U67 Clone : D-U67 PSU problems....

[Lordward]

HELP! 
First of all I'd like to point out that I am a novice but do have a basic understanding of schematic and component reading. I know how to use a DIMM and I'm trying to better my knowledge on a day to day basis.  I've built a total of 5 mics so far, 3 of which were kits on PCB and 2 of which were point-to-point.  I'm pretty good at following directions and all my mics are working.  That's why I'm stumped on this one.

I'm having such an issue with the PSU of this build... First the 15V Zener died on me and I've replaced it (I mean it really burnt out).  When I hook up the Triad (VPT230-110) to AC power (without connecting it to the PCB) I get a reading of about 270 VAC.  Seems normal I would say... *at this point I guess I should point out that I'm living in Germany where we have 230 V*. When I connect it to the PSU and measure the VAC at the "AC in" on the PCB (terminal connectors) I get a reading of 110VAC and the unit is humming relatively loud. I've noticed that the Triad is getting hotter than I remember them getting.  I've tried turning the Rtrimplate with no difference.  I've doubled and triple checked the values of the components and I'm sure that all is correct.

Any help would be greatly appreciated   Thanks!
Dennis

 

[Gus]

Have you worked with tube voltages before?

If I understand your post you are getting 270VAC instead of the 210VAC before the B+ diode and ground
What are you measuring the voltage with?  RMS or peak to peak?
If that is correct you most likely getting greater than 20VAC before the heater diode bridge
Also if the AC voltage drops from 270VAC to 110VAC something is loading the B+. Is this with a microphone connected? It reads like you have added resistance to ground loading the B+ rail or something(s) else wrong.
Is this the transformer? http://catalog.triadmagnetics.com/Asset/VPT230-110.pdf

if the 15VDC zener burned
Is this the schematic? https://dl.dropboxusercontent.com/u/43869772/U67/Du67-PCB%20PSU.pdf
I am surprised it was not modernized

Was the zener heatsinked?
Are you testing the power supply without a heater load? This can be an issue.
1) check you have 20VAC before the heater power supply diodes if much higher this can be a problem
2) check R2 22ohms 2watts

The Zener in this circuit is a shunt regulator. In this case R2 22ohms is part of what sets the current in the zener with the heater load connected when the load is disconnected the current shunts to the zener

The total current is the current in the zener and the current in the tube heater

If there is no tube heater connected max current will flow in the zener  and the zener will be dissipating the max amount of heat

It is a balancing act to build a simple zener shunt regulator that can survive without a having the load connected

 

[Lordward]

First of all, my apologies that my pictures don't upload.  I have no idea why they won't.  They are jpegs and they are about 1mb..

Have you worked with tube voltages before?

Yes, I have.  I've build the D47 a couple of times, the D12 once and 2 x the ELAM251 point-to-point (however one time I just modified the Alctron PSU and one time I built it from the kit of the D251).

If I understand your post you are getting 270VAC instead of the 210VAC before the B+ diode and ground

No, I'm getting 270VAC from the Triad Tranny when it's connected directly to 230V and I measure the black and yellow wires.  As soon as I hook it up to the PCB of the PSU I measure 110V.  It should be ~270VAC as stated in the build guide here: http://www.vintagemicrophonepcbkit.com/D67B/D67B/D-67%20Build%20Guide.html

What are you measuring the voltage with?  RMS or peak to peak?

I dunno really?  I'm using a DMM and I measure with V~ setting

If that is correct you most likely getting greater than 20VAC before the heater diode bridge
Also if the AC voltage drops from 270VAC to 110VAC something is loading the B+. Is this with a microphone connected? It reads like you have added resistance to ground loading the B+ rail or something(s) else wrong.
Is this the transformer? http://catalog.triadmagnetics.com/Asset/VPT230-110.pdf

Yes, that is the transformer. No microphone connected at all.  I'm just in the first stage of testing the PSU as mentioned in the build guide.

if the 15VDC zener burned
Is this the schematic? https://dl.dropboxusercontent.com/u/43869772/U67/Du67-PCB%20PSU.pdf
I am surprised it was not modernized

Yes, that's it.

