Optical encoder for volume control sporadically jumps to maximum

[Panda500]

On my TEAC AG H 600 Reference, the volume control did 2 times suddenly jump to max...!!! It's 10 years old now and it happenend first time about 1 year ago. Yesterday again... Terrible surprise when this happens. Also, more often, it does not react quite accurately i.e. does go down when I turn the knob upwards and vice versa. I can understand it does miss a step but jumping to maximum is more than that and probably not due to a misalignment of the IR-LED's and receivers... Probably a problem in the circuit behind? I did not find any comments on the internet, concerning this effect. Not of any other make either...
Any ideas or comments what to do?

 

[TLS Guy]

On my TEAC AG H 600 Reference, the volume control did 2 times suddenly jump to max...!!! It's 10 years old now and it happenend first time about 1 year ago. Yesterday again... Terrible surprise when this happens. Also, more often, it does not react quite accurately i.e. does go down when I turn the knob upwards and vice versa. I can understand it does miss a step but jumping to maximum is more than that and probably not due to a misalignment of the IR-LED's and receivers... Probably a problem in the circuit behind? I did not find any comments on the internet, concerning this effect. Not of any other make either...
Any ideas or comments what to do?

It must have an intermittent fault. The problem is that is likely to blow up a speaker. I don't think that unit is able to be used safely anymore, and needs retirement.

 

[M Code]

The Teac volume control is a quadrature switch, continuous make/break contact as rotated..
Try and inject some contact cleaner into it and then with the unit unplugged rotate the volume control multiple time as to circulate the contact cleaner....

Just my $0.02...

 

[Panda500]

TLS Guy & M Code, thanks for your reactions!
Indeed, I'm afraid to damage my speakers (and my ears!), although the amplifier gives max 2x75W and the speakers (Dali Zensor 1 + Rell sub bass) are designed for a amplifier range from 25 to 100 Watts... And of course, I keep my finger ready to immediatly change the source to a not connected one (no signal), during switching on the unit. (It only happened at switching on, not later on, spotaneously) But I understand something must be done and asap!
Concerning the quadrature switch, I think it is operated by optocouplers and not by "mechanical" contacts. So, contact cleaner would not help, or even blind the optical path (?) But I will try to find out what kind of "switches" it are, mechanical or optical. And also, if my reflexions are right, "missing" some steps by rotating the knob, I'd think it jumps from 45 to 50 or so (f.e.) but not to max... That's why I think about a problem in the circuit "attached" to the quadrature-switch...
I will look for a TEAC service point in my area (Antwerp/Belgium).