Hi,

There are quite a few Beogram 4000 repair threads here on the forum.  It is a great turntable. However, it is almost 50 years old!  That being the case it really needs a complete going over.  That early Bang & Olufsen linear tracking turntable was their first of that kind and has an early analog control system. It also, surprisingly, has some early logic (AND, NAND) gates to go along with several physical sensor switches that the control system depends on to know what the motors are supposed to be doing. A failure in one or more of those sensors is most likely the cause of your problem. 

The problem could be as simple as a mechanical switch being out of position. The bad thing about buying a used Beogram 4000 that you know nothing about its ownership history is you don't know what other people may have done to it. That is why a complete going over of the unit by someone experienced in these is a must if you intend on having a perfectly working Beogram 4000.

-sonavor

Thank´s,

it seem´s that´s some command that tell to the motor to rotate in fast speed to left direction, maybe some leaky transistor?!

The most common problems are old deteriorated electrolytic capacitors (and tantalum capacitors), connections, solder joints, power supply problems and mechanical mis-adjustments.

A restoration process usually begins with changing out the old capacitors and rechecking the Beogram. The first thing to check is that the power supply is providing the expected voltages to everything it supports. Once that it is working the restoration moves on to basic functional tests which can involve more electrical work. But always suspect a bad connection first before looking at components like transistors, diodes or integrated circuits. On the Beogram 4000 there are also a couple of optical sensors. One in the fixed arm and one in the tangential arm base (for the record tracking). The signal from those sensors should be checked at some point. If all of the electrical components (and their voltages) test out okay then you can work on the mechanical position of sensor (switches). When the control function of the Beogram is working again you will need to go through the service manual mechanical adjustments for the platter and tonearm. 

-sonavor

Problem solved after 3 hard weeks.

The problem was it was on 1TR28 and 1TR29, for further users with same problem, I've changed 1TR30 and 1TR31 either.

Meanwhile I bought another B4000 completely off for parts, but I've changed my mind and I'm working on him, is working at 85%, just need to solve one problem with the detection sensor, the arm always stop at the edge of a 12" l.p. and play from there, if I put a single l.p. (45rpm) the arm lows as I got a 12", but I'll solve that with patients. 

Many thanks to Sonavor for the helping comments here and by email (beolover)

Regards to all.

Problem solved after 3 hard weeks.

The problem was it was on 1TR28 and 1TR29, for further users with same problem, I've changed 1TR30 and 1TR31 either.

Meanwhile I bought another B4000 completely off for parts, but I've changed my mind and I'm working on him, is working at 85%, just need to solve one problem with the detection sensor, the arm always stop at the edge of a 12" l.p. and play from there, if I put a single l.p. (45rpm) the arm lows as I got a 12", but I'll solve that with patients. 

Many thanks to Sonavor for the helping comments here and by email (beolover)

Regards to all.

Hugo

Does the tone arm continue to drive into the centre of the platter when there is no L.P present, or does it still attempt to lower as if a L.P was present?

Craig

Hi Craig,

it attempt always to lower as it was there a LP.
I will change this night probably the OTR4, that seems that could be at short circuit, i have not measure him without connection, i prefer to do that with another Transistor to change if it´s the case.
I took apart  the sensor arm and the photo-sensor is working.
Se, i´m not from electronic, because of that i take more time to understand all the schematic of each process.

Regards
Hugo 

Hugo

How did you test the photo-sensor? do you have an oscilloscope you can use to test the signals....

Craig

No, for the moment i just measure the answer with different light intensity, and i notice that e give an resistance  answer. Probably doesn´t  not completely mislead.