Was the zener heatsinked?

No, and I saw no other build with one on it here at Groupdiy.com.  https://groupdiy.com/index.php?topic=50021.0

Are you testing the power supply without a heater load? This can be an issue.

I was not aware that I had to do this   It also does not seemed to be mentioned in the build guide or on the support page.

1) check you have 20VAC before the heater power supply diodes if much higher this can be a problem
2) check R2 22ohms 2watts.

I'm getting almost exactly 20VAC and R2 is 22ohms 2watts.

The Zener in this circuit is a shunt regulator. In this case R2 22ohms is part of what sets the current in the zener with the heater load connected when the load is disconnected the current shunts to the zener

Is it possible that I've burned out something on my PCB?  That diode did smoke for a second.

The total current is the current in the zener and the current in the tube heater

If there is no tube heater connected max current will flow in the zener  and the zener will be dissipating the max amount of heat

It is a balancing act to build a simple zener shunt regulator that can survive without a having the load connected

Ok, got it.  I have ordered a new PCB and I will take out each component and measure that all is ok then put them in the new PCB.  I hope to get it soon.  Thanks for your help!!

Dennis

 

[Lordward]

x

For what it's worth here are 3 links to pictures of my PSU:
https://dl.dropboxusercontent.com/u/8577693/PSU%201.JPG
https://dl.dropboxusercontent.com/u/8577693/PSU%202.JPG
https://dl.dropboxusercontent.com/u/8577693/PSU%203.JPG

 

[TLRT]

When you are ready with your PSU first test it with load resistors, for heater 33ohm/2W(pin 3-4), and for B+ approx 480kohm/0,6W (pin5-7 as the ground points 3-7 are connected) if your can set your voltages with this way according to the descriptions(-6,3V heater,and 210V B+) then it will be also fine with mic connected.

HELP! 
First of all I'd like to point out that I am a novice but do have a basic understanding of schematic and component reading. I know how to use a DIMM and I'm trying to better my knowledge on a day to day basis.  I've built a total of 5 mics so far, 3 of which were kits on PCB and 2 of which were point-to-point.  I'm pretty good at following directions and all my mics are working.  That's why I'm stumped on this one.

I'm having such an issue with the PSU of this build... First the 15V Zener died on me and I've replaced it (I mean it really burnt out).  When I hook up the Triad (VPT230-110) to AC power (without connecting it to the PCB) I get a reading of about 270 VAC.  Seems normal I would say... *at this point I guess I should point out that I'm living in Germany where we have 230 V*. When I connect it to the PSU and measure the VAC at the "AC in" on the PCB (terminal connectors) I get a reading of 110VAC and the unit is humming relatively loud. I've noticed that the Triad is getting hotter than I remember them getting.  I've tried turning the Rtrimplate with no difference.  I've doubled and triple checked the values of the components and I'm sure that all is correct.

Any help would be greatly appreciated   Thanks!
Dennis

 

[Lordward]

When you are ready with your PSU first test it with load resistors, for heater 33ohm/2W(pin 3-4), and for B+ approx 480kohm/0,6W (pin5-7 as the ground points 3-7 are connected) if your can set your voltages with this way according to the descriptions(-6,3V heater,and 210V B+) then it will be also fine with mic connected.

Cheers, this is great to know   I'm wondering why it's not mentioned in the build guide.  It says:
"Now you should have eveyth ing soldered on the PSU and the Mic. Ensure that the mic is unplugged from the PSU.
Apply power to the PSU.
Check voltages at the AC input of the PSU PCB.
20VAC for th e h eater
~ 2 7 0 VA C at the HT input"

When I had first finished the PSU, before the zener blew out, I had measured these values and was content that all was ok.  There was no mention of needing a load resistor.  After replacing the zener I now measure 110VAC instead of 270VAC (unloaded).  However if I detached the transformer from the PCB I get the right reading, leading  me to believe that I must have destroyed something else as well.  But I'll give it another try with the load resistors. Thanks!

