Unique problem - one channel silent under different variables


Bought a mint (looking) Cary slp 98 on eBay, connected to two reconditioned Hatachi HMA 7500 mosfet amps, work perfectly for years since reconditioning - biamping NHT 4 towers, bought new. 
When the preamp is turned on, a series of pops through the speakers, then Only the right channel plays. Switched tubes, didn't solve issue. Changed inputs from preamp to left and right amp and immediately both channels worked. Switched off, waited 5 minutes and still both channels working. Came back a few hours later, switched on again (having reversed the inputs to normal) and again same sequence: left channel silent and after switching inputs, both work and remain working until I switch off and come back when the units are cold.
I can understand that that there may be a resistor/capacitor that need to be hot before working, but why would switching input cables from left out to right input of amp and vice versa immediately fix it!
so every time I want to hear music I have to go thro this rigmarole! Why does switching cables fix the problem????
any solution will be greatly appreciated! I'm sure it will end up back at Cary but I wondered  if anyone (Almarg???) has an answer?  Does the popping on switching on, both channels pop, provide a clue?

springbok10
Cary gear is noted for not being dependable good luck.

springbok10 regardless of the problem ALWAYS turn your preamp on and then your amps! Turn on sequence........sources>preamp>amp and turn off sequence is in reverse for the safety of your gear and peace of mind!
Hi Denis,

As you’ve surmised, it sounds like the preamp has a problem that needs to be sorted out via professional troubleshooting. The symptoms you’ve described don’t point to any specific cause, as far as I can tell.

But as Jond indicated it sounds like you are not following the proper turn-on and turn-off sequences (with the power amps being turned on last and off first). Also, it sounds like you are disconnecting and reconnecting the RCA cables that connect the preamp to the amps while everything is powered up, which is definitely bad practice and could conceivably damage your speakers.

That said, I wonder if disconnecting the RCA cables and then re-connecting them WITHOUT switching the channels would have the same effect as what you have observed when you disconnected and re-connected them with the channels reversed. It could be that the channel reversal was not what restored normal operation, but rather a transient of some sort caused by the disconnection and reconnection itself, that might have temporarily zapped the defective preamp circuit back into normal operation.

Or if the problem is temporarily fixed only if the channels are reversed when the cables are disconnected and reconnected, that may just be due to the happenstance of the resulting transient being different when the reconnection for the problematic channel is made to a different amp than previously.

Good luck. Regards,
-- Al
I learned 20 years ago to  turn amp on last, off first. What makes you think I do all these cord exchanges with power on? Did I say that? No, I think you assumed it. With due respect, and I know you are being helpful, if I haven't learned that basic, I shouldn't be  wasting your time posting. Thanks for your input,
Denis
Al,
Thanks for your thoughts. I have found that if I leave the preamp on constant standby, the issue is resolved. It seems that the unit/tubes/caps/resistors work if kept "warm". Forgive my indignation at the thought of doing anything with power on! To me that's like driving s car with the hand brake on or playing with the innards of a 1500 w amp with the unit on and plugged in :)

It could be that one of the connectors on the cable is a little tighter than the other and one of the RCA jacks on the preamp is a little looser than the other.

When the right combination is used everything is fine, but if the (2) wrong ones are used, you drop a channel.

Maybe try a different set of cables from preamp to amp and see what happens.
Might be a problem with the left channel amp. Swap the left and right speaker cables and see if the trouble moves to the right channel.
Thanks for the clarifications, Denis.  Apologies if I inferred too much from your initial post (which I did). 
I have found that if I leave the preamp on constant standby, the issue is resolved.
That's obviously a key finding, but again it doesn't point to a specific cause as far as I can tell.  But have you done enough experimentation to be certain that what fixes the problem during the minutes following a cold start is switching the cables, as opposed to just disconnecting and reconnecting them, or not even doing that but simply cycling the power at the corresponding time intervals?

Best regards,
-- Al
  
Yogiboy, I think you're right, because my last preamp was silent on left side and is currently being checked. Never thought it could be the amp - could transients and "pops" emanate from and cause a ss mosfet amp to shut down? How?

I will do the experiment.
Denis, I found a thread from about two years ago at another forum in which the OP had a problem with an intermittent popping noise in one channel of a Cary SLI-80 integrated amp. That amp was introduced in approximately the same timeframe as your SLP-98 preamp.

In that case the problem turned out to be caused by a bad Jensen copper and oil capacitor. It was mentioned by several people that those capacitors had high failure rates in times past, apparently including at least some of the years in which those components were manufactured. It was also said that Jensen confirmed that they had had a bad run of those capacitors.

I was thinking that a bad capacitor might be consistent with the symptoms you’ve described even before finding that thread. It might pay to have a technician (not necessarily a Cary person) replace all of the Jensen caps in your unit.

Good luck. Regards,
-- Al

If swapping the cables left for right causes the problem to go away, the problem is unlikely to be the preamp or amp. Its far more likely to be a failing connection in one of the interconnect cables. The act of switching it to the other channel might be putting some strain or removing some strain in such a way that the broken connection can make a mechanical contact.

 While it is true that the coupling caps could be having a problem, its not been explained how this is alleviated by swapping channels! So IMO/IME the cables themselves are the first thing to check. 
While it is true that the coupling caps could be having a problem, its not been explained how this is alleviated by swapping channels!
Yes.  Which is one reason I had asked:
... have you done enough experimentation to be certain that what fixes the problem during the minutes following a cold start is switching the cables, as opposed to just disconnecting and reconnecting them, or not even doing that but simply cycling the power at the corresponding time intervals?
Best regards,
-- Al
 
I just switched it on cold and switched the left and right cables (there are 2 pairs as I am biamping) and sure enough, the left amp turned off after 5 minutes. So it's the amp! So it cant be the preamp, since the right channel is supplying the left amp and its always been the left side that's muted.

Thank you all!
Post removed 
I’m not sure I understand this. In this latest experiment was it the speaker cables that were switched (per Yogiboy’s suggestion), or the interconnect cables (as seems to be implied when you said "the right channel is supplying the left amp")? Or was it both that were switched?

Also, previously you had found that switching the interconnect cables after a few minutes had fixed the problem. And that leaving the preamp in standby when it was not being used also eliminated the problem. And that popping had been heard in both channels. Not sure how to reconcile all of this.

Perhaps two problems are present. Or perhaps the preamp is the only problem, but its condition has worsened to the point that both channels are now affected in a similar manner, and the preamp is intermittently injecting either DC or some transient from its right channel output that is causing the left channel amp to which it was apparently connected during this latest experiment to shut down.

It all seems very inconsistent. But in any event I would not conclude at this point that the amp is necessarily the only problem, or even that it necessarily has a problem.

Best regards,
-- Al

Confirmation that it was the amp - replaced with another amp and no muting or popping.......