be successful. Without DBT we were able to set DC and BIAS perfectly to zero mV and 20mV for both channels. Cd-player and Spotify over Aux were nice and clean.
When we tried the Phono input however we had a lot of popping and cracking noise. GrisPato suspected some dry solder joints on the Equalizer board or damaged ribbon cables.
I’ll have to dig deeper in that!
Special thanks to GrisPato for his help and an enjoyable afternoon,
To be continued.
 
Thanks to you Hans, your warm welkom to your house, nice conversation with you and your wife were heartwarming.
Really nice to be able to share the passion for music, and especially played on Sansui!
 
GrisPato said:
Thanks to you Hans, your warm welkom to your house, nice conversation with you and your wife were heartwarming.
Really nice to be able to share the passion for music, and especially played on Sansui!
Click to expand...
There still was a job to do:finding the cause of the crackling and popping sounds when playing over Phono. The black ribbon cable from the input board was the main suspect. Checking that cable I found a breach. (See picture). I took both boards (equalizer and input board) out. It was an easy repair.
After that: music maestro!
Both DC an Bias are stable.
I will check the driver transistors on the driver boards tomorrow and maybe replace them. Their hfe’s are very different between the right and left channel.
After that I will play it for a day or two for a proper break-in-
 

Attachments

  • 4798DEF5-884F-4EE8-A0C5-0E4B22C34681.jpeg
    4798DEF5-884F-4EE8-A0C5-0E4B22C34681.jpeg
    93.4 KB · Views: 29
Good find! That happened to an AU717 I was working on. The outside conductors get a lot of stress if you pull out the phono/input select board without removing the input board. i like to re-solder all the wires on both ends of all connectors just to eliminate any problems from occurring later.
 
Jefft91 said:
Good find! That happened to an AU717 I was working on. The outside conductors get a lot of stress if you pull out the phono/input select board without removing the input board. i like to re-solder all the wires on both ends of all connectors just to eliminate any problems from occurring later.
Click to expand...
Exactly what I did!
 
Today I replaced the last transistor pairs on the Power Supply board. (2SD438 and 2SB560) The legs of the transistors were almost eaten away. And I found a capacitor on a lifted pad and two lifted pads on the Collector and the Emitter of two transistors. I fixed them all, and reset DC and Bias. Very easy.
Last but not least I sprayed de-oxit in the main switch.
And now she is singing like a bird on my AR 11. I hope she wil stay stable. Had a lot of trouble with it. I'm going to close the amp know and enjoy!
What started as a simple recap, ended as a complete overhaul in Leestereo style. I learned that old gear may have suffered more than it is showing.
But the recipe of Leestereo, and the help of AK members and GrisPato who came to visit me, helped a lot.
Plus a few bypasses and a stent (just like me) makes her as new.:banana:

I thank you all on AudioKarma!
Hans
 
You must log in or register to reply here.
Back
Top Bottom