Dennis

 

[Gus]

Having issues with looking at the dropbox build links
What transformer connection the the PCB causes the 270VAC to drop to 110VAC?

The heater supply should not change the B+ voltage
The B+ is a positive 1/2 wave rectifier circuit(1/2 wave and a toroid transformer?) and the heater is a negative fullwave rectifier to a shunt zener reg to RC filters that share the DC ground rail

 

[Banzai]

A buzzing transformer is a sign the circuit is drawing too much current. Could be a leaky capacitor (almost easier to just replace all of them vs looking for the faulty one)

 

[Lordward]

A buzzing transformer is a sign the circuit is drawing too much current. Could be a leaky capacitor (almost easier to just replace all of them vs looking for the faulty one)

Thanks for the info.  I'll do just that

 

[dchang0]

"No, I'm getting 270VAC from the Triad Tranny when it's connected directly to 230V and I measure the black and yellow wires.  As soon as I hook it up to the PCB of the PSU I measure 110V.  It should be ~270VAC as stated in the build guide here: http://www.vintagemicrophonepcbkit.com/D67B/D67B/D-67%20Build%20Guide.html"

I'm not sure you should be reading 270VAC on a naked Triad VPT230-110 transformer.

The build guide says:

"Apply power to the PSU
Check voltages at the AC input of the PSU PCB
~270VAC at the HT input"

This implies that the transformer is attached/installed in the PSU (has load).

But you are measuring a naked transformer, not connected to anything but the AC mains and the multimeter, right?

According to the data sheet here: http://www.mouser.com/ds/2/410/media-1067313.pdf

Input Voltage: Series: 230VAC, 50/60Hz
Parallel: 115VAC, 50/60Hz
Output Voltage: Series: 230VAC CT @ 0.11A Parallel: 115.0VAC @ 0.22A
4. Voltage Regulation: 12% TYP from full load to no load

Getting 270VAC on what should be a 230VAC output is a 17% jump. That seems wrong.

Also, double-check your jumpering (series vs. parallel) of the transformer's windings. This quote may be important:

"Primary and secondary windings are designed to be connected in series or parallel. Windings are not intended to be used independently."

If I understand you correctly, you have 230VAC input, so you MUST set up the primaries in series:

Input1: Series – BLUE and BROWN, Jumper GRAY to VIOLET

Perhaps the problem of the secondaries dropping down from 270VAC (still way over the 230VAC) to 110VAC is due to some problem with the jumpering of the secondaries.

If I understand the U67 PSU Build Guide correctly, the intended output of the transformer is 210VAC, so you would run the output secondaries in series too:

Output : Series – BLACK and YELLOW, Jumper RED to ORANGE

230VAC in, 230VAC out, right? This is basically a "unity" transform.

What is your AC mains voltage? It should not be 270VAC at the wall, so it is weird that you are getting 270VAC on the output of a naked transformer set up for unity transform.

I know you're trying to do switchable 115VAC/230VAC input, but for now, it is probably best to remove any switches on the input side and just go with 230VAC input.

 

[Lordward]

"No, I'm getting 270VAC from the Triad Tranny when it's connected directly to 230V and I measure the black and yellow wires.  As soon as I hook it up to the PCB of the PSU I measure 110V.  It should be ~270VAC as stated in the build guide here: http://www.vintagemicrophonepcbkit.com/D67B/D67B/D-67%20Build%20Guide.html"

I'm not sure you should be reading 270VAC on a naked Triad VPT230-110 transformer.

The build guide says:

"Apply power to the PSU
Check voltages at the AC input of the PSU PCB
~270VAC at the HT input"

This implies that the transformer is attached/installed in the PSU (has load).

But the build guide says specifically "without microphone attached" and says nothing about using any load.  As a matter of fact the first lines of the PSU test read "Now you should have everything solder on the PSU and the Mic. Ensure that the mic is unplugged from the PSU". 
If it's meant otherwise than this is clearly confusing... :-\

But you are measuring a naked transformer, not connected to anything but the AC mains and the multimeter, right?

