Sony amplifier problem

Thread Starter

Nick_G

Joined Dec 17, 2006
5
Hi all.

I'm a new member and I'm hoping to get some help and advice on an intermittent problem.

I have an 8 year old TA-FB930R amplifier and occasionally I get the relays for the speaker selector (Speakers A , B etc.) clicking rapidly for no apparent reason. When this happens the sound through headphones cuts in and out.

Is this a simple problem like dirt on the relay contacts or the signs of a bigger fault?

I'm not knowledgeable about electronics so any help or advice much appreciated.
 

beenthere

Joined Apr 20, 2004
15,819
Hi,

Your speaker protection relays might be "seeing" a DC voltage, which is a no-no for healthy speakers. Without seeing a schematic, of course, I can't be sure. You are probably looking at a repair or a new amp.
 

Thread Starter

Nick_G

Joined Dec 17, 2006
5
Hmm, that does not sound good.

When it has done this before, giving the amplifier a sharp tap also causes the relay to switch. This is what made me wonder if it is a dirty contact behind the selector switch, or a dodgy connection somewhere.

Is this also likely?
 

Gadget

Joined Jan 10, 2006
614
Dry joints are a definate possibilty.
Resoldering the PCB around the relays, the protection sense circuitry, PSU regulator components and the Micro may be a good start.
Larger components, and hot components (like Relays, power transistors, regulators, power ICs, anything mounted on a heatsink etc etc) can be prone to the dreaded dry joint.
 

Thread Starter

Nick_G

Joined Dec 17, 2006
5
So if it is dry joints does this mean that the speakers are getting a DC voltage or is it just the relays? I don't want to damage my speakers as well.

Once the relays have started clicking it also seems to aggravate the problem when switching the speaker selector, so I assume it is the selector that is at fault.
 

Sirropo

Joined Nov 24, 2006
3
By dry joints, I'm sure reference is to bad solder joints or the socket the relay
module plugs into (if it does).

Its a excellent point to check.
 

Gadget

Joined Jan 10, 2006
614
Sorry, I thought the term was universal. Yes, a Dry Joint is a bad solder connection of a component or lead on a Printed Circuit Board, caused by heat, vibration, or poor preparation of the joint.... often can be seen as a small dark ring in the solder around the through pin.
 

Thread Starter

Nick_G

Joined Dec 17, 2006
5
Hi all.

Just thought I'd resurrect this with a quick update:

I've had the amp looked at by a qualified electronics engineer. He found several dry joints on & around the selector switch and fixed them. However, the problem is still there.

I'm wondering whether I should just give up & look for a replacement.
 

beenthere

Joined Apr 20, 2004
15,819
That is purely up to you - the problem can arise from causes other than poor solder joints. I'm still using a 35 year old amp with no problems outside of the input selector switches.

Doing more than recreational resoldering might take a schematic to be productive, though.
 

techroomt

Joined May 19, 2004
198
the protection relay typically energizes when a certain dc offset is reached on your amplifier outputs. often, a dc offset adjustment can be made to reduce the offset. you will need a service manual for your amp, they can be found on the web, do a search.
 

Thread Starter

Nick_G

Joined Dec 17, 2006
5
I don't think it is the protection relay as the protection indicator doesn't light up. Also, I still get audio from the speakers - it's just the sound in the headphones that cuts in & out as the relay switches on & off.
 
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