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PS reversed polarity! What did I damage in my ACA & B1?
PS reversed polarity! What did I damage in my ACA & B1?
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Old 20th March 2017, 09:47 PM   #1
BeardyWan is offline BeardyWan
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Default PS reversed polarity! What did I damage in my ACA & B1?

I have just completed my first build using a B1 feeding two ACA boards. Having carefully noted which of the DC input socket pins were plus and minus I inadvertently reversed them and swapped the supply rails into the entire project! Apart from clearly demonstrating my own idiocy, I am now left with a project that neatly lights up three LEDs but doesn't do much more. I am using a Dell 19.5V supply and have the most recent version of the forums boards.

Can anyone help me determine how I get this running?
I have voltmeter.
All help gratefully appreciated.
thanks
Beardy
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Old 20th March 2017, 10:53 PM   #2
Zen Mod is offline Zen Mod  Serbia
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PS reversed polarity! What did I damage in my ACA & B1?
pay price for schooling and replace all semiconductors

learn how to check resistors with DMM
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Old 20th March 2017, 11:01 PM   #3
scottjoplin is offline scottjoplin  Wales
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Hasn't he just payed the price.
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Old 21st March 2017, 12:32 AM   #4
BeardyWan is offline BeardyWan
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Unfortunately this wasn't at all educational as I was already fully aware of the likely consequences from getting this wrong. Nothing more than inadvertently swapping the leads.
I am assuming it took out the semiconductors - I guess what I am asking is
can someone knowledgeable and prepared to share please look at the schematics of the B1 and the ACA and tell me which will have blown and whether it will have taken out all or just some of them.? If `some', which ones? Is there a good way to test using a DMM- diodes and resistors are fine but it would be helpful to know what resistance I might expect to see across the legs of a perfectly healthy semiconductor and what I might expect to see across one that is dead as a result of this type of event?
with thanks
Beardy
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Old 21st March 2017, 12:37 AM   #5
scottjoplin is offline scottjoplin  Wales
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Chances are it's taken them all out. They will be damaged anyway. Replace them all
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Old 21st March 2017, 12:50 AM   #6
phase is offline phase  United States
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I did that when working late, trying to rush things a bit, it took weeks and lots of parts to get it back again.
The light bulb tester is a good thing to have around and be sure to always use any time you are messing around with anything inside. Not sure if that would have been 100% effective here though.
Sucks man, sorry to hear that.
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Old 21st March 2017, 02:43 AM   #7
Loudthud is offline Loudthud  United States
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The Drain to Source diodes in those IRFP240s are pretty robust, they can withstand 20 or 30 Amps all day long. What might have acted as a fuse are the 2 Watt resistors, R1-R4.

The power supply should have gone into protect mode and shut off or pulsed on-off unless those resistors were damaged enough to become open. Check those resistors, if they are ok, chances are pretty good that nothing else was damaged because the Voltage coming from the supply would be limited to about 2V. The power supply should have detected a near short and shut off.

If the ACA does not start to get warm after a minute or so, take Voltage readings at all the transistor or FET pins and post the results. Set the pot about mid rotation.
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Old 21st March 2017, 02:53 AM   #8
BeardyWan is offline BeardyWan
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just started the task of ripping it apart and no signs of heat anywhere.
pulled first 3 semiconductors from one aca board
2sk170 shows ~35ohms d-s or s-d
infinite resistance using negative lead on gate and +ve on either D or S
~5Mohm using +ve lead on gate and -ve on D or s

tested first irfp240 and this checks out per this simple DMM test https://www.utm.edu/staff/leeb/mostest.htm
and doesn't show short drain to gate

ztx450 also seems to check out OK with DMM
-ve on B and infinite resistance to c or e
+ve on base and continuity to c or e
will replace back in board and then fire up single ACA board and test boards individually.
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Old 21st March 2017, 03:01 AM   #9
adason is offline adason  United States
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Consider using proper linear power supply, rather then dell switching noisy computer thingy
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Old 21st March 2017, 03:07 AM   #10
BeardyWan is offline BeardyWan
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r1-4 all measure low resistance and continuity on board but I haven't pulled them off.
all look brand new with no signs of heat.
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