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Old 5th April 2005, 10:08 AM   #1
Tom75 is offline Tom75  Switzerland
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Unhappy Aleph5 problems

Dear DIY community as a Life scientist Im far away of electronics, but Im on a steep learning curve
At the moment I try to build an Aleph5, unfortunately it is not working. So I am asking for your help, I checked and recheckt the cirquit, but I do not find the error.

Some specs:

the voltage after the rectifier is 35 V
voltage over Q4 is 4,4 V
voltage over Q5 is 4,7 V
voltage over R40-42 is 0,69 V
voltage over R64-66 is 0,63 V

this seems rather ok for me

but now:

voltage over Z5 17 V !
voltage over R11 12 V !
and the voltage to the source of the Diff. pair is 13,4 V

any suggestions?

I would really like to hear this Aleph!
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Old 5th April 2005, 10:16 AM   #2
Netlist is offline Netlist  Belgium
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Hi Tom and welcome.

There seems to be something wrong with the diff pair and/or it's current source. Reverse polarity or broken mosfets? Bad joints in that area?
Are you sure the Zener is a 9V1?

/Hugo
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Old 5th April 2005, 08:21 PM   #3
Blues is offline Blues  United States
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Looks like the zener like Netlist said. Per your measurement there's a drop of about 5V across the G-S of your mosfet which makes it good.
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Old 5th April 2005, 09:51 PM   #4
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I would expect a bad Zener, but it's still suspicious that the
diff pair Sources are at 13.4V.
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Old 6th April 2005, 07:25 AM   #5
Tom75 is offline Tom75  Switzerland
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Thank you very much for the quick replies.
I guess I will just exchange Z5 and see whats happening.

By the way, is there an easy way to test whether the Zener is OK or not? I am shure that I intended to ordered a 9.1V one, but maybe I have mixed up the ordering number. Just measuring with the DMM will not work I guess, gives me something like 0.6 V.
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Old 6th April 2005, 07:50 AM   #6
Netlist is offline Netlist  Belgium
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Testing zener voltage can be done by connecting a resistor to a dc voltage greater than the zener voltage to test. Select the resistor to limit the current to a few mA.
Measure the voltage over the zener. Done.

/Hugo
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Old 6th April 2005, 07:53 AM   #7
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The way I have checked a zener:

grab a bench psu of say 12v dc. Tie the banded side of the zener (cathode) to the positive on the psu. Tie the neg lead of your volt meter to neg on psu. Touch your pos meter lead to the non-banded side (anode) and you should read ~9V.

Reverse the diode and read ~.6v just like a regular si diode.

Please note: I am NOT saying to place the diode across the terminals of the psu.

Maybe you have it backwards in the circuit?


Please flame me if this is bad info guys


edit: netlist posted as I was typing, I'd bet his way is better as he is likely more qualified to answer the question....
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Old 7th April 2005, 07:03 AM   #8
Tom75 is offline Tom75  Switzerland
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I tried to check the Zener last evening. Useing one of our normal Lab PSU I connected the Zener, the PSU and the DMM as mpmarino suggested, the PSU starts blinking and telling me that I have an "open circuit", if I reverse the Zener, then I can read approx. 0,7 V. But then again the Diodetest on my DMM tells me that the Zener is OK? I tried this method at 12 and 22 V.

Anyway, do I get it correctly that this Zener should limit the voltage to 9,1 V of the Q3 source? because then I do not see how I do get the approx. 17 V. If the Zener is deffect wouldnt the full 34 V go through?

Additionaly I pulled Q3 that sets the source current for the diff. pair Q1 and Q2. Checking the MOSFET, everything seems to be OK with it. For checking I used the "protocol" found on the Homepage http://www.uoguelph.ca/~antoon/gadgets/mostest.htm
and everything seems to be OK there.
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Old 7th April 2005, 07:43 AM   #9
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Hmm,
If your not seeing a voltage with that test, it is behaving like a normal diode. The forward breakover voltage should be .6-.7v. The reverse breakover normally wouldn't be attained at a low voltage like this with a normal diode...therefore an open. Are you sure you have a zener there?

Normally you can not test the reverse breakover of a 9v zener with a regular multimeter. My assumption is because the meter can olny develop less than 9v (due to the 9v battery inside) and never reach breakover.

I would try netlist's method. maybe your psu needs to see an actual load before it 'turns on'?
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