Quad Esl 2905 reliability issues?

Correction. " one of the panels start to buzz and make audible popping noise after they have been turned on for 30 minutes or more"

It's more than likely a panel and not the power supply. It's going to have to go in for an eval and repair. Unless, your plan is to repair it yourself.

There's a handful of quality repair shops out there. A simple google search will return the usaul shops.

Good luck

Mvp, I am not an expert on Quads but I have read that the panels can arc or short even if they are not abused. It seems to be a fairly common problem with them.

Maybe someone more knowledgeable can help you out.

Panel would be expensive. Try checking replacing the input bipolar lytic and the small 0.1uf cap somewhere midway between input and the panels. Sorry I forgot. Been too long. That fixed my 989.

The thing is one of the speakers is working fine but the other one seems to be faulty. I could still play my music if I just ignore the soft buzz and pops but will it get worse and affect all the other working panels.
Should I replace all the panels of both speakers or just the faulty ones if I don't want sound quality to be compromised .

Mvp100

What is the humidity level in the room since the noises started ?

The reading was about 30. The speakers are in a windowless room with air-con set on timer. What are the signs of high humidity affecting the panels?

Your readings are really low (really dry)
One of my Wayne Picquet 57's a couple of years back in higher humidity started to make a crackling sound that would cycle on and off. It would make the noise for about 20 seconds and stop. And repeat.
It could be heard between songs if 5 or 6 feet from the speaker. It did not affect performance.
In talking with Ken at Electrostatic Solutions higher humidity is to be avoided. This is especially true for the 63's the most vulnerable. The 57's are very hardy compared to them. Not sure of its effect on 2905's.
Now whether the humidity being too low can also cause any adverse effects I don't know. Maybe someone else can chime in.
I keep the humidity around 50'ish or lower in winter and no symptoms anymore.