SVT III Pro schematics

[beans-on-toast]

A general comment, the reference voltages are for a specified AC line voltage. In North America, the schematic for this amp indicates 120VAC. Because line voltages vary, a variac can be used to set the voltage at 120VAC and to check it periodically while taking readings.

Ensure that your voltmeter is working properly. For a handheld, that means a good battery.

The first thing to do is to inspect all the ground points and clean them if necessary. On some amps, may involve checking that all the nuts on the pots and jacks are tight. Inspect and reseat the connectors.

 

[okwestern]

Silly me. My Fluke is a true RMS, so my AC readings was way off. I'm not sure if I'm thinking right, but is it only measuring the top half the sine wave? In order to get peak-to-peak, i have to multiply with two and square root of 2? So my 7V reading is in fact 7*2*1.41= 19.74Vp-p (which corresponds with many of my readings)?

Anyway, I used the oscilloscope and the readings gave more sense. However a few AC points on the power amp is still way off (all DC are good, 99-109%).
Point Spec Measured Off?
TP1: 360mV 360mV 100%
TP2: 23V 20,4V 89%
TP3: 23V 20,4V 89%
TP4: 21V 19V 90%
TP5: 20V 19V 95%
TP6: 2V 2,28V 114%
TP7: 20mV 100mV 500%
TP8: 50mV 100mV 200%
TP9: 250mV 290mV 116%
TP10: 250mV 262mV 105%
TP11: 40mV 80mV 200%
TP12: 40mV 80mV 200%
TP13: 20V 22,8V 114%
TP14: 20V 24V 120%

TP7/8/11/12 seems quite horrible. Common with the bad readings are they are a very noisy flat line on the oscilloscope (should be sine). All other points show me either sine or sawtooth according to the schematics.