Beomaster 4500 remains silent

[david winter]

Hi,

I'm trying to understand why my Beomaster 4500 remains silent.
The front panel operates. When I turn it on, I ear a pop in the speakers and a relay clicks. I did not find any DC voltage before the relay: the output stage (a STK module) works on both channels if I send a signal directly to it.
I tried testing the phones jack on the frond which is known to cause some troubles, but the problem isn't there: the relay clicks when I insert a jack and clicks again when I remove it (so no switch problem).
If I push the volume I can hear a very very faind sound from the tuner, probably by capacitive effect.
Anyone knows where the problem could be ?
I don't have the service manual other than a PDF and the schematic is not really easy to read because all wires go to a bus and each time I see a bus line reference, I can't find it elsewhere on the schematic.


Thanks,

David

 

[scoloheros]

Don't get your hopes up about this, could be a lot of things but I was recently tinkering around with a Sony receiver that was quiet. I tapped a relay switch and heard extra static for a split second. I popped the cover off the switch and sprayed it, solved the problem. I don't know much about electronics and other potential problems though, this just happened to be the problem with this one. Curious to know what the problem is once you find it.

 

[camshaft]

It's been awhile since I worked on my 4500, so I don't remember much. Do you get any sound through the headphone jack? And when you say no sound do you only mean at the speaker-level outputs? Remember that the Powerlink outputs are at line level, so testing to see if you get sound on the Powerlink outputs may help you isolate the problem.

 

[david winter]

I found the problem, so I'm posting what I did to find it.
First, I followed what you suggested: inserting a jack in the phones plug clicked the relay but I still had no sound although the main amplifiers were functional.
I then thought about the electronic switch for the inputs (TC9164 chip).
This could be quickly tested by switching to FM mode, and short pins 11/12 or 17/18.
This didn't change anything but I found that the shorts generated the usual hum, and I found that the chip was ok (moreover, I found that only the radio was silent).
I then checked the FM tuner board and found that something was hot around the LM chip: the 100µF capacitor was simply shorted.
So I changed the three same 100µF caps (two on the FM board, one on the upper (AM) board, and this solved the problem.
I didn't recap the whole thing although I should do it, but as it is, it seems to work great.