1981 V6 (9V) Electric Mistress does everything but flange! Help request.

[tj7]

Very strange.  The blades are doing something 'cos I can hear the BBD clock noise disappear, but it is not flanging.  So there's more going on here than a bad switch.  We'll have to wait for you to post meter readings.

We'll need the voltage on all pins of the LM324.  Pin 8 should have a voltage that varies over a range of a few volts, and you should see this voltage going up and down when you put the RATE to low.

After going through the switch (in FLANGE mode)...

Ok.  I should get my multimeter this week.  I am guessing you use the terms "SWEEP" and "FLANGE" mode interchangeably?  In any case, I am getting the same results no matter which position I have the switch in...

[tj7]

Ok, I have my multimeter.  I am about to do some googling to learn exactly how to measure voltages.  Any idiot proof would be really appreciated.  How do I identify specific number pins?  I presume I'll need to remove the entire casing to access both sides of the circuit board...

[Granny Gremlin]

I don't remember if you did it already - did you check the switch?  If not start there; easy and most likely problem.  Instructions above IIRC.

IC pin 1 is on the top left if the divet is facing up or the corner marked with a circle  if no divet (ignore any circles not in a corner):



Connect one MM lead to circuit/chassis ground and touch each pin with the other lead  to take a reading.  Sometimes you have to fiddle with the test lead to get good contact.  Same as when using an audio probe really.

[tj7]

Ok.  Because I have no idea even which settings to set my multimeter to (the thing has a million dials), I decided to simply buy a new switch and replace the old one.  I have just done this -not a bad soldering job if I say so myself - and the pedal functioning is *exactly the same*.  No change whatsoever. 



Is the likely problem an irreplaceable SAD 1024 chip?

Should I use my multimeter for checking something else?  Pic attached.  If someone could tell me how to se the thing up, I'd be much obliged.... I am a complete noob with this.  Literally.

[tj7]

Bump!

[bluebunny]

Ok.  Because I have no idea even which settings to set my multimeter to (the thing has a million dials), I decided to simply buy a new switch and replace the old one.

That'll keep the switch-maker company shareholders happy!      Anyway, I think you'll find your multimeter only has the one dial.      Granny was asking for voltages at each of the IC pins.  If you have a (black) meter lead with a croc clip, put it in the COM socket and clamp the other end to a ground point - the pedal chassis or (better) a jack socket screen tab will do.  (If not a croc clip, then you'll just have to multi-task and hold that one still with one hand while...) ...you take your red lead and plug one end into the second socket up (VΩmA) and poke the other end at each of the IC pins in turn, having previously turned your single dial to the DCV 20 position (about ten o'clock).

[PRR]

> If you have a (black) meter lead... ... ... . .... . . . ... dial to the DCV 20 position

Picture:

[tj7]

Wow, it's been months....  I've not been terribly motivated here!

Ok, I finally hooked up my multimeter as instructed.

As I have never done this before, and just could not be bothered trying to learn the basics, I tried all permutations of:

Battery connected
Battery not connected
In Flange mode
In Filter mode
Guitar leads in
Guitar leads not in
Switch engaged
Switch not engaged

I also changed the settings of the rate etc knobs and this was the result in ALL permutations:

NO VOLTAGE READ.  At all.  The multimeter read -0.00 at all times. On ALL pins. 
I touched ALL of the pins on every chip with the black lead grounded to the chassis and ZERO read on anything.

Any ideas as to what this means and how to rectify....?

Thanks again to everyone for helping me out!

I don't remember if you did it already - did you check the switch?  If not start there; easy and most likely problem.  Instructions above IIRC.

IC pin 1 is on the top left if the divet is facing up or the corner marked with a circle  if no divet (ignore any circles not in a corner):



Connect one MM lead to circuit/chassis ground and touch each pin with the other lead  to take a reading.  Sometimes you have to fiddle with the test lead to get good contact.  Same as when using an audio probe really.

[tj7]

Just a headsup that I've finally tried this out!  Any advice re my latest post?

Ok.  Because I have no idea even which settings to set my multimeter to (the thing has a million dials), I decided to simply buy a new switch and replace the old one.

That'll keep the switch-maker company shareholders happy!      Anyway, I think you'll find your multimeter only has the one dial.      Granny was asking for voltages at each of the IC pins.  If you have a (black) meter lead with a croc clip, put it in the COM socket and clamp the other end to a ground point - the pedal chassis or (better) a jack socket screen tab will do.  (If not a croc clip, then you'll just have to multi-task and hold that one still with one hand while...) ...you take your red lead and plug one end into the second socket up (VΩmA) and poke the other end at each of the IC pins in turn, having previously turned your single dial to the DCV 20 position (about ten o'clock).

[PRR]

Measure your battery.

Follow the battery wires and go along.

[tj7]

Thanks.  Definitive proof of my noobness.

Ok, I have some results - see attached image.  Flange mode.  Rate set fairly low.

Measure your battery.

