More stupid tales from the bench

[Mark Hammer]

I have a Hot Tubes clone that worked fine for a number of years.  The box was getting a little mangy looking, so I stripped it right down to bare metal and put a nice finish on it with some nice knobs and legending.

Great.  Box it up again, and the damn thing doesn't work.  Looked for all the usual bridges and discontinuities, but no dice.  Tonight, I'm probing around for AC signal voltages and I'm not getting anything.  I mean, I'm getting a couple of millivolts, but no real sign of amplification.

Okay.  What the hell, the battery connector looks good, and there was 9v in all the right places before I took the board out to refinish the box, but I'll check anyways.  Sure enough, no 9v on the V+ lines.  Huh?  I look a little closer, and sure enough, the ring contact on the stereo input jack had been bent back juuuuuuuust a tad so that it looked like the plug made good contact, but in actuality it didn't.  So, no 9v because the input jack was not enabling the battery.  Pulled the plug out and bent the contact.  Plugged it in and fired it up.  Good as new.

There is a lot to be learned by simply checking for the (maybe not so) obvious.

BTW, I dunno why the schematic stipulates a 2M gain pot.  Mine goes from full gain to bland clean within 20k of that pot.  Musta been some weird-ass taper on the original.  I'm just going to swap the one in there for a smaller value.

[mattthegamer463]

A while back I built a Phase 90 clone, and the circuit worked great, but when I boxed it up it wasn't working at all, except in bypass.  I tried the usual suspects: voltage, shorts, making sure nothing was touching anything it shouldn't, but it was still not working.  I took it out of the casing and it worked great again.  In the process I managed to break a solder joint without noticing, and then when I found that I was celebrating a successful repair, until it didn't work in the box again.  I put a test signal through and could see the phasing on my O-scope, so I was baffled.

3 hours later, it turns out when the output jack is plugged in, it bent the tip connection ever so slightly to actually touch the housing (I guess I drilled the holes too close to the top of the 1590B) and the signal would short to ground.  Turning the jack and re-tightening fixed it right up.

I'm glad I finally got it going, any longer and I might have taken my torch to it in retribution.

[Kearns892]

A month or so back I was showing off my newly completed Peppermill build to a friend. I hit the switch to go from clean to some peppery goodness and, of course silence. The back was already off (as I had made the mistake of showing off the guts first, only adding to my embarrassment   ) and I started searching for any sort of intermittent short that may have allowed it to work before. After a few minutes and a lot of lost cred as a guitar DIYer, I realized in my excitement I had reversed the input and output...

Still not as bad as the time I started debugging a circuit for no signal when my amp was really turned down to 0... At least no one was there to see that...

Maybe this thread's name should be changed to "More Confessions from the Bench"

[newfish]

Ins and outs are easily reversed...  (recent Rangemaster build)

It's up there with a tremolo I was building.  For the life of me, I couldn't figure out why the oscillator wasn't working.

After 20 minutes measuring voltages, I realised that the op-amp was still on the bench. 

[therecordingart]

Almost everything I build has some bone head issue that takes me a half hour to trouble shoot and ends with me stomping through the house whilst swearing at myself for being a dumb#ss. Most of the time it is rushing the finally assembly and miswiring the bypass switch.

[gigimarga]

1. My DIYing table is very tight...after I finished soldering something like a MXR Distortion+, I wanted to test it before boxing, I plugged the jacks and the battery and...no sound! I turned the pots, I rechecked all the parts and soldering...all seems to be OK...after another 10 minutes I realized that I powered a MXR Phaser 90 spreaded on my table too instead of the distortion!

2. I made a Tonebender Mk III for a friend and I gave it without any box because he told me that he has an empty box to put in...after a couple of months he gave me back telling me that it stopped working...I opened and I found 2 wires desoldered...I resoldered both and I've tested...no sound...all the voltages seems to be OK...all the parts...ALL seems to be OK...after one hour I realized that he reversed the in and out jacks (in on the left, out on the right)!

[mattthegamer463]

I always manage to scratch my head wondering why my pedal which has worked for months now does nothing, then realize after a minute that the cable I plugged into it is not the one in my amplifier.

Or strumming my guitar trying to figure out whats wrong, only to see my guitar isn't plugged in.  I'm not very bright.

[MmmPedals]

Something similar to most posts here has happened to me. testing with the guitar unplugged is a classic... but its never happened to me 

[newfish]

Yep.

