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WIGGLING 'LITE' IN GUEST MODE

Please Help me to resurrect my SEM filter
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Author Please Help me to resurrect my SEM filter
Supervillain
Hey all!

It think I gonna give a last try at fixing my moogah SEM clone filter (made from a synthcube kit)

- the probleme : frequency (either controlled by cv, or with knob) don't change. Pcb trimmers have no effect...

Here's a short video : https://youtu.be/o8z8T3nAUfs

- what have been tested already : switching TL074 > no change
Switching CA3080 > not better. Reflow all solder joint couple of time with no chance

Some picture :




Picture file

Any help would be greatly appreciated! Dead Banana
synthcube
hello-- please check especially the transistors against the orientation in the guide-- that's often a place to look
Supervillain
synthcube wrote:
hello-- please check especially the transistors against the orientation in the guide-- that's often a place to look


Mine looks like the picture in the build guide.
4302 and 3906 (one 3906 reversed as shown in BG)

Do you notice anything wrong it the pictures I uploaded?
veets
The third transistor from the left in the bottom photo appears to be soldered in the wrong orientation compared to the silkscreen.
veets
veets wrote:
The third transistor from the left in the bottom photo appears to be soldered in the wrong orientation compared to the silkscreen.


Never mind.
synthcube
which way is the TL074 oriented?
Supervillain

As indicated on the slickscreen
synthcube
We can't spot an obvious visual flaw. Have you reflowed the transistors, and individually re-checked the value of all of the resistors? Without an obvious culprit, fully reflowing each joint can often solve something
Supervillain
synthcube wrote:
We can't spot an obvious visual flaw. Have you reflowed the transistors, and individually re-checked the value of all of the resistors? Without an obvious culprit, fully reflowing each joint can often solve something


I reflown all solder joints about 4 times ! cry
i did not DMM checked resistor value because of the need of desoldering everything (and i fear desoldering !). I carrefully followed the BG and i'm quite meticulous when it come do diy. Anyway I checked color codes according to the pictures on BG and it seems ok.

Would you need more spot on pictures of my build ?
Idk, sometimes thing can looks obvious for somebody else...
synthcube
we are hoping others with builds will offer their views on the pictures--- its possible that one (or more) of the transistors is bad, so if nothing else evident appears, it may require one-at-a-time replacement of them
Supervillain
OK,

2n4302 are quite rare, right ?
Maybe i'll buy a couple 3906 first, replace it ans see if it helps
Chrutil
Since nothing obvious has appeared, here is a total long shot.
Recently I had a socket with a bad pin hole.
There were no connection between the leg and the socket pin, turned out the 'inner cup' of the socket was missing on one leg.
I figured it out when I probed the pin and it started working when I touched it with the probe. I'm sure it's super rare, but could be worth to at least take a look.

Supervillain
Chrutil wrote:
Since nothing obvious has appeared, here is a total long shot.
Recently I had a socket with a bad pin hole.
There were no connection between the leg and the socket pin, turned out the 'inner cup' of the socket was missing on one leg.
I figured it out when I probed the pin and it started working when I touched it with the probe. I'm sure it's super rare, but could be worth to at least take a look.



Thanks, i'll inspect IC's sockets!

EDIT : All sockets looks OK...
devinw1
Chrutil wrote:
Since nothing obvious has appeared, here is a total long shot.
Recently I had a socket with a bad pin hole.
There were no connection between the leg and the socket pin, turned out the 'inner cup' of the socket was missing on one leg.
I figured it out when I probed the pin and it started working when I touched it with the probe. I'm sure it's super rare, but could be worth to at least take a look.
[/img]


Oh man, that's brutal! I would have taken a long time to figure that one out. Sneaky.
Barcode
Try pulling the 3080 circled in the picture below.

Supervillain
Barcode wrote:
Try pulling the 3080 circled in the picture below.



Thanks for the advice barcode.

Just tried it, but it make no difference ...
Synthiq
To see if the frequency control works or not, remove the 3080 and then measure the bias current into pin 5 and connect the other dmm lead to pin 4. This current should change with the frequency knob.

In the video I didn't hear much sound at all, so make sure the input signal is also properly connected to the filter.
Supervillain
Synthiq wrote:
To see if the frequency control works or not, remove the 3080 and then measure the bias current into pin 5 and connect the other dmm lead to pin 4. This current should change with the frequency knob.

In the video I didn't hear much sound at all, so make sure the input signal is also properly connected to the filter.


I'll try that. Do you mean same 3080 Barcode circled?

Video was shot with a low volume but I sure have the input right
Supervillain
Tested all 3 3080's, I only get fixed values (see picture)
I tested frequency pot at the components pcb input and I got normal changing values
Synthiq
I was thinking about measuring the bias current, not the voltage on that pin. Without the 3080 in the socket, the voltage on the bias pin will probably be pulled up to a more or less fixed voltage independent of the bias current you try to send to that pin. If you see 0V between pin 4 and 5, the bias current is likely set to 0 or very close.
Supervillain
OK,
I don't know how to measure bias current, can you point out any tutorial?
Jarno
Where did you buy the 3080's? I bought a bunch of them on ebay in Germany, but they were all duds, fakes.
Supervillain
Jarno wrote:
Where did you buy the 3080's? I bought a bunch of them on ebay in Germany, but they were all duds, fakes.


All parts from synthcube kit
synthcube
with our stash of NOS 3080s, we have a 'bad IC' rate of about one in every 95 chips or so-- so if the 3080 is suspect we can send another to try out...
Supervillain
synthcube wrote:
with our stash of NOS 3080s, we have a 'bad IC' rate of about one in every 95 chips or so-- so if the 3080 is suspect we can send another to try out...


Thanks a lot synthcube guys but you already mailed me a bonus 3080, I replaced each one on my built with the new one and it didn't fixed the problem
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