Tricky transistor (debug help)

Started by Crowella, November 02, 2014, 01:58:11 AM

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Crowella

I'm declaring this now, clearly the beings above do not want me to get a working Animato clone. Desperate times here when you are scraping one together on perfboard and with whatever parts you have laying around.  :icon_lol:

Q3 is giving me all sorts of issues and my attempts at debugging have made me think it's time to walk away (or go to work) and maybe ask for some help because the internet collective is always useful and able to see something I cannot.  ;D

Obvious give away to the issue in the first place was a gated sound. You really needed to push the signal hard to get anything to come out.

Anyway, with my trusting multimeter:
Q3 - 2SC2240 (tried several working ones, same results)
C: 0.14V
B: 0.67V
E: 0.05V

All other transistors are in operational ranges including the Sziklai pair.

Schematic (this is correct, standard Big Muff Pi clipping section anyway): http://i.imgur.com/S5catjn.png
Layout of area in question (watch the pinout on the 2SC2240): http://i.imgur.com/Nd8G3Ae.png

Help will be greatly appreciated.  :) The tone knob functions perfectly so it doesn't leave too much there. Would a blown part (resistor or capacitor) cause this issue?

(I can hear my old electrical engineer lecturer crying in the distance)
Rhythm in jump, dancing close to you

GibsonGM

I think you really need to look at what's going on with the cap, clippers above the collector.  That collector should be giving you at least 1/2 supply voltage....suggest there may be a short somewhere in there!  It's pretty much a yes/no issue..if the voltage is there, you'd see it, so something is blocking or re-routing it!    Time for the magnifying glass and continuity tester ;)
  • SUPPORTER
MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...

duck_arse

interesting. the base is higher than the collector, but it is biased from the collector. lift R8, see what happens volts wise. and then it's all magnifying glass, I think gibson has one.
You hold the small basket while I strain the gnat.

GibsonGM

Quote from: duck_arse on November 02, 2014, 09:18:03 AM
interesting. the base is higher than the collector, but it is biased from the collector. lift R8, see what happens volts wise. and then it's all magnifying glass, I think gibson has one.

..good eye on the diff. collector and base voltages, Duck...perhaps I should take out my magnifying glass to read posts now and again! lol
  • SUPPORTER
MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...

Crowella

Played the lifting game.

Lifted R8. No change.
Lifted C8. No change.
Lifted C7. No change.
Lifted R11. No change.

The magnifying glass game showed no connected traces where there shouldn't be. BUT! After tidying up the spot with a craft knife, we have 4.4V at Collector.  ;D

I now have a working Animato. Doesn't sound bang on identical but it sounds a bit more midscooped, tigther lowend, better defined, a lot quieter noise wise, slightly bit of gating on the end of the decay trail. As far as being spot on, about 80% there. For sounding useful it gets full marks. Onto the pedal board.  ;D
Rhythm in jump, dancing close to you

GibsonGM

Good deal!  It's always SOMETHING like that :)
  • SUPPORTER
MXR Dist +, TS9/808, Easyvibe, Big Muff Pi, Blues Breaker, Guv'nor.  MOSFace, MOS Boost,  BJT boosts - LPB-2, buffers, Phuncgnosis, FF, Orange Sunshine & others, Bazz Fuss, Tonemender, Little Gem, Orange Squeezer, Ruby Tuby, filters, octaves, trems...

Crowella

Here I was about to give up too.  :icon_lol: Thank you for the assistance!

Now... to rebias the Sziklai pair... when I can be bothered. Going to enjoy it even with the slightly gatey sound at low levels.  :icon_razz:
Rhythm in jump, dancing close to you