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Old 22nd August 2003, 10:15 PM   #1
Buhl is offline Buhl  Denmark
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Default Voltage question for Zen 4

14 minutes ago, wearing my ski googles as eye protection, I flicked the switch on for my first amp, a Zen 4 - no fuses blew - im SO happy. I checked the voltages in the circut to be good, most of them 0,2 volts higher or lower. I use a 34 volt trafo, so I measure about 44-45 volts on the regulated supply instead of 46 volts - this shouldnt matter ?

But, I measure 1,2 / 1,3 volts across R0, where Nelson says 0,7 is maximum - is this a problem ?

The amp gets hot, VERY hot - has this to do with the higher voltage across R0 ??


Thanx to all for helping me on this journy to DIY-land - I would never be able to do it without you guys !!!


Cheers !

Hans Houmøller
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Old 22nd August 2003, 10:58 PM   #2
eLarson is offline eLarson  United States
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What value did you install for R0? Did you
also install R1?

Erik
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Old 22nd August 2003, 11:16 PM   #3
Buhl is offline Buhl  Denmark
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R0 and R1 is 0,47 ohm and 1 ohm - just like the original circut.
The fuse between the unregulated supply cap and the zen board just blew at 3 amps - this is also to much, as the circut should only draw 2 amps ??


/Hans
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Old 23rd August 2003, 02:11 AM   #4
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Default Check the Current Source Transistor

The voltage across R0 should be .64 - .7 . If you are getting 1.2 the current is running close to 4 amps with the 0.47 and 1 ohm resistors.
The trim pot may be turned the wrong way. When it is turned as the directions, the current is close to zero through the circuit. As a guess put the pot in the middle and remeasure.
Also, the voltage is below the regulated level of 42 volts. This may be caused by the very high current or the lower than spec'ed input voltage. Try disconnecting the zeners. This way the output of the reg will run 4 volts under the input.
Lastly remove the 1 ohm R1. Even if the voltage is still 1.2 volts this will drop the current down to a livable 2.5 amps or so.


Good Luck,
George
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Old 23rd August 2003, 04:40 AM   #5
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Go back and check your NPN transistor. Maybe it's in backwards (they sort of work, backwards) and maybe the gain is too low.

Also, check all your resistor values around that part of the circuit and make sure the polarity of the electrolytic going to the output is correct.
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Old 24th August 2003, 05:05 PM   #6
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by Nelson Pass
Go back and check your NPN transistor. Maybe it's in backwards (they sort of work, backwards) and maybe the gain is too low.

Also, check all your resistor values around that part of the circuit and make sure the polarity of the electrolytic going to the output is correct.

The electrolytic going to the output has correct polarity.

Im suddently not sure about my npn transistor - its an 2n2102 in an TO39 housing. I tried to mount it opposite, but then there was no voltage across R0, and 43 volts between drain of Q1 and ground ?
I then turned the NPN around again, but the voltages didnt change.

Then i by accident shorted drain and gate of Q1 (Quote Nelson: "Watch where you stick those probes...."), and the fuse between the unregulated supply and the board blew - it keeps blowing, so I guess Q1 is dead ?? Changing it now.....

Im not 100% of how to mount the NPN - i have a hFE-function on my multimeter - to check transistors - when i test the two ways of mounting the transistor, I get a scale reading of 5, and one of about 70 - i dont know the value - witch is correct ??



Thanx for the help !!!


Cheers !
Hans
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Old 24th August 2003, 05:10 PM   #7
joensd is offline joensd  Germany
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Google shows you the way : google search.
Always good to have the datasheet.
Of course there´s a good chance now that your transistor is in semiconductor heaven... maybe not..

Jens
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Old 24th August 2003, 05:25 PM   #8
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by joensd
Google shows you the way : google search.
Always good to have the datasheet.
Of course there´s a good chance now that your transistor is in semiconductor heaven... maybe not..

Jens

Thanx for the google link - I have actually tried, but came up with a datasheet that didnt leave me 100% of the pin out - yours did !!

Now the NPN is mounted correct, and a new IRFP240 is mounted in Q1s place - but before i try again, is there a way to check woth a simple multimeter weather or not a MOSFET is "alive and kickin' "?

Thanx so much for helping !

/Hans
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Old 24th August 2003, 05:40 PM   #9
joensd is offline joensd  Germany
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Quote:
is there a way to check woth a simple multimeter weather or not a MOSFET is "alive and kickin' "?
Go PassDIY

There are more complex faults to semiconductors like their operating curve changed after some accident but basically that´s the test to see if it´s broken.

Jens
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Old 24th August 2003, 06:54 PM   #10
Buhl is offline Buhl  Denmark
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Default Problem solved !

Changed board (have 4 lying around, as im building bridged monoblocks..) - and changed Q1. Still the fuse blew. Changed Q2 and Q5 - now there were suddently 0,6 volts across R0, and 44 volts on the regulated supply, but 0 volts between drain of Q1 and ground. The heatsink on witch Q2 and Q5 are mounted got hot, so i continiued from the belief that that part of the amp was OK. Then I changed Q1 (again...) and voila ! - 15 volts between drain and ground - adjusted it to 24 volts (½ of 44 plus 2 volts), and now everything seems to be in order.....Im so happy !
Time (the next hour) will tell if I have been truly succesfull....

Thanx to everyone who has helped me !

Cheers!
Hans
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