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Flanger pcb /Pavs debug thread
MUFF WIGGLER Forum Index -> Oakley Sound Systems Goto page 1, 2  Next [all]
Author Flanger pcb /Pavs debug thread
Pav
Hi, Despite my concerns about shakey hands and smd components in another thread, I overcame these and pretty pleased so far with the smd work on the flanger ..albeit not tested.

Im now bemused to find C61 and C59 have 3 holes in pcb for a polyester (wima) cap that has two pins. for example C17-C20 are all marked up as 2 pin caps..but not C61 the same value.

The schematic shows just two connections. The picture on the product page show wima like caps in those positions on an issue 2 pcb

Im surprised elJay and leverkusen who have built flangers did not remark on this. Perhaps they knew how to resolve.

Should I have purchased a different type of capacitor hmmm..... ?
Synthbuilder
The middle holes are vias and are not connected to the capacitors' leads. Either leave them alone or fill them with a bit of solder once you have finished populating the board.

There's quite a lot of vias on this board as it's the only way to get connections from the top layer of the board where the surface mount components reside to the other three copper layers.

Tony
Pav
thanks. I did think it might be via but thought it best to ask as I had never come across that layout before. Had seen a via under an ic socket though.but saw that these middle holes had tracks to Smd caps so my addled brain wanted some reassurance.

Should be ready to test tomorrow. nanners
Pav
For the record ..first test of flanger failed....so I'm into debugging phase.

I had patched input to an oscillator and dly out to mixer. Without power I can hear dry audio showing there's a passive path from in to out. Switch power on that audio disappears. No led action with drive either.

Power to board is checked ok.
Comms to sock6 continuity checked ok.
Voltage at pin5 of 3207s showing 8.8volts.
No smoke or overheating. Nothing.

I had already checked polarity of Smd diodes in situ and zeners using dmm diode test mode.

So I'm now down to checking soldering of EDIT...just found a solder bridge. END EDIT?
I'm off to examine the schematic , but if there are suggestions as to how to narrow the search radius I'll take them.
Pav
so far corrected solder bridge and also resoldered suspect pin8 on U17.
all tl072s appear to have correct vdd vss except U11 which appears to have -11.11v instead of +15 - though im not sure it was a solid reading. so ill re check.

Would it be fair to say i can ignore decoupling caps from the initial search as they would not deliver a complete failure.?
Synthbuilder
Do you have a scope?

Do you have the dry output from the mix output? If not that may indicate that the fault is relatively simple. It's a pretty short path for the audio signal to go from in to out. Check that you have an audio signal at pin 5 of U14. A simple home made audio probe is useful if you don't have a scope.

If there is a signal at pin 5. Check that the same signal is heard at pin 7 of U14. It should also be present at U15 pin 1 and pin 7.

Tony
Synthbuilder
Pav wrote:
Would it be fair to say i can ignore decoupling caps from the initial search as they would not deliver a complete failure.?

Yes. There are more likely problems to find first.

Tony
Pav
Hi i have scope ... status is I have dry signal to mix out socket now - and U15 is in that .

The signal reaches U9 pin2 , pin 1 c28 pin1 R30 . the output on pin1 through to "limiter" is either nil or a dc offset. does that sound right?

limiter out leads to bbds pin3 ins... so

As i type im struggling to find the piece of schematic that follows on from "dry mix" label as signal sould continue somewhere too. EDIT ok that leads to U15 so thats ok ... so I think U9 is damaged.
Synthbuilder
Pav wrote:
The signal reaches U9 pin2 , pin 1 c28 pin1 R30 .

That's a problem. There should be no signal present on pin 2 of U9. It's wired as a summing amplifier and pin 2 is a virtual earth, ie. the voltage should be very close to 0V.

So I think U9's pin 3 is not soldered to its pad.

Tony
Pav
Im confused sorry. Schematic shows the audio in signal from U14 pin7 through R43 into pin2 of U9 with pin3 connected to ground. Ok If pin2 becomes a virtual ground, then where should i measure the signal next ? I presumed pin1 of U9 to see the triangle i injected, given zero feedback.

EDIT
I reflowed pin 4 which looked like it was hanging..and voila I have signal on pin1 of U9 ...good on to find the next problem as no instant joy.
Pav
just taking a break - i now have signal through to U6p3
I need to reflow now to get a signal from U12 p7 to R18 and on to U7.

Ill then check the clocks..one looks ok @340Khz the other is showing 110Kz but this could be noise... ill keep u posted.
Synthbuilder
Pav wrote:
Schematic shows the audio in signal from U14 pin7 through R43 into pin2 of U9 with pin3 connected to ground.

