Beocenter 7700 power supply problem

[Mark-sf]

What is broken about the relay? It’s a simple DPST relay that is activated by 6v and most like rated at 1A for contacts. You might check whether https://www.beoparts-shop.com/product/relay-for-beomaster-5000-5500-6500-7000/ will work if it truly is bad.

[Xavier]

Thank U for your interest.

I think the relay does not hold a voltage flow.
Sometimes after 2 seconds, sometimes after 2 minutes, and another time after 2 hours, the relay disconnects.
Then it’s usually not possible to re-enable B&O. I mean it turns on, but after a second or two I hear the relay clicking and B&O goes into standby mode.

Now I noticed that B&O had a set input voltage of 240 V, and in the network I have 230 V. Should I switch the voltage to 220 or does it not matter, because there is some tolerance range? Besides, the relay is running at a constant voltage, right?

Xavier

P.S.

As I mentioned, I’ve very poor knowledge of electronics. I would be happy to return the device to the service, but in my area no one wants to undertake diagnostics. Only one electronics has tried and said he could’t find the cause of the fault…

[Xavier]

Hello!

I’ve had B&O 7700 for several years and the relay in the power section has broken. There are no relay parameters on the dust cover, only the model: PASI manufacturer, relay model KS/R-01-C.

I’m weak from electronics and I cannot find the parameters of this relay in the electrical diagrams.

Can anyone help me find the parameters of the relay to find the right replacement? I’ll be grateful for any tips.

Xavier

[Mark-sf]

The fact that the relay does activate even for a short time does not mean it’s broken but that it is losing its 6.5 volts. This will take some technical skill to fix and the service manual is online so it does not require a B&O service tech. How comfortable are you with using a multimeter and desoldering/soldering parts on a PC board?

[Xavier]

I know how to use both 🙂

I soldered the relay by myself. But I don’t want to resolder it again. I’ll put on a new one with the right parameters. Need to buy relay with 6 V coil and the current of 1 A, right?

I’ve got electrical diagrams for beocenter 7700 🙂

What You sugest next?

Xavier

 

[Mark-sf]

First you need to confirm that your standby voltages are fine. TP9 should read 6.5v DC. You should also have 5V DC at pin 5 of the P11 connector. If those are fine, then you likely have a fault in the power amp section that is muting the unit. There is no need to replace the relay as what you have observed is its normal operation.

Finding a fault in the power amp circuit is more difficult since the +/-30v supplies share the same board and there is no easy way to disconnect the power from one channel without pulling the output transistors. Since you are able to get it on for a time, I would try looking for a DC voltage on each channel w/o speakers connected while the relay is engaged and figure out which one is tripping the fault circuit as a start. This all assumes the 6.5 and 5v supplies are fine.

[Xavier]

Okay, thank you very much.
I hope I understand and handle it 🙂
However first I’ve to buy a new relay, because the old one is in small pieces and I am not sure if they’re all. Besides, the thin copper wires from the coil are broken. But I hope that knowing the operating parameters of the relay I’ll easily choose the right replacement in the local store today.
Later, after installing the relay, I ‘ll do voltage diagnostics, as you suggest, and I’ll inform you about the results.
One thing. I’m not sure what You mean, but the beocenter switches off completely – doesn’t mute.

[Mark-sf]

By muting the unit I meant going into standby. The relay does not switch all the power off.

[Xavier]

I thought so 🙂

I already have a new relay. The seller said that it should fit after a small modification – two legs are unnecessary.
But here it’s midnight and I’m tired after work, so I’ll run B&O for diagnosis tomorrow evening.

Greetings from Poland!

X

[Xavier]

Sorry, but a lot of work and Easter. I had no time for pleasure in recent days…
After all, today I installed a new relay to do the diagnostics you wrote about, but after plugging into the power supply, there is no reaction.
I found a burned fuse. I don’t know when and why it burned down. Anyway, I need to buy a new fuse now.
Slowly in small steps forward 🙂

X

[Xavier]

Hello.

I put on a new fuse, but when switched on, it immediately burned it. The same happened to the other. Fuse socket on the attached photo – two green wires.

Where to look for a short circuit?

Earlier I soldered a new relay with eight legs – the old one had 6. I thought that it wouldn’t matter, because there were factory holes for 8 feet in the PCB. Pair for the coil and three pairs for the contacts, with the last two pairs on the same path, including the theoretically unnecessary one.

Can this relay additional pair of contacts cause a short circuit?

Xavier

[Mark-sf]

It most definitely can blow as those contacts conduct when you plug it in.

[Xavier]

OK, thanks.

In a free time I remove the relay and deactivate the last pair of feet. I hope the relay has not been damaged. I’ll let you know if B&O works and if I managed to do more diagnostics.

X

[filip_kbh]

1. Do you know anything about electronics? Otherwise, it is probably best to leave it to somebody professional who can fix it for you before you make matters worse.
2. If the Beocenter shuts off after a few seconds, it is usually a sign that somehing is pretty wrong, and it shuts down to protect itself. This can be because of many things but one of the main suspects in this particular stereo would be the idle current trimmers corroding. When that happens the idle current becomes too high. These two trimmers should be replaced, and the idle current adjusted afterwards.
3. Have you done a visual inspection of suspect components? The reason that I ask, is that a few of the red Roederstein capacitors look very suspicious to me – they look fried. At this point in time, it is fair to say that all electrolytic capacitors in the Beocenter should probably be replaced.
4. If you have not discarded the original relay, I suggest that you clean it with very fine (wet) sandpaper where the metal parts meet each other. It’s an easy fix, and your relay will become as new.

 

.

 

[Xavier]

Thank you Filip.

Ad.1.

As I wrote, I don’t know almost anything about electronics. I use the internet and tips from users.
I gave the B&O to a local electronic service – it returned unrepaired. Another service didn’t want to try fix it.
I’m afraid that shipping somewhere further for repair can be more expensive than the value of B&O. That’s why I tried to fix it locally, and now on my own with your help.

I have not much to lose 🙂

Ad.2.

What do the idle current triggers look like? Where are they? Will I be able to adjust the idle current myself?

Ad.3.

I read about the aging of electrolytic capacitors. Do you mean those with the RDE logo in the middle (marked in the photo – yellow rings)?

Ad.4.

I cannot save the original relay. The coilwires are broken.

Xavier

[filip_kbh]

3. Yep. Those red caps will need replacement.

The Idle current trim pots are marked 3R124 and 3R224 on the board. Replace them with trimmers of similar ohms value. Read in the service manual how to adjust the required 10mV.  You can download the service manual if you are a gold member (and at the same time help keep this site up and alive)

[Dillen]

You need to diagnose the problem before replacing any components.
Make sure that the problem really IS with the idle current before replacing anything.
Chances are that you will only introduce more problems, that could make repairs more difficult – as in f.e. being unable to set the new trimmers right because the original fault is still present, keeping the Beocenter from staying powered up – and even if the original fault is found and fixed the new trimmers setting could be wrong so it still keeps shutting down.

I would also leave the capacitors alone for now. At least until the present problem has been diagnosed.

One thing at a time.

Martin

[Xavier]

Good point.

Thank you for the helpful
notes, Dillen.

First I’ll fix the relay and focus on diagnostics, as Mark-sf suggested. Replacement of components will be the next step if necessary.

Xavier

[Xavier]

Hello again.

The modification of the relay (remove the pair of feet) has almost nothing changed.
Now it burns the fuse in the second circuit.
In general, I bought the wrong relay, which causes a short circuit. I have to find the right one.

X

[Mark-sf]

You need one which is “NO” for Normally Open and is DPST with the correct pin-out.

[Author]

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