Beovision 4402 (20AX Chassis)
26th August 2008
This old set still produced an outstanding picture but every now and then it would shut down, perhaps only for a fraction of a second, before resuming normal operation. Dry joints and poor soldering were not the reason on this occasion so a new EHT cable was tried. This also failed to clear the fault which after many more hours was traced to a defective standby relay. The contacts were so burned that they only just touched, a modern replacement provided a complete cure. [Beovision 4402]
Beomaster 2400
26th August 2008
The left hand channel of the FM tuner section of this receiver was initially silent but eventually gave weak, distorted output if the set was left switched on. As the tape input worked normally the amplifier section was deemed to be in good working order and attention focussed instead on the stereo decoder. The decoder chip IC2 was replaced but this made no difference, the faulty component being the coupling capacitor C201. A small leak had biased the following transistor into full conduction, removing the signal. The high value of the biasing resistors for the transistor’s base clearly makes this stage very sensitive to any leaks in the coupling capacitors. The equivalent capacitor in the right channel is C301. [Beomaster 2400]
Beovision 6000
26th August 2008
If a replacement EHT tripler is required for this model (or any of the others that share the same chassis) it is useful to know that the same type is used in the Philips KT3 chassis, a much more popular design that was also made more recently. [Beovision 6000]
Beocord 5500
26th August 2008
This cassette recorder would play normally for up to ten minutes at a time before shutting down, necessitating the interruption of the mains supply to unlock the keypad so that operation could continue. This strange activity was due to the protection circuit operating, this stops the recorder if excessive current flows into the deck motors and solenoids. A long and protracted series of measurements proved that the reel motor circuit was the one that was triggering the overload condition but both the L272 motor drive IC and the reel motor itself proved blameless. Oscilloscope checks showed that the output voltage of the IC was unstable, resulting in it attempting to drive the reel motor in two directions at once. This of course resulted in an excessive current being drawn, operating the protection circuit.
The datasheet for the L272 shows that when the device is used as a linear amplifier it is advisable to include a small filter network from the outputs to ground consisting of a 220nF capacitor in series with a 1R resistor. Adding these components to the Beocord 5500 circuit resulted in completely reliable operation, one wonders why the designers did not include them from new? [Beocord 5500]
Beovision 8802 (77XX chassis)
25th August 2008
Whenever a set like this is serviced it is a good idea to remove the IF unit from the tuner panel and make a thorough inspection of all the soldered joints. Symptoms range from no picture or sound to erratic search tuning, loss of luminance and general instability. Later versions of the previous 33XX chassis use a similar unit which should also be inspected whenever the opportunity arises. [Beovision 8802]
Beocenter 7000
25th August 2008
The turntable of this music centre would only turn if the “turn” key was kept pressed. Pressing “33” or “45” would activate the solenoid but as the motor did not start the mechanism could not engage. What seemed like a complicated fault turned out to have a simple cause, the motor contacts, which are part of the solenoid assembly 15RL1, were so tarnished that they could not pass sufficient current to run the motor. Cleaning and resetting them provided a complete cure. [Beocenter 7000]
Beomaster 901
25th August 2008
This receiver worked normally except that FM reception was always in mono (green light off) despite a strong aerial signal being applied. A fault in the stereo decoder was suspected but measurements showed that the second transistor 2TR9 was biased off as the stereo gate transistor 2TR15 had only 0.4V on its base and so was not being turned on. The stereo gate is signal strength sensitive so attention returned to the tuner and IF sections. As the tuner AGC line behaved normally the front end and early stages were cleared of blame, leaving the detector driver IC 2IC1 as the chief suspect. This proved to be correct and a replacement restored normal operation. [Beomaster 901]
Beocord VHS 63
25th August 2008
If the fault is no sound, before delving in too deeply check the capacitors on the sound panel (mounted vertically immediately behind the deck). If the blue metal Philips types are fitted it is highly probable that one of the 330uF ones has gone short circuit. No other damage seems to result from this however. [Beocord VHS 63]
Beomaster 2200
25th August 2008
The fault was low and distorted sound on FM, all other functions being normal. The MC1310 stereo decoder IC was defective, replacement restored the normally excellent sound quality of which this model is capable of. [Beomaster 2200]
Beomaster 6000
20th August 2008
No output from the right channel on either set of loudspeaker sockets was reported. Audio signals were present at the input of the power amplifier but the output transistors and their emitter resistors were OK. Careful measurements revealed that transistor TR107 (BF423) was open circuit, fortunately this had not caused any further damage in what can be a very fragile circuit. While the power amplifier was on the bench new pre-set potentiometers were also fitted and set up as per the manual, this can help make the set more reliable. [Beomaster 6000]