Follow the battery wires and go along.

[DrAlx]

The voltages are mostly OK.  3 voltages seem suspect but that may not be the ICs  fault. It could be the wiring. The suspect voltages are the ones near the top right (1.01, 0, 7.6).

Now when you are in flange mode, the pin where you measured 1.01 should actually be showing a voltage that varies from roughly 1.01 to 1.85.  So the first thing to do is double check that pin voltage and see if it varies at all or is really stuck at 1.01.

The zero voltage at the pin next to it looks wrong because it should vary too (from about 1.01 to 1.85 also).

I think the cause of your problem is a bad connection to the Range pot. The pin with the bad voltage of 0 should have a connection to one end of the Range pot and the pin the bad voltage of 7.6 should have a connection to the other end of the Range pot.

Using the exact same set up, measure the voltages at the 2 pins used on the Range pot and post them here.
EDIT: Also let us know how the Range pot was configured , i.e. was it at maximum range or minimum.

[tj7]

Thanks.

I carefully did the test again, with the range pot at min and again at max.  This made no difference at all.
The three pins at top right (as far as the diagram I drew goes) gave me the *exact same results* as in my first test.

FYI I did this with the rate knob at min and max also, and this again made no difference.
 
That 7.6 is actually 7.59, and also this particular pin will sometimes revert to 0 depending on exactly where on the pin I touch with the multimeter needle.

The voltages are mostly OK.  3 voltages seem suspect but that may not be the ICs  fault. It could be the wiring. The suspect voltages are the ones near the top right (1.01, 0, 7.6).

[DrAlx]

What voltages did you measure on the terminals of the Range pot?
I asked you to measure at those terminals (i.e. directly on the pot) in order to see if they agree or disagree with the bad pin voltages. If they disagree then you have a wiring problem.

[tj7]

Sorry, my bad - Ok -

Range @ Min
Left pin:  7.53 - 7.54
Right pin:  7.53 - 7.54

Range @ Max
Left pin:  6.85 - 6.86
Right pin:  7.53 - 7.54

What voltages did you measure on the terminals of the Range pot?
I asked you to measure at those terminals to see if they agree or disagree with the bad pin voltages. If they disagree then you have a wiring problem.

[DrAlx]

Bingo. So there is a missing connection from the left terminal to the pin with a bad voltage of zero. It might be a broken wire or bad solder joint or bad track on the PCB. Probably a bad solder join.

[tj7]

Hopefully this means a solution!

Here's what I can see when I flip the board - can you advise me exactly what I need to solder?

Bingo. So there is a missing connection from the left terminal to the pin with a bad voltage of zero. It might be a broken wire or bad solder joint or bad track on the PCB. Probably a bad solder join.

[DrAlx]

You have marked the correct points. They are already connected by a short green trace on the PCB so in theory should measure the same voltage.
Now the problem is that applying heat to the IC risks damaging it. 
So before soldering anything, double check that the two points do indeed read different voltages. Do that on the side of the board shown in your photo measuring directly on the solder blobs that you circled in red. I only mention this because I am not sure which side of the board you took your measurements on. For example, the lower solder joint could be bad in different ways.  The solders job is to connect the pot to the trace on the PCB. If it is a bad joint, then the solder might be connected to the trace but not to the pot, or it might be connected to the pot but not the trace, or it might not be connected to either.

Before soldering anything, get a piece of scrap wire and use it to manually connect the solder blobs in the two red circles.  i.e. with range at max, manually hold the wire onto those two solder spots and see if you get flanging.  If that works then it shows a fix is possible by using the short piece of wire, but you might find that just remelting the lower solder blob used to attach the pot could do the trick. Definitely do not solder anything before doing the manual test.

Edit: just noticed something else that is a bit poor quality. The top ted circle has a pad to the left of it and someone soldered a grey wire there directly on an IC pin which is a dodgy thing to do as it risks damaging the IC with heat. The PCB has a pad for that grey wire immediately to the left of the lower ted circle (you can see the trace).  That's what they should have used. I am not suggesting you change that, only pointing it out.

[thermionix]

I would just add, sometimes a 0 reading is the result of a bad contact with your meter probe.  It looks like you're touching it solidly, but some flux or oxidation or something is preventing good contact.  Might help to lightly scratch at the solder with the tip of the probe.  Could still be a bad trace, though, just sayin'.

Can't be sure, but in the pictures, the range pot pin on the right looks like a cold solder joint, with corrosion on the pin.  I would recommend desoldering that pot, hitting the pins with a bit of sandpaper, and soldering it back in.

Edit:  Just noticed (duh) that the pin in question is connected to the wiper, so probably not related to your problem.

[PRR]

Agree that the pot soldering is dubious.

Pot legs need cleaning and pre-tinning. When soldering, heat the fat pot leg more than the thin PCB trace. Your solder is not "blobby" (good!) but could be thinner so you KNOW the solder "wet" both the leg and the PCB. Sheer blouse, not a Maine parka.