Luxman A-357 schematic

[Pacorl]

Does anyone have the schematic for this amp?

I have been able to find some similarities with Luxman A-321/331 schematics, but I´ve come to a point where I cannot progress anymore

I bought the amplifier as scrap, in order to use as many parts as possible for a diy project. I saw a condenser with a loose leg, and after resoldering it, the amp was running with a pure, sweet sound. The day after the amp died without apparent reason.

I think the issue is located around speaker protection relay circuit.

Thanks in advance.

....I love this site

 

[JohanH]

Hello,

don't know if this helps but on a dutch forum someone mentioned a small sub-standby switch on the bottom of the amp which caused it not to work when he accidentally switched it to the other position

Cheers
Johan

http://www.circuitsonline.net/forum/view/73756

 

[Pacorl]

Hello Johan,

I knew about that switch.Unfortunately this is not the cause. Thank you for your interest.


I´ll post new doubts in the coming days if finally schematic is not arriving

regards

Paco

 

[Pacorl]

Findings:

Luxman A383 schematics has a lot of similarities with A-357 too.

I found a thermal resistor poorly welded attached to heatsink and connected to protection circuit IC(TA7317P).

Relay now allows to activate speakers, but amplifier is not working yet.

I found that neither preamplifier nor volume control have no voltage,volume potentiometer is attached to an opamp (NJM4580) , that´s why it uses voltage.

I´m thinking about to remove the following:

-Removal of Source selection IC (NJU7312A) and send CD signal straight to amplifier, that would be a pity because there is a nice phono stage in place.
- Removal of preamp, opamp, and leave only volume pot.

In any case I´l try to fix PS for preamp & vol. pot first. Regulated PS seems to be easy for back engineering even for a newbie like me.



IF anyone has this amp and is interested in more details let me know.

 

[Pacorl]

I replaced almost every part in PSU for preamp section , including 7815 & 7915 regulators , and now is working fine. Amp is back to live. However, tone control section is working badly. Thanks God the amp is fine in direct mode. Therefore will not do anything else.

I´m very proud of my first job at "diy-ing"