Sansui AU-317 turns on but no sound

[Florin_mol]

A few weeks ago I bought this AU-317 MK 1off eBay however when it arrived there was no sound coming out of it. Went back and forth with the seller and ended up keeping it at a significant discount.
I've checked all of the audio inputs (AUX and Tuner) and channel outputs with no success of getting any sound out. I've also checked the headphones output and there is nothing coming out of it either.
I've opened it up had a look at the fuses and they are all ok. I've taken the front cover off, removed the washers from the pots and sprayed all of the switches and pots with Servisol Super 10 with no success. Still no sound.
I've checked then the speaker outputs with a multimeter and surprisingly enough there is voltage on the outputs. I've added an image that shows the values below.
Another curious thing is that when I touched the pre amp. / main amp. links at the back there is some buzzing going in the speakers and that's pretty much the only sound that goes to the speakers, no static as I increase the volume, nothing, just the buzz when I touch the links at the back.
The protection relay kicks in however don't know if it works correctly as I remember the protection relay on my Sansui 881 was making a small spark when I was turning it on, this one doesn't but it does the familiar "click" a few seconds after flipping the on / off switch.
Any ideas would be helpful. Many thanks!

 

[CrSens]

Almost certainly fuse resistors in preamp are open or very high value. Here is the thread explaining it all, there is Au-317 further down the page.

https://audiokarma.org/forums/index.php?threads/fuse-resistors-the-wheres-whys-and-hows.430439/

 

[skippy124]

Hi and welcome to AK

The 317 is a great amp, and it is worthwhile getting it working properly

Another thing to check is the series pass transistors that form the plus and minus power supplies for the preamp section, TR601 and TR602 on the main board. These can be susceptible to dry solder joints, I have seen plenty of 317’s and 317ii’s with dry joints on these transistors.

Hope this helps

Cheers
John

 

[Florin_mol]

Hi and welcome to AK

The 317 is a great amp, and it is worthwhile getting it working properly

Another thing to check is the series pass transistors that form the plus and minus power supplies for the preamp section, TR601 and TR602 on the main board. These can be susceptible to dry solder joints, I have seen plenty of 317’s and 317ii’s with dry joints on these transistors.

Hope this helps

Cheers
John

Hi John.
From what you are saying the transistors you've mentioned should be on the F2751 or F2752 boards in the preamp section.
Here is a link to a picture showing the two boards in the Sansui AU-317 https://www.audiovintage.fr/wp-content/gallery/sansui-au-317/DSC07007.JPG
If so then I will have a look the respective board in the morning with the magnifier glasses.
Many thanks!

 

[JoseHH]

You have the option to input signal (music from an mp3 player with volume adjustable for example) to the output amplifier via the pre-out main-amplifier rca connectors on the back. If i were there i eoud try this to see if the problem is in the power amplifier section or before it as @skippy suggests.
I suspect it is before thr amplifier because you mentioned hum heard at thr speakers at some point.
But it will be reassuring to know.

 

[petehall347]

main amp is working because it buzzes . pull jumpers and replace .

 

[Florin_mol]

main amp is working because it buzzes . pull jumpers and replace .

I don't have another preamplifier to check so what I understand from you is to plug in the RCA left and right that would normally go into the AUX into the power amp in.
In this case wouldn't the amp send signal at full power to the speakers? Obviously I can control the volume from the input device.

 

[AudioModern]

I don't have another preamplifier to check so what I understand from you is to plug in the RCA left and right that would normally go into the AUX into the power amp in.
In this case wouldn't the amp send signal at full power to the speakers? Obviously I can control the volume from the input device.

Yes, turn down the volume to maybe 10% on the device just to be safe. Hopefully it’s got a volume interface that doesn’t let you accidentally go full volume with a single tap (e.g. touch screen volume slider interface).

It looks like the AU-317 is like the AU-717 in that the headphone jack is driven by the amp output (with attenuation). So you could do this testing on a cheap pair of headphones instead of risking speaker or ear damage playing through big speakers.

 

[petehall347]

i meant to pull jumpers then replace them in case they aren't connecting properly

 

[JoseHH]

If you have a mobile phone and a cable that plugs into the headphone socket on the phone on one end and that on the other end you connnect to the rca input (you can cut a cable from broken headphones and solder RCA plug conectors onbthe othe end to use a a test signal) . Plug this cable into the power amplifier-nput at the back and see if you get sound on the speakers or on a headphone plugged in the au-317 headphone output. Adjustvthe volume on the phone to avoid blasting sounds.

You can download mp3 or stream frim the web.

Next if the main-amplifier is working then plug the rca connector in the Aux input of the au-317 and play music on the phone while the addapting cable is plugged in it. Use another headphone and addapt it to connect it on the pre-out RCA connnectors. Try to see if sound can be heard on the earphones from the preamplifier out. Adjust the volume on the phone while listening on the earphones. If you hear some sounds, play with the switches and controls on the au-317 and see if there is any effect on the sound you hear.
If the problem is in the preamp start by looking at the schematic and locate the corresponding boards.
First check for dry solder joints.
Carry out these elementary tests and comment here what you get.

