Author Topic: Help with borked Spitfire build.  (Read 237 times)

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slashandburn

Help with borked Spitfire build.
« on: December 30, 2017, 01:19:06 PM »
Holiday season and I'm digging in again. Was on a bit of roll and managed to throw together a few clones for friends and even finish off an Engineers Thumb for myself with surprisingly few problems. For some reason,  rather than carry on with this new confidence I decided to dig through my complete failures and see if there was anything worth salvaging. Another one of dead astronauts Spitfire's fell out that I don't remember building, and looking at the soldering job on the 3pdt I was likely inebriated. Looks like I can save it but I can't for the life of me figure out why it won't fire up.
Fine in bypass. Engage the switch and the led fires up but I just get silence.

I've checked everything I can think and swapped in a few different jFets (j201 and a few 5457), checked for continuity everywhere I can think and checked, double and triple checked all component values. Voltages also look somewhat in the right range my completely untrained eye. Q4 Source kinda jumps out as a bit suspect but I don't know what I'm looking for.

Supply 9.8v
Q1
D 4.9
S 2.5
G 2.5

Q2
D 9.8
S 4.9
G 4.58

Q3
D 9.8
S 5.6
G 4.5

Q4
D5. 6
S 0.2
G 0.0

Q5
S 9.8
S 6.3
G 5.6

One peculiarity, when I first opened this sucker up to have a poke about, the source and gate legs of Q4 were twisted and swapped round (all j201) and I did actually have some slight output with the pedal engaged. Very slight, though.  I studied the schematic  and concluded they shouldn't be twisted and the orientation on robs pcb layout from his gallery appears to be correct. So sticking with that I have to try to get to the bottom of why this sucker doesn't want to work for me. I don't want to assume fake jfets because I'm almost certain I've built from this batch before but the twisty leg Q4 giving me faint output has me suspicious.

Here's the links and photos. Feel free to ridicule my dodgy soldering.  The switch is a disgrace and the pcb looks like I went a bathed it in flux. I genuinely don't remember building it so I'll blame late nights and alcohol for my poor skills.

BOM and build doc
http://www.aronnelson.com/gallery/main.php/v/chickpea/SPITFIREV3.pdf.html

Schematic
http://www.aronnelson.com/gallery/main.php/v/chickpea/SPITFIREV3.jpg.html?g2_imageViewsIndex=1

My shame worthy abomination:










Cheers in advance. And Merry Christmas to you all. If I can get this working I'm not even sure what to do with it. Have one (it lives at rehearsals) and already gave one to my mate who loves it. Probably rebox it, tidy up the offboard and give it away as a gift again. Too good a pedal to go to waste sitting in my drawers of failures.

Oh, the funny looking c8 is two 105s in series. The only other deviation from the build notes I can see is C10 where I used 8.2n rather than the specified 6.8n.



garcho

Re: Help with borked Spitfire build.
« Reply #1 on: December 30, 2017, 01:46:08 PM »
certainly not the reply you're hoping for, but did you try using an audio probe? like a dangly wire with a trs jack at the other end plugged in to a crappy amp with a speaker that you don't care about? trace the wet signal until you hear something or until you don't hear something. that will often give you a juicy clue.
"...and weird on top!"

slashandburn

Re: Help with borked Spitfire build.
« Reply #2 on: December 30, 2017, 01:57:43 PM »
Yes! My probe must also be borked, more weirdness there. With the effect engaged, I couldn't get signal even on the tip of the input jack.  Bypassed I could get signal all the way across the switch.

Too baffling for my small mind. I figure it must be broken. Unless I've somehow grounded the input? I still think I'd hear something on the tip?

garcho

Re: Help with borked Spitfire build.
« Reply #3 on: December 30, 2017, 02:00:56 PM »
if you grounded the input you would hear literally nothing. EDIT: the audio probe doesn't really alter the circuitry, whatever grounds the input while engaged will ground the input even while using the audio probe
"...and weird on top!"

slashandburn

Re: Help with borked Spitfire build.
« Reply #4 on: December 30, 2017, 02:04:09 PM »
... Son of a

Edit.  I'll investigate later tonight, tomorrow. That's a load off though. Thanks. I was already stressed when I reached for the probe. When I couldn't find audio on the tip of the input jack I just decided the probe must have a loose connection or something.  I can see where, I'll have to look over the board with eagle eyes tomorrow.
« Last Edit: December 30, 2017, 02:13:02 PM by slashandburn »

Kipper4

Re: Help with borked Spitfire build.
« Reply #5 on: December 30, 2017, 03:15:54 PM »
Check the instrument is on the input NOT the output.
Start with the basics.
Jellybean dodging since 2012.
Smoke me a Kipper. I'll be back for breakfast.

slashandburn

Re: Help with borked Spitfire build.
« Reply #6 on: December 30, 2017, 05:24:12 PM »
Thanks man. I've definitely double and triple checked the switch wiring. The enclos8nure this is in is base minted in that makes sense, so j was aware that the stitch wiring would be somewhat backwards. Still seems good. If there's a ground shorr uessing it's on the board or within my cackling handed switch/off board wiring.

I realise the board pictured is an absolute atrocity. My apologies. Robs work deserves better. My other two spitfires are awesome.

Slowpoke101

Re: Help with borked Spitfire build.
« Reply #7 on: December 30, 2017, 05:50:30 PM »
May have a solder bridge.





Check the rest of the board. There may be more.

..

EBK

Re: Help with borked Spitfire build.
« Reply #8 on: December 30, 2017, 08:01:25 PM »
Do you have anything insulating that board's bottom from the enclosure other than a piece of tape?  Pointy solder joins can poke pinholes through that, grounding places unexpectedly.  Perhaps, try some double-stick foam tape instead, and trim the leads as flush as possible.
No affiliations. If I glowingly mention specific merchants or products, it is because I like them without having to be paid to like them.

EBK

Re: Help with borked Spitfire build.
« Reply #9 on: December 30, 2017, 08:13:04 PM »
Here's the links and photos. Feel free to ridicule my dodgy soldering.  The switch is a disgrace and the pcb looks like I went a bathed it in flux. I genuinely don't remember building it so I'll blame late nights and alcohol for my poor skills.
We've seen much worse. No ridicule here.  We're all on the same team.
No affiliations. If I glowingly mention specific merchants or products, it is because I like them without having to be paid to like them.

slashandburn

Re: Help with borked Spitfire build.
« Reply #10 on: December 31, 2017, 08:08:19 AM »
Got it! Thanks everyone.

That wasn't the only solder bridge, Slowpoke. Well spotted. Fixed that it still did nothing, then noticed the input pad and ground looking suspiciously close, (bottom right of the photo) and it came alive after hitting those with a hot iron.

Happy days.  Cheers again.
Have a good one!