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Joystick Interface Chip (74LS541) Failures


Ikrananka

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While it's well known that the joystick interface chips (U18 & U19 : 74LS541) are prone to failure, I had been lucky enough to have never suffered this problem, that is until today!!!!  Having recently finished quite a few mods on my unit, a week ago I finally reassembled it, tested it for full functionality, and set it aside as a completed project and for use as my main CV.  Well, today I set it up to play some Frenzy and found that the controller was acting weird with the fire button seemingly always active and no ability to move right.  Testing various joysticks with a test rom showed that joystick inputs were often being misinterpreted, not interpreted at all, and sometimes would become stuck on.  All indications seem to be that the 74LS541 for Joystick 1 is failing.

 

I was very cautious to avoid touching the controller pins during my modding and to discharge myself of static before and during the work.  I also never plug in or unplug joysticks when the console is powered on.  Plus it was fully working the last time I powered it on.  So, my question is this, seeing as I don't believe I fried the chip during my modding, do these chips sometimes just fail with age?  Or must I have done something to trigger the failure?

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It was my understanding that these were really vulnerable to static. I've never had them go wrong either, but bought a couple replacements just in case. I keep reading that they always go bad as well, so I wanted to be prepared.

What's the test rom you used?

James

Sent from my Pixel 2 using Tapatalk

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The test rom is the System Test rom that comes with the AtariMax cart.  Although this relies on you pressing 3 on the keypad to select the joystick test which sometimes wouldn't work so I couldn't get the test rom to run - lol.

 

I just disassembled my CV and tested pins 2 to 8 on U19 (Port 1) and 3 to 9 on U18 (Port 2).  While all of the Port 2 pins are good with a consistent 2.5VDC, Port 1 (U19) has well below 2.5 VDC on pins 2, 7 and 8.  So, looks like my U19 has definitely suffered a failure.  Time for a replacement.

 

I'd still like to know if these do fail spontaneously.

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1 hour ago, Ikrananka said:

I'd still like to know if these do fail spontaneously.

Well, in general it's not a question of whether a chip will fail, but of when it will.  Many factors contribute to useful life:  Heat, static discharge, manufacturing defects, external stress from propagated mistakes, etc.  Many will only reduce its useful life rather than killing it right then, meaning that you may not know exactly when the problem started, only when it finally took its toll.

 

Some useful information for the curious:  https://en.wikipedia.org/wiki/Failure_of_electronic_components#Semiconductor_failures

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14 hours ago, ChildOfCv said:

Well, in general it's not a question of whether a chip will fail, but of when it will.  Many factors contribute to useful life:  Heat, static discharge, manufacturing defects, external stress from propagated mistakes, etc.  Many will only reduce its useful life rather than killing it right then, meaning that you may not know exactly when the problem started, only when it finally took its toll.

 

Some useful information for the curious:  https://en.wikipedia.org/wiki/Failure_of_electronic_components#Semiconductor_failures

Thanks - this at least makes me feel a little better that it may well not have been my fault that the chip failed.  That said 99% of that wikipedia article went over my head - thank goodness for fiddlepaddle's easy to understand summary ?

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Replaced the faulty 74LS541 and port 1 is now working fine with one of my newly refurbished controllers.  Interestingly though the joystick I had been using has gone faulty with the keypad being totally non-functional.  So, I wonder if the failure of the keypad had anything to do with the failure of the 74LS541 or vice versa.

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My initial guess is probably not.  The entire joystick works by grounding inputs, aka shorting them out.  Since the system is designed for this, it doesn't cause damage.  At worse, it causes unexpected inputs.  If pins 5 or 8 were shorted to ground (not possible through the controller port, but...) it would affect the selector circuit (the 7400), but not the 541.  And that circuit has a 120 ohm resistor that ought to protect it too.

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2 hours ago, ChildOfCv said:

My initial guess is probably not.  The entire joystick works by grounding inputs, aka shorting them out.  Since the system is designed for this, it doesn't cause damage.  At worse, it causes unexpected inputs.  If pins 5 or 8 were shorted to ground (not possible through the controller port, but...) it would affect the selector circuit (the 7400), but not the 541.  And that circuit has a 120 ohm resistor that ought to protect it too.

Thanks - nice to know.

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Just now, Bmack36 said:

https://console5.com/store/anti-static-d9-joystick-port-esd-set-pair-of-2-static-protection-add-on-pcb.html?fbclid=IwAR3f077t2UP92tYh3DawfAovJ3_JS4Re00tirH4poRPdTF9x6_0roBZ1lUs

 

Ruggers Customs made this ESD board for the CV joystick ports to add the Zener Diodes that the Adam used as well as some factory reconditioned cv systems.

 

Yep, I saw those when Ruggers recently announced their release.  I'm certain that I didn't fry mine with an ESD and have never had issues with these chips in all the years I've worked on CV motherboards.  So, while I think it's great these boards are available, and perhaps I'll add some at a later date if I have other things to order from console5, but at the moment I'm in no rush to buy any.

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