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Is this occurrence known by another title?

Thread starter #1
This is a more detailed follow up of my Electronics freezing up thread.
I'd like to know if this is a common thing and what is it known as? I call it Logic Loop.


Logic loop! An explanation of an electronic anomaly
What is it?
A phenomenon whereas an Integrated circuit gets 'Locked' into a state and remains as such. And even after isolating the main power it remains in place and therefore causes the entire unit to fail in it's usual operations.

Causes:
Integrated circuits are complex pieces of technology and like all components - there is the threat of failure. It is thankfully rare but when it occurs, not having the relevant hindsight or experience can make it annoying and even expensive. Because of the complexity and density of the internal workings, the chances of the latter increase.
It could be a design flaw, a fault in manufacture, a power surge, bad grounding.
The list goes on but these issues are generic and can also cause problems elsewhere.
I use Integrated circuits as an example but there is the possibility of this being caused by a single Transistor; which are general purpose switches in many circuits. For a time I suspected faulty Capacitors that were leaking power to the chip and keeping the fault 'Alive' but I have since become sceptical.

Why does it lock - even after power off?:
Some level of data must be feeding into the tainted chip that makes it remember 'Where it was' so to speak, when powered down. It could be part of the Firmware or a list of commands stored in a ROM chip.
This is why, in my view why the loop remains. Various Gates that send appropriate data to other circuits jam up and the information stops.
So the unit is rendered useless.

What equipment can this occur in?:
Anything electronic that requires a series of commands to 'Boot' it up and bring it to life. It is a very rare occurrence and may have evaded conventional repair procedures, as a self-trained repair engineer I used many unorthodox methods with the risk of permanently destroying what I was working on. Or in the case of a Logic Loop - making an important discovery that has aided me greatly over the years and saved many items from the landfill.

Example:
I work with Jukeboxes as well as professional audio repair, sometimes the Coin Mechanism would reject coins. I powered down and restarted the (Digital) Jukebox and the issue remained. But, when I disconnect the Coin Mech multipin connector while the unit is on and then reconnect it - the coin Mech starts working again.

Any idea's people?
 

Pommie

Well-Known Member
Most Helpful Member
#2
Do you have an example circuit? Isn't it just that you didn't power down long enough or you need a bleed resistor on your main storage caps?

This is also why many circuit designers go to a lot of trouble to make sure an adequate reset circuit is incorporated.

Mike.
 

JimB

Super Moderator
Most Helpful Member
#3
But, when I disconnect the Coin Mech multipin connector while the unit is on and then reconnect it - the coin Mech starts working again.
Maybe there was a bad contact on the coin mechanism connector and wiping the contacts against each other cleaned the contacts sufficiently for to make a good enough contact for the mechanism to work again.

I have had similar problems, numerous times during the electronics fixer part of my career.

JimB
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#4
You seem confused as to what's happening and why - it sounds more like a 'fault' rather than a simple 'lock up'.

In micro-controller based equipment (almost everything these days) by FAR the most common problems are down to faults on the inputs to the processor, so it's been provided with the wrong signals, or no signals at all, and it's waiting for something to happen. A fairly common problem is in the reset circuitry, where it's never getting released from reset - this was a common problem with 'super capacitors', which were often used for memory backup and reset functions, and they don't have a very long life.
 
Thread starter #5
The coin mech was one example! I've also seen this happen to Pro CD players, Audio mixers. 'Faults' don't just go away, they have to be physically identified, located and remedied. Whereas this 'Lock' can be reset by merely starving it of current temporarily while the rest of the unit is powered.
 

alec_t

Well-Known Member
Most Helpful Member
#6
A lot of modern electronics contains a MOSFET or two. If the gate terminal of a MOSFET becomes disconnected, the gate capacitance can hold its charge level for a considerable time, so the MOSFET becomes locked in a certain state.
 

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