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Collosalus 2015 won't bias??

Started by Bio77, July 25, 2020, 02:32:43 AM

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Bio77

July 25, 2020, 02:32:43 AM Last Edit: July 25, 2020, 02:38:32 AM by Bio77
I have a working unit from a few years back.  I built a new one, clock sets up nice but it won't bias (judged by scope).  Switched the 3007 from the old one into the new one, same problem.  Socketed R32, tried lower and higher values, same problem. Is R32 the right value to change? Am I missing something else? Any help would be greatly appreciated.

Scruffie

#1
July 25, 2020, 03:06:34 AM
V-o-l-t-a-g-e-s.
Works at Lectric-FX

Bio77

#2
July 25, 2020, 01:57:15 PM
Sorry Scruffie, I thought I was making an easy mistake  ::)



Scruffie

#3
July 25, 2020, 02:15:43 PM
Quote from: Bio77 on July 25, 2020, 01:57:15 PM
Sorry Scruffie, I thought I was making an easy mistake  ::)
:-[ Wasn't trying to chastise if you took it that way, just mixing things up a bit ;D

Okay apart from the MN3007 they all look okay, can you sweep the voltage on pin 3 of the MN3007 with the bias trim? Right now its cranked.


Works at Lectric-FX

Bio77

#4
July 25, 2020, 02:50:43 PM
Quote from: Scruffie on July 25, 2020, 02:15:43 PM
:-[ Wasn't trying to chastise if you took it that way, just mixing things up a bit ;D
Didn't take it that way, appreciate your help immensely  8)

I can get voltages 1.5-14.8 on pin 3 with the trim and a 100k in R32.  On the scope, there is only signal on the last half of the trim but I can only get the upper part of the waveform at max.

Bio77

#5
July 25, 2020, 03:24:22 PM
Should mention I have subbed TL072s for the 4558s and I have a TL022 in the oscillator section.

Scruffie

#6
July 26, 2020, 01:38:27 PM
Those subs should be fine.

So, you definitely have the scope & signal generator set right, have you tested you have good anti-phase square waves on the BBD clock pins and also that the signal isn't getting lost before the BBD?

If so the problem must be on the output of the BBD, perhaps Q4.
Works at Lectric-FX

Bio77

#7
July 26, 2020, 03:37:54 PM
Ah ha, no signal at the input.  I have square wave at 2 and 6, not sure about the phase because no input  to compare it to ::)

I'll trace back and figure out where I'm losing the input. Thank you!

Bio77

#8
July 26, 2020, 04:46:15 PM
I have signal at the output (pin 7) of IC4 but no signal on either side of R31. Seems weird to me.

Scruffie

#9
July 26, 2020, 05:05:33 PM
Continuity?
Works at Lectric-FX

Bio77

#10
July 26, 2020, 07:06:56 PM
Quote from: Scruffie on July 26, 2020, 05:05:33 PM
Continuity?
Nope, bummer.  It has continuity with C16, R29, D1, and D2.  I'll pull R31 and see if I can get something from the pad.  If not should I put a jumper from pin 7 to R31?
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