R605 is high, but it is not likely to cause any significant problems. R606
and R607 are effectively paralleled in circuit because of the low
resistance of the 6.3V winding on T601, so the measured value is
reasonable. (Basic circuit theory here for combining discrete circuit
elements: Requivalent = R1*R2/(R1+R2) = 100*100/200 = 100/2 = 50 ).
With V20 and V634 removed, you can get readings of the 500V bus at D612 or
either side of R626. Be sure to follow the advice others have given before
about making sure the charge on this bus has dissipated before contacting
it. Regardless of whether or not the tubes are still installed, you should
see the resistance to ground steadily climb until reaches about 300k (more
if you're on the far side of R626). If it is less than that something's not
right, probably with C611/C612, D611/D612, or R611/R612.
The +85V bus can be measured at the socket of V659. If you look at the back
of the socket, you will see only three pins are actually connected. Two are
tied together; these are pins 1 and 5 and are the +85V bus. If you look
closely, you will see pin 2 is the only other connected pin, and it is tied
straight to the chassis ground.
A variac lets you do several things. The manual is showing it used to
adjust the input line voltage to exactly 117VAC for the purpose of precise
measurements or calibration. But the variac is also a useful
troubleshooting tool. It allows you to ramp up the voltage slowly, and do
sanity checks along the way. For example, if you have a failing filter
capacitor such as C611 or C612, you could use the variac to supply only 10%
of the nominal supply voltage and expect to see 10% of the expected no-load
output voltage on the +500V bus. At this point, leaky capacitors wouldn't
be stressed as much because they're not near their rated voltage. You can
expect the +500V bus (with V620 and V634 removed) to linearly track the
variac setting. If you observe a non-linearity, then it's possible that the
diodes or capacitors are leaking at higher voltages.
Keep in mind also that the GFCI only protects you on the input side of the
T601 power transformer. It's like wearing a helmet - it makes what you're
doing safer, but you shouldn't expect it to make you completely safe. The
+500V supply will still kill you even with the GFCI.
On Thu, Apr 13, 2017 at 12:09 AM, enchanter464@... [TekScopes] <