AU-517 checkup

[Gian Luca]

Hello,
I purchased a 517 and I’m trying to check if all it’s ok.
Now first of all as for DC adjustment on left and right channel, I have to check the the dc voltage on speaker terminals.
How to proceed for this? I know that the volume must be at minimum level and input selector to AUX. The question is, the speaker selector must be set to OFF or set to speaker A (where I measure the Voltage)? because I measure values much different in one or others case. About the bias adjustment, I can’t read any voltage in the TEST terminals. Rotating the VR03 potentiometer the measure don’t change: always 0 mV. About this I read in this forum that the cause can be the fuse resistor R23 and R25. it’s true? I proceed to replace these?

 

[GrisPato]

set to speaker A (where I measure the Voltage)

Correct setting, to Off will indeed mean Off, not connected to speaker terminal.

About the bias adjustment, I can’t read any voltage in the TEST terminals. Rotating the VR03 potentiometer the measure don’t change: always 0 mV. About this I read in this forum that the cause can be the fuse resistor R23 and R25. it’s true? I proceed to replace these?

You should replace them, even when measuring good, but can be many other reasons for not being able to set bias. Even as simple as oxidation on testpoints. (there is change but you are not able to measure it). Be careful moving the trimpot to much in these cases. Also not to little sometimes you have to clean them first and although they will seldom have to be turned to max sometimes they need to be moved considerably before getting movement on the meter.
So ideally you clean trimpots and test terminal first, replace those fuse resistors and than set the bias.
Good luck

 

[Gian Luca]

Correct setting, to Off will indeed mean Off, not connected to speaker terminal.


You should replace them, even when measuring good, but can be many other reasons for not being able to set bias. Even as simple as oxidation on testpoints. (there is change but you are not able to measure it). Be careful moving the trimpot to much in these cases. Also not to little sometimes you have to clean them first and although they will seldom have to be turned to max sometimes they need to be moved considerably before getting movement on the meter.
So ideally you clean trimpots and test terminal first, replace those fuse resistors and than set the bias.
Good luck

Ok, good, 4 fuse resistors on driver circuits board all open! And now I have set with pots booth dc offset on speaker terminals and bias! Before of this I put some deodorant over the pots. It’s usual for you that a very minimum movement on pots, the voltage Change? I put so many time to achieve the goal of 20mV and 0mV for his reason.

You suggest me, now, to replace also the other fuse resistor in the other board ( I know that there’s also other 4 fuse resistor 82ohm in preamp board)

 

[GrisPato]

It’s usual for you that a very minimum movement on pots, the voltage Change? I put so many time to achieve the goal of 20mV and 0mV for his reason.

This is normal, especially with the original trimpots in there. In my experience more with the DC offset than the bias current. You can replace them with multiturn types but if you can get the DC offset within + - 10 mV it's good. Bias being of a few mV is also no problem as long as it is reasonable stable. I would recommend to replace all of the fuse resistors right away they became at best unreliable.
Good work already done

 

[Gian Luca]

Ok thanks, can you tell me if these fuse resistor (150 and 82 ohm) are 1/4 or 1/2 W?

 

[GrisPato]

Ok thanks, can you tell me if these fuse resistor (150 and 82 ohm) are 1/4 or 1/2 W?

I can advice you to learn to do that yourself. On the schematic diagram of the au517-717 it states all resistors 1/4 watt unless otherwise noted. Then it showes that fuse resistors are marked *3. So for example the emitter resistors r47-50 from the eq output stage ( board F2723 ) are noted with a value in the left channel and in the right channel with *3. On the other hand r04 on board F2721 is noted 2,2k (2) in the left channel, so value and power, and in the right channel with *2 what means non flammable ( most often metal oxide resistors).
Enjoy discovering.

