[Dillen]

Oh, I agree that looks horrible. It would be difficult to restore back.

Beocenter 4600 and Beocenter 7002 use different tonearms. The one in your photo could be
from a Beocenter 4600.
Which one do you need, – I could look in the dungeons for the right part.

Martin

[Dillen]

That’s not antiskating. It’s the tracking force setting.
It’s something you would normally not take apart. Originally, it was sold only as a complete assembly and, unless you are a really skilled DIY’er, I would recommend you replace it as such.

Martin

[Dillen]

And use ESD-protection!
These things are highly sensitive to static electricity.
Many owners experience that new lasers don’t work, – and while it is correct that
many asian “counterfeits” won’t work, or only work for a few hours, many lasers
are damaged by static electricity, – either during shipping, if shipped without
shorting clamp and/or ESD-shielding or by handling without taking
proper ESD-precautions.
I have seen many of both cases.

Martin

[Dillen]

There can be many reasons.
A photo or two would help us diagnose the issue.

Martin

[Dillen]

The belt will not be the problem then.
I suggest you add a small drop of oil to the motor bearing. Usually, the outer (visible) bearing will dry out before the inner, and it’s also the outer bearing that takes most
of the sideways load, so I would start there.
A little sinter/spindle oil would be the choice.

Martin

[Dillen]

What “special lubricant” did you use?

Martin

[Dillen]

You can be sure to find the correct part here:
https://www.beoparts-shop.com/product-category/beogram/beogram-rx2/

Martin

[Dillen]

It can be the idler wheel. A short production run of wheels was completed, and some
were already sold, before it was discovered, that the rubber compound wasn’t quite
as homogenic as it should have been from the raw material supplier.
Production was of course halted, and most buyers who potentially could have been affected, were contacted directly.
Luckily, the majority reported no problems but a few had issues as you describe.
I cannot say if the wheel you sit with is one from this batch, – but it could be.
If the wheel is indeed the problem, I suggest you contact the shop. They will have a solution.

Martin

[Dillen]

Is the tape under a hinged lid on top or in a drawer coming out the front?

Martin

[Dillen]

Does it click on and off and play as it should?

Martin

[Dillen]

Since this is a single-supply amplifier, apprx 50% of VCC is to be expected on the output rail – with respect to ground.
(Hence the need for an output series capacitor).

Martin

[Dillen]

28V across R491? That resistor is no more.

I am referring to all electrolytic capacitors in the output stage, and also in the preamp for that matter.
= All electrolytics on the board.

Martin

[Dillen]

The idle current should be expected to be around 7,5-15mV or something within that range.
The service manual will specify what’s correct for your model.
But the idle current is not the primary problem in your amplifier. If it’s wrong, it’s because something else is amiss.

Which resistor are you measuring across?

Martin

[Dillen]

Wumpi wrote:

So should I measure volt from the resistor from tr49 emmiter and with ohm law to adjust the current?

Sounds right. But the idle current is not the problem in your case.
You will have to find and correct the problem first.

Martin

[Dillen]

Mark-sf wrote:

The 250-ohm trimmer and TR45 governs how much no load bias is applied to each base. It is mounted on the heat sink to sense temperature and also adjust the bias. It’s possible that transister is bad or the adjustment is too high. The circuit calls for a BC311 and since the bias is not separately adjustable for its BC310 mate its possible that your BC161 is a poor match. Sorry, but its been too many years since I worked on one of these.

TR45 is usually a small BC183 or such.
TR44/47 does not have to be matched, as they see the same current flow regardless (more or less – in a working circuit).
Even the output transistors doesn’t have to be exactly matched, really.
The above also goes for them, and their emitter resistors will compensate a little for minor differences in hFe as well.

But the problem in this case is of a different scale.
A DC reading in a “controlled” environment (variac and a couple of multimeters) on the output rail would tell something. As would DC-readings
on the driver transistors.

Replacing components just to see if they burn, will not help in any way.
You need to find out what is really going on.

Martin

[Dillen]

Mark-sf wrote:

The base of TR45 should be adjusted to 27.2

– No.
You adjust the idle current to a given current flow at the output stage emitter resistors as stated and shown in the manual.
The voltages stated in the schematics are not for alignment purposes.
They are merely to help diagnosing in that you can see if a voltage is far off.

In a working circuit, the voltage(s) stated at TR45 will change with temperature, as will the voltages stated later in the circuit, because that is what
the circuit is built to do.
TR45 measures the temperature on the cooling fin and adjusts the final
output stages accordingly.
A transistors amplification increases with temperature, so if nothing grabs
and controls it, it would run astray until something starts burning.
That’s also why idle currents always are to be set with the amp (output stage/cooling fins) at room temp.

Martin

[Dillen]

Don’t get me wrong, it may sound harsh but I mean this in the best of ways when I say that
I have a feeling that you will not be the right person to do this repair.
Your methods will only bring more headache, and it appears your electronic education and experience is limited. Right?

Every educated electronic technician will know what the emitter resistors are and how to
measure idle currents.
The manual may state a mA figure, which is and refers to the actual current,
but a brief look at the emitter resistors value and a little bit of Ohms law will
allow you to measure the current through a resistor as a voltage across it, and
as an added bonus you can measure it without disturbing the circuit by lifting components.
You only need to take the top cover off to measure and adjust.

And I wasn’t referring to the output series capacitors. I was referring to the capacitors
in the output stage itself, as that is where the problem is.
They must be replaced, and it’s good advice to never fit low-ESR types in a circuit like this.

Output stages like this can give even trained tech people a good run for their money.

Martin

[Dillen]

Stop swapping components. It will only up the risk of more trouble.
The idle current settings and measuring ponts are given in the service manual.
It’s a voltage measured across the emitter resistors with no speakers attached and volume at zero (hence the term idle current).
7,5 mV if I remember correctly – see the manual.
But if a transistor burns, there is something else wrong – the burning transistor is not the reason.
And if you replace one or more semiconductors in an output stage, you MUST set the idle current again at first power up.
Bring the Beomaster up slowly on a variac while monitoring the idle current – power down immediately if something looks wrong.

Did you replace the electrolytic capacitors in the output stage? If you did, did you fit low-ESR types? You shouldn’t, as that will often be asking for trouble.

Martin

[Dillen]

Where are you?

Martin

[Dillen]

Actually, both are correct.
Early Beocenter 3300s have the platter from Beogram 2200/2400 etc.
Later the one from Beogram 2202/2402 was fitted, – and it has the extra black weight strip
underneath.
The later and heavier one has marginally better specs.

Martin

[Author]

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