Karl vd Berg
Super Member
Hello to all Sansui fans,
A quick thread with some pictures of a classic "little" integrated, one my favorites... I want to thank to all those who shared previously info on various threads...
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... and I have had another (3rd unit, so far) AU-317, first version, on bench and this one is in quite good cosmetic condition. However, the sound was "cutting off", sometimes on left channel, sometimes on the right. Chances to be only the relay is remote, in all the other units I had the relay worked pretty good.
So I decide to work on it, inspect where the problem was and rebuild the PSU, plus the regulator to the preamp part and the protection circuit by replacing and upgrade all the electrolytic caps, some ceramic ones, the Zeners and small signal diodes, the trimpots, some resistors and other components we'll see along the posts...
I'm working on F-2754 and F-2752 boards here, since most of the time I use "Line In" stuff (tuners, CD players, DACs, other preamps, etc).
So, this is the unit under the cover...
Voltage masurements on TM22, TM23 and TM24 cable connectors showed different DC voltage to the preamp boards, something like 27Vdc in one channel to ~31Vdc in the other, so I decided to start around the regulator.
Disconected and cleaned the main F-2754 board and there were cold and broken solder joints everywhere...
On the left, TR601 (2SD356), at regulator circuit...
Cold/broken solder joints in other locations...
Before reflow the cold/broken solder joints, I started checking the electrolytic caps and their values to see how they drifted over the last 4 decades.
Below, C608 (220uF/35V):
The cap was replaced to 270uF/63V that fits in size... (thanks to Leestereo for the suggestion here)
Then, ZD601 and ZD602 - 30V Zeners - had to be replaced to BZX55C30 ones (thanks to AUD101 for the suggestion in previous threads).
Next, the four capacitors (C609~C612) that feed the preamp board are essentially a couple of 147uF caps arranged in parallel (100uF + 47uF / 35V). I upgraded these with two of 150uF/ 63V, low ESR.. (thanks to Leestereo for the suggestion here)
And here we have the regulator rebuilt, fresh solder joints (the new Zeners are in a next picture)...
DC voltages are +/- 30V!
Now, C605 and C606 (470uF/50V) with the dreadful glue, that "contaminates" the the surrounding components, were also below capacitance value...
These - dated 1975 - were replaced and upgraded to a higher value, 820uF/50V. (Thanks, Leestereo).
I wanted to use this "new product" (dated 2016) from Nichicon, UHW series, low ESR.
Their rectifiers (D606~D609) were the 10D1 types and were replaced and upgrade to STTH208 types (thanks to Hyperon and Avionic for suggestion in previous threads)
The same STTH208 replaced also D601 (rectifier for the protection relay circuit), and D610 as the original was also 10D1 types...
And here we have the power supply section rebuilt, plus the relay and protection circuit and regulator for the preamp... My only doubt here is that the bypass caps 1uF/100V (C901, C902) should remain in parallel with the big ones, or they are not necessary with modern 12,000uF/63V capacitors...
A quick thread with some pictures of a classic "little" integrated, one my favorites... I want to thank to all those who shared previously info on various threads...
--------------------------------------------------------------------------
... and I have had another (3rd unit, so far) AU-317, first version, on bench and this one is in quite good cosmetic condition. However, the sound was "cutting off", sometimes on left channel, sometimes on the right. Chances to be only the relay is remote, in all the other units I had the relay worked pretty good.
So I decide to work on it, inspect where the problem was and rebuild the PSU, plus the regulator to the preamp part and the protection circuit by replacing and upgrade all the electrolytic caps, some ceramic ones, the Zeners and small signal diodes, the trimpots, some resistors and other components we'll see along the posts...
I'm working on F-2754 and F-2752 boards here, since most of the time I use "Line In" stuff (tuners, CD players, DACs, other preamps, etc).
So, this is the unit under the cover...
Voltage masurements on TM22, TM23 and TM24 cable connectors showed different DC voltage to the preamp boards, something like 27Vdc in one channel to ~31Vdc in the other, so I decided to start around the regulator.
Disconected and cleaned the main F-2754 board and there were cold and broken solder joints everywhere...
On the left, TR601 (2SD356), at regulator circuit...
Cold/broken solder joints in other locations...
Before reflow the cold/broken solder joints, I started checking the electrolytic caps and their values to see how they drifted over the last 4 decades.
Below, C608 (220uF/35V):
The cap was replaced to 270uF/63V that fits in size... (thanks to Leestereo for the suggestion here)
Then, ZD601 and ZD602 - 30V Zeners - had to be replaced to BZX55C30 ones (thanks to AUD101 for the suggestion in previous threads).
Next, the four capacitors (C609~C612) that feed the preamp board are essentially a couple of 147uF caps arranged in parallel (100uF + 47uF / 35V). I upgraded these with two of 150uF/ 63V, low ESR.. (thanks to Leestereo for the suggestion here)
And here we have the regulator rebuilt, fresh solder joints (the new Zeners are in a next picture)...
DC voltages are +/- 30V!
Now, C605 and C606 (470uF/50V) with the dreadful glue, that "contaminates" the the surrounding components, were also below capacitance value...
These - dated 1975 - were replaced and upgraded to a higher value, 820uF/50V. (Thanks, Leestereo).
I wanted to use this "new product" (dated 2016) from Nichicon, UHW series, low ESR.
Their rectifiers (D606~D609) were the 10D1 types and were replaced and upgrade to STTH208 types (thanks to Hyperon and Avionic for suggestion in previous threads)
The same STTH208 replaced also D601 (rectifier for the protection relay circuit), and D610 as the original was also 10D1 types...
And here we have the power supply section rebuilt, plus the relay and protection circuit and regulator for the preamp... My only doubt here is that the bypass caps 1uF/100V (C901, C902) should remain in parallel with the big ones, or they are not necessary with modern 12,000uF/63V capacitors...