Albrecht AE 5090 New, AE 4200 MC Service Manual

Service Information to Discriminator- Modifications of AE 5090 , AE 5290

and similar CB radios (August, 29, 2007)

Problem:

receiving audio in FM is reduced until nothing can be understood any more.

During hot summer temperature periods (40°C and more) in car installations, the

Reason:

radios may have a discriminator
coil (type ST435) with white
coloured core, which is not
optimised in the present circuit,
while the circuit is optimised for a
former filter version with ferrite
cores in dark grey colour.
In the photos, You see the filter
type with the white painted core.

Recently produced

Solution:
b) adding parts to optimise the circuit with existing filters

Add a capacitor 390 pF between PIN 4 and 5 and a resistor 47 kOhm between PIN 5 and 6 of
the FM discriminator IC as indicated here: This photo shows AE 5290, but in AE 5090 it is
possible in a similar way, too:

The parts can be SMD or conventional parts (if well insulated and carefully placed)
In AE 5290 the parts should be SMD type, in AE 5090, where there is more space, the parts
can be conventional parts.

Re-Alignment of the FM Discriminator:

Please check the receiving audio quality and volume with a distant station. Set the volume
knob to moderate receiving volume. Ask a distant station to talk continuously and tune the coil
carefully to maximum obtainable speaker volume at best receiving quality of the distant station.

If a modulated signal generator for the exact operating frequency is available, the alignment
will be more precise.
Select an output level of 1-2 µV, modulated with 1 kHz audio and a test deviation of 1.5 kHz.
Align the coil to maximum audio output volume point at best sound.
It is recommended to use an oscilloscope connected to the speaker output to watch the wave
form, or connect a SINAD meter with psophometric CCITT filter enabled . You should obtain a
SINAD of 20 dB or better at 2 µV EMF and about 30 dB or better at larger input signals.

Other models like AE 5090, AE 485 S and AE 5800:

It is also possible that recent production lots of these radio may use the same white coloured
core in the discriminator filter which had been described at the AE 5290 model.
Add the capacitor and the resistor in the same way as described for AE 5290 to improve the
temperature effect.