R43, along with the actions of the U9, turns the signal into a current proportional to the signal voltage. Your scope only measures voltage so it appears as if the signal has gone but it hasn't.

Quote:
I reflowed pin 4 which looked like it was hanging..and voila I have signal on pin1 of U9 ...good on to find the next problem as no instant joy.

If you have one unsoldered joint there may be others. Before you go probing around any further, go grab a magnifying glass and look at all the IC pins to make sure they are making good contact with the PCB. Sometimes an unsoldered joint will work because it is in physical contact with the board only to fail later when the board is flexed or the solder pad tarnishes.

Tony
Pav
All my looking is under a magnifying glass these days. Ive looked and nothing obvious shouts out and Ive reflowed U2,3,4, in passing. i cannot see any output on U12 pin7. I can on pin 1. So the inverting BBD is not receiving any signal. Reflowing is not fixing.

Further activity is on hold.. On monday i order a hot air rework station to replace U12.
Synthbuilder
Pav wrote:
i cannot see any output on U12 pin7. I can on pin 1. So the inverting BBD is not receiving any signal. Reflowing is not fixing.

What is the voltage on U12 pin 7? If 0V then I would expect the op-amp to be working but R57 not soldered, or R56's two tabs shorted. If it's +14V or -14V, the op-amp is probably toast, or R56 is not soldered.

Also, you should be now getting an audio output from the delay output of the module if everything else is working. Having the non inverting channel functioning should mean you'll just hear only the non-inverting BBD's output. Which means the module will work, albeit very quietly.

Before you splash out on a hot air workstation, have a look at Chip Quik:

https://uk.farnell.com/chip-quik/smd1/removal-kit-smd/dp/1850214

I've not got a hot air station - I just use a Weller TCP soldering iron and Chip Quik.

Tony
Pav
Thanks for the chip quik guidance - ill hold off rework station and try it.
Ill do the U12 checks tomorrow.

I had small success today....U11 has correct vdd now I mentioned in previous note. , and the clock pins on the bbds are getting clocked.
Pav
Tony I can confirm The voltages at U12 pin1 pin7 and both sides of r56 and r57 are -13.8v.
The voltages of R63,r54,r55 all read zero. (measured with dc setting)
I see a clipped version of my input signal through r63,54,55 to pin3 U2,
Synthbuilder
Pav wrote:
Tony I can confirm The voltages at U12 pin1 pin7 and both sides of r56 and r57 are -13.8v.

U12 could indeed be dead. However, just check that pin 8 is +15V.

Quote:
I see a clipped version of my input signal through r63,54,55 to pin3 U12.

That sounds right. You should get a +/-1.8V peak to peak clipped wave here. Turning down the drive control should give a cleaner unclipped signal.

Tony
Pav
I have managed thru reflow 4th time to get u12 working nanners
I now have my test signal displaying at U12oin7 and then pin3 of both bbds U6,7. No audio at delay_out still.

for both bbd

I have 8.8v on vdd on both.
I see square waves on pins 2 and 6. the clks .
pins 9 and 10 o/ps ..and are showing a slowly descending voltage
from 5v. on dmm and scope hmmm..... not expected.

I reseated the 3207s in sockets and soldering there looks ok.
but no joy - As both delay lines are acting the same You would think it something in common to both. Extremely bad luck if they were both delivered dead.

Thank you for all suggestions so far - another welcome.
Synthbuilder
Pav wrote:
Extremely bad luck if they were both delivered dead.

The 3207 is being made again from several places. The V3207 is perhaps the most consistently good one. The problem with MN3207 is that there are probably quite a few fakes around from not so long ago when the 3207 was no longer made. Don't buy from places that sell them as 'genuine NOS' and other guff.

Banzai and Musikding are usually good places to buy from - although I did get some fake MN3007s from the former earlier this year.

Check that pin 4 on both BBDs is roughly 8.2V. If not D6 & D7 might not be soldered correctly.

What is your clock frequency? And does it vary when your sweep the delay control on the front panel?

Tony
Pav
BBD pin 4 does have 8.2V

Clk issue Too high and not varying with Delay control.
Clk 1 = 2.8Mhz clk2= 2.4Mhz

EDIT -
Reflowed U10 and clk2 is now a nice steady @148khz
clk1 at U11 both are fine.
at bbd clk1 is distorted and unsteady 59-178khz and still no delay ctrl.
U10 pin 7 stuck at -13.8v think suspicious. pin6 input varies with delay as does r41 just before.. so still a soldering issue.
tune and scale controls are changing input values.

