Onkyo A-803 (90's) Amplifier Headphone Issue

[jiot]

My daughters amplifier is having issues at the moment..When headphones are plugged into this Amp..the headphone relay does not kick in...and sound comes out of both headphones and speakers at the same time! I have the circuit (see attachment) was wondering could anyone help me understand the logic from this circuit diagram of how exactly plugging in the headphones makes the relay energise...Im struggling to follow the diagram..... Looking at it the 'headphone' relays contacts are normally closed... any help most appreciated in helping me understand further. I must add the amp has had problems recently where one channel starts to crackle...Ive found a couple of dry joints..and currently its under test to see if it comes back...not 100% that is cured at this stage....it seems these issues can be a combo of things and Im not counting my chickens just yet ..! The speaker relays (one each for A and B speakers) seem to work fine...Ive cleaned their contacts with some deoxit...however the 'headphone relay' is of a different type and appears sealed. Any help given is most appreciated. Cheers

 

[Mooly]

The diagram is a bit to small to look at detail but at first glance I can not see any auxiliary contacts on the h/phone socket that could be used for sensing when a plug is inserted. It is drawn as a conventional socket with three terminals.

Are you sure it should operate automatically ? or does it rely on the user turning the speakers off via the front switch ?

 

[jiot]

Hi Mooly Thanks for replying!

Ive attached the manual for this unit

Im not sure how it actually works tbh...Im used to plugging in the headphones into an amp and the speakers stop speaking...this might be a different one...but then what is the headphone relay doing/ for ?

 

[Mooly]

I would guess the relay is used for normal muting and for switch on delay protection to avoid thumps and so on. And DC offset protection as well of course.

The headphone output has to be treated as if it were speaker as far as the listener is concerned with no untoward noises and so on being allowed to get through.

 

[Mooly]

The circuit and the block diagram both seem to confirm that no sensing of a plug being inserted is present.

 

[jiot]

Actually ..I think you are right with where you were going! the relay must be simply protection for the headphone on startup...just proved it IS kicking in by turning to OFF speaker selection switch then pressing Standby to turn off amp....then listening to headphone and relay pressing standby to turn amp back on....no sound from headphones until 'click' from what has to be the head phone relay!...case I think solved! Cheers 🙂

 

[Mooly]

that's good. Those are the faults we like 🙂

 

[jaycee]

I can confirm that, from looking at the front panel of the unit it would seem they expect you to turn the Speakers setting to OFF if you only want to listen to headphones.

A bit of a silly design choice...