*solved* Shift button is permanently stuck on now. Halp

I finished my build about a year ago and have had no issues with it until last night when I sat down with it, turned it on, it looked fine, and then all of a sudden it started playing at some super high tempo... I pulled the plug, plugged it back in, and now it wont make a sound. I can't start the sequencer and I can't get it to function in expander mode either. All 6 LED's on the left side are lit solid, and if I go into init mode all I have to do to initialize the machine is press start. So my suspicion is that something in the shift circuitry died,but I'm not sure where to look... I don't see any obviously burnt or physically damaged components or bad solder joints.

Suggestions? It's pretty strange that it just randomly died on me like that.

"Shift" button could be stuck by the metal case.

Best regards,
e-licktronic

Thanks for the reply, i have the pcbs removed from the case and it is still behaving this way. The switch itself still appears to function correctly physically but it has no effect electronically, the rest of the machine acts as though the shift button is being held.

Sawwaveanalog wrote:Thanks for the reply, i have the pcbs removed from the case and it is still behaving this way. The switch itself still appears to function correctly physically but it has no effect electronically, the rest of the machine acts as though the shift button is being held.

Check voltage value at IC7 pin 12 you should have 0v. If it's not the case , desolder the shift button and measure again, if you still have a value different to 0v at IC7 pin12, look for a solder bridge or a bend resistor touching an other.

Best regards,
e-licktronic

Hey, thanks for the advice again, I had some bad stuff in the real world happen right after you posted so I didn't have a chance to try your suggestions until tonight and here are the results:

There is +5v at pin 12 of ic7 at all times

I then desoldered and removed the shift button and there was no change, there is still +5v on pin 12 of ic7.

I am looking around and don't see any obvious bent parts/bridged connections, I'm at a big of a loss. The thing was working perfectly for a year and then my friend slightly hit the table it was on and now it is very sad...

Any other suggestions of where I should be looking would be very much appreciated

with the yocto powered down, measure the resistance from pin12 to pin16 (VCC)
if it's pretty much zero ohms - then you have a short somewhere.. if it's a higher value then maybe a resistor is just slightly touching somewhere..

Resistance between pin 12 and pin 16 on ic 7 is 71 ohms. I still have absolutely no clue what is wrong. No resistors in the sequencer section are visibly touching and ive blasted everything with air for minutes.

This thing worked perfectly for over a year, and then a slight bump of the table caused this. I'm at a loss.

71 ohms won't let too much current flow, so that's good, otherwise, a full short would cause something else to heat up a lot
now, if you don't see a resistor touching somewhere, then maybe it could be inside the shift register
if the shift register (IC7) is socketed - remove it from the socket, and check resistance between the two points on the board again
if the resistance is still ~71 ohms then the problem is certainly somewhere on the board
if the resistance is towards infinity - then the problem is in the shift register (busted probably) - get a replacement and plug it in

antto wrote:71 ohms won't let too much current flow, so that's good, otherwise, a full short would cause something else to heat up a lot
now, if you don't see a resistor touching somewhere, then maybe it could be inside the shift register
if the shift register (IC7) is socketed - remove it from the socket, and check resistance between the two points on the board again
if the resistance is still ~71 ohms then the problem is certainly somewhere on the board
if the resistance is towards infinity - then the problem is in the shift register (busted probably) - get a replacement and plug it in

Hey, it has been a while (again lol) but I finaly got back to the yocto today and desoldered ic7, resistance betwee pins 12 and 16 on the ic out of circuit is still 73 ohms, resistance between those points on the board is 15k ohms and climing. Soooo the shift register ic is dead yeah??

Thanks again for all of your help, I'm ordering another one now

Sawwaveanalog wrote:
antto wrote:71 ohms won't let too much current flow, so that's good, otherwise, a full short would cause something else to heat up a lot
now, if you don't see a resistor touching somewhere, then maybe it could be inside the shift register
if the shift register (IC7) is socketed - remove it from the socket, and check resistance between the two points on the board again
if the resistance is still ~71 ohms then the problem is certainly somewhere on the board
if the resistance is towards infinity - then the problem is in the shift register (busted probably) - get a replacement and plug it in

Hey, it has been a while (again lol) but I finaly got back to the yocto today and desoldered ic7, resistance betwee pins 12 and 16 on the ic out of circuit is still 73 ohms, resistance between those points on the board is 15k ohms and climing. Soooo the shift register ic is dead yeah??

Thanks again for all of your help, I'm ordering another one now

Order a few extras. Also order other IC's (they're not that expensive). It's frustrating to order just one and then needing two...