Re: Hacker Hunter
Hello again. The radio hadn't been used for about 3 days and guess what - the fault has returned. I measured the total current drain from the dc supply while switched to FM with vol at minimum. At switch on when there was brief sound the current was 21mA and when the radio went silent the current only dropped to 20mA. However, under the same conditions the mid-point voltage changed from 9v to 12.6v. Readjusting RV3 brought the voltage back to 8.5v and sound returned but the quiescent current through the output pair had increased to 8mA (should be 3mA). Adjusting RV4 to short circuit would only bring the current down to 4mA. As happened before I couldn't set the midpoint voltage and the quiescent current to 8.55v and 3mA (per service sheet) simultaneously. I could get the set to operate without distortion by setting 6mA and 8.5v. I'm thinking something odd is happening to the output transistors. I have previously tried another AC128 but the fault was still present. I have ordered a replacement AC176 and a full set of new capacitors for the amplifier board. Cheers, jerry
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