Home › Forums › Vintage EHX › Vintage Black Finger Help?
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April 20, 2010 at 3:20 am #79464ranjamMember
Help! I have an old Black Finger that is now giving me the finger! Bypass mode is fine :roll:, but in effect mode I just get a weak and distorted signal. Man, I hope it ain’t the 3080. Where the !#$% am I gonna get a soup can 3080? :facepalm: Anybody got any troubleshooting ideas so I can cross my fingers it isn’t the 3080? Thanks in advance.
April 20, 2010 at 9:56 am #96392The EH ManModeratorBest way to go about it is to audio probe the circuit and trace the signal to where it’s weak and distorted. You can replace the 3080 with a plastic one. It won’t make a difference.
Also check that the batteries are connected properly. Yours should have a 741 IC in it as well. Check that you’re getting +9 on pin 7 and -9 on pin 4.April 21, 2010 at 12:21 am #94209ranjamMemberWell, my B+ is correct, and with what I think is an accurate schematic (a couple I do find have subtle differences), my signal dies at the output of the soup can 741. I may lift pin/leg #6 and see if the output is OK, or else it’s find a soup can 741. At least that seems less painful. I should have thought of that, but thanks for the tip. It is appreciated.
April 22, 2010 at 2:13 pm #91847StephengilesMemberQuote:Best way to go about it is to audio probe the circuit and trace the signal to where it’s weak and distorted. You can replace the 3080 with a plastic one. It won’t make a difference.
Also check that the batteries are connected properly. Yours should have a 741 IC in it as well. Check that you’re getting +9 on pin 7 and -9 on pin 4.And where pray do you suggest one buys a CA3080?? Perhaps one could do a retrofit for a CA3094 lol!!
April 24, 2010 at 2:46 am #108971ranjamMemberI still have to try the 741 first, but now my mind is resting a lot easier.
April 29, 2010 at 1:14 am #96299ranjamMemberWell, the new soup can 741 is in, and the volume is back. :thumb: However, it’s still very distorted. :angry: The volume and tone controls work, there is a big volume boost, and the sustain control seems to work. But it goes from ‘buzzy’ distorted to sounding like a broken transistor radio with no bottom end at all. I don’t believe this is how it is supposed to sound.
Should I think about swapping transistors? I can test them with a decent transistor tester. Hmm, maybe I will do that before I try and beg for some free advice. Or if anyone has other thoughts? Thanks.May 2, 2010 at 2:19 am #94666ranjamMemberWell, the transistors test fine, but I did find a shorted capacitor. I haven’t plugged a guitar into it yet, but a ‘scope check shows it isn’t all that much better. The waveform is leaning towards a triangle shape, and as soon as the tone control is turned up, it looks like a nice cranked Marshall. I don’t know what to think. I’ll plug a guitar into this thing tomorrow and continue. But is it looking more like the 3080? 😥
May 9, 2010 at 2:20 am #104397ranjamMemberDoes anyone have a working pedal that can make a few voltage measurements? Knowing my luck, I put a good transistor back in lined up askew, so voltage measurements would tell me if everything else is OK and the 3080 is bad. Thanks.
October 23, 2011 at 12:01 pm #116212makepeaceMemberDid you manage to come right with this?
I have the EXACT same problem. Like a gated, clipped output. Farty and horrible.
If you’ve come up with a solution could you give it to me from the ground up?
Cheers
EDIT: just realised you’re talking about the vintage one.. I’m talking about the tube one. But its strange as we seem to have a similar problem..
October 23, 2011 at 2:48 pm #116213ranjamMemberWow! Over a year later! I think I did ‘fix’ it, but it still isn’t a completely usable compressor. I found a soup can 741, and a 3080. I had to salvage a 3080 from a scrap board, but the leads were pretty short. So, I actually grafted on some leads with some solder and heat shrink tubing, and away I went. It actually works OK now. However, the ‘Sustain’ control goes from ‘a little too squishy’ to ‘waaaaay too squishy’. I haven’t figured out why. Some schematics show a resistor in series with the wiper of the Sustain control, so I’m experimenting with a value that will make happy. But since I have over a dozen compressor pedals, it isn’t high on my priority list.
All in all, it sounds clean and not too noisy. If I can tame the Sustain control (a different value control?), it will be quite usable.
For the tube unit, I’d check capacitors, and change tube(s). I don’t have that unit, so I can only guess. But start with capacitors and tubes. The schematic is actually out there, albeit with a caveat that it may contain errors. Still, you have an idea where to scope it, and figure it out.October 23, 2011 at 3:26 pm #116214makepeaceMemberAwesome! Hoped you still trawled this forum!
Actually the first thing I did was replace the tube (arguably the most obvious denomination).
I have checked over the capacitors (aesthetically, they look fine, and this thing is not that old so they shouldn’t be expected to have popped, however, the unit worked before I left it powered up for a day).
I don’t actually have a scope (I do have access to one though if worst comes to worst), but I will subject it to some multimeter testing when I get mine back.
Symptomatically speaking, it does sound like an incorrectly biased gain stage does it not? So its likely that something has gone either on the tube stage side or the opamp side. I will most probably sequentially replace the semiconductors and see what happens.
Thanks for your reply!
October 23, 2011 at 11:11 pm #116220ranjamMemberIf you have a scope and a signal generator, you can trace it and know where the signal gets mangled. Here is that schematic;
You can almost ‘undo’ the ‘Compress’ control and if you have four gain stages that amplify the signal, the problem is in the solid state section. Then you can try the TLO74, the transistors, or the 1N4148’s. It shouldn’t be too time consuming. Frustrating, sure, but even the shotgun method should have it figured out soon enough. Here is a page with a lot of internal pictures; http://analogguru.an.ohost.de/193/EH_Blackfinger-T_dissecting.html
You’ll get it, and learn a lot in the process. -
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