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Hi everyone,
the 2018 mini-me was my first build. And after some troubleshooting and patience (not to speak of obvious and embarrassing mistakes of mine) I’ve managed to get some things working. Bypass works and I think that I’ve found the sweet spot on the trimpot. But unfortunately, P1 has never done anything. Among other things I checked the voltages of the ICs and IC4 seems way off (see readings below)
IC1 – 4558 (pins)
1 – 4.40 | 4.55
2 – 4.40 | 4.54
3 – 4.29 | 4.43
4 – 0.00 | 0.00
5 – 4.38 | 4.49
6 – 4.40 | 4.50
7 – 4.39 | 4.47
8 – 8.75 | 8.99IC2 – MN3007 (pins)
1 – 8.11 | 8.33
2 – 4.04 | 4.14
3 – 4.33 | 5.72
4 – 0.00 | 0.00
5 – 0.00 | 0.00
6 – 4.03 | 4.13
7 – 4.40 | 5.60
8 – 4.40 | 5.60IC3 – CD4047BE
1 – 8.09 | 8.17
2 – 0.09 | 0.09
3 – 7.25 | 7.57
4 – 8.25 | 8.33
5 – 8.25 | 8.33
6 – 8.25 | 8.33
7 – 0.00 | 0.00
8 – 0.00 | 0.00
9 – 0.00 | 0.00
10 – 4.09 | 4.13
11 – 4.20 | 4.14
12 – 0.00 | 0.00
13 – 7.97 | 8.19
14 – 8.11 | 8.33IC4 – LM358P (pins)
1 – 2.62* | 7.55
2 – 4.03 | 6.94
3 – 3.80 | 8.91
4 – 0.00 | 0.00
5 – 2.52* | 7.50
6 – 2.18 | 4.90
7 – 2.62* | 7.65
8 – 8.75 | 8.99
* voltage swings up then down-oscillatesQ1 – 2N5087 (PNP)
E – 3.60 | 5.20
B – 3.10 | 4.58
C – 0.00 | 0.00Q2 – 2N5088 (NPN)
E – 3.66 | 4.90
B – 4.23 | 5.46
C – 8.65 | 8.99Q3 – 2N5088 (NPN)
E – 8.08 | 8.33
B – 8.70 | 8.96
C – 8.76 | 8.99I’ve already checked the forum to see whether some of you have had the same issue (doesn’t seem to be the case) and what usually causes problems in this build. I made sure that g2 is grounded, I resoldererd some joints, I checked the voltages of the components around IC4 and I have even replaced it with another LM358P (which delivered the same voltages), so now I am kind of out of ideas.
Does any of you guys have some ideas what I could do/check next? Any help is much appreciated!
Post some nice clear pictures of your build so we can see all components clearly
Check components from pin 3 of the 4047 to pin 1 of the 358
Thanks, I will do that as soon as I can lay my hands on it again. Wouldn’t have expected you to be that fast 😉
So, I did what Billy suggested. If I read the schematics correctly, the interesting readings would be
R29 – 39k | 38.9k
C19 – appears to store energy (my multimeter doesn’t have a capacitor setting; had to go by checking the resistance)
P1 – range between 3 and 10kI wasn’t sure whether or not to include the following but I did so anyway
R27 – 68k | started at 38k then slowly increased to around 45k after a minute
C18 – same as C19I hope these pictures will suffice. I’ll gladly take new ones from a different angle if it should be necessary!
R26 looks like a 180 ohms not 180K ohms
Colour bands should be brown grey black orange brown
Yours looks like brown grey black black brown
Check all resistor values by colour band make sure they’re correct here
https://samstechlib.com/610938/en/
Hi Billy,
thanks for your reply – you must have the eyes of an eagle! The readings of R26 confirm your assumption (178.5 Ω ). I’ve checked the values of all other resistors by multimeter and colour band in case the readings were off (R17 and R24 gave me some rubbish readings but the colour band was fine). So it looks like R26 really is the culprit here. Thank you so much for providing some much needed hope 🙂
Since I don’t see a 180 Ω resistor needed anywhere in the kit, I’ll assume that it was an honest mistake by my vendor. Therefore I’ll get in touch with Klaus of musikding.de and see that we’ll work things out. I’ll report back here in any case!
Meant to say I checked what I could see and everything looked good
You won’t get accurate resistance readings in circuit because of connected series and paralell resistance
Just for info when checking resistance along a circuit path always make sure there is no power to the circuit for example if you wanted to check resistance on the path between +9v and IC4A pin 3 you’d expect at least 180K (R26) + perhaps some of R27 68K
Try it yourself and see what you get I’m never sure with series resistance
Here’s the promised update:
Yesterday I received the correct resistor (180k) and soldered it in. And what can I say? Everything works fine now. Still can’t believe it.
Thanks a lot for your support, Billy! I am very happy to finally have a functioning mini me and am looking forward to putting it to good use 🙂 I guess you can close this thread now and mark it as solved
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