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Beomaster 7000 No sound on all inputs

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Baegle
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Baegle posted on Tue, Apr 28 2020 3:37 PM

For the last few weeks my Beomaster 7000 has not always played radio on the first attempt. The system turned on, the radio displayed the right station, frequency locked, just no sound.  Turning it off and back on again usually fixed the problem. Things got worse, then it needed to be switched to CD and back to radio to get sound output. Then I noticed sometimes CDs were not very loud and I needed to increase the volume. 

Now it has stopped outputting sound completely. Both pairs of speaker outputs and the headphone jack do not make any sound at any volume on any input. The mute relay operates (I can hear it clicking) but it has no effect.

I suspected the program select IC 1 (TC9164N TOSHIBA, HIGH VOLTAGE ANALOG FUNCTION SWITCH ARRAY) just because of the way it would come good if you switched between inputs, but I'm just guessing. No obvious circuit damage apart from a bit of discolouration on the fan control board under the big transistors.

Has anyone fixed a similar fault. I haven't worked on this type of electronics for over twenty years so any help would be greatly appreciated. 

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Schletti82
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Suggested by Schletti82

Could you try if there is sound on the headphone socket on the front, or even better on the MCL socket for passive speaker’s?

If sound is on the headphones or on the mcl socket, than it is an easy fix. Muterelais must be cleaned or better replaced.

Please try first this two posibilitys. If there is no sound we will look to the amp

Baegle
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Baegle replied on Wed, Apr 29 2020 2:56 AM

Thanks Schletti82,

No sound on the headphone socket. I have cleaned it with contact cleaner.

No sound on either SPEAKERS 1 or SPEAKERS 2 MCL. I have four rooms set up with extra speakers using four  MCL2A Type 2045 links. None of them have sound but all will send the correct commands to the BM7000. I've tried passive speakers (RL45.2) in both speakers sockets. No sound. I haven't investigated the POWERLINK sockets. No suitable hardware.

I've measured the MUTE relay contact resistance. 0 ohms across both terminals and I can see and hear it operate.

Baegle
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Baegle replied on Thu, Apr 30 2020 9:33 AM

More info if anyone can help with what is a much simpler problem than I first thought.

Checked power supply voltages on plugs P14 and P15. Sometimes I'm missing all the voltages on P15, sometimes not. Set up the BM7000 with a couple of inputs and some speakers and it worked OK for a hour or so. I could switch between inputs, turn it on and off. Then failed again no sound.

Removed the PCB2 and re-soldered all the connections around the power supply. Could not see any dry or cracked joints. Opened and cleaned the contacts on relay RL1. Reassembled and tested-still no good.

RL1 is not operating. Contacts are closed with no 240V power so the coil is not energised. They open when power is applied, but do not close again when the amp is turned ON. Voltages on pin 7 of P15 (ST BY RL) are 1.3V with the amp ON and 3.8V in standby. So the problem is either around TR19 on PCB2 or coming from PCB9 (I hope not!)

I've yet search the forums for standby relay faults. I can't be the first one!

Baegle
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Found the problem, then created a much worse one!

Problem is the standby relay itself. It contacts don't reliably close when de-energised to 1.3 Volts (fatigued spring, residual magnetism, worn pivot points???). I shimmed under the relay armature with one thickness of 80 gsm paper and it worked reliably. Switched between inputs and would power up from standby or power off reliably. I tested it dozens of times. Went shopping for a new relay.

The next day tested again and it worked a few times, then there a buzzing sound, then smoke came out! Now Fuse F1  is blown. 

Not Happy!

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