Sansui au-777d or au-777a need schematics

[zeste]

Hello, I have a Sansui AU-777d, the main fuse is blowing as soon as I turn it on. I check all the power transistor. I replace a 1sd143 which was out.

But I still have the probleme. I have downloaded fuzzy schematics of a 777a which look like the same, it's hard to read it.

If someone have hi-res schematics of the 777a, it would be nice if he can send me. And if anyone has an idea about the problem or have had the same problem and solve it, I will be happy if he give me the solution.

 

[stereofun]

I have a real nice schematics - whats your email ?

When you replaced the 1sd143, did you properly seat the mica insulator ? - also I'd double check the other outputs / drivers one more time. A general but thorough visual inspection is really worth its time. I once had an Eight with a wire gone loose from one of the driver board slots due to heat/age - while it wasn't touching anything it could easily have - so take the time and look everything over. You will likely find suspect joints and so forth.

 

[zeste]

I start a conversation with you and I post you my email

I check the insulator and I check it with the multimeter

 

[stereofun]

Schematics in the mail ;-) Also check the rectifier - this is a single rail amp so the rectifier delivers plus 75vdc (53vac / .707) and ground instead of plus / minus 75v - these old rectifiers are known to be a weak link on the first gen. solid state.

 

[zeste]

Thx for the schematics. It's perfect.

I have checked the rectifier with a Diy transistor, Lcr tester, and he look good

 

[Hyperion]

I have checked the rectifier with a Diy transistor, Lcr tester, and he look good

It will until it goes 'bang' and messes up some other components in your amplifier - best to change it.

 

[zeste]

Ok, I will change it.

 

[zeste]

It will until it goes 'bang' and messes up some other components in your amplifier - best to change it.

As I have some caps not in good condition (see pics above), I started the recaping



After recaping, when I put it on, I have the same problem. So before un solder all wire, I disconnet the bridge and the fuse didn't blow. So I replaced the bridge. And now it runs but heating.

I have a Japanese version and the transformer I have, step down only to 110V not to 100V. So I have 80V on B0 instead of 70V. I going to see if I can replace it by a custom toroidale transformer.

 

[slimecity]

Ummm yea, you really want to have between 80-100VAC running these 100VAC japan amps. You could use a decent VA-rated torroid (300-400VA depending on the amp's running wattage) that is 50-0-50VAC - I have used all these arrangements on my JP amps at moderate volume with no problem.

Running 110VAC into these amps isnt great on the long term and it will exceed some component specs on the short-term too I suspect, as well as some components which are known to fail too (like your bridge).

Hopefully you are also running this thru a DBT, especially as your primary voltage is too high?

 

[zeste]

Sorry for the late reply, but I order custom toroidal transformer with the specifications of the electrical schemes. For the current I have asked for the secondary voltage, I had to high voltage.

As It is a custom transformer, I could return it. So I have modified it. I had to remove some coil of the secondary voltage to get the rigth voltage.

Here is some pics of my work :

IMG_777D_Transfo (3)

• zeste
• Jul 17, 2018

IMG_777D_Transfo (2)

• zeste
• Jul 17, 2018

Now it works good, the Power transistor stay cold when I listen it for a long period at a normal volume.

But I hear a noise at a low volume. It comes from the pre-amp board and on both channel. Anybody has an idea of the cause ?

 

[slimecity]

Nice transformer solution.

Describe the type of noise you are getting - is it on all inputs?

 

[zeste]

Thank you,

It's a white noise (I don't know if it's the correct word in english), I hear it at very low level (when the volume is around 1), it's on both channel exactly the same noise and same level.

When I remove the jumpers that connect the pre-amp to the amp, I have no noise.

I check some component that are in common for both channel (the power supply) but I didn't find something wrong. I have recapped all the amp and changed the transistors (by BC550C and BC560C). To be sure I change again on one channel of the pre-amp board all the transistors but it's still the same.

 

[slimecity]

I have a sansui X1 that I just got back from being repaired.

