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

[tj7]

Thanks everyone!

I did the wire connection test that DrAlx suggested, and I believe the evidence is that he was right.  I can hear intermittent spurts of flanging when I hold the wire there with one hand as I attempt to strum with my other.

The signal also intermittently cuts out altogether and makes other noises - I presume because of how clumsily maintained the hand-holding-wire process was.

Here's audio in case anyone hears something I need to be warned about...listen to the whole thing as the clearest moments of flanging are towards the end.

https://soundcloud.com/matthew-h-slaughter/ehx-em-flange-test

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. 

[DrAlx]

Doesn't sound right to me. I cant here any sweeping but then I dont know how the pots are set. Set both range and rate pots to maximum and if possible see if you can feed the pedal with a noisy guitar signal (from a distortion pedal) rather than a clean signal. If you pluck a single string rather than strum then you should hear a wobbly pitch effect when the wire is in place.

You may have other problems apart from that bad connection.

When you do the wire manual test, try and measure what the voltage on the wire goes to. When the wire is not there the two solder pads would have had different voltages. Adding the wire should give them a common voltage. Tell us what that voltage is using the original pot settings that you used for the IC pin measuremnts. You don't need to play the guitar to take the measurements.

[tj7]

I just need to clarify -
Am I touching the multimeter needle to the actual wire that I am holding in place to measure "what the voltage on the wire goes (UP) to"?  See photo of what I was doing.

Range Min and Max - wire reading was 1.01
However I managed to *once*  get a moving reading cycling up and down from around 0 back up to 1 at each setting, but only after moving the wire around the solder points and reading - rereading about 20-30 times.



(apologies for the orientation, tiny pic did that)

Here's a new recording:

https://soundcloud.com/matthew-h-slaughter/ehx-2

When you do the wire manual test, try and measure what the voltage on the wire goes to. When the wire is not there the two solder pads would have had different voltages. Adding the wire should give them a common voltage. Tell us what that voltage is using the original pot settings that you used for the IC pin measuremnts. You don't need to play the guitar to take the measurements.

[DrAlx]

Yes that's correct measurement and correct voltage but that does not sound like flanging. Let me explain the three problem voltages on the IC pins...

You had this:
Pin1: 7.6
Pin2: 0
Pin3: 1.01

The job of that bit of the IC is to take whatever voltage is input on pin3 and then scale it up and output it on pin1.  The scale factor is set by the Range pot, and when all wired properly, pin2 will read the same voltage as pin3. If pin2 shows a lower voltage than pin3 then the output voltage on pin1 will max out. That is what is happening in your case, and the output voltage is going as high as it possibly can regardless of the voltage input on pin3. Fixing the bad connection to the range pot causes Pin2 to show correct voltage. Good. So why no flanging?
Well this bit of the IC is just setting the size of the control voltage that determines location in the flanger sweep. In this case, the 1.01 volts input at pin3 gets scaled and output on pin1 where it will be between 1.01 (when range pot is at minimum) and some larger number (when range pot is max).
If the voltage input to pin3 does not change then there is no way that the output voltage on pin1 will change either. Therefore no sweep. So that fixed voltage on pin3 is the next thing to investigate.
Now the switch that toggles between filter matrix mode and flanging (I.e. sweeping) determines the voltage passed into pin3. In filter matrix mode,  it gives pin3 a fixed voltage of around 1.01.  In sweep mode, it will give pin3 a varying voltage between 1.01 and 1.85.  That varying voltage produces the sweep.  So I am wondering if you are not using filter matrix mode by mistake, or have the switch wired wrong? Toggle that switch to the other position and then see if that gives you a varying voltage on pin3. You don't need to have the manual wire in place for that measurement. If you don't get a varying voltage on pin3 then we have to investigate the switch and how it is wired. That will involve taking voltage measurements on the 6 terminals of the switch.

[tj7]

Yep, I think you nailed it!

I was referring to my "No. 1" EHX EM as a reference unit, and *that* one has the switch wired the opposite way!!

That 3rd pin now does vary in a cycle from around 1 to 1.78. Up and down.

Here's audio of my manual wire and strum job:  https://soundcloud.com/matthew-h-slaughter/ehx-3

The thing flanges definitely now.  So I guess the next thing for me to do is follow the advice I've been given about resoldering the range pot pin etc.  Man, I hope I don't mess this up.  Any further advice on this delicate operation based on my pics?

Also, re: "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." - I should not touch this, correct? 

So I am wondering if you are not using filter matrix mode by mistake, or have the switch wired wrong? Toggle that switch to the other position and then see if that gives you a varying voltage on pin3. You don't need to have the manual wire in place for that measurement. If you don't get a varying voltage on pin3 then we have to investigate the switch and how it is wired. That will involve taking voltage measurements on the 6 terminals of the switch.

[DrAlx]

The two most likely causes of the problem are the lower solder joint on the pot, or a break in the track close to that joint. The solder on the IC pin is probably OK. I would leave it.  Regarding the grey wire soldered to pin 3, I would leave it alone. No point risking damage to the IC.

Note that you might not see a break in the track because the copper track is underneath the light green paint.
The problem with having the pot mounted directly on the board is that it puts mechanical stress on the track near the mount point, which is why a track break is more likely to occur there than on the IC end of the track.

If it was me I would just remelt the solder on the lower solder blob, and see if that fixes things.  If that does not work then I would get a solder sucker and remove that lower solder blob and then resolder it with fresh solder. If that still doesn't work then I would scratch away a small portion of the green paint covering the track close to the pot in order to expose the copper track and lay solder onto that track. Basically I would avoid putting a wire directly on the IC pin. My prefered option would always be to use the track that is already on the board. 
Edit: Note that there is also a third solder blob on that track (north of the lower blob in the picture) for a resistor leg.  You can solder there instead of the  IC pin. So I probably would not expose the track. I would run a small wire fron the pot to that resistor leg.
Hopefully just redoing the solder on the pot pin will be enough to fix things.

[thermionix]

How did that picture turn into an RPG?

[yeeshkul]

I had the similar problem and it was the BDD chip (very unfortunate). When it burns down the old Mistress will pass the clean signal.

EDIT: oh i overlooked the Filter mode works, the BDD should be fine then.

[tj7]

Lo and behold, IT FLANGES!

Remelting the solder didn't work, so I had to remove it with my solder sucker (so THAT's what that thing was for, that came with my solder kit) and did a reasonably neat job of scraping away a tiny section of the green track to expose the copper, then resoldered the pin in place. 

Here's how it looks now:



I resoldered the pin that is right in the centre of the pic - i.e. the left side range pot pin.

THANKYOU for all of the help - everyone!                     

Hopefully just redoing the solder on the pot pin will be enough to fix things.