Hi not sure if this is the correct place to post about this topic
Recently put together the stripboard layout for the cem3340 VCO and not having any luck. Not getting any sound from any of the outputs nor any wave forms when using my scope.
And ive been following the troubleshoot guide
Using the scribled version of the stripboard layout as reference all voltages are checking out other than pin 3 of cem3340 it says there should be -7.2v but im getting -1.5v after the 620ohm resistor and at pin 3. There is -12v before the 620r from the power suplly
When scoping the saw,square and triangle at cem3340 im not getting any wave form nor at the out puts of the opamps
If anyone could shed any light it would be much appreciated.
My soldering isnt the greatest as The solder i was using at the start was pretty poor as i ran out of good stuff . I bought some better quality solder which definitely helped but at that point it was nearly built.
Ive been staring at the solders for hours and i can see any bridging or anything that could cause issues
It’s really hard to see on the solder points if there is something, and sometimes it’s not necessarily visible to the eye.
Personally I check with a magnifying glass after each weld, and after I always pass a cutter blade or knife between all the lines of the stripboard (and after a little brush stroke).
But I don’t know if the problem comes from there.
That’s definitely not good, and there’s very few possibilities. First, are you sure of those voltage measurements? They all should be measured between the point in question and ground. If so…
Make sure the 620R resistor really is 620R and it’s really connected to pin 3. There’s also a 5.6k resistor and a jumper to the 10k trimmer at that pin and you should check those values and connections. (You may not be able to make a reliable resistance measurement in circuit but you can at least examine the color bands and see if they’re right.) See if the voltage on pin 3 changes when you change the trimmer setting.
It seems to me either one of those components much be completely wrong, or there’s a bad connection on one of them, or a solder bridge but I see no sign of one (but definitely reflow the solder joints on the pin 3 strip), or the 3340 chip is defective or damaged.
I mean, there’s so little that could be wrong. Inside the chip at pin 3 there is a Zener diode. Put -12 V on a resistor connected to it and you have to get about -7.2 V, unless there’s a short or low resistance path to ground that shouldn’t be there.
Okay i just checked and it definitely is a 5.6ohm resistor. oops
seems i accidentally bought the wrong values.
i’ve checked the other resistors and they are correct.
success! i put a 4k7 and a 1k in series measured the combined resistance and had 5.66kohms measured the voltage at pin 3 and found -7.2v.
hooked up the jacks to the speakers a finally got some noise from all outputs!
initially had some background noise which later found i wired the ground of the jacks incorrectly but ive now corrected that and is now working perfectly!
so gratefull for everyone who went out there way to help
especially SCGator for being keen eyed for spotting the 5.6ohm resistor. hats off!
i was so close to giving up but that wasn’t an option considering how much i’ve all ready spent on this project so far haha
lesson now learned always check for the correct values!
Wow… what a state of affairs. Brick and mortar shops around here all switched to consumer electronics ages ago, but there’s still a couple of shelves with resistors and caps. You’d think it would be economic for some business to carry them… like you say, there are times when the wait and the postage don’t make sense
I can remember when there were not only Radio Shack but Lafayette Electronics stores all over the place, both carrying large selections of parts, but those days are gone. There used to be a local electronics parts store in Syracuse, NY fairly near the University, but that closed about a decade ago. There is another electronics store outside the city I’ve been meaning to visit sometime, but currently I generally don’t go into places I don’t need to go into, so it’ll have to wait. Looks like either a disaster area or a wonderland based on the pictures. But that’s the only place in the area I’d be reasonably confident of having any basic electronics parts.
I’m lucky enough to have an RS trade counter a couple of miles away, so I can get things there. Until very recently their website had free next day shipping on everything - I used that a LOT, getting things like a pack of absurdly specific capacitors for under two quid, delivered - but there’s a minimum spend of £30 (+ VAT) now on certain lines (including packs of 10 5.6k resistors).
Edited because I discovered I could still get free shipping on some things
