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Old 30th November 2011, 07:31 PM   #1071
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Hi Zen,

these fets were sent me by Wayne .... I assumed they had been matched .
Rich
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Old 30th November 2011, 07:38 PM   #1072
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then even worse , because we can't doubt jfets came from that direction

now is time for learning ; desolder , one by one , each semiconductor and test it

bjts with diode test , jfets in testing/matching jig

it really doesn't pay of , when you troubleshoot circuit randomly .
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Old 30th November 2011, 07:55 PM   #1073
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I have this made up for testing IRF240 ,but never sure i was doing it right ?

I have a variable DC power source ..... how many VDC for these little suckers ?


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Old 30th November 2011, 08:20 PM   #1074
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search through forum

"testing jfets"

or search through Papa's articles
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Old 2nd December 2011, 01:46 PM   #1075
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A simple way is to go for their IDSS without any RS (Source resistor) because jfets self bias pretty easily.
A 9V battery, and + to drain and - to gate/source shorted together. in series you put the mA meter, let them idle and just read values

For P types, just reverse the battery polarity

Best,

nAr
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Old 2nd December 2011, 01:55 PM   #1076
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Quote:
Originally Posted by richluvsound View Post
I keep blowing fuses .... I have checked one board and I'm with 1.5 VDC .
I unplugged it and plugged back in ... LOL fuse blew . Would an NTC across the
IRC stop it ?

I'm going to check the other board against the Voltages I have from Wayne . I'm checking one board at a time - the other board just blows the fuse as soon as I power it up !

Any guidance would be greatly appreciated

Rich
Check for shorts on the faulty board first with continuity meter. Probably a solder joint touches somewhere it shouldn't ...

The read values seem fine at a quick glance except the -26.2 V at led reference point. Obviously value reading here should be : about 1,6V - 1,8V across LED1. Or, -22,4V to -22,2V between up leg (seen on schematic) of the LED and GROUND.

Best,

nAr
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Old 2nd December 2011, 10:47 PM   #1077
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Thanks Nar,

I have removed all the active parts and checked voltages after regs and all good ...

I will test Jfets tomorrow . I have a transformer that will give me 9.75 VDC
will this be ok to use ?

best, Rich
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Old 3rd December 2011, 03:20 AM   #1078
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You should use a 9 volt battery, because you need a fairly stable DC power source. If you have a good adjustable bench top power supply, you could use that, but a battery is a very good substitute.
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Old 3rd December 2011, 03:05 PM   #1079
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Ok , now I have got 6L6 lost too ... when I wire one board at a time to PSU all good ,but when both are wired the fuse blows ( no actives on either board- all voltages are good post Reg ) . I'm sure that .250 mA is advised for 240 AC - 3.15 at IRC

6L6 has checked pics of wiring and confirms its correct . I'll put some on here if needed .

Thanks , Rich
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Old 3rd December 2011, 04:01 PM   #1080
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Photos of wiring .
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