Correct. And as soon as I attach it to the circuit board I get the humming and a reading of 110VAC.

According to the data sheet here: http://www.mouser.com/ds/2/410/media-1067313.pdf

Input Voltage: Series: 230VAC, 50/60Hz
Parallel: 115VAC, 50/60Hz
Output Voltage: Series: 230VAC CT @ 0.11A Parallel: 115.0VAC @ 0.22A
4. Voltage Regulation: 12% TYP from full load to no load

Getting 270VAC on what should be a 230VAC output is a 17% jump. That seems wrong.

Also, double-check your jumpering (series vs. parallel) of the transformer's windings. This quote may be important:

"Primary and secondary windings are designed to be connected in series or parallel. Windings are not intended to be used independently."

If I understand you correctly, you have 230VAC input, so you MUST set up the primaries in series:

Input1: Series – BLUE and BROWN, Jumper GRAY to VIOLET

This is the way I have the tranny setup, yes.  Blue and brown to the mains, gray and violet connected in series (2 x 115 = 230).

Perhaps the problem of the secondaries dropping down from 270VAC (still way over the 230VAC) to 110VAC is due to some problem with the jumpering of the secondaries.

I have connected red and orange in series.  This should be right.  And I need to point out again that before the Zener blew out that I was getting the right settings while the tranny was connected to the circuit board.

If I understand the U67 PSU Build Guide correctly, the intended output of the transformer is 210VAC, so you would run the output secondaries in series too:

Output : Series – BLACK and YELLOW, Jumper RED to ORANGE

230VAC in, 230VAC out, right? This is basically a "unity" transform.

Yes, as I said.  I have posted a link with pictures of my build as well:
https://dl.dropboxusercontent.com/u/8577693/PSU%201.JPG
https://dl.dropboxusercontent.com/u/8577693/PSU%202.JPG
https://dl.dropboxusercontent.com/u/8577693/PSU%203.JPG

What is your AC mains voltage? It should not be 270VAC at the wall, so it is weird that you are getting 270VAC on the output of a naked transformer set up for unity transform.

Yes, it's weird.  And I'm getting about 230VAC at the wall.

I know you're trying to do switchable 115VAC/230VAC input, but for now, it is probably best to remove any switches on the input side and just go with 230VAC input.

Actually I am not, that's why I've soldered the gray and violet cables together.
Thanks!

 

[dchang0]

Re: "But the build guide says specifically "without microphone attached" and says nothing about using any load.  As a matter of fact the first lines of the PSU test read "Now you should have everything solder on the PSU and the Mic. Ensure that the mic is unplugged from the PSU". 
If it's meant otherwise than this is clearly confusing..."

By load I meant the PSU PCB, even without the microphone attached. No worries. It doesn't matter now that you've answered the other questions.

It sounds then like I misunderstood your prior post and that yes, the problem is indeed somewhere on the PSU PCB and not within the transformer or its wiring.

But just to confirm, please do this test:

1) Disconnect transformer secondaries from PSU PCB.
2) Measure AC voltage at wall socket.
3) Plug in transformer (observing all safety precautions) and measure AC voltage across black and yellow wires.

The two values should match within a few percent. If they do not, then I think something is also wrong with the transformer (in addition to whatever may be wrong on the PSU PCB). It should be 230VAC in, 230VAC out. If you are really getting 230VAC in and 270VAC out, then perhaps some windings on the primary side shorted out, resulting in a 1:1.17 ratio.

We'll have to look at the PSU schematic more closely and try to trace possible problems. For now, try everyone else's suggestions.  Banzai is correct--there are so few capacitors that it is easier to just replace all of them. It may even be cheap enough to replace all the resistors and diodes too.

BTW, the drop to 110V is probably the result of an accidental voltage divider forming due to one or more of the components dying or shorting or a miswire. You should not re-attach the transformer until you have verified the board's components are good and all connections are correct.

