Author Topic: No buttons or encoders - solved  (Read 1245 times)

Road_Kill

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No buttons or encoders - solved
« on: February 09, 2016, 08:32:32 AM »
Hello Xavier,

I just built a PreenFM2 kit and had an issue I haven't seen on this forum before that I thought I would share.  When I first turned my preen on, I got the boot loader screen and none of the buttons or encoders would work.  After poking and prodding, I could get the synth to boot normally, but still with no encoders or buttons. A reboot would simply put me back to the boot loader screen.  After much more poking and prodding, I came to find that if I so much as lightly touched the leads around the resistor networks, I could boot into the normal screen.  Every subsequent reboot would take me to the boot loader screen until I lightly touched the leads anywhere around the control scanning circuits a which point I could reboot to the normal screen again.  I suspected a poor solder joint but could never locate one.  Eventually I got the schematic and systematically checked connections until I realized that pin 1 from both 74165s were not reaching pin 6 of the 405.  This turned out to be a defective trace on the pcb as opposed to anything I did or didn't do while assembling the circuit. A small wire soldered between pin 6 on the 405 and pin 1 on one of the 74165s was all it took to have my preen up and running! Now it's hooked up to an Undead Instruments Timefrog purring in the background while I write this email. Time to go play with it some more!

Xavier

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Re: No buttons or encoders - solved
« Reply #1 on: February 09, 2016, 09:14:59 AM »

Thanks for the feedback and congrats for fixing the problem.
From what i remember, this is the first PCB trace problem i hear about.
They are rare but very very annoying.

Glad to read your preenfm is now working  :)


Xavier

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Re: No buttons or encoders - solved
« Reply #2 on: February 09, 2016, 09:20:49 AM »

Just a question : did you order the PCB from me or did you make it yourself ?
Note that i don't have any problem at all with the latter when not for resale  ;)

I ask that because i tried to find what batch was your PCB from and i don't see any PCB associated with your email.

Thanks,

Xavier


Road_Kill

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Re: No buttons or encoders - solved
« Reply #3 on: February 09, 2016, 09:42:29 AM »
I picked up the kit from Van Daal.  I'm not 100% certain where the trace is broken, but I suspect it's where it passes between the pins (9&10 I think) of the 74165.

Xavier

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Re: No buttons or encoders - solved
« Reply #4 on: February 09, 2016, 10:17:25 AM »
I picked up the kit from Van Daal.  I'm not 100% certain where the trace is broken, but I suspect it's where it passes between the pins (9&10 I think) of the 74165.

Ah OK thanks.
That's my latest PCB batch.
Sorry to ask that but are you sure it was not a bad soldering point ?

Road_Kill

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Re: No buttons or encoders - solved
« Reply #5 on: February 09, 2016, 02:56:27 PM »
No need to be sorry! First of all, as you probably figured out, I meant to say I thought the break was in the trace between pins 15 and 16 of the 74165.  Im on the other side of the pond and it was way past my bedtime!

I'm not the greatest craftsman when it comes to yielding a solider iron, but I've been involved with electronics most of my life thus have some experience.  The connections were all good with no bridges, cold joints, over or under soldiering.  While I reflowed the contacts in question, none of the pads were overly cooked and damaged.  I felt I checked my work and the schematic about 1000 times before I applied the jumper wire fix.  Again, I could occasionally get the synth to boot up in its normal mode as opposed to the boot loader screen.  At first I thought this was because I hadn't seated the chips properly, but it would only boot up right after my pressing or somehow slightly flexing the board and won't boot right on subsequent tries.  That's when I really started suspecting a crack in a trace.  Then, when I found that just the application of my finger around the 74165s and resistor network while the synth was unplugged was enough  'stimulus' (charge or discharge of what ever small voltages were there at the time) to consistently allow the synth to boot in the right menu (but still w/o button or encoder functionality), I became convinced there was an open in the curcuit somewhere and I began the steps to find and fix it.

BTW, the forum topic where mmarsh had no button functionality really helped me narrow the problem down.  Not only because of how it was related to my problem, but because I figured if someone like him could resolve his problems to go on and create fantastic sounding music and demos with the Preen, than maybe there was hope for some poor soul like me!

Xavier

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Re: No buttons or encoders - solved
« Reply #6 on: February 09, 2016, 09:28:44 PM »

Thanks for the details  ;)
I'm glad it works because debuging that kind of hardware problem is not easy.