Can you offer any advice on getting these things open?

Yes and as I thought, it was packed reasonably well but there was the capacity for it to move around in the box.

So annoying! (and it doesn't pick up FM in Stereo, the volume treble and bass pots are scratchy and the left channel doesn't sound as present as the right through the tape input)....

Very few of these machines have stereo decoder as it was an extra accocery at the time, that needed to be mounted by a service workshop..

The potentionmeters are sometimes scratchy.

The 900K came in different versions, and differ a bit to open.

Usually there are screws under the cabinett to unscrew, and a couple of smalls screw on the backplate on the bent horizontal plate.

Then unscrew the wheels to the potentionmeters

When you pull out the amp from the cabinett, take it easy and slow as the internal speaker needs to be unplugg when you have for 25% of the amp out. of the cabinett. 

Christian 

I have seen lately quite a few of the 900M - post facelift models on ebay, they have the darker face on them.

Being the later type do you think they would be more likely to have the stereo decoder in them?

Colin wrote:

I have seen lately quite a few of the 900M - post facelift models on ebay, they have the darker face on them.

Being the later type do you think they would be more likely to have the stereo decoder in them?

I believe it depends more on the original country of sale than the actual model. If the country had no regular FM stereo transmissions when the unit was first sold, it's more unlikely the original buyer had this rather costly option installed. I have three earlier gray fascia 900s (one from Finland, two from Germany) and they all have the decoder.

*

For many variants, you don't need to take of the knobs as the entire fascia comes out with the chassis (from the rear).

Do you think you might like to sell me one of those decoders?

Nah just kidding.

I think my whole 900k is showing signs of its 50 years.

I'm struggling to get anywhere near a decent sound out of it.

I probably should start with the speakers.

How do you go about getting them? Can I just remove mine and take them to a speaker repairer?

What's likely to have failed internally? For a start my "stereo" light doesn't work when I have stereo stuff connected to it.

I don't think you'll find anything wrong with the speakers, unless somebody has been deliberately poking at them. Try a known good pair of external speakers to isolate the problem. More likely the unit is in need of a fresh set of capacitors and/or a transistor or two. Also, as you say, it is soon 50 years old - you shouldn't expect that great a sound out of it, although it does sound nice when in good order.

The stereo light has nothing to do with the actual signal (except on FM). If you select the tape input for example, it should just light up. If it doesn't, the bulb has failed, its socket is oxidized, or the switch bank has bad contacts.

Spend a few minutes pushing every button on the switch bank if you haven't already. That often restores the operation (or you might hear where the problem is) and might even improve the sound in case there are oxidized contacts.

Some of the early BM900K speakers actually dry out. The cardboard becomes brittle and
falls apart around the flexible area resulting in a distorted and "flapping" sound (as you know it from 1980s woofers
with foam rot).
The solution (apart from finding good original replacements) is to brush on a good contact glue of a type
that stays flexible (I find the black 3M type particularly good). Just "paint" the whole cone using a soft paintbrush
and of course treat the damaged areas.
This is, of course, only possible if there are no parts of the cone missing. In severe cases a replacement is
the only way.
Some speaker repairers can't do much to oval speakers - but some can.

Martin

I Have used these PHILIPS AD4681X4  4x6" as replacement speakers. The fit the mounting holes without modification

Apart from the ideological issues arising from the bastardising a piece of B&O history, (I would need to go to confession to clear my conscience!)  how did the Philips speakers sound?

Apart from the ideological issues arising from the bastardising a piece of B&O history, (I would need to go to confession to clear my conscience!)  how did the Philips speakers sound?