Beogram 4002

16th June 2013

In this early version of the Beogram 4002 (AC motor type) the arm would move across when “Play” was selected and stop in the correct position but would then not lower onto the record. After ensuring that the linkage was not seized, attention was turned to the drive circuit for the magnet coil 0RL1. 22V was present at the collector of 0TR4 (TIP41A) and 1R60 was overheating badly. These two observations pointed towards 0TR1 being open circuit, which it proved to be. A replacement returned the cueing system to normal functioning. [Beogram 4002, Beogram 6000]

Beomaster 6000 4channel

16th June 2013

When switching this receiver on the display for the sound functions illuminated but no sources could be selected and the outputs were silent. The only control which functioned was the standby key, which worked correctly. The +18V supply was found to be low at +0.8V and the -5V supply high at -22V, with 5TR2 (BC119) overheating. This suggested that there was a short circuit across the +18V supply somewhere, with a resistance of only 35 ohms being measured accross the collector and emitter of 5TR2. Disconnecting the +18V feeds to the various PCBs narrowed the area of interest down to PCB8, where 8C24 (4.7uF) was found to be short circuit. A replacement restored normal operation, surprisingly the power supply regulator circuit had not been damaged by this fault. [Beomaster 6000 4channel]

Beomaster 1100

28th April 2013

This receiver suffered from low sensitivity on the FM band, with only strong stations being able to activate the stereo decoder and weak ones vanishing altogether. 2IC1 (TBA460) can be responsible for these symptoms but a replacement made no difference, so low output from the front end unit was suspected. On investigation, 1TR1 and 1TR2 (TIS88A) proved to be defective. Since these transistors are both fragile and difficult to obtain the decision was made to replace both of them with a single more modern dual-gate device, in this case a BF998 (as used in the Beomaster 5500, Beocenter 9000 and derrived types). With 1TR1 and 1TR2 removed, the BF998 was mounted on the print-side of PCB1, elevated from the surface by attaching the source connection (the largest of the tabs) to the non-grounded end of 1C4. Short lengths of fine wire were then used to connect the drain to the junction of 1C5, 1C6 and 1L2, the first gate (G1) to the junction of 1C1, 1D1 and 1L1 and the second gate (G2) to the junction of 1C3 and 1R2. Since the gain of the BF998 is much greater than the pair of TIS88As it is also necessary to change the value of 1R3 from 100R to 2K2 to avoid instability.

The modification proved successful but having completed it, it is advantageous to trim 1L1, 1C1, 1L2 and 1C6. This can be done without an RF generator if a strong aerial signal from a properly matched source is availalbe. The procedure is to connect a DC voltmeter to the AGC terminal of the front end unit (e.g. at 0C3) and to make the following adjustments using an appropriate non-metallic trimming tool, do not adjust any other items:

1) Tune to a strong signal around 88 MHz and adjust 1L1 for a minimum reading on the meter
2) Tune to a strong signal around 104 MHz and adjust 1C1 for a minimum reading on the meter
3) Repeat these steps a few times for optimum results
4) Tune to a strong signal around 88 MHz and adjust 1L2 for a minimum reading on the meter
5) Tune to a strong signal around 104 MHz and adjust 1C1 for a minimum reading on the meter
6) Repeat these steps a few times for optimum results

If executed with care, this repair yields results which are at least as good as those obtainable from the original design, which was known to be of exceptional quality. Similar front end units can be found in many of the Beomaster and Beocenter models of the 1970s, typically those with pre-set stations on FM. Different component references will be found on the circuit diagrams for the other models, but otherwise this modification is applicable to all similar types. [Beomaster 1100]

Beomaster 900K

20th December 2012

Weak operation of the stereo indicator lamp if an FM stereo decoder is fitted is a common problem with these models due to the poor current gain of the original circuit. Matters can be greatly improved by adding an extra BD135 transistor which is easily mounted on the noval plug that connects the decoder to the main chassis. Disconnect the purple wire from pin 7 of the plug and connect this to the base of the BD135, then connect the emitter to the now vacant pin 7 of the plug and the collector to pin 6. A 100nF 63V ceramic capacitor should also be connected across pins 6 and 7. If the indicator still performs poorly check the existing driver transistor AC128I (AC128) for leakage and broken connections (it is easily damaged if the amplifier panel is opened carelessly) and the alignment of the decoder. [Beomaster 900K, Beomaster 900M, Beomaster 900RG]

