failed High Voltage Power Test [resolved]

[Dynakitbuilder]

#2

[Paul Birkeland]

If a lead from power transformer terminal 7 touches a lead from power transformer terminal 8 (on the UF4007s), then you'll short out the high voltage wiring.  To avoid this, pull a little tension into all the diodes at the terminal strips so they stay away from each other.

[Dynakitbuilder]

Separated the diodes, and did the correction @ 35 to 33.  Reheated all connections from 31 to 33U.
Got 24 VDC that slowly went down to 13 VDC +/-.

[Paul Birkeland]

Is your fuse blown?

You absolutely need to use more solder on those 3 lug strips, especially on the lower lugs.

What is the DC voltage between 37 and 39?
What is the DC voltage between 34 and 36?
What is the DC voltage between 31 and 33?

[Dynakitbuilder]

fuse blown - replaced
added solder to all joints, esp lowers
VDC readings on all three points:  0.00 VDC
Obviously, fuse blew again

[Paul Birkeland]

Heat up the solder joint on power transformer terminal 7 and pop the diodes out temporarily, then check to see if the fuse holds and let us know.

It might be a good idea to post some fresh build photos. 

Stuff that causes fuses to pop instantly like this:

1. Backwards diode(s).
2.  Leads from power transformer terminals 7 and 8 touching each other.
3.  Backwards capacitor.
4.  Solder or debris shorting terminals to the chassis that shouldn't be.

Less possible:
1.  Defective diode (very rare, but we can test for this next)
2.  Defective power transformer (if the fuse holds with the diodes disconnected from one end, then the PT is fine)

[Dynakitbuilder]

fuse did NOT blow with diodes on #7 disconnected

[Dynakitbuilder]

#3 & #4 photos

[Paul Birkeland]

What I would do next is to disconnect the diodes from power transformer terminal 8 as well, then use the continuity beep setting to test all your diodes to see if any are shorted.  It's super rare to end up with a shorted UF4007, but not impossible.  Also keep in mind that some meters may beep on every diode but only in one direction, so before declaring a diode bad be sure to swap the leads around. 

If you do not find a shorted diode, that's also valuable information and there's certainly another path to take after that with more debugging.

-PB

[Dynakitbuilder]

Sorry, but I do not know what the "continuity beep setting" is.  I have a basic Fluke 101 meter.

  Also, the beep means the diode is OK and should be checked in both directions on all diodes?

[Dynakitbuilder]

Diodes: all measure 0.68 to 0.66 m ohms in one direction, 0.L in opposite direction.  Never got a beep.

[Paul Birkeland]

Put the diodes back in place, then remove the lead of the 270 ohm resistor that goes into terminal 37L and leave it poking out sideways, then let us know if the fuse holds.

[Dynakitbuilder]

with 270 ohm resistor detached from 37L and all diodes re-attached -- fuse held, did not blow

[Paul Birkeland]

OK, go ahead and reconnect that resistor.

There's another 270 ohm resistor between 34 and 31, go ahead and disconnect it at 34 and repeat the test.

[Dynakitbuilder]

disconnected resistor @ 34L -  fuse not blown