Got home today to find a very nice Beogram 4002 waiting for me. Bought it on Ebay as faulty, the seller said the arm got to the end of a record  and would not return. My first thought was that the small belt for the arm had snapped. This was not the case. When I press << the arm moves left at the correct speed, until it get to the end of it's travel. Although the motor is still running. Also noticed that as it is moving, if I press >>. It does not stop, but will slow down quite a lot. Any help appreciated as always.

Craig

Hi Craig,

Does this example use a bulb in the arm position detection circuit by any chance?

Is this the IR one inside? If so, I don't think mine is working. Checked it last night with digital camera.

Craig

Check the transistors in the H-bridge.

Martin

Dillen:

Check the transistors in the H-bridge.

Martin

Can you supply these and any other parts, should I need them? What about the little I.R. thing which seems dead?

Craig

Craig

The transistors are very common modern BC550 NPN, BC560 PNP or the BC639 for high current applications, and can be sourced at any quality electronics store. You do not need the original spec metal cans.

Check this article, section 7 B&O BeoGram 4002, 6000 Turntable Restoration Repair

Of course, you should be sure that all existing capacitors are OK (which they are generally not), before replacing the transistors.

The H bridge is 1TR24 thru 1TR31. I used hFe matched transistors throughout.

Menahem

Yes, I have correct transistors if you need.
I see absolutely no need for hFe matching of any of these transistors - why would you ?

Martin

The 2 identical circuits are staring at each other on either side of the motor, and I want the exact same voltage in both directions.

It's my perfectionist attitude again ;-)

The current is the same as it is a series circuit, regardless of the direction and there
are other components in the controlling circuit (before amplification !) that will possibly
cause greater "disturbance" than non-matched hFe transistors.
The two "sides" of the H-bridge are not controlled the same way anyways and there
are trimmers provided to adjust the desired speed in both directions.

Menahem likes to measure transistors, that's fine. But it is far from needed in this circuit.
What was that about the dead IR ?

Martin