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Euro MosPhaser 95% working (SOLVED)
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author Euro MosPhaser 95% working (SOLVED)
Pav
Hi, just to let you know i have the Euro MOS Phaser build completed.

I have 2 outstanding symptoms which highly likely to be related.

a) Calibration With freq and modulation at minimum, I cannot get the voltage to change at D3 from 0.31V using Tune trimmer.

b There is only one sweet spot position of the frequency knob between 1-2oclock that when cv or lfo modulating , that is actually sweeping phase .
Tweaking the Tune trimmer can stop the sweep.

Ive checked the VDD and VSS pins on the chips to ensure they are powered.
I believe the schematic between TUNE and CONTROL_CV is the best place to start checking soldering further.

Keep you posted.
Synthbuilder
A few thoughts:

D1, D2 or D4 could be around the wrong way.

Check the soldering around that weeny dual transistor, Q1.

Check the output of U1 (main board) at pin 1. You should see the main CV there, ie. the frequency pot, the tune trimmer and the modulation depth should have an affect on the voltage at that pin. With the Frequency pot and tune trimmer in their middle positions, and the modulation pot to its minimum, the voltage at pin 1 should be around +2V.

Tony
Pav
>>>D1, D2 or D4 could be around the wrong way.

checked and right way around

>>Check the soldering around that weeny dual transistor, Q1.

soldering is ok but i cannot tell if its the right way around ..i need to invest in a microscope, my magnifying lamp doesnt cut it. supposed to have a dot on pin1 or a line.

Check the output of U1 (main board) at pin 1.......

This is fine +2v I achieved using trimmer ..prior to this i measured
CCW +7.93 CW -3.81 and centered 1.1V

still have the symptom.

But cry I then replaced the 4009 (U3) thinking i had fried it trying to remove solder bridges. I had no inverted voltages on the pins. I then thought i introduced a bridge on the replacement.. But i now see that what i thought was a solder bridge now appears to be a tear in the green protective coating over a track that goes underneath pin4 from pin3 now shorting 3,and 4 together . Suspect a Dead Banana again,

This is my doing with soldering iron not a board fault i hasten to add.

looks like i will have to remove the 4009 ((cliqQuick style) to see if i can seal the tear. and try again.

U3 pin14,15, is part of the feedback on U2 ..so if not working is this a possible cause of my problem ?
Synthbuilder
Pav wrote:
But i now see that what i thought was a solder bridge now appears to be a tear in the green protective coating over a track that goes underneath pin4 from pin3 now shorting 3,and 4 together.

Shorting pins 3 and 4 may well be the cause of the fault. And if not, it would certainly need to be fixed. That's an input connecting to an output.

I've not got a board in front of me right now so I'm unsure which track has been uncovered. Even so, the solder mask only prevents solder from wetting the copper surface and is not relied on as an insulator as such. So remove the solder on pins 3 and 4 with a bit of wick. You should find that the pins are still soldered enough to work and any solder that is not where it should be has now gone.

BTW this is the best solder wick I have found that you can buy in the UK:

https://uk.farnell.com/multicore-loctite/nc-bb/braid-desoldering-1-5m- 2-59mm/dp/252505

Tony
Pav
apologies, Tony the pins shorting are actually 13(NC) and 14(Input), with what appears to be a track from pin 16.



given my difficulty with braid to remove bridge, im wondering if pin 13 had a track to pin 14 or another possible is ive lifted pin13 pad across to 14.

either way bridging to an NC is not likely to be my problem.
Agree?


FYI pin 16 and NC pins of U3 main board do not appear in schematic.
(or if they do i didnt spot them. ) Im asking myself why pin16 is connected to pin 14 with a track ? EDIT - Is answer Control_CV being used as vdd voltage?
Synthbuilder
Pav wrote:
given my difficulty with braid to remove bridge...

Might not be your fault. There's a lot of poor quality braid about. The only stuff I have found that actually works well is the Multicore NC-BB stuff.

Quote:
im wondering if pin 13 had a track to pin 14...

Pin 13 and pin 14 are joined together on the PCB. So they should be reading as shorted.

Quote:
Is answer Control_CV being used as vdd voltage?