That volume control on your guitar.  What does that do again?   
Have actually done this at a gig way back when I was as green as I was nervous...

Finished the first song.  Rolled back the voulme to mute the strings.  Drummer etc start the second song, I'm playing, but not hearing anything.
How very odd. 
Sound Engineer is looking at me and 'doing gestures' to say that my fader is maxed-out - but still no sound.

Then the penny drops.

I've never made that mistake again.

Almost like having a pedal working fine - then not working as soon as you put it on your board.

...then realising you've got the FX Bypass master switch engaged...

More sleep required I think...

[gtudoran]

Have any one tryed to discharge a 100uF/450v trough his finger? Well i did... and now i have a nice little hole in my index how smart is that ...? I'm telling ya ... is STUPID. Felt like a lightning bolt went trough my brain, witch defently i didn't had at that moment )

Best regards,
Gabriel Tudoran
Analog Sound

[dschwartz]

Have any one tryed to discharge a 100uF/450v trough his finger? Well i did... and now i have a nice little hole in my index how smart is that ...? I'm telling ya ... is STUPID. Felt like a lightning bolt went trough my brain, witch defently i didn't had at that moment )

Best regards,
Gabriel Tudoran
Analog Sound

wow that´s dumb!..
i´ve tried with low voltages caps and got sort of a shock, but nothing harmful...but a 100uF/450V?  damn!!

the most stupid thing i did was destroying a pcb because i was frustrated it didn´t work and couldn´t find the issue...when picking up the pieces, i found a short to ground at the input...
i felt so stupid to loose my temper...

[davidallancole]

I did the high voltage think a time or two.  When rebuilding my Epiphone Valve Junior I shorted the supply through my hand.  That wasn't fun.  Once I got the amp finished I fired it up and it was the quietist amp I have ever heard.  No hum or noise anywhere when you cranked the volume.  So I started probing and found the problem.  I cut the core of my coax to close to the shield and what was left melted away, thus my shield and core were soldered together shorting the input to the amp.

[DaveM]

While building a FF, I had very intermittent sound. It would cut in and out like crazy.  So I checked the circuit over and over again, and nothing was shorting out.  After some DMM probing, I found the output shorted to ground.  Checked my foil insulation job. It was fine. Took the output jack out and resoldered it.  Many, many times. After an hour of "I'm gonna smash this piece of (insert curse of choice here) to bits if it doesn't start working"  I discovered it was the $2.50 output jack I bought from RadioShack.  Intense frustration.

I also learned not to touch a soldering iron to a circuit that is plugged into an amp, as that is extremely loud.

[JKowalski]

Just spent days going back and forth trying to troubleshoot some onboard bass effects I put together recently when I realized the contacts on the top my PCB mount pots were shorting out on the black conductive paint of the cavity.  It's always the simplest things with me.

[joegagan]

a music store owner told me that years after the brass craze of the 70s, people were coming to him with problems. he said that the brass had built up enough corrosion to not make good contact between the jakcs and plugs.

[phector2004]

AAAAHHH!!!!

Just spent the past hour continuously flipping, rewiring, and retrimming trimming a JFET. Thought I had it in the wrong way cause the pinout is reversed. After swapping in new FETs 3 times, changing the trimmer, rewiring that same section over and over, I notice I hadn't connected my Opamp to ground...  

[amptramp]

We on this forum are pikers in the area of screwups.  You need major projects to really get it wrong.

When I worked at Spar Aerospace, we had consultants in on a long-term basis from Lockheed Missiles and Space Company who were the experts in the field of three-axis stabilized satellites to help us with the Hermes satellite that was launched successfully on 27 Jan 76.  After all, LMSC had actually put some up that worked and that put them ahead of anyone else.  On the last day one of the consultants was there, we took him out to the local pub (the other one was a holy roller who kept a Bible prominently displayed on the upper left corner of his desk and would never be caught dead in a pub).

1. The first satellite was a spin-stabilized one.  There are solar cells all around so as it spins, there is no need to point an array – but only the equivalent diameter is active, rather than the circumference.  But it offered a simple design that was used throughout the 1960's and beyond.  Imagine the left front wheel of a car: if you turn to the right, gyroscopic force will tend to add camber, meaning the top of the tire will move away from the car and the bottom will tuck under.  Spin-stabilized satellites make use of gyroscopic force to maintain a stable pointing angle as determined by a star sensor that finds Cassiopeia and the position of the antenna that is pointed to the earth.  In this era, most satellites were for communications and pointing accuracy was essential with the low-power transmitters in use.

