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Old 2nd Mar 2018, 1:30 pm   #5
GeoffK
Heptode
 
Join Date: Mar 2016
Location: Essex, UK.
Posts: 602
Default Re: Akkord Pinguin U60

If you take voltage readings of the transistors and get nearly battery voltage of minus 6 Volts at the collectors of T2, T3, T4 and a volt drop of around 300mV between the base and emitters it is reasonable to say the transistors are working, (along with a foward/reverse ‘diode’ junction check with power turned off) as far as their DC condition is concerned. If you are getting a tone through T2 then it must also be amplified by T3 if you can hear the audio tone. The audio tone from the base of T3 should be louder than the audio tone at T4 and the detector diode. But you need to find out if T2 is oscillating on the AM band and that could be down to one of the switches in its base circuit not closing or the switch associated with L4 the oscillator coil. C21 C22 C23 are the coupling capacitors around the oscillator stage. The switches although complex can be broken down into stages one switch bank at a time and comparing with the schematic, print off a copy and mark each switch off as it is checked, this can be done with the power off and a resistance check either at the switch contacts or where the switch is meant to connect. For example the LW (tag 58,59) and MW (tag 51,52) aerial coil (L8,L6 secondary) switch, in turn, go to C21 and the switch to L4 should then close (tag 20, 21 on my schematic). In the schematic the switches are shown set to FM, the MW LW ferrite aerial is open circuit and L4 the oscillator coil is shorted by tags 21,22. T2 then acts as FM first FM IF amplifier via switch tags 17,18 in T2 collector.
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