Rotel RA-930AX - right channel down

[hergest74]

My old Rotel RA-930AX amp has been flaky for some time with the right speaker cutting out. Tweaking the function knobs back and too has usually helped but it always comes back. This time it just won't play any sound except (when turned up very loud) a crackly, broken thin version of the audio. I have swapped speakers, cables and checked it all and the fault persists. Checked connections which are all rock solid. I then tried plugging in my headphones. Strangely this amp has never isolated the signal to just phones like other amps, with the signal still coming out the speakers. That aside, the signal also only plays in the left channel with the same crackly, broken audio in the right ear.

Obviously a problem with the amp that no amount of knob twiddling, Servisol Super 10 spray can solve.

If anyone can help I would appreciate it as I don't want to have to open it up as I am no electrician.

[paulsherwin]

Rotels of that era seem to be particularly subject to switching problems. The tape monitor switch is a prime candidate. The switches are difficult to clean effectively.

If the switchgear is all OK, then the next place to look is the speaker protection relay.

[PaulR]

My Rotel receiver has jumpers on the back so that the pre and main amps can be separated. The connection sometimes becomes intermittent. Might be worth having a look to see if yours has those

[hergest74]

The issue isn't with the speaker connectors on the rear, it seems to be internal.

As for the speaker protection relay, I am not familiar with this. Is it something I could fix / clean ?

[paulsherwin]

The protection relay contacts may be dirty, or there may be dry joints where the relay is soldered to the circuit board. It's not possible to give more detailed advice without seeing the amp under discussion.

[hergest74]

Googling it seems to be a common problem with other owners. Some have put it right by cleaning the potentiometers, and or changing the fuse.

I shall have a look inside an start by cleaning the switches etc with Servisol and report back. Its a nice amp so I want to keep it.

[paulsherwin]

That should certainly be your first move.

[theredhouseinn]

Had a quick look at the cct.
There is no speaker protection relay.
There are fuses between the o/p transistors and the speaker selector switch. F1 and F4.
Check the ends of the fuses for tarnishing and that the tension of the fuse holders is good, and the fuses themselves.
Failing this you will need some test equipment and apply basic fault finding techniques.
John.

[hergest74]

Well, pretty gutted as I unplugged everything, opened it up and gave a good clean. Fed an audio signal into both the tape and cd in and heard everything clearly through the headphones. Great! I thought. Then I tested with the speaker cables into the rear. Left channel fine, right channel absolutely no different. Plugging the red + of the right speaker cable seemed to exacerbate the problem, even affecting the headphone signal. Unplug the right speaker cables and normal L and R signal through headphones.

I didn't notice any blown fuses (ie, black glass) and they were holding with good tension.

Any clues as to what to try next folks ?

[jamesperrett]

I haven't checked the circuit but I would guess that the headphones have something like a 100 ohm resistor in series to limit the level with low impedance headphones. As soon as you plug the speakers in, which require more current to drive them, the sound goes which implies a high resistance at the output. I'd try measuring the dc resistance between the speaker + terminal and the components that feed it - gradually going back to the output transistors. It sounds like you have a poor connection there somewhere.

[hergest74]

What I don't understand is why the front switches were initially causing the intermittent cut out of the right channel, which I resolved by rapidly turning them. I will try a different speaker cable in the right channel to at least eliminate the issue being the cable. I do have an electrical tester but I'm only a novice. What you are asking me to test is beyond my knowledge, but I am willing to learn if guided.

[stevehertz]

If the "front switches" have been proven to resolve the problem (at one time), then they're very likely still the problem. Dirty switches can be a tough nut to crack, you may have to repeatedly clean them/it and even then the switch may not be making good contact due to a purely mechanical, poor contact issue.

[hergest74]

Oh dear, I hate this kind of thing you can't quite put your finger on. I can't really get into the switches as they seem sealed, even with the lid off.

[Goldie99]

From online images of the RA-930AX, several of the front controls seem to be pcb mounted rotary slide switches, which in my experience can be a real pain to get properly cleaned - that's where I'd focus my efforts. They are likely to be difficult to get cleaner actually to the contact surfaces - I have had to remove & dismantle them for cleaning in the past, for other makes / models.

[hergest74]

So I'm pretty much stumped then as probably not worth the cost of a professional repair.

[PaulR]

Could you hard wire to a particular switch setting , say, Aux? You could use an external Aux switch unit and if required an external phono amp. Not ideal, but if you like the amp it may save it.

[hergest74]

Not sure I want to do that really. I still think it is a speaker connection issue as that is what is affecting the interruption in the signal

[PaulR]

Yes, just reading the thread again I see what you said at post #9. It does sound like some sort of odd intermittent connection, maybe a dry solder joint?

If you haven't already done so you could try running it with the cover removed and tap/flex the circuit boards with the handle of a small screwdriver to see whether that affects the problem. You could also try poking around the headphone socket with something insulated. Not very scientific but you never know!

[ajgriff]

Originally Posted by PaulR

You could also try poking around the headphone socket with something insulated. Not very scientific but you never know!

Scientific or not I often use a plastic chopstick when searching for intermittent faults and it's surprising how often it comes up trumps!

Alan

[hergest74]

Chopstick it is then. Wish me well.