Beocord 8004

23rd May 2014

All the mechanical functions of this cassette deck worked but there was no sound and the PPM display was blank. Recordings could bot be made either, and it was soon discovered that the 7V bias supply was absent from pin 5 of both Dolby NR processor ICs 2IC101 and 2IC201. The cause was 2C3 (220uF 10V) which was short circuit. This is a common fault with the smaller Beocord models (Beocord 4500 etc) but is is seldom encountered in the larger ones. [Beocord 8004]

Beocord 1700/2200

23rd May 2014

Capacitors 5C1 and 5C4 (both 10uF 16V tant) are inserted wrongly in these machines, correct operation of the headphone amplifier can only be obtained if it is the negative terminal of the capacitors which is connected to the bases of 5TR1 and 5TR2. Note that the circuit diagram is also drawn incorrectly in this respect. It is therefore wise to replace 5C1 and 5C4, fitting the replacements in the reverse direction, if 5TR1 and 5TR2 are found to be overheating and the DC voltages around them are incorrect. Electrolytic types can be used instead of tantalum if necessary.

Hum on both output channels can be due to AC field from the mains transformer being picked up by the power supply regulator. Adding a 10uF 50V capacitor between the base of 2TR23 and a local ground point (e.g. the cathode of 2D3) will eliminate this problem, a similar addition was made in the factory to later examples. [Beocord 1700, Beocord 2200]

Beogram 4000

2nd July 2013

This machine would switch on with the platter rotating and light displays working normally but the arm would not move because the servo motor was not turning. There was no voltage across the motor but each terminal was a +24V, so something was clearly amiss in the tracking circuit. Both 1TR29 and 1TR30 (BC143) had shorted junctions, presumably the failure of one had overloaded the other – replacement cleared the fault with no other components damaged. A BC161 can be used to replace the BC143 if the latter is unavailable. [Beogram 4000]

Beovision MX 4000

23rd June 2013

All was not well in the line output stage of this set, the width was lacking and the set would revert to standby mode after a short period of operation. 3R13 (5.6k) on the tube base panel was found to be burned out and an attempt to operate the horizontal shift switch lead to arcing from inside the switch body. Of a few components which can be responsible for this fault, 4L4 (10mH) was found to have shorted turns, as indicated by a drastically reduced resistance of 3 ohms (around 40 ohms is the correct figure) and 4C105 (560nF) had a bulge in its side. Replacing 4C105, 4L4 and 3R13, as well as cleaning the switch, restored the width and allowed the set to operate normally. The failure of 4C105 probably instigated the fault, a 470nF capacitor was used in this position in some sets. Diodes 3D17 and 3D18 could also be damaged, depending on the position of the horizontal shift switch. [Beovision MX 4000]

Beocenter 7700

16th June 2013

This music centre would only play a cassette for a second or so before returning to stop mode, with the winding functions being similarly affected. Since the tape transport was mechanically in good condition with adequate torque present on both spools the hall sensor 12IC14 was first suspected, but the presence of large pulses at 11P2-6 when the take up spindle was rotated proved that this was not the case. The real cause was 11C15 (10uF 63V) which was leaky, replacing this cured the fault. 11C17 (4.7uF 63V) was also replaced for good measure. [Beocenter 7700]

Beovision MX 7000

16th June 2013

As the Unity 2 chassis sets near the end of their second decade of service some new faults caused by poor soldering are beginning to emerge. Shutting down and returning to standby after a short period of use can be caused by cracked soldered joints on the primary side of the power supply, especially at the legs of the small components around the chopper transistor 4TR1. The components which are most commonly affected appear to the those whose legs are left straight and not stapled over, sometimes it is possible to observe a small arc at this point when the set fails. Resoldering the complete area is the most effective cure. Intermittent loss of signals can often be cured by resoldering all the connections to 38IC3 (TDA8120) on the tuner PCB. Unity 2 chassis sets include the LX 5000, LX 6000, LS 5000, LS 6000, MX 4000, MX 4002, MX 6000, MX 7000, MS 6000 and AV 9000. [Beovision MX 7000]

Beomaster 4000

16th June 2013

No FM reception with all other functions was the fault with this receiver. Faults in the tuner and IF sections of FM receivers are most easily tackled by first checking that the DC conditions around the relevant transistors are correct before getting to involved with the more complex aspects of the circuit, and it was soon found that voltage drop across resistor 63 (1.5k) was negligible and that only a very small voltage was present across resistor 66 (also 1.5k). These two measurements suggested that TR5 (BF194) was open circuit, and a replacement solved the problem. A BF240 or a BF494 make a good replacement for the BF194 in this circuit. The same basic FM stages are also used in the Beomaster 3000, 3000-2 and Beocenter 3500. [Beomaster 3000, Beomaster 3000-2, Beomaster 4000, Beocenter 3500]

Beomaster 3000-2

16th June 2013

Noise on the right hand channel, unaffected by the volume or tone controls, was traced to to TR42 (BC212B) being defective. A BC556 can be used as a replacement if the original parts are not available. [Beomaster 3000-2]

Beovision 5500

16th June 2013

This set would show the red “standby” LED when switched on and the the LED extinguished correctly when either of the programme step keys was pressed but no picture or sound appeared. Since the tube heater was out and the EHT was not present it was clear that the power supply section was not working. There was 330V across 6C7 (220uF) and at the collector of 6TR1 (BU208A) but no drive was present at 6TR1’s base, so attention was turned to PCB7. Here it was found that 7R6 (220R) was getting hot since 7TR3 was turned fully on with 0.7V at its base. 1.4V was measured at pin 11 of 7IC1 (TDA2581) with no drive signal present, so 7IC1 was repalced. This made no difference but as the DC conditions around the stage were otherwise basically correct attention was turned to the electrolytic capacitors in this area. 7C5 (4.7uF), 7C10 (33uF, replace with 47uF as shown in some versions of the diagram), 7C13 (22uF) and 7C15 (4.7uF) measured out of tolerance so in the interests of reliability all were replaced. This restored normal functioning and an excellent picture. [Beovision 33XX series, Beovision 77XX series].

Beovision 8100

16th June 2013

No raster or picture although the tube heater was lit and the EHT present were the symptoms with this set. It was noted that the normal “buzz” could not be heard from the frame coils in the deflection yoke and that the heat sink for 5TR9 and 5TR10 was unusually hot. The cause was 5C33 (2200uF 25V), which was short circuit. This is a very common fault if the four-legged “ROE” type of capacitor is fitted in the 5C33 position. [Beovision 33XX/77XX series]

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