SAD1024 clock noise help

[four_corners]

Does this looks like the correct flanged BBD signal? Or possibly this is just the second half of the BBD, and not the first half with the audio.

Not be the "flanged" signal, because the real flanging sound happens not before R62 & R79 join.
But it does look like a time-modulated keyboard saw, i.e. the variably delayed (not: "flanged") copy of your input signal varying in pitch at the rate of the LFO.
This signal was what I expected to see at pin1 of IC9 (as well as on pin7 of IC9, and as a matter of fact on TP8 too, just with lots of clock-frequeny-artefacts spoiling a sharp scopetrace).
Now while you get a keyboard-signal at this TP8, look at it with one scope-channel, and "follow" the signal from there with the other channel (same settings), to see where it suddenly seems to vanish. (VR2 wiper, both sides of C34, R73, R75, R76, R77, R78, pin1. - You won`t see much on the pin6-side of R74).

Leave Feedback-pot at zero, because it might show a parallel ghost-trace.

Set the scope timebase so only a few sawteeth show up, so that the low-frequency "wobble" doesn`t disturb the view.

Eek, scratch that, I just realized TP8 does NOT have the keyboard signal, it is just the modulation signal.

So that really leaves only 2 potential problems:

1. Something between q17 and the BBD killing the incoming keyboard audio signal. The only thing in between Q17 and pin2 of the BBD is really C32... Not entirely sure what is happening between R70 and pin 5 and 6 on the BBD, and I don't know exactly what pin5 and 6 do (pinout says Out A and inverted Out A).

or

2. The first half of the BBD is dead and only outputting the modulation and not the audio.

[Rob Strand]

[I haven't addressed your post just before mine.]

So here is something interesting. This is a video of my scope directly out of the BBD pin 11/12, at TP 8.

https://www.veed.io/view/44d3f7bd-8cb4-4e5d-b2ae-c009006c40b8

Does this looks like the correct flanged BBD signal? Or possibly this is just the second half of the BBD, and not the first half with the audio.

That just looks like the BBD clock bleeding through.  The frequency is quite high (not the incoming saw tooth).   From that we would conclude the VCO is working but it doesn't tell us why the audio isn't getting through.

The weird thing though is if I barely touch the Speed or Intensity pot, all hell breaks loose (maybe my fault? Not a good probe connection/ground? Or touching the pot is doing some sort of grounding thing). Here is a video of that...
...
I'm a bit confused how the LFO is showing up at IC9 pin1, especially since I disconnected R103.

The flickering is just the oscilloscope not triggering correct.   This will especially be the case when the LFO is running and not manual.  The waveform *frequency* is varying and the oscilloscope just mis-triggers or blurs a whole lot of waveforms on top on another.

I'm a bit confused how the LFO is showing up at IC9 pin1, especially since I disconnected R103.

All OK since it's not the LFO or the audio but clock.    We have three signals to decipher on the oscilloscope: 
- LFO - low frequency (~ 2Hz)
- sawtooth - audio frequency
- Clock - high frequency (1MHz)

On the base and emitter of Q17 I get the keyboard signal sawtooth wave. The collector is +15V. IC8 pin 7 I get the same waveform as Q17, pin 5 and 6 I'm getting nothing but noise.

That's all good and expected.     If the audio signal gets to the emitter Q17 then that mean the audio should be going into the BBD, well it needs to pass through C32.

IC12 pin7 is just messy waveform of some kind right now so I'm not sure if the LFO is getting through (I dont think it is, but it might), this is correct though as I have R103 disconnected, right?

If that IC12 circuit is working I wouldn't expect too much out of it.   If you set the LFO to about 2Hz and crank the intensity you might see 100mV to 200mV of LFO signal coming through.   When you back-off the intensity to zero nothing should get through.

The wiggle in the oscilloscope pic in reply #91 could still be the LFO coming through since you have the intensity on full.

Most of the stuff you measured are artifacts, all possibly explainable.

The thing that doesn't look good to is the audio is making it to Q17 emitter, then at BBD pin 2, but nothing at BBD pins 5, 6.

From reply #91 I was fairly convince the BBD was passing signal from BBD pin 15 to BBC pins 11, 12.



As a double check can you confirm the clock is present on both test points 6 and 7?   You may have already done this but it's worth checking.  Maybe you have already

[puretube]

Had you already tried to add some constant DC to pin6 of IC12?
If not, try it now.
If yes: remove that added 510k-resistor and the help-trimmer, and re-connect R103 to where it used to.

[puretube]

Maybe I have mistaken a rounded-off clock-bleedthrough that looked like a sawtooth for a keyboard signal because I didn`t know the scope`s freq.-setting?

[Rob Strand]

1. Something between q17 and the BBD killing the incoming keyboard audio signal. The only thing in between Q17 and pin2 of the BBD is really C32... Not entirely sure what is happening between R70 and pin 5 and 6 on the BBD, and I don't know exactly what pin5 and 6 do (pinout says Out A and inverted Out A).

