Mysterious host footswitch design - Page 1
Forum section: electronics / repair

author: AndreyS
author_rank: Regular Contributor
timestamp: July 25, 2020, 01:14:38 pm
content: Long story short. I've been having Digitech GSP1101 guitar processor for some time and it worked perfectly.The problem appeared out of nowhere, and I can't specify when and why. The symptoms of the problem are:The footswitch FS3X doesn't work if I'm using GSP with an amp, when used with headphones it workedSometimes crackling noises were recognizablewhen GSP connected to amp and turned on, bypass mode activated itselfafter further research I discovered that when I touch amp grounded metal parts with sleeve jack (which is connected to GSP), the GSP turns on/off bypass modeUpon disassembling GSP I found that grounding sleeve draws 330uA at 3.3V, which means there is somewhere 10k Ohm resistor (image #3, marked with white text top right).So finally after digging all this: there is a useless capacitor C349 (image #3 above 10k resistor), because the sleeve pin of jack socket is always touching metal shield around the jack thread which is always connected to GND pin of capacitor.When I removed that sleeve jack pin, it started to work properly, except when I plug out footswitch jack cable from the socket while GSP is on, it goes crazy, as someone epileptically hitting phantom footswitch button.This made me think the wrong jack socket was soldered into during manufacturing. But I am still confused how it could have possibly happened.What are your thoughts on that matter?

author: shakalnokturn
author_rank: Super Contributor
timestamp: July 26, 2020, 03:41:49 am
content: Although I don't know how the footswitch itself is wired, it looks as if the first contact ground/sleeve is used to detect if the footswitch is plugged.Agreed that C349 looks useless in this case but may be there for revisions that do not have the metal reinforcement on the jack thread.What is your reference point for the 3.3V measurement on the jack "sleeve"? Footswitch connected or not?The first things I'd check are cable continuity (starting with ground/sleeve) between footswitch male jack and inside pedal, same for amp to effects processor.

author: AndreyS
author_rank: Regular Contributor
timestamp: July 26, 2020, 04:14:10 am
content: Quote from: shakalnokturn on July 26, 2020, 03:41:49 am

author: AndreyS
author_rank: Regular Contributor
timestamp: July 26, 2020, 04:22:01 am
content: Quote from: shakalnokturn on July 26, 2020, 03:41:49 amIt is referenced to the ground (for example heatsink of 7805, I colored black those contacts on photos)The cables are checked and working properly.Also, as you can see the sleeve contact on that jack socket is not switchable, therefore it cannot be used as a detect. It is always touching the shielding and that's it.Now I am trying to find a supplier for Nuetrik NRJ6HF, which has all contacts TRS switchable. It this case placing C349 would make sense

author: AndreyS
author_rank: Regular Contributor
timestamp: August 04, 2020, 09:13:40 pm
content: An update.I've ordered a jack socket where all three contacts are switchable, and soldered it into GSP1101. Now footswitch works perfectly, no issues at all.Therefore, I believe the wrong jack socket was soldered at assembling manufacture (where only two contacts are switchable TR)