Re: Hacker Hunter
Morning all, the fault has returned. To recap (if you'll forgive the pun) when the set is switched on it works fine for about 5-10 seconds then the sound rapidly distorts and cuts out altogether. Switching the set on and off repeats the symptoms. If I leave the set on, after a couple of minutes, the sound comes back distorted at first then slowly clears. After that it works normally until after the set has been switched off for 24 hours or so. I have copied the circuit of the AF amplifier and attached it for clarity. The only difference from the Hacker schematic as far as I can see is that on mine R10 is 82R and R11 is 180R whereas on the Hacker schematic both resistors are 150R. To date I have put replacement components in for the following, and refitted the originals because the same fault returned: C10, T6, T3. I have fitted a new RV3 which was faulty. All of the voltages on the transistors were measured close to the spec in the service sheet although I could not measure all of them while the fault was present as the set would start working before I finished measuring! This morning I measured the mid-point voltage (junction of R14 and R15) and it was 8.3v. The service sheet specifies a setting of 8.55v for an 18v supply. My supply is running at 17.7v. However, tweaking the new RV3 (which sets the mid-point voltage) increased the midpoint voltage and sound appeared immediately. Backing off RV3 caused the sound to distort and disappear. The acceptable setting range of RV3 (by which I mean the range over which I could get clear sound) seemed to increase after the set had "warmed up". To my mind this is pointing towards a leaky capacitor reforming? Maybe C8, although I have disconnected one end and reformed it OK on the Avo after which the set worked OK for a few days. Please can I have some advice, as I have just about exhausted my powers of deduction on this?. Cheers, Jerry
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