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Beomaster 8000 Restoration

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dahiyas
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dahiyas posted on Tue, Oct 13 2020 5:47 AM

This weekend I started on trying to restore a Beomaster 8000. 

Couple of issues before I started -

1. Three buttons missing on the panel - Martin found the replacement buttons in his dungeon and sent over the same.

2. The system has the standby light on but does not come out of standby.

3. The volume dial makes a scratching sound when turned. Looks like something is out of alignment.

So last 2 weeks were spent reading all Beomaster 8000 related messages to prep for the project. Rudy's (Belover) detailed blog was really helpful to get started.

I will also do a complete recap while trying to fix the above issues.

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dahiyas
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Yesss !! It works. Looks like it was the capacitor. So now the sound does not fade in and out. No distortion.

BUT

1. I felt the BF858s were really hot. But Krais also mentions the same and Martin/you confirmed that its normal.

2. I also noticed that D5 on the power PCB is also hot. Is it because of the proximity to the voltage regulators ? 

3. I checked the trimmers again. The idle current keeps increasing in small increments after setting to 18mV. Similarly, the offset output keep on going higher. Anyways after getting closest to 18mv and 0V, I tried playing music for 30 secs and I switched off the system.

Any guidance on pt. 3 ?

 

dahiyas
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Looks like our messages crossed !! It did work.

Sonavor...I really appreciate your guidance on the additional equipment. I have quite a few things on my list and projects that can use the items.

But just when I am ready to buy the next item..something else shows up. I was ready to order power supplies (3 x 60V) and a MS150.2 showed up in DC. I ended up buying it (Cost of shipping from DC to ATL is same as the MS150.2 :-()

so power supplies get pushed out Big Smile..for now. Have to deal with a upset better-half when the boxes show up !!

Hopefully..the BM8000 can be ready before they show up.

 

sonavor
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While the Beomaster 8000 is warming up the idle current can drift. It should settle in though. The DC offset should stay withing the service manual tolerances.
You are measuring the idle current with the speakers not connected and the volume level at zero right?
Monitor it for a while and see that it stays around the 18mv across the emitter resistors.

Those BF858 transistors do get up around 160°F.  That's why I use 105°C rated capacitors. 

-sonavor

dahiyas
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dahiyas replied on Wed, Nov 25 2020 11:57 PM

To be honest I have read about the 105°C rated capacitors but feeling the heat coming from the regulators after just 5-10mins and the BF858s, it makes more sense now.

Played a bit more today and no more heating of heat sink.

New challenge - I just have one speaker connected. BALANCE controls - When moving balance to the right the speaker volume increases and when moving to left the volume on right comes down again till 6 and then cuts off completely at "<".

I would have expected the volume on right to go down gradually when moving balance to left and also volume on right should not be increasing when moving to the right.

Not sure if this is normal behavior on the BM8000 or I have messed up some connectors.

dahiyas
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I checked the connections again and they are ok.

Volume Offset adjustment ? I did replace both the trimmers on the tone control board.

Can I do this without a scope ?

 

sonavor
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I have done it without a scope. If you are in a nice, quiet environment you can hear any clicking through speakers or headphones when adjusting the volume (with no music playing). Adjust the trimmers where there is no clicking sound. If you changed components with that circuit then you might need to start with any removed resistors reinstalled to begin the procedure.

-sonavor

dahiyas
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Thanks Sonavor. 

What about the balance control - When moving sound balance towards a side..does the volume on that side go up ?

 

sonavor
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When you say the volume on one side goes up does the Beomaster 8000 volume indicator go up?

-sonavor

dahiyas
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So lets say volume level is currently 4.0.

I have only one speaker connected on right.

When I press balance right, (1 > 6), i can definitely hear a volume increase with each press, and so does the balance indicator BUT not the main volume indicator.

Similarly when I am at max ">" on right and I start reducing (press balance left).. there is a audible volume decrease till 0..then as I move towards left 6, the volume does not reduce till 6. It cuts out for right speaker at "<".

-------------------------------

I would have made a video but I have run into new issue now.

After I switch on the system and play music..the displays either switch off completely or partially. The music continues playing. The keyboard becomes unresponsive. unplug the system and plug again and same behavior is repeated.

 

sonavor
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I have never tested a Beomaster 8000 in that condition. I always have to load resistors or speakers connected.
With two speakers connected and music playing the balance control works just as other amps. It removes sound from one channel down to where it is silent. The volume level of the remaining channel doesn't change.

On your new problem it is difficult to diagnose.
Have you checked the voltage adjustment on the Display board? Make sure it is set properly and not interfering with stability on the Microcomputer board. Just something to check. 

-sonavor

dahiyas
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The system has now gone to where I started. Not getting out of standby mode. Looks like the CPU PCB is still causing issues. I will check again today.

I also have the ribbon cable connectors on my list (already bought). Need to change those. Couple of them are loose. Have adjusted the pin for tighter fit for now but I will replace them.

Yes, I had forgotten about the voltage adjustment on the display PCB. I will do that if and when the standby issue is fixed.

I will wait for my MS150's to arrive tomorrow and try again. 

Thanks again Sonavor !!

 

 

 

 

sonavor
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The voltage adjustment on the Display board can keep the Beomaster from switching out of Standby mode.

dahiyas
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So before I tried anything on the system I tried getting it out of standby and it came alive without changing anything Surprise.

Standby..TP1..standby..tried multiple time...it behaved properly except once where after switching on the volume indicator showed ".4" and system became unresponsive again. I am going to leave it on for sometime to see if I see the issues come up again.

Meanwhile I did measure v at 8TP14. It was 5.075V. I did get it to 5.0V.

 

 

sonavor
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sonavor replied on Fri, Nov 27 2020 10:22 PM

The next time your are seeing the problem check 8TP14 and make sure it is correct. You might also monitor your +5 VDC supply on the Power Supply board (PCB 6). Perhaps it isn't regulating properly.

-sonavor

Sehrbug
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Sehrbug replied on Fri, Nov 27 2020 10:32 PM

Hi, there, sorry for jumping on the thread, I have just finished recapping BM8000 since it was completely dead, 

All the functions are working, but no sound and reservoir capacitors are measuring 105VDC. 

any suggestions?

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