Beogram 2402

24th November 2012

A Beogram 2402 was reported to have always needed its speed tuning control to be set on the positive side to obtain the correct speed (on both 33 and 45 RPM) but this was now no longer sufficient after a few records had been played. Checking the voltage at the output 12V regulator (0IC1, 7812) showed the correct 12V but there was excessive AC ripple present at the input. 1C1, (1000uF) was the first suspect and when it was replaced it was possible to centre the speed tuning control using 1R7 33 and 1R9 45. The turntable speed stayed constant after this. During testing it was found that the front panel switches were intermittent, polishing the contacts cured this fault. [Beogram 2402] (submitted by Mike Phelan)

Beocord 9000 (Original Version)

24th November 2012

Dull sound when using Dolby noise reduction is usually due to misadjusted playback level or the use of unsuitable cassettes. However, in this case it was due to dead spots having formed on the P.B. Matching pre-set controls 2R141 and 2R241. An application of contact cleaner and a few rotations of each control cleared the dead spots and then the adjustments were re-made as per the procedure in the service manual. If the manual is not available then noting the initial positions of the controls and returning them as accurately as possible after cleaning should give approximately correct results. The Rec. Matching pre-set controls 2R142 and 2R242 should be dealt with in a similar manner at the same time. These components are not present in the later version of this model. [Beocord 9000]

Beomaster 5000

18th November 2012

Random problems with the microcomputer section of these receivers such as loss of displays or front panel functions, starting on maximum volume, loss of pre-tuned stations etc. is most often due to a fault in the reset circuits for the microcomputer and is normally resolved by replacing 4C59 (33uF, replace with 47uF), 4C65 and 4C68 (both 100uF). On one occasion this failed to cure the problem and in addition when first powered, the set would not show the standby indicator and the standby relay clicked on and off at roughly one second intervals for about 10 cycles. The 5V supply was present but the 13V supply from which it is derived was low at 10.5V with heavy 100Hz AC ripple present. This pointed towards 2C13 (4700uF) being open circuit and on replacing this component the receiver once again worked normally. [Beomaster 5000]

Beolab Penta 3

18th November 2012

This active loudspeaker gave normal results when playing but when the main system was switched off the indicator lamp at the base was sometimes observed to be glowing orange instead of the normal red. Since an orange light here indicates a fault (normally overheating or excessive DC at the output of the amplifier) the symptoms were investigated. Nothing could be found amiss except that even in “off” mode a small voltage drop was still present across the standby relay coil 4RL1. Since this same point also controls the driver transistor 2TR4 (BC557B) for the green section of the indicator lamp this was clearly the reason for the orange light. The relay control transistor 2TR3 (BC337-40) had a small and varying amount of bias present at its base but this was not coming from the preceding stage; instead 2TR3 was found to have had an internal c-b leak. A replacement transistor cured the fault. [Beolab Penta 3]

Beomaster 5000

31st August 2012

If strong FM radio stations give only mono reception (green ‘locked’ indicator illuminated but the green ‘stereo’ indicator out) the first component to suspect is the stereo decoder chip 1IC4 (TDA4500A). However, before replacing this it is worth gently adjusting the oscillator control 1R82 in both directions as this may restore stereo reception. If the stereo indicator then lights an approximate setting for the control can be determined by connecting and disconnecting the antenna whist noting which position of 1R82 gives the most rapid and reliable “lock”. The service manual gives a more accurate method if instruments are available. Note the position of 1R82 before commencing so that it can be returned to it if indeed 1IC4 turns out to be faulty. [Beomaster 5000]

Beocord 2000

31st August 2012

It is not unusual to find that the belts in any of the 1980s Beocord cassette decks (and their Beocenter equivalents) have deteriorated to a point where they stretch easily and become entangled in the mechanism. This can sometimes stall the motor, which will burn out if left in this condition. Having replaced both the belts and the motor in a Beocord 2000 it was noticed that although the machine played well and at the correct speed the Advance and Return were sluggish, with the tape slowing down considerably after the first few seconds of operation. It was found that in normal playback the motor voltage was slightly low at just under 12V (it should be 14.8V) and that this fell to 8.5V after a few seconds of winding. The cause was 1R8 (4.7R, safety type) which was open circuit, leaving the motor to be supplied only via 1R9 and the B-E junction of 1TR4 from the 15.5V supply rail. A replacement resistor cured the fault, the original must have failed when the original motor was stalled. Note that the Beocord 3300 uses an identical circuit with the same component reference numbers and values. [Beocord 2000, Beocord 3300]