Drip Opto 6 LA2A - Low voltages across the board

[furn1979]

If the measuring channel on the scope is set to AC, turn it to DC, and
if the measuring channel on the scope is set to "invert",  please turn it off.

Switch the power off, disconnect the secondaries from the board (keep CT connecting to power ground) and measure the resistance using a DMM of the each winding to the power ground. They should be almost the same. If it is true connect the secondaries back, turn the transformer on and measure waveforms at the secondaries connections referencing to power ground. Scope probe gnd should be connected to the power ground. Place pictures here (downsize them to cca 800 pixels). Write the vertical setting of the scope channel.

1st secondary (500 VAC, red pair): 193 ohm on one side to power ground and 183 ohm on the other side to power ground
2nd secondary (6.3 VAC, green pair): 0.5 ohm and 0.6 ohm

Should they all be the same? Should I stop my testing here?

 

[moamps]

1st secondary (500 VAC, red pair): 193 ohm on one side to power ground and 183 ohm on the other side to power ground

That's good.  Keep going, please. 

 

[furn1979]

That's good.  Keep going, please. 

On channel 2.
Probe set to 10x
Vertical set to 5 Volts/Div (cal button turned all the way counter clock wise, else the waveform doesn't fit in the screen)

See attached picture for 1st side of 1st secondary 500VAC. 2nd side is exactly the same.

 

[furn1979]

This is the 2nd secondary (6.3 VAC).

Probe still on 10X
Vertical set to 0.2 Volt/Div, Cal'd

Both sides of the secondary give the same reading so I will upload just this one

 

[moamps]

The same scope I have as a third line spare. 
The reading is fine. Now measure the DC voltage after the rectifier. Turn the scope to cal. Set the position down. Don't measure now heaters....

 

[furn1979]

The same scope I have as a third line spare. 
The reading is fine. Now measure the DC voltage after the rectifier. Turn the scope to cal. Set the position down. Don't measure now heaters....

There you go... had the same result with diodes.

 

[moamps]

There you go... had the same result with diodes.

Measure now the DC  voltage at the electrolytic caps and observe the difference. Post the readings.
Then power it off, remove all tubes, power it on, and measure this once again. Keep silicon diodes. Don't use the tube rectifier right now. I will be back in 1.5 hours.

 

[furn1979]

Measure now the DC  voltage at the electrolytic caps and observe the difference. Post the readings.
Then power it off, remove all tubes, power it on, and measure this once again. Keep silicon diodes. Don't use the tube rectifier right now. I will be back in 1.5 hours.

Back on diodes... (same waveform on the scope after the rectifier diodes)

At all 4 filter caps WITH tubes:
248VDC
193 VDC
148 VDC
86 VDC

At all 4 filter caps WITHOUT tubes:
337 VDC
329 VDC
293 VDC
277 VDC

 

[moamps]

Back on diodes... (same waveform on the scope after the rectifier diodes)

Please post the scope readings on both sides of R29 (4k7) with and without tubes inserted.

 

[furn1979]

Please post the scope readings on both sides of R29 (4k7) with and without tubes inserted.

Will do tomorrow!
Thank you so much for your help!

 

[moamps]

Ok, you can also use short wire instead 2k resistors.
https://ws.onehub.com/files/c6vrw6ko

 

[CJ]

try and jumper the two diodes to the dropping resistor with the tubes in>

 

[furn1979]

Please post the scope readings on both sides of R29 (4k7) with and without tubes inserted.

Without tubes:
This photo is on the first side of R29, 20mV/DIV, scope set to AC. This other side of R29 is a straight line, scope set to 5mV/DIV

 

[furn1979]

Please post the scope readings on both sides of R29 (4k7) with and without tubes inserted.

With tubes:
This is first side of R29, scope set to 50 mV/DIV, AC. Other side has negligible ripple (1mV PtoP).

 

[furn1979]

Ok, you can also use short wire instead 2k resistors.
https://ws.onehub.com/files/c6vrw6ko

I didn't have that document when I built it!

So I just shorted the 2k resistors... here are the voltages at the filter caps, with tubes:
281 VDC
220
171
98

 

[furn1979]

try and jumper the two diodes to the dropping resistor with the tubes in>

Did that too, shorted the 2k resistor too, as suggested by moamps. Still same half-rectified signal straight out of the diodes.

 

[moamps]

I didn't have that document when I built it!

So I just shorted the 2k resistors... here are the voltages at the filter caps, with tubes:
281 VDC
220
171
98

So, you solved the problem. Congrats.

 

[furn1979]

So, you solved the problem. Congrats.

Yay!
So the half-wave rectification was normal all along?

 

[scott2000]

:-[
are those voltages right? Or still low???

 

[furn1979]

This power supply is a half wave rectifier type.....


are those voltages right? Or still low???

Still a little under according to test points but within normality. Passing audio as we speak and no visible sag so far.

Thank you all for your time and help!