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General Discussions => The Lab => Topic started by: furn1979 on November 06, 2018, 02:33:44 PM

Title: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 06, 2018, 02:33:44 PM
Hi!

My Opto 6 has been acting up lately. It'll work fine until a little power dip seems to occur within the unit... my meter lamp will dim, meter will dip a little and a slight hum can be heard in the audio signal.

Also, I can sometimes hear a slight creaking sound from within the compressor itself... maybe from the power transformer (Hammond 369JX) but I'm not quite sure. Wiring has been checked many times.

I'm measuring lower than expected voltages across the board.

At secondary #1: 547 VAC (normal)
At secondary #2: 6.5 VAC (normal)
At filter caps (275V): 196 VDC
At R13 (134V): 93.5 VDC
At TP 1 (110V): 73.7 VDC

Aren't these figures lower than normal? Where should I look?

I used diodes in the power section (checked them, they're fine).

Thanks!

Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: PRR on November 06, 2018, 02:43:49 PM
Link to schematics and docs?

Tube or diode rectifier?

What gets hot when voltages sag?
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 06, 2018, 02:50:28 PM
Link to schematics and docs?
See manual attached.

Tube or diode rectifier?
Diodes

What gets hot when voltages sag?
Nothing seems to get physically hot.



Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 06, 2018, 03:37:37 PM
Kinda like an Ikea manual......

wow....6x4 rectifier too?? what are the diodes doing??? you have a choice???
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: mjrippe on November 06, 2018, 03:41:16 PM
Sounds like filter caps going south to me.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 06, 2018, 03:51:12 PM
Would the dropping resistors create issues if going bad too???
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 06, 2018, 03:56:54 PM
Kinda like an Ikea manual......

wow....6x4 rectifier too?? what are the diodes doing??? you have a choice???

Yep. Went with diodes, as the originals were.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 06, 2018, 04:08:36 PM
Ah right....I see that now....Pretty cool.....

What power are you using for your lamps??? That comes from the 6.3 from the hammond as well??
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 06, 2018, 05:42:09 PM
Ah right....I see that now....Pretty cool.....

What power are you using for your lamps??? That comes from the 6.3 from the hammond as well??
That’s correct.
No DC heater on that model.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 07, 2018, 03:36:44 AM
First, confirm that the red/yel wire from  power transformer (CT wire) is connected to the "power ground" pin on the board.
Then measure DC voltage on both side of R16 and 29 referenced to the power ground pin and post it here.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: CJ on November 07, 2018, 04:25:09 AM
if no heat or exploding capacitors, then t sounds like you lost a phase of the pwr xfmr,

since you measure good on the secondary, the phase loss would have to be at the diode cathode junction, possibly a solder joint or fried trace, measure DCR between the two diode cathodes (unit unplugged and caps drained)

if no joy, try pulling the 12BH7 and measure B+ voltages,

if no luck, give it the chop stick test (mechanical problem) tap the chassis with a pen or pencil and see if the meter jumps,
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 10:20:12 AM
First, confirm that the red/yel wire from  power transformer (CT wire) is connected to the "power ground" pin on the board.
Then measure DC voltage on both side of R16 and 29 referenced to the power ground pin and post it here.

CT Wire to ground, confirmed
Across R16 = 194VDC and 147 VDC
Can't seem to find R29 (?) Where should it be located? Which value?

Not all resistors are numbered on the board/schematic.

Thank you for your help
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 10:24:01 AM
if no heat or exploding capacitors, then t sounds like you lost a phase of the pwr xfmr,

since you measure good on the secondary, the phase loss would have to be at the diode cathode junction, possibly a solder joint or fried trace, measure DCR between the two diode cathodes (unit unplugged and caps drained)

if no joy, try pulling the 12BH7 and measure B+ voltages,

if no luck, give it the chop stick test (mechanical problem) tap the chassis with a pen or pencil and see if the meter jumps,

Will begin these tests right now.

On the scope, the signal at the rectifier's diodes cathodes looks like this (see photo attached)... I'm guess my problem's here right?
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 07, 2018, 10:34:39 AM
CT Wire to ground, confirmed
Across R16 = 194VDC and 147 VDC
Can't seem to find R29 (?) Where should it be located? Which value?

Not all resistors are numbered on the board/schematic.

Thank you for your help

R29 is probably under R28 (4.7k 2w) .....you may have already posted one side value 196v....... at least if it's going by the original schematic
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 10:43:03 AM
R29 is probably under R28 (4.7k 2w) .....you may have already posted one side value 196v....... at least if it's going by the original schematic

So across that 4.7k 2W, I'm getting 247 VDC and 194 VDC
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 07, 2018, 12:15:46 PM
Definitely low on that..... should be around 350 instead of 247 ???

have you tested filter caps???diodes??

pulling the tube CJ said...???

So across that 4.7k 2W, I'm getting 247 VDC and 194 VDC
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 12:41:19 PM
ok... so I'm only half-rectifying, although my 1N4007 test ok... I'll install brand new ones and see how it goes.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 01:20:39 PM
So I didn't have a pair of 1N4007 around BUT, I have a 6X4 tube and socket.

Installed it and now measuring this signal at the output of the tube (see picture attached).

Still only rectifying only one phase... is my power transformer secondary out? I'm still getting 549 VAC on that secondary.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 07, 2018, 01:43:02 PM
I don't think so??? But I'm not the one to know.....

