Pioneer A400 - After Plugging Headphones In No Signal On RH Channel

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jmartinbaugh

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Joined 2011
#1
Hi
Can anybody help my Pioneer A400 was working OK until I plugged my Goldring DR-150 Headphones into the speaker socket. The system worked Ok for the time it took to play two CD's then the output on the RH channel failed. Has anybody got any ideas where I should start to look for the problem.

Many thanks

Martin
 
#2
Does it still work on the headphones ? Thats where to start 🙂 It may just be a coincidence if the amp worked OK for some time afterwards.

If it does work on headphones then look how the speakers are muted (maybe just a switch contact on the headphone socket)

If it doesn't work on either phones or speakers then you need to do some basic checks on the power amp stage.
 
#5
Wow that was quick :- No their is no sound from either Phones or speakers. Winding up the Volume has no effect until the right channel is at Max Volume then very faint sound could this be crossover sound from the left Channel. I will check the relay's and give them a gentle tap.

Many thanks for your help so far, I purchased this AMP of EBAY and was very suprised with the quality of the sound and have aquired the necessary Capacitors for a Re-Cap. So any advice on that would be welcome.

Regards

Martin
 
#7
Well you have to start somewhere with the faultfinding 🙂 One last thing to check before "getting technical" and its you saying there is faint sound... crossover from the good channel ? that makes me think this.

Could the amp have physical damage somewhere such as cracked print around a front panel control/switch etc ?

Failing that it needs a quick check of the DC conditions of the power amp, offset and quiescent current and then if thats OK, a scope check to see whats going on.
 
#8
Also could it be just a confusion ??? your amplifier features protection that works through a relay and as said this is common for both ch. If in protection mode simply no sound at all .

there is no fuses inside that might have the specific result so the above points to something else like a broken interconect or a dirty selector/tape monitor switch ...takle over relays but before openthe unit ensure the interconnect , use some other input , play a bit with switches and pots before assuming a failure

kind regards
Sakis
 
#10
Well I have have tried a couple of things, I lifted the lid to check for any leaking capacitors or scorch marks by any components but it all looks OK but very dusty. I have found two relays on the main PCB one at the front which is the mains on/Off relay and a single relay at the back of the PCB in front of the speaker terminals and next to it is another empty position for a relay.

One thing that might give someone with much more experience than me a clue is the fact that with a CD player connected with the selector switch at the CD position I have sound from the RH Channel only if I put the switch in the Tuner position I get sound out of the Left Channel Only.

This has me confused but hopefully it will give somebody a clue.

Many thanks for all your kind help

Regards

Martin
 
#11
So with the CD player correctly connected you can get sound from one channel (left) if you switch to the tuner input ?

If so then that sounds like a physical issue somewhere.

Have you tried the CD player in all the other inputs as a test ?

You need to get a copy of the manual which is widely available on the net as that will help you trace the signal path. I'm guessing you haven't a scope (and that is what is really needed) as that would find a fault like this in minutes.
 
#12
Yes I have a copy of the 400HB schematic and parts list, I will try all the other inputs but it does seem to suggest a physical issue Sound out of left speaker when selector switch set to CD and out of Right Speaker when set to tuner but still only one channel has sound.
 
#13
If you are getting audio from either left or right speaker outputs then that rules out any problem with the power amplifier stages and comes back to the input selection side of things.

It sounds a very odd issue but will almost certainly have a really simple cause. With the amplifier OFF and UNPLUGGED you should be able to trace the signal path with a meter on low ohms range, starting from the input sockets and following it through the selector and so on.
 
#14
Many thanks Mooly I will try that later, one other thing I have just remembered is that after the unit lost the input the CD Player started skipping tracks and I thought that as it is a NAD 455BEE I had got the common Nad Skipping problem, after turning of the CD and letting it stand overnight it worked perfectly next day, it was almost as if a voltage spike had gone up the input leads to the CD. Well I will start tracing the input circuit after supper so you will be left in peace.

Kind Regards

Martin
 
#17
I'm looking at the standard A400 and that shows a passive preamp.

With the CD input selected and your meter set to a "low ohms range" connect or push the black meter lead into the Left CD input socket and trace the continuity through the PCB to the input selector switch and then on to the main volume control. Repeat this for the other channel (using the Right input socket) and see if you can find any open circuit connection anywhere.
 
#18
Well thanks to all the help recieved I have got it working. It seems to have been caused by dirt and a small piece of very fine wire which must have got through the cooling slots in the top and the headphone relay is sticking. The piece of wire looks like a strand of 13amp mains cable probably when wire was trimmed to attache mains plug. I spent most of yesterday afternoon cleanining out all the dust and muck from the PCB, I think it had been in a loft for about 20 years. Giving the relay a gentle tap started the relay working it was showing no connection between phones or speakers until I gave it a sharp tap. As it is sealed it looks as if I shall have to find a replacement. Can anybody help with a makers part number. Once again many thanks for your help.

Best regards

Martin
 
#19
Thats great news 🙂 Well done.

If the relay is faulty (it will just be tarnished contacts that need cleaning) then its worth removing and seeing if it can be opened. Most types can although there will always be an exception. A good close up picture might help. Relays tend to conform to standard pin outs although coil specifications vary.

See if you can open it first, if not you'll have to identify the package style. Does it say the coil voltage on the relay ? The circuit feeds the the coil via a string of resistors so virtually any coil voltage can be made to work OK if needed.
 
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