EH Clone Theory w/SAD1024

[BDuguay]

Hey All. I have one of these and it's not Chorusing or Vibratoing. This one is clean as a whistle and all original to the best of my knowledge and upon inspection. It passes signal in bypass and when engaged but the engaged signal has no effect accept for added hiss. Manually adjusting the Depth Knob affects an audible change as does the Chor/Vib knob. The rate does nothing. I've no clue how to calibrate but slight adjustments of the trimmers did nothing. Anyone out there with more experience with this circuit?
Here's the scheme.
http://www.freeinfosociety.com/media/images/4110.jpg
B.

[Scruffie]

Take voltages of all the ICs, can't tell you anything without them.

[BDuguay]

SAD1024
1. 0
2. 5.36vdc
3. 0
4. 0
5. 0
6. 6.9vdc
7. 14.2vdc
8. 7.5vdc
9. 14.2vdc
10. 7.5vdc
11. 5.5vdc
12. 5.5vdc
13. 0
14. 7.5vdc
15. 5.4vdc
16. 0

4047
1. 3vdc
2. 11.8
3. 6.2vdc
4. 15vdc
5. 15vdc
6. 15vdc
7. 0
8. 0
9. 0
10. 7.5vdc
11. 7.5vdc
12. 0
13. 0
14. 0

4558
1. 0
2. 5.1vdc
3. 7.5vdc
4. 0
5. 3.9vdc
6. 7.5vdc
7. 4.2vdc
8. 15vdc

4558
1. 5vdc
2. 5vdc
3. 5vdc
4. 0
5. 5vdc
6. 5vdc
7. 10vdc
8. 15vdc

[Mark Hammer]

So, your voltage readings show 0V on pin 14 of the 4047.  The schematic shows it tied to V+.  While pin 13 is not used for anything, it is supposed to be an oscillator output.  Pins 10 and 11 are also oscillator outputs, so I'm not sure you should be reading/measuring them as DC voltages.

Long story short, if the clock generator (4047) ain't working, you won't get any chorus, so verify that it is producing the HF clock pulses required.  Is it socketed?  If so, save yourself some troubleshooting aggravation and just replace the darn thing.  I'm not saying the problem is definitely the 4047, but they're cheap, and if you have a spare one sitting around, it's an easy way to save time and headaches.

[Scruffie]

Sorry to disagree with you Mark but I think the pin 14 reading is a mistake, pin 4,5 & 6 are correct at 15V and Pin 10 & 11 should have half voltage as they do so I assume 14 is a mistake.

However, the 4558 with 10V on pin 7 looks suspect, the other 4558 I assume is the LFO which should have some moving voltages could also be suspect.

Edit: I just reread your original post which says you get a change in sound with the depth pot, that confirms to me the 4047 is okay, so I think the LFO 4558 is the issue.

[BDuguay]

Sorry to disagree with you Mark but I think the pin 14 reading is a mistake, pin 4,5 & 6 are correct at 15V and Pin 10 & 11 should have half voltage as they do so I assume 14 is a mistake.

However, the 4558 with 10V on pin 7 looks suspect, the other 4558 I assume is the LFO which should have some moving voltages could also be suspect.

Edit: I just reread your original post which says you get a change in sound with the depth pot, that confirms to me the 4047 is okay, so I think the LFO 4558 is the issue.

I just checked again and you were right in suggesting 0 on pin 14 was a mistake. There's 14+vdc there. I beat myself up terrible about not knowing what I should with regards to all this stuff but I can say that I too thought it might be something with the LFO. Before I posted even! Heck, there was a time not so long ago that I didn't even know what LFO stood for!
Anyhow.
Odd thing about this particular build is that all the chips are socketed except for one of the 4558's. The one that isn't is the one responsible for the LFO I believe. Back at it and will report my findings. Thanks to the both of you!
B.

[Mark Hammer]

Okay, I think we're back on track.  I took Brian's listed reading as accurate, hence indicative of something wrong.

Good call on Scruffie's part.  As they say from behind the backstop: "Good eye, good eye".

[BDuguay]

And a bum LFO opamp was indeed the culprit. Now if I only knew how to calibrate this thing for optimum performance...
B.

[Scruffie]

Wonderful, glad you got it sorted

Okay well assuming you don't have a scope, you'll have to calibrate by ear.

Put the effect on with a reasonable sounding setting (all pots half way?) and locate the bias trim, then tweak it while playing your guitar or with some other input source for the least distortion, an audio probe on the middle pin of the balance trim might be helpful if you have one to help hear this more clearly (although it'll be noisy). It'll have a small range where it works.

Next, the gain trim, if this is like the 3007 model, you basically want to set it so that the Chorus/Vibrato knob gives an equal level at full CW & CCW at the output so that'll just involve lots of turning the pot back and forth and tweaking.

Finally, the balance trim, you can either leave it dead center and call it good or stick an audio probe on the middle pin and adjust it for the least noise from the BBD.

[BDuguay]

I'm almost embarrassed to admit this but yes, I do have a scope and I built a function generator from a kit by Elenco. I think I know the basics but exactly how does one utilize the scope for calibrating?
Thanks again.
B.

[Scruffie]

Okay, well I don't have the factory set up procedure but I can give you an outline.

Connect a sine wave to the input and then adjust the bias trim for the maximum unclipped signal at the middle pin of the balance trim.

Adjust the gain trimmer for equal level at pin 1 of the audio 4558 and at the middle pin of the balance trim.

Disconnect the input and adjust the balance trim for the minimum clock noise.

[PRR]

> Connect a sine wave to the input and then adjust the bias trim for the maximum unclipped signal

+1; except: use different input levels. Start small, trim so something comes out. Increase level until one side is clobbered. Re-trim so it isn't. When both sides are clobbering, set level and re-trim so both sides are just lightly clipped.

This can actually be done with just a steady adjustable signal and an amp/speaker. There is a different sound for one-side clip and both-sides clipped.