 

[skippy124]

Hi John.
From what you are saying the transistors you've mentioned should be on the F2751 or F2752 boards in the preamp section.
Here is a link to a picture showing the two boards in the Sansui AU-317 https://www.audiovintage.fr/wp-content/gallery/sansui-au-317/DSC07007.JPG
If so then I will have a look the respective board in the morning with the magnifier glasses.
Many thanks!

Hi,

The transistors are on the power amplifier board F-2754. They are on the front edge of the board ( looking from the front of the amplifier) and towards the main filter caps.

Cheers
John

 

[Florin_mol]

As a quick update I've connected the RCA to the "power amp in" directly and I can confirm that the amplifier side is working.
I will look tonight for those transistors.

 

[Florin_mol]

Hi and welcome to AK

The 317 is a great amp, and it is worthwhile getting it working properly

Another thing to check is the series pass transistors that form the plus and minus power supplies for the preamp section, TR601 and TR602 on the main board. These can be susceptible to dry solder joints, I have seen plenty of 317’s and 317ii’s with dry joints on these transistors.

Hope this helps

Cheers
John

Really grateful John for pointing out the TR601 / TR602 on the main board. I've now refreshed the solder on those and the amp is up and running
A specialist would have charged me £75 for flushing the pots and "fixing" the amp which I did in about an hour.

 

[Florin_mol]

I'm coming back to this to ask a question regarding possible upgrades to this amp.
I've been in touch with a professional for recapping and upgrading the AU-317 and one of the points he mentioned was the volume control for which he said he can find Alps "Blue" units for under £20.
Now I find that with the stepped attenuator I have less control in the low volume when say listening at night. This is not a dealbreaker when sending signal through AUX as I can lower the volume on the source however I have no control over the volume when the amp is hooked to the TU-217 I have which doesn't have an output level pot. I would have to upgrade past the TU-317 to the much larger TU-417 which has an Output Level in order to be able to have the tuner running at lower volume for late night listening.
Looking for some opinions as to whether it would be a good idea to drop the attenuator in favor of a quality Alps Blue potentiometer or just keep it as it is for as long as it's working.

 

[petehall347]

an inline attenuator will do what you need .

 

[JoseHH]

The original volume control in the AU-317 is very special. It is not easy to find a genuine Alps potentiometer with the lodness tap. The original is B taper but almost all the Alps potentiometers with loudness tap you find are A taper. Also lots of fakes.
If you end up changing the volume control please keep the original with you.
An input attenuator or an external box with a good Alps potentiometer is all you need to solve the issue. (In this case no need to get one with loudness tap since you will use only 3 pins per channel).
Mouser sells Alps potentiometers RK27

 

[Hyperion]

an inline attenuator will do what you need .

An input attenuator or an external box with a good Alps potentiometer is all you need to solve the issue.

Or a pair of fixed in-line RCA attenuators as @petehall347 has suggested - much simpler - 10dB should be enough.

 

[Florin_mol]

OK. Many thanks everyone for the input.
So I've listened on the lowest step of the attenuator and after a few minutes the sound lowers to a very low level, then over a 10 minutes period it fluctuates going down to almost inaudible levels and then raising again slightly. Does that mean that the attenuator is faulty? (maybe due to being used on that value of attenuation for too long)
I've played also some music through the aux at low levels from the source in order to use the middle section of the attenuator (assuming that this part of the attenuator has seen less use) and indeed the volume has stayed stable. So unless I want to use the amp that way I will have to upgrade to a new potentiometer. I'm guessing that the attenuator can't be repaired somehow..

 

[Hyperion]

So unless I want to use the amp that way I will have to upgrade to a new potentiometer. I'm guessing that the attenuator can't be repaired somehow..

No, that isn't the best way to solve the problem as I understand it. From what you say the volume control seems like it needs cleaning. However the way to solve the volume control position issue is as explained, i.e. by the use of in-line RCA attenuators that you plug into the inputs on the amp and then plug your source into them. A quick and easy solution that will mean a comfortable listening level will be reached with the volume control set higher.

The problem arises due to the standards for input levels for vintage amplifiers, being a bit too sensitive to match with the output levels of more modern sources, whose relatively high output levels are often without the means to reduce their output level. Looking back in the thread I see that one issue you have is with the output level of a TU-217 being too high. Obviously this is also vintage, and is in the same model range, so it is a bit of a puzzle as to why you are having an issue, unless it is a somewhat different issue?

You have also had suggested to you to construct an external variable attenuator box with an Alps potentiometer in it, that gives you more flexibility but is not an ideal solution in my humble opinion.

 

[AudioModern]

I haven’t caught up on the whole thread but the fluctuating volume at low levels reminds me of a dirty relay on a 717 I worked on. At lower levels the volume would fluctuate, but if it was turned up somehow the relay connection would improve and the output would become reliable. Like maybe some amount of current burns through the oxidation and forms contact.

Anyway, I need to read more of the thread and then I’ll probably realize I misunderstood something…