AE 5800
Service Information to Discriminator- Modifications of AE 5290 and similar
CB radios (August, 2, 2007)
Problem: During hot summer temperature periods (40°C and more) in car installations, the
receiving audio in FM is reduced until nothing can be understood any more.
Reason at AE 5290:
Recently produced 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.
Solutions: There are two possible ways for improvements:
a) changing the filter: Open the radio and delete the discriminator filter with the white
coloured core
and replace the filter by an improved type, 27- 8128 or ST 435 with dark grey core.
Alternative solution instead of changing the filter:
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:
The parts can be SMD or conventional parts (if well insulated and carefully placed)
Re-Alignment of the FM Discriminator:
In case of changing the filter to filter type 27-8128, which are pre-tuned when shipped by us, a
re-alignment may not be necessary in most cases.
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:
Up to now, the new filter types have not been used in these models. But it is also possible to
add the capacitor and the resistor in the same way as described for AE 5290 to improve the
temperature effect.
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