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gunnadoo

Nov 9, 2017
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hi, i hope this is off topic enough ,as it is not a question. anyway it all started many moons ago, when old mate give me a beginners electronics book. i knew the basic ohms law, as i have been off grid power for 27 years now. so i tried to make a transistor work. so after lots of tries/ failures, i swore and cursed and gave the bloody book back. fast forward to 5 days ago, i decided a transistor would solve my problem .
so get on www and try and learn again, [i am proficient with metal and wood though], i still had a couple of bd139,s from way back ,so give it another go. i sort of got one to work, but the relays stayed latched on , after i turned base off!...? . ok try the other one, FAIL !. during these tests i destroyed the MA function on 2 dmms.
so, off to jaycar , [electric/onics retailer] for $10 dmm and 4 [bc338] and 4 [pn2222a] transistors]. at home i double check data sheet and EPs guide/equations [pn2222]. all good, connect c/e to load [40MA relay coil] and on it goes !..what the *%&#. the base was not connected yet . so i triple check data sheet , equations and wire connections again. try again , same thing , this is really starting to do my head in , [doubting my sanity] , flash backs to my first attempts etc. i was at a loss and ready to kill anything with a transistor in it.
arghh, then the "penny dropped" , to check numbers on transistor, so,i had to find a microscope [nearly] to read the numbers [p2n2222a], back to google ,123=CBE whereas [pn2222a is 123= EBC] . they are one and the same. i specifically asked for [pn2222].... what is it,? about engineers ,that they have to complicate everything..the moral about this story is, rule #1 never trust a salesman. rule #2 [see rule #1] sorry about the rant , and i will ask my questions in the appropriate forum...

regards..
dennis..
 
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HellasTechn

Apr 14, 2013
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during these tests i destroyed the MA function on 2 dmms.

This story reminds me of myself... Never i had started a project and had sucess right from the beginning.

Anyway the DMM's have a small fuse inside. You should check it before you throw them away.

Also you should buy one of theese... I can not live without it anymore !
it measures transistors, fet's, diodes, capacitors, resistors and many more.

https://www.ebay.com/itm/LCR-T4-LCR...hash=item5d6b4d939a:m:mVttfkmvKz6Sp-ldjPpNqOw
 

gunnadoo

Nov 9, 2017
17
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Nov 9, 2017
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thanks for the link, just bought one. also does anyone know if there is a gadget/shunt type of thing that will measure, say , 1 mA to 10 Amps

thanks..
 
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Bluejets

Oct 5, 2014
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Most standard, elcheapo even, multimeters will cover from 1mA to 10A dc.

You just need to learn to double check connections before switching on the power and set the meter to the appropriate scale beforehand.

If in doubt, select high range first.

As far as transistor testers, one can get by with just the add-on again in the elcheapo meter.

Most of my bench work is done with a $50 digital multimeter and a capacitance meter.
Also keep an old analog meter handy for when the digital will not cut it.

In the field with electrical it is a different story requiring the up market gear.(high catagory meters)
 
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gunnadoo

Nov 9, 2017
17
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thanks, but my impatience/dementia fails me lots of times and changing the plugs and switching from mA to A often, annoys me. [ maybe i need impatience counseling ].
i was thinking a meter with 2 leads that would measure both.

thanks..
dennis
 
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Bluejets

Oct 5, 2014
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It's not that difficult.:confused:

If you are having trouble now, wait until you get past basic on off.
 

shrtrnd

Jan 15, 2010
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Impatience with those amperage readings will blow the multimeter internal fuse.
If you think you get frustrated now, it'll be worse after blowing your meter fuses a few times.
Try to remember to stop and think before making those current measurements and you'll stay happy.
 

HellasTechn

Apr 14, 2013
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Well, Its normal to make mistakes and blow a few instruments and destroy a few boards... Who has not done that as a beginner ?
 

bushtech

Sep 13, 2016
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Sep 13, 2016
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gunnadoo, I feel for you, been in that boat too many times myself. My current head do inner is isolating a BD139 from a heatsink.
 

bushtech

Sep 13, 2016
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Yes, but the underside has got a metal pad for heatsinking
 

FuZZ1L0G1C

Mar 25, 2014
366
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Mar 25, 2014
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366
Letting the smoke out occasionally is a hazard of the profession / hobby.
My Major-Tech DMM which knocked me back several grand recently blew a PCB track when I tested 220V AC while still on 'inductance' scale.
Early morning hours, brain tired, lack of concentration, etc...
 

HellasTechn

Apr 14, 2013
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My friend this is only normal. We are Human not robots.
My worse accident was breaking an 50" lcd panel of an expensive LG television... It was late in the night and i was tired, not to mention i have not sleept all night thinking how much i had to pay to replace the tv.
:)

Only those who do not work, do not make mistakes !
 

HellasTechn

Apr 14, 2013
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Yes...
I had successfully disassembled the lcd panel, located and replaced a bad led and after re assembling it I noticed that the diffusion lens has not placed correctly. I had to disassemble the lcd panel again to reach the lens and that was when I heard that awful crack sound !!!
 
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