TELEFUNKEN 711 CHASSIS

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The trouble with this set is bowing at the sides of the raster,
plus slightly too much width. The east-west correction and
width controls have been adjusted as per the service manual,
but the bending at the sides remains — and the width control
has no efect on the width.
There is clearly a fault in the east-west modulator circuit —
the width control sets the bias conditions here. A common
culprit is the bridge coil itself (L564) which tends to overheat,
melting the plastic core and ending up with shorted turns.
Other than this, the east-west output stage can prove
troublesome, with both the transistors (T591 and T592)
breaking down. T591 (BD135) is mounted on a heatsink,
which will remain cold if the transistors have failed. If this is
found to be the case, remove the transistors and check them
with a multimeter to establish what faults are present — the
most common is collector-emitter punch-through in the
BD135. Take care when replacing the BD135 — some sets
have incorrectly marked boards, making it easy to connect its
base wrongly.

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