One thing I note about it is the volume pot is a bit noisy when at full counter-clockwise - when you turn it a smidge to the right - the noise disappears. I think in my case that particular issue is juts inherent in a slightly worn pot. It may come right with a clean. This could be your issue.

Remember these are vintage amplifiers - they arent perfect and its all relative - sometimes the circuit design will come with a little bit of noise that is noticeable on todays equipment. You MAY be able to eliminate it by replacing all caps in the signal path with upgraded types (like film caps) but on the other hand this may not help. There are other threads on 777 restoration on this site you can refer to.

 

[zeste]

That's exactly what I have. It's not a big problem, I asked in case that someone has a solution.

I have fully recapped may amp and I am very happy with it.

 

[alanku]

Hello, I have a Sansui AU-777d, the main fuse is blowing as soon as I turn it on. I check all the power transistor. I replace a 1sd143 which was out.

But I still have the probleme. I have downloaded fuzzy schematics of a 777a which look like the same, it's hard to read it.

If someone have hi-res schematics of the 777a, it would be nice if he can send me. And if anyone has an idea about the problem or have had the same problem and solve it, I will be happy if he give me the solution.

Hi zeste I have a same unit AU777D as you, I am facing the transformer issue , I wish you can help me the Schemetic and the specification about Au777D transformer specification, I cant confirm the Voltage spec , since you have wining a new transformer, do you have the detail about This transformer

 

[zeste]

Hi Alunku,

I haven't wide a new transformer, I have order a new one to a french compagny that build custom transformer. Below, there is the spécification that I gave for the quotation.



I ask a too hight current for the 53V winding (Green and Red) and the voltage was too hight. I have to modify it and I remove I think about 10 turns. And It is OK now.
I think 3.65A for the 53V winding is to hight. I think the correct value would be 3A.

The manufacturer of the transformer didn't send me details about the number of turn for each coil nor for the section of the wires.

Hope I answer to your question.

If you need the schematics, send me a message with your email, I will send you.

 

[alanku]

Hi Alunku,

I haven't wide a new transformer, I have order a new one to a french compagny that build custom transformer. Below, there is the spécification that I gave for the quotation.

View attachment 1753890

I ask a too hight current for the 53V winding (Green and Red) and the voltage was too hight. I have to modify it and I remove I think about 10 turns. And It is OK now.
I think 3.65A for the 53V winding is to hight. I think the correct value would be 3A.

The manufacturer of the transformer didn't send me details about the number of turn for each coil nor for the section of the wires.

Hope I answer to your question.

If you need the schematics, send me a message with your email, I will send you.

Hi Zeste
I am very appreciate your advice and schematic diagram, However,my set before I change the Transformer, the current transformer parting in from
previouse owner is measuring 41V and 33V only,the VOLTAGE of the transformer is 16V-0-16V ,39V-0-39V the current model of transformer from previouse owner is sansui A1620XX transformer. now I am makaing my new transformer as
26.5-0-26.5 4A,33-0-33 2A,0-6.3 0.5A .do you thinkg is voltage is suitable to the AU777D schematic.
or you make it is 0-53V 3A,0-33V 2A ,0-6.3 0.5A.

 

[alanku]

Hi Zeste
I am very appreciate your advice and schematic diagram, However,my set before I change the Transformer, the current transformer parting in from
previouse owner is measuring 41V and 33V only,the VOLTAGE of the transformer is 16V-0-16V ,39V-0-39V the current model of transformer from previouse owner is sansui A1620XX transformer. now I am makaing my new transformer as
26.5-0-26.5 4A,33-0-33 2A,0-6.3 0.5A .do you thinkg is voltage is suitable to the AU777D schematic.
or you make it is 0-53V 3A,0-33V 2A ,0-6.3 0.5A.

 

[alanku]

The au777D transformer replace completed ,all the voltage perfect as describe from your schematic .

 

[zeste]

I am glad that help you. If red/green winding are higher than 53V, the power transistor will heat to much !! That's happen to me when I have used a 230Vac to 110Vac transformer to power the unit.