Phono II looses right channel

[Greg.]

Hi All,

I've still got alot to learn and this is a classic example.

When playing vinyl the system works fine for about 7 minutes and then I loose the right channel. This fault has been there for a while and the amount of time it takes for the right channel to cut out has gradually been getting shorter. To be accurate, this channel is still passing signal and is detectable with the ear close to the speaker, but from a listening position one would not know. There is no pop, other noise or gradual right channel fade. It just simple goes immediately away.

I'm satisfied from my elimination experiments that the problem is located within Phono II, but I'm struggling to identify the cause.

On the bench, all voltages measure correctly. I use a dummy speaker load so it might be that at the time of test, both channels are working well. Maybe I should check when a signal is being passed with speakers connected so that I know I am measuring when I'm sure the right channel has been lost.

Otherwise, any suggestions on the likely cause of this? Could it be a valve or something else breaking down and where should I look and how should I check?

I've done the usual stuff running the iron over joints etc. Where measurable, continuity is fine throughout the right channel circuit in an unpowered state.

Please help me........I hate not being able to listen to the best music source available

Best wishes,

Greg

[John Caswell]

Greg,
When you lose the channel does the background noise go as well? Without playing an LP but with the volume up high when you tap the PU arm ,NOT stylus, can you hear anything through the dead channel? with the cover off is there equal hum on both channels?
Give me a bell can probably sort it

John aka Dr John

[Mark Wood]

Hi Greg,

I guess you've more than likely checked this but a valve fault should be identifiable by swapping the two over to see if the fault moves to the left channel.

Mark

[Richard]

I'd swap the valves for different ones as there are 3 twin triodes shared between the 2 channels so it may be possible any valve fault would stay in the same channel.

Greg, your cdp lost a channel after fading recently also. Are you sure it's not a problem further down the chain such as pre II? Is it possible to try these items in another system?

Rich

[John T]

I had exactly the same fault with mine! After checking different sources, I checked the obvious weakest link - the valves. As Rich says, it's no good moving them around because they all share the same channel. I just swapped each one in turn, with a new valve until I found the faulty one.

John.

[Greg.]

I had a few minutes this morning to play. With no music coming from the right channel, I still have phono roar with volume turned up. I also get the microphonics when tapping the arm. I'm starting to think this is a cartridge problem

Richard. my CDP had some bad joints which were easily repaired. At least that works ok now, but it's not the same as my vinyl.

I'll try a complete valve change tonight, but I'm doubtful this will be the problem.

Best wishes,

Greg

[Richard]

Hi Greg

Yes try the valves and a dry joint (changing resistance as it warms up)would be a possibility too.

Good luck,

Rich

[Gerry]

Greg

had the same problem with mine not too long ago...would play and then cut-out.
I re-soldered everything...one of the coupling caps had a bad joint....but then it happened again.
Turned out the be the cartridge tag at the arm...very poor connection...hence the noise etc etc.

Best of luck
Gerry

[Shane]

If you think it may be a source problem, then first swap left and right inputs into the Phono II, then swap the cartridge connections. Or alternatively try a different turntable (haven't you got a spare DD somewhere, or am I thinking of someone else?)

[Greg.]

Don't you just love it. For all of this week my lovely missus unusually hasn't watched the box at night and has been happy on her computer. The box is in the lounge along with the hi-fi. I get in tonight after a late shift, eager to do some more experiments to properly identify the fault, and there the dear soul is, feet up on the sofa with that bloody box on It'll have to wait until tomorrow, but then, I'm also expected to get on with some decorating Oh well............

Thanks for all the suggestions guys, a number of which I've tried already. When I do get the chance to play again, I'll report back.

All you guys who have a dedicated listening room (even if it is a converted garage with a carpet nailed to the ceiling, Nick ) don't know how lucky you are.

Best wishes,

Greg