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Old 3rd October 2011, 04:14 PM   #1371
AndrewT is offline AndrewT  Scotland
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The jFETs are not easily damaged.
I rarely use the heat shunt (sitting on the shelf) when soldering any semiconductors.

I handle all my FETs except opamps.

So far I cannot blame my bad handling/soldering methods for any failures.
Plenty of failures due to mis-connecting.

I think you have a broken connection somewhere.
If one or other of the jFETs had gone bad, then I don't think the output offset would be near zero.
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Old 4th October 2011, 08:47 AM   #1372
cersepn is offline cersepn  United States
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So this time i tried taking out the male 3 pin molex at the output, to see if that was the problem because i was fiddling with the pins before and bent it quite a bit. Measured the right channel output directly at the pcb and the offset is ~ 0.. so the right channel is probably close to dead (since there is *very* slight sound) i guess? Possible relay problem? Looks like i'll have to do proper testing as Salas rightly advised!
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Old 4th October 2011, 10:14 AM   #1373
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I think the relay would cause a problem with both channels.
Measure agross the pins of 4 2SK's. D-S.
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Old 4th October 2011, 10:33 AM   #1374
weskoki is offline weskoki  Europe
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Here's my dcb1 strapped on card board for now.I think i need bigger sinks
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Old 4th October 2011, 10:46 AM   #1375
AndrewT is offline AndrewT  Scotland
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How hot do your heatsinks get?

Are the sinks large enough that the circuits & components survive for the two worst case faults?

Worst case for CCS mosFET is maximum mains voltage and shorted output.
Worst case for Shunt mosFET is open circuit output.
In both these fault situations the Amplifier is not working, so sound quality is not the issue. Survivability is the only issue.

Note, both these worst case situations cannot occur at the same time. With shorted output the sink only has to cool the CCS mosFET. The shunt mosFET is dissipating no power. You have a coupled sink. What is the dissipation of the normally operating stage. It has to dissipate and operate while the other half is in fault condition.
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Last edited by AndrewT; 4th October 2011 at 10:50 AM.
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Old 4th October 2011, 10:57 AM   #1376
weskoki is offline weskoki  Europe
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I can't hold my hand on the sink for more than 5 sec. I have let the pre working for 30 min and it survived.
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Old 4th October 2011, 11:10 AM   #1377
AndrewT is offline AndrewT  Scotland
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5sec tolerance to sink temp is not a test for survivability.
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Old 4th October 2011, 12:04 PM   #1378
cersepn is offline cersepn  United States
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Quote:
Originally Posted by Tea-Bag View Post
I think the relay would cause a problem with both channels.
Measure agross the pins of 4 2SK's. D-S.
Thank you for your advice, Tea-Bag.

Is this the right way to test?
How to test FET’s-Jfet and Mosfet - Electronic Circuits and Diagram-Electronics Projects and Design

Am i supposed to test the 2sk while the dcb1 is on?
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Old 4th October 2011, 12:49 PM   #1379
AndrewT is offline AndrewT  Scotland
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No,
the measuring/testing is done with the DUT in a jig.

You can check the accuracy/repeatability of your testing by measuring the output offset from the completed DCB1.
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Old 4th October 2011, 02:13 PM   #1380
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I measure voltage across the 2Sk's then run a test signal (can be a line source) into the input, and measure AC out voltage from the output. The voltage should be in the 9-10v range.
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