Need Help with weird UNIVOX Micro-Fazer

[Gokarna]

Hi,

still i didn’t manage to fix an old UNIVOX Micro Fazer, I already questioned some details about the opamps and the f-jets in this thread:

http://music-electronics-forum.com/t12767/

(Sorry, the by me attached schematic in that thread wasn't really a correct/ right one.....)

I changed and tested the opamps, also the F-jets seems to be okay. Still no success, the guitarsignal comes through with little cut-off highs and that’s it.....

So I drawed a complety schematic of my (PS-110) pcb and found some strang differences to other schematics I found in the internet.
I’ ll attach the schematic I found made by Mr. Gottfried Divos in 2003.


So here are my questions , where I need help:

1.) On my pcb R1/C1; R2/R3(values don't match); C8/ R31 and R19/R22 (values don't mach) are soldered in reverse.

- On my pcb R2 is 100kΩ; R3 is 220kΩ. R2 in both other schematics is 220kΩ, R3 470kΩ , respectively 1 MΩ in a original schematic of the MELOS Mini-Fazer (similar pcb).
- the original cap C8 is soldered in with reversed polarity than the other schematic.
- the schematic of Mr. Davos / Melos schematic shows R19 with 100kΩ; mine: 47 kΩ,
and “my R19” is set between R21 and the switch, both other schematics show R19 between C6 and R21.

2.) The poti P1 is also reversed installed and also instead linear in my device instead logarithmic.

3.) R17 & R18 have total differnt values on my pcb ( 12 kΩ / 33kΩ ) instead of 1kΩ / 2,2kΩ in the other drawing
( the Melos Mini-Fazer has here 820Ω (R18) / 2,2 kΩ(R19)).

4.) R22 has 47k (Melos 33K) instead of 330k on my pcb.

5.) R21 is 27k on my pcb, 22k on Davos- and 33 on Melos- schematic
I guess, that's okay - I read somewhere else, that R21 is one idea for another potentiometer.

6.) C6 is .1uF on my pcb, in the Davos-schematic it is 1uF, Melos is .1uF. Also here, I think is only a writing mistake in the Davos-schematic

So can anyone here tell me, which parts I have to change / resolder ?
I must say, my pcb does not look like as if anybody has worked on it after leaving the manufacture, all parts look original.
Can you also tell my, if it could have worked with this layout ?

Happy easter days to all of you and thank you for your help.


Regards

Till

[Gokarna]

No idea from anybody ?

Hello,

due to no answers until now, I've started to change parts according to the original schematic.

Now there are only 4 points left, where I have no clue, if I have to change them or not.

Please take a look at the new attached schematic, the blue parts beside the original values/drawing are how it is installed on my pcb.

Any comment will be helpfull,

Best regards


Till

[Steve Conner]

Most of the blue part changes would work either way round. The only thing that might be important is the polarity of C8. If it was installed backwards, it might fail short and mess up the operation. I think the positive end should be towards OP6's output.

Do you have a scope, or some other way you can check if the sweep oscillator is working?

[Gokarna]

Hi Steve,

thank you very much for this first answer

Do you have a scope, or some other way you can check if the sweep oscillator is working?

No, nothing like that, only a multimeter and a (selfbuild) J-Fet Matcher.

What arbout the position/value of R19;

what is the purpose of this resistor ?

Thank you again

Till

[Steve Conner]

R19 sets the DC conditions on C6 to avoid pop sounds when switching the effect on. It works the same in either position.

You can probably use your meter to test the sweep oscillator. Test it on the DC volts range, the value should change constantly. If the meter has a bargraph it should pulsate.

[J M Fahey]

If the pedal worked before, up/down grading it to another version is not the solution.
You have a *functional* problem there.

1) Start by checking DC voltages.
We expect +9V rail, *around* +4.5V "half rail/bias" voltage, should check the actual D1 zener voltage but can't be far from that, and I expect about same voltage at all Op Amp outputs.
That alone tells us a lot.

2)If it doesn't sound, it doesn't sound, check **that** problem before worrying about "the effect".
As Enzo says: "first repair, *then* Mod"
Inject signal at the input (100mV, 1 KHz) and follow it along the path until it reaches the output, which will be connected to some amplifier.

If not possible, do it backwards, inject said signal at the output jack , at the junction of R20/R22 , you *must* hear it in the amplifier, then work backwards, at the + inputs of OP5/4/3/2/1 , then on both sides of C1, then same on R1.

Signal source: download a 1KHz MP3 tone, play it with an MP3 player.
Use a miniplug cable and the other end free , ground the ground wire and with the other touch all places I mentioned, through some capacitor, from .01 to .022uF, whatever you have.

Only when you find a place where sound dies you start looking around.
Shotgunning parts "just in case" does not work.

[Mark Hammer]

The original R22 arrangement seems more sensible than what you redrew. De-popping of C6 is provided by R19. R22 provides a suitable output impedance for both effect and bypass modes, and R21 is the mixing resistor for the phase-shifted signal.

Unless you see clear evidence that parts have been changed post-manufacture, I would leave all the values where they are. These sorts of circuits were frequently changed, with the changes intended to arrive at the same destination. For example, R3 partly sets the gain of OP1 (setting it just a bit over 1x). Dropping the value of R3 from 470k to 220k increases the gain a bit, but then dropping R2 from 220k to 100k provides a bit of attenuation of the input signal feeding OP1. More gain applied to a smaller signal = less gain applied to a larger signal. Like I say, many paths to the same destination.