Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Debs.]

I actualy think its scared of your wallpaper.....

  Hahahahahahaha!

[jereboam]

I can see the problem, it's that fried spider in the bottom right hand corner

That's young Arthur.  I've been wondering what happened to him.  RIP Arthur.

[waspy]

I can see the problem, it's that fried spider in the bottom right hand corner

That's young Arthur.  I've been wondering what happened to him.  RIP Arthur.

Young!!! He looks like he's been in there since new along with all the dust & cobwebs. He probably choked on the dust & fell onto the mains feed 

[jereboam]

I can see the problem, it's that fried spider in the bottom right hand corner

That's young Arthur.  I've been wondering what happened to him.  RIP Arthur.

Young!!! He looks like he's been in there since new along with all the dust & cobwebs. He probably choked on the dust & fell onto the mains feed 

Well he was young the last time I saw him...

[waspy]

I can see the problem, it's that fried spider in the bottom right hand corner

That's young Arthur.  I've been wondering what happened to him.  RIP Arthur.

Young!!! He looks like he's been in there since new along with all the dust & cobwebs. He probably choked on the dust & fell onto the mains feed 

Well he was young the last time I saw him...

PMSL

[Jimbo B]

It's probably a capacitor somewhere they are always favorite

[Dishevelled Den]

See those 4 diodes in the 1st picture just below the wire link by the screen print on the pcb saying 4A....measure them with a DVM set to resitance

Once again, it will all have to wait until madam goes to bed.  I'll check them, and post the results later.

I actualy think its scared of your wallpaper.....

It's lovely wallpaper!  I chose it.     You should have seen what the wife wanted.  I could not survive a Laura Ashley living room.  Much prefer the aspirational Regency stripe.

  splendid  8-) 8-)

[jereboam]

Diodes. 

Hazy memories of A-level physics (about 45 years ago) told me that polarity was involved, so I Googled diode testing.     There really is an amazing amount of misinformation available on the Worldwide Web

Anyway, I eventually worked out what I had to do. 
The two diodes on the left give a reading of about 0.550 on the 2k[ch8486] scale.  The two on the right seem to be open circuit, which I presume isn't right. 

My very elderly analogue meter confirmed this, and, as usual, proved easier to use.  Regrettably, I don't trust it completely, as it gives duff readings when used for battery testing.

Will have to clean the amp tomorrow, as I can't use the vacuum cleaner at this time of the night/morning.  I'd really love to get a decent night's sleep, but it's months since I managed more than 3 hours.  Usually do better dozing in front of the TV.  But I'll pop up to the spare room and try to get a couple of hours now.

[Omegadoha, Desert Member]

OK

It's a Sansui AU4400, and it was the 1.5A case-mounted fuse which blew.  As far as I remember, its rated at about 30w RMS per channel.  Shouldn think it's got any valves in it, but from the 1975 vintage, I'd guess it's mostly discrete components.

It's unlikely to be the external connections, as nothing else in the stack has been affected. 



Beautiful!

Thats certaintly a classic. I  remember those big flick switches from the eightes when I was growing up. 

[Andy B]

Diodes. 

Hazy memories of A-level physics (about 45 years ago) told me that polarity was involved, so I Googled diode testing.      ....

Think none return valves!!       

[Kevin Wood]

Diodes. 

Hazy memories of A-level physics (about 45 years ago) told me that polarity was involved, so I Googled diode testing.      ....

Think none return valves!!       

Indeed - so measure each one with the multimeter leads round each way and you should get conductivity in only one direction. Even better, if the multimeter has a diode test mode (little diode symbol on the switch?) it will tell you the voltage drop, which should be 0.6 v ish in one direction and off the scale in the other.

TBH, I would expect one or more to be a dead short if it was faulty, and that doesn't look to be the case.

Is that the fuse that failed on the LHS of the back panel in your photo? Did you have anything plugged into the aux. mains outputs next to it? Just wondering if something external has dragged it down?

Can you trace the mains input wiring into the mains transformer and measure the resistance across the primary of the transformer, and also between that and chassis?

Next step - does the secondary of the mains transformer have a connector where it feeds the amplifier PCB? If so, can you power up the transformer with the connector disconnected - without the fuse popping?

Kevin

[jereboam]

Indeed - so measure each one with the multimeter leads round each way and you should get conductivity in only one direction. Even better, if the multimeter has a diode test mode (little diode symbol on the switch?) it will tell you the voltage drop, which should be 0.6 v ish in one direction and off the scale in the other.

The two diodes on the left give a reading of about 0.550 on the 2k[ch8486] scale. 

TBH, I would expect one or more to be a dead short if it was faulty, and that doesn't look to be the case.

The two on the right seem to be open circuit, which I presume isn't right. 
When a rank amateur of advanced years uses the term "open circuit" at 05:48 it should be obvious that he just read it somewhere and confused it with the term "dead short", which on this occasion I won't take to be a personal insult.  The readings for the two two diodes on the right were both zero - no resistance.  Many apologies for the confusion.

Is that the fuse that failed on the LHS of the back panel in your photo? Did you have anything plugged into the aux. mains outputs next to it? Just wondering if something external has dragged it down?

Yes.  How can you recognise these items from the picture - you must have looked at quite a lot of them to identify the stuff so quickly.  Never had anything plugged in there - they are American style sockets.

Can you trace the mains input wiring into the mains transformer and measure the resistance across the primary of the transformer, and also between that and chassis?

Not at the moment.  All the transformer connections are underneath the chassis plate on which it is mounted.  I've just had another look, and it seems that that area is quite easily accessible by removing the the base of the casing - four screws.  Unfortunately, this means I've got to remove the amp completely from the "hi-fi unit" in which it lives, which in turn means scrabbling about on the floor in an attempt to extract the mains cable from the rat's nest carefully designed wiring scheme connecting the 11 or so TV and audio components crammed in there.  As my arthritic knees are playing up something rotten today, it will have to wait until the lad comes home from his "walk" - I think he's gone for a smoke.

Next step - does the secondary of the mains transformer have a connector where it feeds the amplifier PCB? If so, can you power up the transformer with the connector disconnected - without the fuse popping?

Kevin

Thanks a helluva lot to all of you for all your help.   

Sorry about the wallpaper...

[Kevin Wood]

The readings for the two two diodes on the right were both zero - no resistance.  Many apologies for the confusion.

Ahh. Now we're getting somewhere. Sounds like that might be the problem.

Yes.  How can you recognise these items from the picture - you must have looked at quite a lot of them to identify the stuff so quickly.  Never had anything plugged in there - they are American style sockets.

    

Not at the moment.  All the transformer connections are underneath the chassis plate on which it is mounted..... 

Well, I wouldn't worry too much. If 2 of the diodes are reading 0 ohms I think diode failure might indeed be your problem.

Thanks a helluva lot to all of you for all your help.

No problem.

So, how are you with a soldering iron?

Kevin

[jereboam]

So, how are you with a soldering iron?

Kevin

Used to be OK, but I'm cautious about PCBs.  From what I can see, it's all been hand-soldered, so it should be possible.  (I don't actually mean hand-soldered, but it definitely hasn't been built using the techniques they use today - can't remember the right term.) 

Mind you, my shaky hands and deteriorated eyesight are going to slow me down a bit!   Definitely a kitchen table job.

[Shackeng]

It's probably a capacitor somewhere they are always favorite

Agree with Jimbo, check any capacitors. Tend to fail with age. (from someone who trained in electronics 40 years ago & has forgotten it all!!!)