Repairing my Sansui AU-D33 Stereo Amplifier

#1

Hi everyone,

Was in the other day working on repairing a cracked circuit board in my Sansui amplifier. Successfully got that sorted and now the amp successfully goes out of protection mode!

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Right channel works ok and the left not so much, waiting on some new capacitors from China to fix that.

In the mean time, there used to be some DeOxit around the bench, @electrotechs know where it may be or can we order more? Need to clean some scratchy pots- also any alcohol to clean up flux etc?

So far a very fun project!
Cheers!!

Humming/ whining audio power amp
#2

Is possibly in the chem cabinet in the snug , but I would avoid to use it , I think is too aggressive with electronics parts…

#3

There was defo some around, like @emuboy said, they the metal cupboard in the snug.
Switch Cleaner should be OK for the Pots ? its kill or cure, they are already noisy so it wont make it any worse.

Let me know if you can’t find any. If you can’t i’m in town a few days a week and will see if I can pick up a can of switch cleaner from Maplin.

Courty

#4

Ok thanks! I will take a look!

The trick is there is lubricant in there as well- if you can find any DeOxit Fader F5 that would be ideal, as it has even more lubricant than the regular one…

Here is some analysis on the subject for those that may be interested:

I am sure there is some personal preference involved at then end of the day as well though!

#5

The Deoxit and contact cleaner were indeed in the chemical box in the snug, so thanks for that!

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Got the new caps installed! Both channels seem to be working strong now! Will be testing out at home and see how it goes!

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#6

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All good! Been running this amp for a couple months, works/sounds great! Success!

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#7

Hello, I’m new on this forum and also owner of a Sansui AU-D33 that I purchased in the late 80’s with the first money I earned…
I have an issue with the speaker relay that takes time to close and regularly reopens. It seems to do the same even without speakers.
I saw that this kind of problem could be solved by replacing some resistors on older Sansui amps.
Can somebody help me with this? Should I open a new discussion?

Thank you for your comments,

#8

It might be as simple as adjusting the dc bias .

First thing to check is the dc voltage on the output .

#9

https://www.manualslib.com/manual/1000279/Sansui-Au-D33.html#manual

See page 10 / 11 for dc bias setup

#10

Thank you for the infos and the Service Manual.
I made a simple measurement right after my post (I should have done it before, sorry…).
Voltage at speaker relay coil: 25.2 Volt DC !!
In other words, the relay is adequately powered but does not directly opens, taking his time, hesitating, changing his mind…
So, I’ve ordered a new relay and hope this will solve the issue.
Based on your infos, I’ll also spend some time to check the bias and adjust them if required.

Many thanks for your support,

PS: WHat can be wrong in a relay to get such a strange behaviour?

#11

I doubt that the relay is the problem, it’s fuction is to protect the speker from switch on thump and dc on the output if the amp developers a fault , so the first thing I would do is check the dc voltage on the speaker output when the relay is closed and the input is disconnected, because I would suspect that it might be opening for all the right reasons.

#12

There is a pot at the bottom of the long tailed pair at the input of the power amplifier

#13

Thanks for the additional inofs.
I’ll further work on the amp within 2 weeks from now and hope getting it back perfectly working!
Regards,