In order to get the required spin, small thrusters using hydrazine as a propellant were used.  They launched one satellite and proceeded to spin it.  They got no signal.  Not even telemetry.  They checked the star sensor output.  Lots of light but no edges.  Finally it dawned on someone.  The thrusters were pointing the wrong way.  The satellite had stabilized with the star sensor pointing at the earth and the antenna pointing out into space.  There was no way to correct the problem.  They lost the satellite.

2. The second satellite was a three-axis stabilized one that always pointed a flat sheet of solar arrays to the sun, one on each side of the satellite, increasing the power available.  These satellites were launched into synchronous orbit at a 22,000 mile altitude and appeared to stand still in the sky.  The pointing angle of the satellite is controlled by an earth sensor that aligns the satellite with the edges of the earth to maintain a stable antenna position.

In those days, a program that went smoothly without glitches was something of a fantasy.  Launch vehicles blew up on the pad.  Stuff that was tested exhaustively failed once it was installed.  There was plenty of trouble before launch as well.  Electronics failed or did something different from what was expected.  Parts that should connect together seamlessly didn't.  Integrating the satellite to the launch vehicle was something that was part mystery, part Rube Goldberg and usually took a lot of unscheduled schedule.

But Lockheed seemed to have a program that the gods smiled on.  The electronics and optics all worked.  The electronics did exactly what it was supposed to do.  Integration with the Thor Delta (the same launch vehicle we were using) went off without a hitch.  Certainly this program was blessed!  All LMSC had to do was deliver it into orbit, despin it, acquire earth (using the on-board earth sensor) and show that it was stabilized and they could collect the $30,000,000 launch cost.  At the time, a house cost $20,000, so this would be about ten times that amount today and would buy a community of 1500 houses – a good chunk of change in those days.

The launch went perfectly.  The Thor stage with its nine solid-fuel rockets surrounding it lifted off and delivered the Delta stage with the satellite on it into a low orbit 120 miles up.  The Delta stage delivered the satellite into an elliptical orbit with the perigee at 120 miles and the apogee at 22,000 miles.  The satellite had an additional rocket that was fired at the apogee to circularize the orbit.  It all went smoothly.  They spun up the internal momentum wheel and fired the small pitch-axis thrusters to eliminate any residual spin, and waited for the attitude control system to stabilize.  Nothing happened.  The earth sensor did not appear to see the earth.  They checked the telemetry.  The earth sensor power supply voltages were in spec.  The clocks for the digital logic were running.  But it was like they were out in deep space.  They were starting to get worried now.  $30,000,000 and the reputation of the company were at stake.  Finally, one program manager decided to look back over the preflight checklist to see if there was anything that would give them a clue.  One box was not checked off:

Remove Earth Sensor Lens Cap

They couldn't stabilize.  They lost the spacecraft and their $30,000,000.

[petemoore]

  Dah..could happen to anyone, even with a 30 dollar lens, just have hire a new lens technician next time.
  It's always something with this kind of stuff.
  Why doesn't it work  ?  Plug it in.
  What should I do/it's smoking ?  Unplug it.
  Where are the problems likely to occur?
  Every place...except for those without a problem.

[Taylor]

One box was not checked off:

Remove Earth Sensor Lens Cap

They couldn't stabilize.  They lost the spacecraft and their $30,000,000.

Oh come on, seriously? Can't they send somebody up to take the lens off? I realize that's not exactly like driving out to the mailbox, but surely it would cost less than $30,000,000 in 70s money to fix that, no?

Nice stories, in any case. It does help us put our stuff into perspective - it doesn't really matter if our pedals don't work, compared to that. This is why I avoid situations in which I could make such an expensive blunder. I haven't ever been in control of a $30m machine, but I have lost/cut/bled on $20,000 works of art a few times. Somehow I got away with it each time, but even that was too much stress for me.

[DiamondDog]

Ins and outs are easily reversed...

Even when your name is David Gilmour, the pedal is a wah, and suddenly you have the seagull effect in echoes

It's not a mistake, it's experimentation. It's always experimentation...