Help - Yamaha CR-450 - No Output

[yammy45]

Hi All,

First time poster but have been lurking as a guest for a while..

I've recently acquired a faulty Yamaha CR-450 receiver as a small project.

The fault is that the unit does not output any sound to the speakers.. For ease I'll bullet point my observations:

• The unit powers up (lights, etc come on)
  
• Have tried aux, phono and receiver outputs
  
• Tried changing speakers over
  
• When the volume is turned to max and the 'tape' switch is on the 'source' position I can very faintly hear the music from within the unit NOT from the speakers though)
  
• Previous owner says they connected an amplified turntable into the phono stage and heard a 'pop'

I haven't opened her up yet, just thought I'd throw it up on here and see where you guys suggest starting with my diagnostics. I'm reasonably competent with electronics - have tinkered a bit over the years but I'm by no means an expert as I know many of you are.

I look forward to your responses and thanks in advance!

[ajgriff]

Hello and welcome. A few questions to begin with:

1. What test equipment do you have? In particular do you have a DMM and some means of audio signal tracing?

2. Do you have a copy of the service manual? If not one can be downloaded from Hi-Fi Engine after free registration.

3. Is there any sound (hiss/mush) coming from the speakers with the volume turned right up and no signal applied?

4. Can you hear the protection relay clicking when the receiver is first switched on? These relays are prone to failure due to pitted or dirty contacts.

From what the previous owner has said it could be that the input stages have been severely overloaded causing semi-conductor failure. Might be worth looking in the vicinity of TR451/2 (after phono stage ICs) depending on the answers to some of the questions raised.

Alan

[yammy45]

Thanks for the quick response Alan!

I do have a DMM and have just invested in a cheap tracer (though I’ve never used one before!).

Service manual I have downloaded

Absolutely no sound/hiss or otherwise from the speakers - even at full volume

Protection relay I don’t recall hearing.. I’ll check this this evening though

I plan on opening her up this weekend and having a proper look - I’ll take some photos and let you know.

Thanks again for the response.

Ps. Is it normal that sound should be coming from inside the receiver (albeit extremely faint) seemed quite odd to me but this is my first foray into ‘vintage audio’ repairs

[micheal]

Can you hear the relay click a few seconds after switch on? If so output stages probably ok.
The relays have silver contacts and silver is prone to tarnishing, contacts can cleaned with switch cleaner, by removing clear plastic housing, do this by squeezing fore and aft on housing and pulling upwards then clean with small piece of card and switch cleaner.
Do not use any thing abrasive.

Mike

[paulsherwin]

The first thing to do is try a pair of headphones in the headphone socket.

The sound you are hearing is some component inside the amp acting as a tiny speaker. This suggests that quite a bit of power is being delivered, so the fault may simply be a blown speaker protection fuse.

The story about plugging in an amplified turntable is tosh.

[ajgriff]

Is it ok for me to post a copy of the Hi-Fi Engine manual download Paul? The speakers are protected by the relay but the fusing arrangement is a bit unusual so seeing a copy of the schematic might help people to diagnose the problem.

Alan

[ajgriff]

In the meantime here's a low res copy of the schematic.

Alan