Yes. By doing so it removes the upper half of the output MOSFET pair. It's not on the schematic because the 4009 is a logic chip and as such its power pins are automatically connected to Vdd and 0V by my CAD software and not shown on the schematic. I had to join pin 16 to the CV on the PCB layout manually which doesn't back annotate to the schematic.

Tony
Pav
Thanks. I will go invest in new braid, mine is Maplins and v old. I'm now assured I can refit 4009 and continue fault finding.
Synthbuilder
How are you doing your surface mount soldering? The picture shows some of the components a little off axis. The way I do it is to add a tiny amount of solder to one of the solder pads on the PCB. Barely a raised bump of solder is all that is required. Then with tweezers place the component next to the bump of solder. With your soldering iron reheat the solder pad (but add no more solder) and with your tweezers slide the component onto the pad. Make sure the component is lined up and flat against the board surface and remove the iron.

Now do the other pin or pins of the component by adding solder to the pad.

With ICs I solder the top right pin first, eg. pin 8 for a dual op-amp, pin 14 or 16 for a bigger chip. Once that is done and lined up, solder the bottom left pin, eg, pin 4 for the op-amp, pin 7 or 8 for the bigger chip. Then the rest can be soldered without fear of the chip moving.

The solder used should be of decent quality, eg. Multicore, Kester, Warton and be no more than 0.7mm in diameter. Probably best not use own branded solder, like Rapid's or Maplin's.

Tony
Synthbuilder
For decent tweezers, use stainless steel ones and remove any flux or solder every so often.

https://uk.farnell.com/duratool/1pk-102t-f/tweezer-super-fine-straight -110mm/dp/3127576

Or if you feel like spending some more cash:

https://uk.farnell.com/lindstrom/tl-4-sa-sl/tweezers-extra-fine/dp/177 9180
Pav
thanks for asking , its my shakey hands that are at fault more than the tools. When i hit a problem, the nerves often get the better of me. I try not to go back to slightly off axis resistors and caps as ill make a worse hash of it.

I follow the technique you mention but im probably guilty of not heating the pads enough and then the solder blobs for fear of frying components. I also remove the tweezers a tad quickly and the chips move as the solder not solid.

I get better with each build.

Today i replaced the 4009 again - without problem, but then replaced that tiny tiny transistor pack Q1 ..and bridged two pins again. Could not remove the bridge and so had to remove the new one and and try again later.

Question - what should the voltage of Q1 pin6 show ? I got 0V.
Synthbuilder
Pav wrote:
what should the voltage of Q1 pin6 show ? I got 0V.

That's right. The op-amp will act to make its inputs both the same. Since pin 5 is bolted to 0V the op-amp will make its output such that there is also 0V on pin 6 (which is connected to pin 6 of Q1).

Tony
Pav
ok ta. Ive put Q1 back on and doublechecked orientation and symptom persists.

Here is a short video clip of the symptom again for future reference.

https://youtu.be/3Y5GXMB8wNA

EDIT - learnt a little more .. measuring at D3 when phasing voltage btween1-2v, when freq knob is moved counter clockwise voltage goes to 4.95V and when moved clockwise of the sweetspot - 0v. Trimmer is moving that sweetspot. So something is pulling too high and too low.
Synthbuilder
Not sure what's wrong actually. It sounds right at least when it's phasing.

Maybe R8 isn't soldered properly, or R7 is the wrong value?

With the module unplugged measure the resistance between pin 2 of Q1 and pin 5 of U1 (0V). It should be about 1K.
Pav
applause applause applause

I had 192K resistance not 1K ..and R8 is the culprit.

R8 which is the 1K tempco connected to pin2 looked to be perfectly soldered but it fell apart on removal.

I didnt have spare tempco but replaced R8 with regular 1k - And problem solved ! All is well.


Thanks again Tony. Next smd job is your sequencer hyper
Synthbuilder
Pav wrote:
R8 is the culprit.

Rockin' Banana!

Quote:
replaced R8 with regular 1k


Yeah, the PTC is a little unnecessary in a phaser.

Quote:
Thanks again Tony. Next smd job is your sequencer hyper


You're welcome. And enjoy building the sequencer. The only real difficulty in that one is lining up the LEDs if you have to take your panel off.

Tony
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