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 Post subject: ohmeter test failed
PostPosted: Mon Oct 22, 2018 3:20 pm 
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Joined: Mon Oct 22, 2018 3:07 pm
Posts: 6
the test 1,2,3 are not following manual values.

test1 = 0
test2 = 220 Ohm
test3 = 30 Ohm

maybe my ohmmeter is not fully aligned, but test results are not as aspected

any suggestion ?

thank
Don


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 Post subject: Re: ohmeter test failed
PostPosted: Tue Oct 23, 2018 5:23 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1103
Hi Don,

There is definitely something wrong with your measurements because it would be physically impossible for test 2 to show more resistance than test 1. In test 1 you are measuring the MOSFETs Drain to Source resistance with the MOSFETs biased off, which should be very, very high. In test 2 you are adding the rest of the HR50 circuitry in parallel which, if you don't have the QSK board, should be about 1.9K and if you do, it should be about 400 ohms.

If, in fact, one of the MOSFETs is shorted and test 1 reads 0 ohms, then test 2 would read 0 as well.

73,
Jim WA2EUJ


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 Post subject: Re: ohmeter test failed
PostPosted: Fri Oct 26, 2018 1:11 pm 
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Joined: Mon Oct 22, 2018 3:07 pm
Posts: 6
Hi
wrote a wrong thing and also a limit of my DMM

Test1= reading is excessing the DMM limit and now resistance can be read
Test2= abt 300 ohm
Test 3= all 4 mosfet abt 40

and so based on the test 1 I do not know if proceed to next tests or not.....


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 Post subject: Re: ohmeter test failed
PostPosted: Sat Oct 27, 2018 7:42 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1103
Does you amp have the QSK board?


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 Post subject: Re: ohmeter test failed
PostPosted: Sat Oct 27, 2018 10:40 am 
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Joined: Mon Oct 22, 2018 3:07 pm
Posts: 6
hi,
yes, QSK board mounted and motherboard version G


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 Post subject: Re: ohmeter test failed
PostPosted: Sat Oct 27, 2018 9:31 pm 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1103
With the QSK board installed you should be OK. Since your meter reads 40 ohms from the gates to ground, I believe that you ohm meter is reading about 20% lower than the actual value. If that is the case, then reading 300 ohm on test 2 would be OK.

Do you have a know resistor that you can verify that your ohm meter is reading correctly?

73,
Jim WA2EUJ


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 Post subject: Re: ohmeter test failed
PostPosted: Sun Oct 28, 2018 4:40 am 
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Joined: Mon Oct 22, 2018 3:07 pm
Posts: 6
hi
yes instrument is not so good, and it provides a little low measure( I did a benchemark).

I went forward and verified currents and mosfet bias.

everithing was fine and I will connect to power RF ;)
Thanks andkeepin touch on Forum

73
Don


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