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Protection Issue on my Sansui 517

Z

zyggypop

New Member
Hi there
I'm new among your community and even Know lots of comment have been made about this amplifier I don't seem to find an answer to my problem.
I started to restore my 517 with a recap I've used the same value capacitors just a notch higher voltage (100V instead of 63V) I didn't touch the 4 big filter one (12000uF 63V)
Here Are the symptoms when I power on the protection doesn't come off and I stay with the blinking power light

when I go to separated amp/pre or capacitor coupled the protection does come off (and the red light stop blinking)
even when I link the pre & amp and switch the subsonic filter ON the protection comes off and the relay comutes
At this stage only one chanel is working fine (the right one) the other one has almost no signal only background noise (souffle in french) the defeat filter make a big noise when switched but seem to work
I checked the 2 fuse resistors on the 2 drive boards (R23 R25) and they all seems to be OK (150 ohm)
For info I 've just cleaned and recap the power supply board and the 2 drive board all the rest was left untouched and it was working perfectly before the recap.
I really Hope you can help me with this problem
Thanks
Samy
 
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The situation is.

  • The amplifier worked before anything was done to it
  • Sammy has recapped the PSU/Protector PCB and both Driver boards

The amplifier now wont come out of protection unless the connected separated switch is NOT set to direct.

Sammy has checked the regulated PSU voltages which are a little unequal, but not enough to cause the problem he is seeing here.

A couple of questions - you say you can get it to come out of protection - have you attempted to adjust the offset trimmers? - to zero the DC voltage out of the speaker terminals. Is this offset stable or is it wandering about? compare both channels.

Have you checked your work??? - are you SURE all of the replacement capacitors are round the right way? it looks like your regulated PSU capacitors are OK but what about the ones on the driver boards? - have you checked these against the schematic for correct orientation?

You say you have used 100V rated capacitors - have you made any other component substitutions, or changed any other components?

Also check for bad solder joints, solder splashes, component lead offcuts causing shorts etc.

Good luck. and keep us posted
 
OK I Might have use what I had in stock
47 uF 63V in place of 47/50
100uF 63V instead 100uF/35v
33uF /50V in place of 33uF/50 and 33/25 capacitor
I've double checked all polarities all soldering and didn't see any trace Cut
I've use 3 in 1 contact spray (against grease dust and oxydation) to clean the switches
 
Thanks for the help Guys
The schematics is on this page http://www.scribd.com/doc/58111061/Sansui-AU-517-AU-717-Service I follow the procedure for DC offset and Bias
the DC Offset is now dead on 0 with a tiny variation off 0.5mV and the bias is set on 20mv on both side
when in pre /amp separated mode I've tested to input directly in the amplifier with my phone and both side work even know right one sound clearer and bit more powerfull than left
When switching back to the connected mode the amp still stay in protection when switching On subsonic filter protection comes OFF but left channel is really low t (almost dead) like before
 
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Recheck all your wiring connections, especially all those wires coming and going from the PS board. Logic dictates that if it worked fine before you worked on it, your work went bad somewhere. Only you can find it. Did you take good pictures of the 'before' layout of the wiring and connectors?

Scott T.
 
thanks Scott
yes I Did take pictures of the wiring and connectors before
I did check all te soldering I've made and polarities everything seems
to be fine .
I will recheck everything asap
 
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New investigations have been made today
it seems like the protection problem is cause dc voltage (3,5V on knot 8 on 2722 schematic/Orange wire from amp section to psu board) that appears when pre amp and amp are connected.
Since it isn't here when separated I assume this Voltage is coming all the from the preamp .
But the problem is I havn't touch anything on this section
 
OK this information is confirmed when I have taken out the plug that feeds the amp section the security comes OFF and I have 100mV DC voltage on the plug
since the Input Voltage are quiet OK (a bit unbalanced) on the preamp I will carry on investigation on this Board
 
Got it! :banana::banana::banana:

I've tracked down de DC voltage as far as I could And it was present before the switches

As I told you the PSU voltage was a little unbalanced but not enough to Cause the problem according to Hyperion (thanks again to you John)

I have checked before the DC voltage coming from the PSU to the preamp but I did it from the top of the connector
while I was tracking down the 150mv DC voltage I rechecked the dc voltage coming from the PSU but this time directly on the board and BINGO one of the voltage was down to 25V instead of 31
one of the pin from the connector didn't have a enough contact acting there by as a resistor.
I played with the pin with a little screwdriver switched back on and Everything was back to normal
I've reset the dc offset and the bias now with the preamp fully fonctioning
switch the Amp back on and OMG it sings :music:::tresbon::music:
the recap really did wonder but had really given me troubles:tears:

Thanks for the help Guys:thmbsp:

Samy
 
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