My understanding was the audio was making it to BBD pin 2,  it that correct?

Try measuring the DC voltage at the output of IC12 pin 7.

2. The first half of the BBD is dead and only outputting the modulation and not the audio.

Try puretube recommendations and my last two points.

I'm not sure what point to conclude the first half of the BBD is dead.

This scheme would bypass the suspect half of the BBD:

- Lift the Q17 emitter end of C32 and lift the end of the 100nF cap (C33?) that goes to R71.
   I cannot read the part designator on that cap  on the schematic.

- Now wire the lifted end of C33 to the emitter of Q17.

You would need to be *really* careful doing this. 

[four_corners]

The thing that doesn't look good to is the audio is making it to Q17 emitter, then at BBD pin 2, but nothing at BBD pins 5, 6.

From reply #91 I was fairly convince the BBD was passing signal from BBD pin 15 to BBC pins 11, 12.



As a double check can you confirm the clock is present on both test points 6 and 7?   You may have already done this but it's worth checking.  Maybe you have already

I'll address everything in a couple posts as to not confuse yours and Puretube's.

Sorry for negating past posts, but it does look like I am getting something at pin 2 and pin 5/6 on the BBD. The noise just was confusing me and I wasnt getting a decent scope reading.

Here is pin 2. Playing the keyboard DOES make this waveform change frequency, so definitely the synth audio signal.



Here is pin 5/6 (I had to probe R71 to get a clean image, but it is the same connection). This waveform changes only with the Intensity and the Speed pot.



For whatever reason TP8 is only passing pin 5/6 through and not the audio signal on pin2.

[four_corners]

Had you already tried to add some constant DC to pin6 of IC12?
If not, try it now.
If yes: remove that added 510k-resistor and the help-trimmer, and re-connect R103 to where it used to.

Haven't added DC to pin6. Just from my bench power supply? If so, how much? Could I just short pin 2 and pin 6 as they both are inverted inputs or is that a bad idea as well?

[four_corners]

My understanding was the audio was making it to BBD pin 2,  it that correct?

Try measuring the DC voltage at the output of IC12 pin 7.

audio is making it to BBD pin 2, and DC voltage at IC12 pin7 is +4.83V.

[Rob Strand]

Here is pin 2. Playing the keyboard DOES make this waveform change frequency, so definitely the synth audio signal.

Here is pin 5/6 (I had to probe R71 to get a clean image, but it is the same connection). This waveform changes only with the Intensity and the Speed pot.

So pretty much clock leakage but no audio from the first half of the BBD.

It's worth checking the DC voltage at BBD pin 2, and IC12 pin 7.  If the DC is bad the first half of the BBD won't work.
Also check the DC voltage at BBD pin 15, it should be the same as BBD pin 2.

For whatever reason TP8 is only passing pin 5/6 through and not the audio signal on pin2.

Actually TP8 (BBD pins 12/13) will have the same looking waveform as BBD pins 5/6 but it didn't necessarily pass through the BBD.   Both halfs of the BBD produce the same kind of clock leakage at the output.

[puretube]

Had you already tried to add some constant DC to pin6 of IC12?
If not, try it now.
If yes: remove that added 510k-resistor and the help-trimmer, and re-connect R103 to where it used to.

Haven't added DC to pin6. Just from my bench power supply? If so, how much? Could I just short pin 2 and pin 6 as they both are inverted inputs or is that a bad idea as well?

Add the +DC from the Flanger-unit PCB, e.g. from VR11, and some ground-point on the PCB.
DON`t short!

[four_corners]

It's worth checking the DC voltage at BBD pin 2, and IC12 pin 7.  If the DC is bad the first half of the BBD won't work.
Also check the DC voltage at BBD pin 15, it should be the same as BBD pin 2.

BBD Pin 2 and Pin 15 are  +4.75V

IC12 pin 7 is  +4.83V


Clock at TP6 and TP7 are much higher than they used to be. VR4 and VR3 bias all of a sudden aren't letting me go down below about 900 kHz.

[puretube]

Re-connect R103 (and disconnect extra 510k-resistor, if added).

[four_corners]

Re-connect R103 (and disconnect extra 510k-resistor, if added).

I hadn't done the +DC voltage yet as I was a little confused as IC12 was already grounded, and pin 8 already had constant positive supply from the same source as VR11, so it seemed like I'd just be shorting pin8 to pin6.

But i did just resolder R103.

Not entirely sure why the clock signal out of the 4013 is so much faster now. Maybe because it isn't a motorola chip right? I can't imagine the the CD4013 totally making the whole circuit not pass audio.

It is almost as if the audio is getting stuck inside the BBD, which makes me feel like it got fried. Unless it just really doesn't like this non Motorola 4013. I'd use the other one but it was the one that randomly ended up with pin 14 shorted. I ordered some NOS motorola ones though on ebay last night.