END EDIT.

I have 2 coolaudio 3207s from banzai.

Its a pain but I can also do a substitution swap with one of four cool audio 3207s in my sre330 which are known to be working.
Synthbuilder
Both clocks should be the same frequency. One is simply the anti-phase of the other, so that when one clock is high, the other is low. If they are oscillating at two different frequencies it may be that your scope probe is causing one of them to misbehave, perhaps because it can't drive the probe.

Check that pins 10 and 12 of U2 are oscillating with a square wave at 9V high and 0V low. Both should be the same frequency and both should be affected by the delay pot, and any external CV. The frequency should be able to go from around 20kHz to well over 1MHz.

Pin 6 of U10 is another one of those virtual earths, so it should be at 0V. The right hand side of U10 is probably either dead, pin 5 not connected or R39 not soldered.

Tony
Pav
Rockin' Banana! Rockin' Banana! Rockin' Banana! Rockin' Banana! utube video pre calibration: https://youtu.be/5Eka4NaBP28

You will be pleased to know i have a working Flanger !
At least .grungy triangle out of the delay output.
Well mostly ..tomorrow i need to fix led circuit and then i can calibrate.

I used the clikquik and replaced U10 and R39. R40 adjacent was accidental casualty too.. that stuff FLOWS.. and before you know it it could be everywhere.

I then a couple of reflows of U2 and U3 and resistor and finally got to U16 ..and bingo.

Thanks for the excellent support we all have come to appreciate.

Just one last question sorry - the Drive control is loudest in full CCW position and quietest in CW. Is this normal or a symptom as i would expect the drive to increase gain turning cloockwise. and set off the led circuit ?
Synthbuilder
Pav wrote:
You will be pleased to know i have a working Flanger !

Yay!!! It's peanut butter jelly time!

Quote:
... that stuff FLOWS.. and before you know it it could be everywhere.

Yeah, go easy with it. It's terribly expensive. I tend to cut off a 10mm piece and then feed it onto the iron with a pair of tweezers.

Quote:
... the Drive control is loudest in full CCW position and quietest in CW.

It shouldn't be too different but it will be loudest at its minimum setting. The reason being that the BBDs and limiter will be affecting the sound more with the drive turned up. With big signal inputs - and a direct output from a VCO would constitute a loud signal - the level of limiting is significant at higher drive settings.

Once the BBDs' offsets have been trimmed the level of clipping within the BBD stages should be minimal which should mean less discrepancy between the drive settings.

Tony
Pav
very frustrating Calibration reveals more issues.

Tune: pin6 U7 I cannot trim down to 33khz only to 54.9khz.


Null1,2:
I merged two blurry triangle waves into one wave.
I only saw and heard extreme clipping at the extreme ranges of trimmer.
I did check the scope settings were as required.
But think this is ok.

FBK: .. pots and switches as per calibration guide i get max distortion a 9 oclock and cannot trim it out. Now with Drive fully CW it oscillates around 9oclock and max distortion at 11.o clock.

I have a Moog MF Delay pedal I use with modular ..so i know this isnt right.
I still do not have LEDs working - so thats likely all part of the same problem. I have reflowed the VU_DRIVE circuit today with no joy.

So ..not out of the woods yet ..Still Having great Fun Noise making nanners
Synthbuilder
Pav wrote:
pin6 U7 I cannot trim down to 33khz only to 54.9khz.

What's your lowest voltage on pin 7 U10 (delay pot at min and trimmer down as low as it can go)? It should be around -6.5V. If not that negative then check circuitry around U10.

If it is -6.5V then the problem could be the VCO based around U2 - perhaps R1, R2 or C5 the wrong value. You should have -100mV at the base of Q1 when the output of U10 is at -6.5V.

Quote:
FBK: .. pots and switches as per calibration guide i get max distortion a 9 oclock and cannot trim it out. Now with Drive fully CW it oscillates around 9oclock and max distortion at 11.o clock.

With the FBK trim we are looking to set the maximum amount of feedback. We're not really looking at distortion but the level of self-oscillation. There should be no input signal used in this part of the calibration.

Drive will affect the amount of feedback because of the compressing affects of the BBDs and limiter circuitry. It is best to set up FBK with the drive pot at its minimum.

Quote:
I still do not have LEDs working - so thats likely all part of the same problem. I have reflowed the VU_DRIVE circuit today with no joy.

Have you checked that the LEDs are the right way around? Check the voltage at pin 5 of U13. You should see a positive voltage at this point when you have a signal present at the input of the module. The voltage should be proportional to the signal level.

Tony
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