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Sansui AU-X701, relais not closing

GrisPato

GrisPato

Super Member
I took on an attempt to repair this amplifier for a fellow Sansui enthusiast living near by.
He bought the amplifier two years ago, restored.
Has been working fine up to some time ago when it would start with intermittent faults, no sound output.
Owner managed to get sound by working the speaker switches for a-b.
The last time it had sound output was on the B-terminals, A-terminals not working at all.
I asked him to bring it to do an easy check of DC-offset(s).
Then I found out the multifibrator is not active, no blinking/flashing light. Owner was not aware if it did before.
After checking DC-offsets and bias, right-channel was high, 170 mV, adjusted to close to zero. Hot/Cold to ground is not this close but doesn't go higher then 180 mV.
Bias was a little of on 3 of 4, 0 on the other. Because i don,t think this is causing the current fault i just left that for now.
Output from the protector boards on top of the driverboard is 0,7 V (pin 31,32), as far i can find info this means they are functioning as they should.
Measurements of the TA7317P also don't show any weird values for as far i can understand. Emitter of lQ1-2 have the 10 VDC.
The A-B speaker switches work.
The only thing of I could find besides the protection light not flashing is that the replacement relais are rated just 5 ampere
 
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There is an exact replacement for the speaker relays with contacts rated at DOUBLE the current rating of original relay - it has a black plastic case.

Do you know if the input selector lights work? have you checked that power is getting through the speaker selector switches?

I would be having a serious look at the voltage regulator on the protection board. ;)
 
Thanks Hyperion for a quick response.
I get 15 vdc on pin 6 of the TA7317 what I am assuming is stopping the multivibrator circuit from switching. Is this to low for the relais?
About the powersupply for the protection.

Screenshot_20211218-193639_Moon+ Reader.jpg

Can I assume 30 vac, 24 vdc after regulation, based on the 24v zener?
 
Not sure about that voltage - but check you are getting ~24V (=27V minus 2 x VBE drops) out of mQ1 regulator transistor - if that voltage is too low it will screw everything.
 
Hyperion said:
have you checked that power is getting through the speaker selector switches?
Click to expand...
Yes, that was the first thing I checked. Was hoping not having to take of the front! Difficult enough to get to the protection board. The person that restored it put in modern RCA connectors so I can hardly move the left side of the back panel. The TA 7317 P gives me all normal values as far as I have been able to find on 4-5 different schematics from amps where Sansui used it.
 
Hahaha (or lol, but I am from before that)
It started working when I measured the power supply voltage on the emitter of lQ1 which by the way measured 24,7 vdc , so good.
I can not find an obvious cold joint but just going to reflow them to be sure.
Don't know why this resistor is not in the schematic, dropping the voltage to 17 v.
20211218_200519.jpg

Like I said, basic first steps: power supply and solder joints.
Because of a more difficult access I assumed it was something different, mostly because of the protection light not flashing which by the way is still not flashing. It just is more dim and then more bright when relais engage.
So will check involved components to.
Thanks for the direction @Hyperion .
 
Last edited:
Finally had the time to finish this one.
I put the protection board back first time, no relais click.
Take it of again, some more reflowing, relais works again.
Put it back, still works, put the back cover on, no click.
In the end I made some padding around the edge of the board to be able to tighten the screws without putting tension on the board and it worked.
I have a feeling the amplifier fell on the back once, because the speaker terminals were changed, and there is some micro crack in the board.
Negative side of the left power amp had no bias, 0.0, was worried about just dailing it up all the way without any value.
Luckily remembered Hyperion giving the advise of measuring at the pre-driver/ driver transistors in some thread last week.
So I measured at the emitter resistor at pre drive and drivers and was adjustable but around 750 mV to low.
With this knowledge I could crank it up till I saw some voltage at the emitter resistors. Is the first time I work on someone else's amplifier so wanted to be sure to not break something!
The other 3 outputs were biased to 10 mV? The restorer even wrote it on the chassis.
Service manual asks for 17 mV so that's where I putt them.
Last check in the main system.
Not bad at all and looks really good.
Here in the Netherlands they are one of the lower priced ones.
 
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