AVO EA113 dead

[perdrix]

I replaced the batteries and confirmed that volts were getting to both rails of the DC amplifier.   A bit puzzled that the input to the DC amp appears to be AC coupled (C1 to base of VT2)!!??   Update I worked it out - see PS at the end)

I was getting no meter reading in either of the battery test positions of Switch C.   I spent quite a while going round in ever diminishing circles, but then discovered that when I pressed the "Reverse" button the meter moved negative.

Thinks - maybe exercising the "Reverse" button a few times might help. Bingo!  After about five or six press/release cycles I got a full scale deflection in both battery test positions, and the meter came back to life!

I'm struggling to make sense of Figure 4 in the service manual (not helped by the fact the scan isn't the best).  Does anyone have a really good high resolution scan of that page of the service manual?

For future reference any guidance on debugging these if there are problems would be most helpful.

PS VT1 works as a DC chopper driven by the multi-vibrator comprising VT9 and VT10 and then VT4 demodulates the chopped DC.

Thank you, David