I feel like I should just go through ever pin on the BBD, and write down voltage and what happens on the scope (i mean I've pretty much done that it seems).

I'm really sorry for taking up so much or your time, this was never my intention...

[Rob Strand]

BBD Pin 2 and Pin 15 are  +4.75V

IC12 pin 7 is  +4.83V

Certainly close to the money here.

If you want you can try adjusting trimpot VR6 to see if the BBD starts to pass audio all the way through.
I don't have a lot of hope but it's worth a try.

If no good, set VR6 so IC12 pin 7 is back to the original value of 4.83V.

Clock at TP6 and TP7 are much higher than they used to be. VR4 and VR3 bias all of a sudden aren't letting me go down below about 900 kHz.

Not sure what's happened here.  Check the voltage at Q22's emitter over the range of the Manual control and see if it still has the same range as before.   From you previous posts I'm pretty sure there's something wrong around Q21's collector.   You might have an intermittent connection there.   Also, we don't know if Q19 has been damaged or not.

[four_corners]

Scope of BBD

1. ground
2. Keyboard signal wave
3. Correct TP 7/8 wave, bouncey modulation wave with Intensity, speed with Speed
4. ground
5. bouncy modulation with ghost image (posted earlier in video)
6. bouncy modulation with ghost image (posted earlier in video)
7. very artifacty wave (voltage?)
8. Correct TP 7/8 wave, bouncey modulation wave with Intensity, speed with Speed
9. very artifacty wave (voltage?)
10. Correct TP 7/8 wave, bouncey modulation wave with Intensity, speed with Speed
11. bouncy modulation with ghost image (posted earlier in video)
12. bouncy modulation with ghost image (posted earlier in video)
13. ground
14. Correct TP 7/8 wave, bouncey modulation wave with Intensity, speed with Speed
15. bouncy modulation with ghost image (posted earlier in video)
16. ground

Voltage

1. ground
2. +4.9V
3. +3.2V
4. ground
5. +2V to +2.7V
6. +2V to +2.7V
7. +6.5V
8. +3.2V
9. +6.5V
10. +3.2V
11. +3.75V
12. +3.75V
13. ground
14. +3.2V
15. +4.9V
16. ground

Pin7 and 9 seem low right? Or is that correct?

[Rob Strand]

7. +6.5V

9. +6.5V

OK that's very significant.  Might even explain why audio isn't passing through the BBD.

Those voltages should be 14V to 15V.

First, check the +/- 15V rails coming into the board to see if they are OK.

Check the voltages on Q20.  I'm pretty sure the base voltage is going to be about 7.2V (should be close to 15V).

If the 15V rails are OK but the Q20 voltages are not they could mean Q20 is damaged, or it could mean the BBD or IC7 is pulling a lot of current and that's causing the voltages on Q20 to drop.

[four_corners]

7. +6.5V

9. +6.5V

OK that's very significant.  Might even explain why audio isn't passing through the BBD.

Those voltages should be 14V to 15V.

First, check the +/- 15V rails coming into the board to see if they are OK.

Check the voltages on Q20.  I'm pretty sure the base voltage is going to be about 7.2V (should be close to 15V).

If the 15V rails are OK but the Q20 voltages are not they could mean Q20 is damaged, or it could mean the BBD or IC7 is pulling a lot of current and that's causing the voltages on Q20 to drop.

FIXED!!!!!!!

When the Motorola 1403 died earlier, I had first changed Q20. Turns out, I bought C945s from Tayda, and they send me a bag of 9 C945's and 1 other random transistor (the text is so tiny I can't even make it out). I even checked and accounted for all the transistors I've used during this process, so it isn't that I grabbed one from somewhere else.

What a dumb issue!!!

Moral of the story, just because the bag of parts says one thing, always double check.

I'm not messing with this thing any more, tick or no tick, time to close it up. One of the mods I wanted to figure out myself was to add a speed control to the String section "ensemble" button (which is 3 MN3004 chorus that have absolutely no control or trimmers for aligning them in a nice way), but I'm second guessing that after all this, haha.

Maybe this sounds silly, but is there any way I can compensate y'all for your time and help? If you are ever in Austin, TX, a meal is on me at the very least!

[Rob Strand]

Woah, great news.

I understand 100%.  Freaks you out when the shit hits the fan like that. 
Nonetheless your perseverance paid off at the 11th hour - so all the credit goes to you.

[anotherjim]

IMHO, there's a very narrow range of good settings for a string ensemble triple chorus, at least for use on a string section. There may not be much setup information for the chorus as the LFO always runs so the BBD clocks are a moving target but the LFO speeds should be measurable. Is it the same chorus as the Korg Delta with a 4069 chip in it? Post the schematic and we can cogitate.

[puretube]

Congratz!