 

[fineline]

I have the exact same toroidal transformer (VPT230-110) for the build I'm doing (poctops D-47) and I get 260VAC from the secondary. So that is also off I guess!(?) Have not connected it to the PCB or anything...havn't even tried so far....

Hooked it up the exact same way, i.e. Grey to Violet in series, Blue and Brow to mains (which is about 220V here in Sweden) then on the secondary Red-Orange i series, measuring from  Yellow and Black.

/Johan

 

[dchang0]

I have the exact same toroidal transformer (VPT230-110) for the build I'm doing (poctops D-47) and I get 260VAC from the secondary. So that is also off I guess!(?) Have not connected it to the PCB or anything...havn't even tried so far....

Hooked it up the exact same way, i.e. Grey to Violet in series, Blue and Brow to mains (which is about 220V here in Sweden) then on the secondary Red-Orange i series, measuring from  Yellow and Black.

/Johan

In that case, it is not likely to be a problem, although we won't really know until someone who has built a fully-working PSU using the same transformer confirms that the output voltage is that high without the transformer secondaries attached to anything.

 

[wave]

I'm in the US so my wall voltage is 122V. I'm using the same Traid transformer
Mic unconnected from PSU
273VAC from black and yellow
20.24VAC from heater transformer (Hammond)
255VDC on B+
-16.5VDC on heater

Mic connected to PSU
273VAC from black and yellow
19.7 from heater transformer
210VDC on B+
-6.3VDC on heater

Dave

 

[Lordward]

Oh boy, this is no fun 

So, I bought a new PCB and replaced all the components.  I've double checked that my Triad Transformer is wired right (for 230 V) and confirmed that they are producing the approximate voltages.  I've double and triple checked my polarities and wiring. 

As soon as I turn on the PSU (with load) about 5 seconds later I see a very thin stream of smoke.  I don't think it should do that...
I still cannot figure out why the photos I upload to this forum are not visible... For what it's worth I've uploaded pics to dropbox if anyone cares to have a look: https://www.dropbox.com/sh/ushs2hht0y5lqz8/AAB4l1WAnPp5QRtCmbvRa66Ea?dl=0

I'm reluctant to go any farther with this project.  So far it's the only one I've had real issues with.  I don't get it.
Could anyone chime in?

Cheers,
Dennis

 

[ln76d]

Deifnately check whole wiring including multipin cable. For me looks like short in the circuit.

 

[Lordward]

Deifnately check whole wiring including multipin cable. For me looks like short in the circuit.

I've totally rebuilt it.  I only used the same Triad transformer, the switches and the Pots from the first build attempt.  I can't believe I would have shortened anything out, again.  I've checked the Triad and it seems to be working as expected...

I am a bit curious about the cable.  Using the cable color chart (GAC-7) I am wondering something:  In the PSU I have not soldered the ground lug of the 7 and 3 pin XLR to anything.  Should I do this? 
And, on the cable, I'm using the cable shield on pin 3 on both ends.  I also do not have the ground lugs soldered to anything.  Needed?

 

[Lordward]

I've noticed something quite interesting:  On this page https://groupdiy.com/index.php?topic=50021.0 at about 80% down on the page there is a pic of the AMI transformer (from the back) mounted onto the AMI Adapter.  There are colored cables connected to 1, 7, 5, 12, 10, 4 pins on this board and the cables are connected to the microphone PCB.

Now if I look at this build guide: http://www.vintagemicrophonepcbkit.com/D67B/D67B/D-67%20Build%20Guide.html
at about %90 of the the bottom of the page I see the same cables are hooked up differently.

I can also see that the transformers are not inserted the same way...hmmmm?
I do have that AMIT T67 transformer too, by the way....

Might this be my "short circuit" issue?

 

[ln76d]

Sorry, i can't help you with that. I will have to investigate all the connections etc. and i really have no time currently.
With multipin cable, use multimeter beeper and check all pins for the shorts. One pin from one side and test all the pins from the other side, then another pin and exactly the same procedure.