Your transformer secondary is a bit high .....is that  because it's 500v rating is at 100v primary ???  No mention  in the guide of this???
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 07, 2018, 02:15:32 PM
Installed it and now measuring this signal at the output of the tube (see picture attached).

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.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 02:33:31 PM
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?

Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 07, 2018, 02:37:41 PM
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.  :)
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 03:09:15 PM
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.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 03:11:48 PM
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
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 07, 2018, 03:15:27 PM
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....
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 03:39:23 PM
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.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 07, 2018, 03:46:32 PM
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.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 04:09:03 PM
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
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 07, 2018, 05:07:32 PM
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.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 07, 2018, 05:14:07 PM
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!
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 07, 2018, 05:21:29 PM
Ok, you can also use short wire instead 2k resistors.
https://ws.onehub.com/files/c6vrw6ko
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: CJ on November 07, 2018, 05:27:28 PM
try and jumper the two diodes to the dropping resistor with the tubes in>
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 01:20:44 PM
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
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 01:25:05 PM
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).
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 01:43:06 PM
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
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 01:44:50 PM
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.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 08, 2018, 02:52:13 PM
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. :)
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 03:00:38 PM
So, you solved the problem. Congrats. :)
Yay!
So the half-wave rectification was normal all along?
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 08, 2018, 03:13:16 PM
 :-[
are those voltages right? Or still low???
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 03:49:53 PM
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!
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 08, 2018, 04:41:04 PM
Yay!
So the half-wave rectification was normal all along?

It's full wave rectifier. Please check the frequency of the residual ripple with the scope or write here the time divisions setting.
It's 100 or 120Hz for sure depending of your location.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 04:50:37 PM
It's full wave rectifier. Please check the frequency of the residual ripple with the scope or write here the time divisions setting.
It's 100 or 120Hz for sure depending of your location.

Where on the circuit should I get residual ripple? At the fourth filter cap?
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 08, 2018, 05:00:19 PM
Where on the circuit should I get residual ripple? At the fourth filter cap?

You already measured it on R29 (post 33).
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: scott2000 on November 08, 2018, 05:01:00 PM
It's full wave rectifier.

doh...  :-[ edited
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 08, 2018, 08:29:13 PM
It's full wave rectifier. Please check the frequency of the residual ripple with the scope or write here the time divisions setting.
It's 100 or 120Hz for sure depending of your location.

Time is 2ms/DIV, so I'm measuring a full ripple cycle at 8.2 ms (120 Hz, I'm in Canada).

Where do I go from here? I'm getting the DC I want out of the filter caps BUT, my power supply isn't doing what it's supposed to do.
The original problem is fixed, although there's still something going wrong.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: PRR on November 09, 2018, 01:26:18 AM
You have a "bad" rectifier. Check the joints. Replace the tube. Replace the diodes. In that order.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 09, 2018, 03:17:44 AM
Where do I go from here? I'm getting the DC I want out of the filter caps BUT, my power supply isn't doing what it's supposed to do.
The original problem is fixed, although there's still something going wrong.

Your power supply works as it should. It's perfectly normal that there is a small ripple at capacitors in the row in an unregulated power supply.  And you can't avoid it. Just move on, and remember what you learned about using a scope.

Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 09, 2018, 08:39:49 AM
Your power supply works as it should. It's perfectly normal that there is a small ripple at capacitors in the row in an unregulated power supply.  And you can't avoid it. Just move on, and remember what you learned about using a scope.

Alright. That’s great! You’ve been really helpful and patient moamps... thank you!

But just out of curiosity, why can’t I measure full-wave rectification on the scope?
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 09, 2018, 09:27:11 AM
But just out of curiosity, why can’t I measure full-wave rectification on the scope?

Of course, you can measure full wave rectification  with a scope. You already did it. :)
But, if your question is why you don't see it on your scope, that's because  you already have the smoothing capacitors connected.

Here is a very nice explanation about  rectifiers.
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

(direct link doesn't work    go:  electricity and magnetism- dc circuits-power supplies-center tap rectifier)
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 09, 2018, 09:40:02 AM
Of course, you can measure full wave rectification  with a scope. You already did it. :)
But, if your question is why you don't see it on your scope, that's because  you already have the smoothing capacitors connected.

Here is a very nice explanation about  rectifiers.
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

(direct link doesn't work    go:  electricity and magnetism- dc circuits-power supplies-center tap rectifier)

Actually, my question is: Why am I not seeing this? (see picture attached)
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: moamps on November 09, 2018, 10:19:35 AM
Actually, my question is: Why am I not seeing this? (see picture attached)

The original reading shows full wave rectifier with partially smoothing capacitor connected thru resistor 2k2W which you shorted in last version. The red waveforms would be 240Hz ripple which can not appear.
If you like to see the full wave rectifier alone, you should omit 2k2w resistor and bridge on it near the rectifier diodes, and then measure the voltage on connection of two diodes (anodes) using your scope.
Title: Re: Drip Opto 6 LA2A - Low voltages across the board
Post by: furn1979 on November 09, 2018, 10:28:29 AM
The original reading shows full wave rectifier with partially smoothing capacitor connected thru resistor 2k2W which you shorted in last version. The red waveforms would be 240Hz ripple which can not appear.
If you like to see the full wave rectifier alone, you should omit 2k2w resistor and bridge on it near the rectifier diodes, and then measure the voltage on connection of two diodes (anodes) using your scope.

Gotcha! Thank you again!