Fried Micro820?

RobertB · May 6, 2020

Good day to all,

I have a Micro820QBB Ser B. Manfactured 2017.
Bought it off Ebay.
Appears to be in good shape.

I am noticing that as soon as I connect +24vdc to output common "+CMO".... I immediately get 21.5vdc on outputs 0/0, 0/1, and 0/2.
Power supply is 23.99vdc.

I thought maybe an old program was still inside... keeping outputs high.... so I downloaded a new program and even programmed these outputs as -(/)-, ODE.

Outputs still have 21.5vdc on them!!!!
Allen Bradley manual says these outputs can be used for analog also, soooo is this maybe 'parasitic voltage'? (inducted voltage from nearby traces, but can't feed a real load)
????

Thanks for reading.

Maxkling · May 6, 2020

Have you put a load on them? It can be current leakage from suppressor or solid state relays.

RobertB · May 6, 2020

Output terminals are empty. Not even a short testing wire.

geniusintraining · May 6, 2020

99% of the time a transistor output will short out closed when bad

Only V0-0 is your analog output, the other are digital and you will skip 0-0 if your using V0-0

Try using a meter as a load or even if you have a LED 24 lamp

RobertB · May 6, 2020

I did use my Fluke meter which is technically a tiny load. Maybe that's why it is reading 21.5v instead of 24v. I have a 20mA LED indicator light. I will hook it up. If this is parasitic voltage??, I bet that LED will quickly snuff out this 'hinky voltage'.
The adjacent outputs tied to +CM1 are doing the same thing. It's hard to believe ALL the outputs are fried???

Maxkling · May 6, 2020

RobertB said:
Output terminals are empty. Not even a short testing wire.

Try to hookup a load like a bulb or relay. Or use a solenoid meter like a Wiggy. I still think it’s just current leakage, your DMM won’t be able to draw it down.

RobertB · May 6, 2020

Wiggy! Haven't heard that in a while. Bullet proof V meters, though.
I will give you all update after the 20mA LED hookup.

geniusintraining · May 6, 2020

RobertB said:
Wiggy! Haven't heard that in a while.

They still make them last time I looked, I still have a Simpson analog, if its fast the DMM will not catch it but on the Simpson you will see the needle move

RobertB · May 6, 2020

Sad news...
All outputs are lighting the indicator light (24vdc/.48watts)
Out of curiousity, I turned ON the outputs.
Indicator lights got brighter. (probably 24v instead of the 21.5v)
sigh....={
Anybody want a cheap Micro820??

Ken Roach · May 6, 2020

The -QBB model has solid-state power transistor outputs, rated for a nominal 1A each at 24V and 30C.

The Installation Instructions call out a 10 mA minimum load, and specify a 1 mA maximum leakage.

That's consistent with the schematic for a P-channel MOSFET power transistor shown in the Micro 820 User Manual.

I think you will find that when you connect any sort of drain load to the output that can sink more than 1 mA without turning on that you won't measure that voltage anymore. If you can grab an incandescent bulb or relay load, even better.

Edit: you often get damaged stuff on the aftermarket.

RobertB · May 6, 2020

After the previous owner smoked 2 or 3 outputs, you'd think he would have said, "****, this ain't working!"
Why all 7 outputs!??!?

geniusintraining · May 6, 2020

So I just tried new out of the box... I have 8.5 from ground to output, I also have the positive and negative wired up, I have 4.5 on outputs that are wired but not on, what about your LEDs for the outputs are on the PLC are they on also?

RobertB · May 6, 2020

I do not have the -CM0 wired ALSO. Just the +CM0. As for the indicator lights on the front of the processor... they work as they should. My 'snitch' program was simply I:0/1----(O:0/1)-,
I:0/1----(O:0/1)- etc.
All front screen processor I/O lights fired as expected.

Just can't get rid of the +21.5 on the outputs when they are LOW.

Wandering if I could wire SINKING outputs?

geniusintraining · May 7, 2020

RobertB said:
I do not have the -CM0 wired ALSO. Just the +CM0.

Its a transistor... you MUST hook up all wires, positive and negative, you are backfeeding voltage through the transistor through your meter and you are reading line voltage

Hook up both wires then test the output again

RobertB · May 7, 2020

I thought if you sourced, then connect outputs to a common available positive.
If you sinked, " " negative.
In my mind, seems like I am creating a dead short by connecting both to the available common.
But like you said, QBB is TRANSISTOR outputs. I connected both. There was a little spark, but it didnt blow anything. Now, my OFF outputs are 8.5v. My indicator output lights correctly now. The output to the indicator light is 2.0 when OFF. Plenty low enough to keep a 24vdc output OFF.
Thanks for your help. You're the best!

Fried Micro820?

RobertB

Member

Maxkling

Member

RobertB

Member

geniusintraining

Lifetime Supporting Member + Moderator

RobertB

Member

Maxkling

Member

RobertB

Member

geniusintraining

Lifetime Supporting Member + Moderator

RobertB

Member

Ken Roach

Lifetime Supporting Member + Moderator

RobertB

Member

geniusintraining

Lifetime Supporting Member + Moderator

RobertB

Member

geniusintraining

Lifetime Supporting Member + Moderator

RobertB

Member

Similar Topics