My new-to-me Beomaster 4000 looks good, sounds very good, the only fault so far (and I haven't looked hard yet!) is that the main tuning slide/cursor doesn't seem to be connected to anything. The presets work well (fiddly) but the main tuning control just slides back & forth.

I'm tempted to leave it alone (after grim experiences re-threading the volume control display on a Beomaster 6000 in the past) but it seems a shame to have a prominent control on the front panel which is just an ornament!

Does anyone have any advice... the service manual doesn't show any cords or tensioning springs as far as I can see.

Adam K, London.

There is a dial string but it's usually OK.
The common fault is the tuning slider breaking off one or two of its tabs at the back. The tabs that grip
the dial string.
If one or two of the original three tabs are still good, you can simply glue the dial string to the remaining
tab(s). Make sure to have the slider aligned according to frequency - tune in to a station with a known frequency by
pulling the string by hand and place the slider accordingly.

Martin

Thanks. Having looked inside, there is no string... so this clearly isn't a new fault. Is the string on a spring with a single turn around the drum?

Yes, and around two small wheels apprx 15cm apart.

This is the same thing from a Beomaster 3000, it's very similar to your Beomaster 4000.
You can actually see glue remains on the string from a previous repair:

Martin

Thanks, the picture made the repair much easier, but unfortunately it stll doesn't change tuning - presumably why the previous owner removed the string.

It's permanently on about 105kHz, the top of the band (mine only shows 104 on the cursor - I also wondered if I could increase the range to 108 with a different resistor?). I presume that the variable resistor has gone open circuit on the wiper arm; it doesn't look like any of the usual rheostats stocked by local suppliers - are they still available?

I agree, it sounds as if a lead or a solder tag has broken off the tuning potentiometer it something broke inside.
I may be able to find some good used parts if you need.
Will it tune correctly if you use the FM presets (small fingerwheels) ?

Martin

Yes, the presets all tune well, so I don't really have to have the main tuning... but it annoys me to have a main cursor which doesn't do anything!

Any thought about extending the tuning range above 104MHz - would adding a small resistor before the rheostat (perhaps on one of the presets?) move the whole range upwards? I realise that the tuning scale numbers would be wrong.

As I have a BM 901 coming, I'm very interested in the above 104 Mhz.

I have now checked the tuning potentiometer solder connections, all looked fine but I 'refreshed' them anyway. The tuning potentiometer shows resistance on my meter, with variation as expected between the centre and end tags as it is turned, so it is therefore behaving properly. Since that left the 0,47mcF electrolytic capacitor between the centre tag and the earth 'bar', I have changed that, too.

Tuning is still 'stuck' at about 105MHz - top of the dial. The small presets still work; as all the tuning buttons are effectively in parallel, individually brought into circuit as required, I suppose that leaves only the switch to check.

Is my logic correct? Have I missed something obvious? Or not so obvious?

All advice gratefully received...

Sounds reasonable.
There are also one or two trimmers (small board mounted potentiometers) on the
long switch PCB, almost right below the large tuning potentiometer pulley.
(They may be accessible from the underside - I don't remember)
One of them could be bad due to oxidation and/or loss of slider tension.
Worth checking.

Martin

Have you checked that the tuning pot is supplied with the correct voltage? I suppose it is hooked up as a voltage divider.

Preset potentiometers were indeed a mess - actually the 'preset' one (10kOhms) was salvageable, the FM one (50kOhms) was open circuit. An equivalent was fitted (not a cosmetic or size match, but all that was available). I can't understand from the circuit why the potentiometers are different values, or indeed why there is a separate one for the FM circuit as all the presets and the FM circuit are effectively similar, parallel circuits.

Remaining problems: the preset circuit will adjust to the 4,5v tuning voltage (with the preset tuner set to just below 88MHz) but the FM voltage will not go above about 3,5v. Thus the tuning is inaccurate and doesn't cover the full range... and there is a loud 'buzz' between stations, too.

Time to take it all apart & start again.

If your Beomaster still has the black square rectifier in the corner of the tuning board, I suggest you replace it.
They will almost always be faulty and sometimes even falling apart physically.
Note the pinout and twist the pins of a modern replacement to fit.
Replace the 470uF cap next to it as well, it's almost guaranteed to have a bulge outwards.

Will the presets (fingerwheels) cover the full range ?

Martin

The rectifier & adjacent capacitor both look (physically) fine but I will check them & try to find replacements.

The frustrating part is that the presets cover the full range - the main FM tuning is the problem. And I didn't have the 'buzz' between station before I started - I think I have mis-wired or disconnected a 'ground' somewhere. I'll take it all apart & start again.

There are small wire "leads" from the tuning board to the board with the switches.
Depending on the version, these will be either short flexible leads (good) or one-core stiff leads (bad).
The solder joints will often crack at the tuning board with the latter.
Same issue at the connections from the tuning board to the FM frontend casing.

Martin

kimberley:

I can't understand from the circuit why the potentiometers are different values

If they're connected as voltage dividers, the resistance value isn't critical. Maybe they just used what they had a good supply of?