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Author Topic: Not sound related, but lots of eletronics intelligencia here (updated AGAIN)  (Read 17638 times)

Steve M Smith

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #10 on: January 10, 2017, 03:45:34 AM »

You have a 5v regulator there.  That will want 7 to 8 volts of input.

DC voltage is around 1.4 x the AC input to the rectifier, so transformer output would want to be around 8/1.4 = 5.7v

A 6 volt transformer should be fine.

The only thing which might complicate this is if the unregulated voltage is used anywhere else.


Steve.



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David Allred

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Re: Not sound related, but lots of eletronics intelligencia here (uodated)
« Reply #11 on: January 10, 2017, 07:20:15 AM »


What you have labeled as M7 is D1-4, the four diodes that make up the full wave bridge rectifier.  The circuit described in Nathan's post.


Diode's are easy to check, put your meter on resistance, they should measure a short one way and an open the other.  Fluke meters have an aural diode test mode.


Those big caps are the filters.  The regulator has an innie and and outie.  Verify you have input.
M7 referred to the stencil on the components. 
I will check the diodes, just to verify.
I know that I don't have input, because the transformer is dead.  I am seeking to figure out the unlabeled specs of the transformer.
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Nathan Riddle

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #12 on: January 10, 2017, 10:43:50 AM »

Honestly, without seeing a picture (both sides) of the circuit board so we can trace the traces I'm not sure what the transformer is rated at.

1) The regulator is rated up to 35v IIRC allowing for a far larger voltage range from the transformer, though the 25v caps reduce that.

2) The transformer is center tapped meaning the AC could be used elsewhere or theres a different rectification going on somewhere else.

3) The transformer is quite a bit larger than what that regulator can provide current wise, makes me curious as to where all that extra current is going?

4) Diodes are rated at 1A, which would limit transfomer size if the transformer only feeds the circuit.

Just like everything else, "it depends," can be judiciously applied here.

I think a different angle might be in order, call manufacture, find someone else who has a working one, try and find schematics online, call repair centers across the nation to see if they've fixed one before.

There's a good number of EE's and related types on the forums here that could build the circuit and say for certain. But we don't have enough info to make a useful call.

Sure a 6v transformer would work for THAT regulator. But what current supply? Why the center tap? What about other parts of the board using transformer power?

You could hook it up to a variable AC power supply and slowly increase the voltage until it works again, then that's probably the correct voltage?

Edit: fixed input voltage range, didn't see attached pic in reply #8, revised thoughts
« Last Edit: January 10, 2017, 11:02:22 AM by Nathan Riddle »
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David Allred

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #13 on: January 10, 2017, 12:48:21 PM »

Honestly, without seeing a picture (both sides) of the circuit board so we can trace the traces I'm not sure what the transformer is rated at.

1) The regulator is rated up to 35v IIRC allowing for a far larger voltage range from the transformer, though the 25v caps reduce that.

2) The transformer is center tapped meaning the AC could be used elsewhere or theres a different rectification going on somewhere else.

3) The transformer is quite a bit larger than what that regulator can provide current wise, makes me curious as to where all that extra current is going?

4) Diodes are rated at 1A, which would limit transfomer size if the transformer only feeds the circuit.

Just like everything else, "it depends," can be judiciously applied here.

I think a different angle might be in order, call manufacture, find someone else who has a working one, try and find schematics online, call repair centers across the nation to see if they've fixed one before.

There's a good number of EE's and related types on the forums here that could build the circuit and say for certain. But we don't have enough info to make a useful call.

Sure a 6v transformer would work for THAT regulator. But what current supply? Why the center tap? What about other parts of the board using transformer power?

You could hook it up to a variable AC power supply and slowly increase the voltage until it works again, then that's probably the correct voltage?

Edit: fixed input voltage range, didn't see attached pic in reply #8, revised thoughts

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David Allred

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #14 on: January 10, 2017, 12:48:56 PM »

You have a 5v regulator there.  That will want 7 to 8 volts of input.

DC voltage is around 1.4 x the AC input to the rectifier, so transformer output would want to be around 8/1.4 = 5.7v

A 6 volt transformer should be fine.

The only thing which might complicate this is if the unregulated voltage is used anywhere else.


Steve.
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Daniel Levi

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #15 on: January 10, 2017, 01:38:06 PM »

From what I can see the 2 outer pins on the 3 pin AC transformer inlet are going to the bridge rectifier but I can't see where the middle pin is going, although, it could be going to the ground plane but why it would go there I don't know, there is also a designator for ZD1 which would mean a zener diode, I would have expected that to be for another DC voltage which may require a higher output from the transformer..

One thing to be wary of is that the part of the board around the isolation slots will be at full mains potential.



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Scott Helmke

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #16 on: January 10, 2017, 01:51:54 PM »

I don't there there would be a need for a full four-diode bridge unless the power supply is producing both plus and minus supply voltages. Also there are two capacitors.  I would guess that there's both split (+/-) supply rails *and* one of the rails is supplying voltage to that 78xx regulator to provide a third (lower) voltage for something.
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Daniel Levi

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #17 on: January 10, 2017, 02:16:21 PM »

I don't there there would be a need for a full four-diode bridge unless the power supply is producing both plus and minus supply voltages. Also there are two capacitors.  I would guess that there's both split (+/-) supply rails *and* one of the rails is supplying voltage to that 78xx regulator to provide a third (lower) voltage for something.

That would make sense, although, the only component that might need a dual supply is the 8 pin chip in the mains voltage section as I can't see anything else that would need it.
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David Allred

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #18 on: January 10, 2017, 02:43:42 PM »

I don't there there would be a need for a full four-diode bridge unless the power supply is producing both plus and minus supply voltages. Also there are two capacitors.  I would guess that there's both split (+/-) supply rails *and* one of the rails is supplying voltage to that 78xx regulator to provide a third (lower) voltage for something.

The caps are connect in series from D2 (+), and back to D4 (-).  D4 is connected to the 100 ohm r to the right of and below D4, if that helps.  The 100 ohm r above the 2 caps links the regulator to the 8 pin chip, if that helps.
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Scott Helmke

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Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #19 on: January 10, 2017, 04:12:14 PM »

That would make sense, although, the only component that might need a dual supply is the 8 pin chip in the mains voltage section as I can't see anything else that would need it.

There's the question of what the actual working stuff is, though - the board is PSU and control, but there's a heating element?  What exactly does this "T-shirt press" do?
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ProSoundWeb Community

Re: Not sound related, but lots of eletronics intelligencia here (updated)
« Reply #19 on: January 10, 2017, 04:12:14 PM »


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