Thank god the plastic only gets yellow on the inside!

Easy things first... transformer primary wiring before (top) and after (below). Just two wires to move, and there's even enough length in the existing wires, a refreshing change from normal.

Earlier, the Beomaster stayed warm even in standby. This should help with that, and as a nice side effect, cuts the power consumption by 10%.

tournedos wrote:

Finally, I'll rewire the transformer to 240V instead of the original 220V so the Beomaster doesn't warm up so much as it does with the current nominal 230V mains voltage.

That's the best idea IMHO ever since I've lost a BM901 (early version) left channel by forgetting that one :-(

And those dam*ed Motorola BD697/698 are nowhere ever to get except from other 901's. The 901 seems to be at the upper limit of the voltage scale...

They changed the Trans's to other ones that had to be mounted on the other side of the PCB.

hemenex wrote:

That's the best idea IMHO ever since I've lost a BM901 (early version) left channel by forgetting that one :-(

Yes, I guess that one has particularly tight speced components... many filter caps in vintage kit are also at the edge of their limits, even at nominal voltage.

On to the tuner then - as I said, that's my most used source, so it will receive some special attention (in addition to being fixed).

Once you remove the correct screws (and only them), the tuner board flips up nicely and locks in the service position. For the other work, it could actually remain like that, but I'll remove it completely to make work easier.

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Be careful with this kind of connectors, which are common in B&O kit from the '90s and on. The wires have only a single strand of copper and break easily where they have been pinched by the forks of the connector. They can be reattached if you dismantle the entire connector and cut a few millimeters off, but it is a pain as the wires are usually separate (not a ribbon cable) and non-marked!

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tournedos wrote:

Be careful with this kind of connectors

Mika, again I have to second that 😉

Had exactly this problem on my BC9500; thank god it was only a 5 pin connector; And I had to find out they were cross-wired so pin5 went to the opposite pin1 and so on.

But those were even worse on the other end 😡

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As you can see they loosened from the glue and those are pretty complicated to fix as you can't strip them one by one...

That's a BM8000, BTW

  Gunther

After all connectors are off, the tuner board detaches from its hinge (no need to remove the screws this time either!) and here it is.

There are a few electrolytic caps that are purely on the AF signal path, and I'm going to upgrade them - that brought an audible improvement to FM radio in a Beomaster 5000 I restored one time. These are

• C201/401 (10 µF) - measured ESR 4 ohms: out of spec, replaced
• C207/407 (4.7 µF) - measured ESR 11/23 ohms: way out of spec, replaced with MKS foil caps
• C35 (10 µF) - barely acceptable, replaced anyway as it is on the FM audio path

The circuit boards in this Beomaster are not too good quality IMHO, and the PCB pads come off all too easily even if heated carefully. Therefore I'm going to disturb them as little as possible and replace any other caps only if they measure bad. None of them actually do, so they can stay. I'll just redo any dubious looking solderings and hope that corrects the little problems I had.

That completes the tuner board.

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tournedos wrote:

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Colemans mustard? Why is it you electronic buffs always have to have some kind of sauce to hand?🤔

Stonk wrote:

Colemans mustard? Why is it you electronic buffs always have to have some kind of sauce to hand?🤔

😁

I keep pens in it. The empty tin can, that is.

We are now working our way up higher on the ladders of annoyance (and I should apparently clean the lens of my phone).

Underneath the now removed tuner board, is the preamp board, and on the corner of it, the speaker muting relay that often gives problems. So did mine in the beginning, but it magically fixed itself after some use, and I'll let it stay.

The preamp board has plenty of electrolytic caps on the signal paths and they could be replaced with fresh caps or upgraded - if you're interested in that, visit Die Bogener's workshop thread on BM6500/7000 in the archived forum.

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The caps I'm actually interested in now are on the power supply & power amp board, behind the relay under the plastic fan duct.

The duct will need to get out of the way for any hope of access. There's only one screw and two clips through the circuit board below, you'll need to ease them out with a screwdriver. Then you can flip the cover, which also holds the two main power supply filter caps, and swing it away with the caps still attached in their wiring. You may need to rotate them little by little to free all the length of the wires.

Power amp is between the fan and the cooling fins, and between the cooling fins and the transformer, most of the power supply section. There are four small electrolytics in there, and they'll all be ripe for replacement after all these years of baking in the heat.

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But, before you remove the duct 😳 , you flip the Beomaster over to remove the bottom plate and gain access to the solder side of the PCBs. Four big screws, three smaller, and a lot of trouble later on aligning the bottom plate properly so that the front panel buttons will still work...

Under the bottom plate, you will find a lot of dust and a duplicate of the type / serial number sticker from the rear panel.

Nice work Mika :) I think I am going to have a look at my 5500 soon, mostly to redirect the line out but also to give her a checkup :)