 

[Gian Luca]

The work is in progress.....
I have a question for the next work I would do in my 517: replace the speaker connectors. To do this I need to remove the back panel. Can you help me about this? I see that the rca input board is in place throws some small black plastic connectors. I try to pull up one but without success

 

[Hyperion]

I see that the rca input board is in place throws some small black plastic connectors. I try to pull up one but without success

The 'small black plastic connectors' are called 'snap rivets' - they consist of two parts - the 'rivet' (whose head you can see on the outside of the rear panel), and the 'insert' which the rivet is inserted into. To remove them you need to push the end of the rivet from the inside, you can tap gently on the end of the rivet to do this, until you can see the head of the rivet coming away from the rear panel - then you can ease the rivet out with pliers. Sometimes there is varnish or paint on the rivet and insert which make the rivet much more difficult to remove. I have found 'IPA' or even 'Flux Cleaner' will loosen this varnish if applied to the rear of the insert, which makes rivet removal much easier. They are completely re-usable IF you are careful when removing them.

 

[Gian Luca]

@Hyperion , thanks so much, I’m following literally your suggests and I’m going to pull up the rivets. Now I’m at the 5th rivet extracted

 

[Gian Luca]

Hi all, After replaced all fuse resistors and vd1212 diode all over the boards, now I start to replace the electrolytic caps.
In 2721, 2722 (drivers) and 2723 (equalizer) I purchase all Elna silmic II, using the same capacitance and voltage as the original.
Now I’m at the 2675 (power supply & protection). Which types of electrolytic caps is better to use?
@zoeffiex and others seems that used nichicon UPW, but seems to be not audio specific capacitors....
Ask help also from @Leestereo , @Hyperion , @GrisPato and others from forums, thanks!

 

[GrisPato]

Which types of electrolytic caps is better to use?

Ohoho, that's a good question. Where people will have different answers to.
I am still a novice in this electronic adventure. But with reading a lot ( and I mean aaaa lot) I can not find the specific, special specifications from these so called audio capacitor. I can find that an real capacitor is far from the ideal theoretical capacitor. Things that are different are: esr, esl, current leakage, heating up, etc. So I tend to focus on those values. Want to try one day to do a comparison myself. Your amplifier is DC coupled so there are almost no capacitors directly in the signal path. ( Ask some people, they say some capacitors are in the path of the current that becomes the signal and that matters to for them).
So in the end you have to make that decision for yourself because you are going to listen to the amplifier with your choices. Just one exception I think is maybe the power supply board where it can get hot, I would always go for lower esr and higher temp.
Good luck with deciding!

 

[Gian Luca]

Finally I recapped all electrolytic on 2721, 2722 (drivers) and 2723 (equalizer) and 2675 (power supply). I leave only the 4 big capacitor, the original 12000 uF ELNA.
Now, is this a good choice? How can I valutate if these capacitor are efficient?
In yours 517, if you switch off the power, the music still sound for few seconds or not? (In my AU-117 the music still play for 2 or 3 seconds, but in the 517 cut off instantaneously. The same is fir the light on the power led. This can be a test?

 

[GrisPato]

The playing after shutting off I think is because the au117 doesn't have an output relay and the au517 does so the loudspeakers are disconnected with the au517.
Are they still good? I measured mine for esrband capacitance, inspec, I can not measure leakage. I bought new once already so I changed them out, but I could not notice a difference. I think you good try to measure the ripple on your DC rail, if this is large ( no idea what is a good value ). May be to finish of your restoration/ recap you should replace them because they are going out somewhere in the next few years, can be 2 y can be 10 y.

 

[lbcgav]

The 'small black plastic connectors' are called 'snap rivets' - they consist of two parts - the 'rivet' (whose head you can see on the outside of the rear panel), and the 'insert' which the rivet is inserted into. To remove them you need to push the end of the rivet from the inside, you can tap gently on the end of the rivet to do this, until you can see the head of the rivet coming away from the rear panel - then you can ease the rivet out with pliers. Sometimes there is varnish or paint on the rivet and insert which make the rivet much more difficult to remove. I have found 'IPA' or even 'Flux Cleaner' will loosen this varnish if applied to the rear of the insert, which makes rivet removal much easier. They are completely re-usable IF you are careful when removing them.

You can also purchase replacements if needed: https://www.mouser.com/ProductDetail/Keystone-Electronics/3443?qs=sGAEpiMZZMvIGAkyPb0MlDWZt5Cpdj%2Be