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RYO Penta issues - help me troubleshoot?
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Author RYO Penta issues - help me troubleshoot?
OB1
Just built the RYO Penta and I have a few issues with it...

1. Steps 1 and 4 have limited range, i.e. at fully clockwise the note only seems about an octave or so higher than fully counterclockwise. Steps 2, 3 and 5 seem to be have a full range.

2. The LEDs are not working correctly. They operate as follows:
Step 1 - LEDs 1, 4 and 5 are dimly lit
Step 2 - LED 2 is fully lit
Step 3 - LED 3 is fully lit
Step 4 - LEDs 1, 4 and 5 are dimly lit
Step 5 - LED 5 is fully lit
In fact, “at rest” LEDs 1, 4 and 5 seem to be dimly lit all the time.

3. 3 step mode is not working. It plays all 5 steps. 4 and 5 step modes work correctly

I’ve checked all my soldering for dodgy joints and retouched pretty much everything. I deviated slightly from the BOM and used yellow LEDs rather than orange - not sure if that might be a problem? I’ve used all yellow LEDs in lots of my builds previously with no problems at all.

Does anyone have any idea where I should look, or what the issue might be?
mcop
First thing I'd check is that R10 and R15 are the correct values (100K).
OB1






mcop
From your pictures those resistors look correct. How much lower than the other three outputs are 1 and 4?
OB1
Hopefully this should illustrate it:

https://youtu.be/glWD7cdWFPY
mcop
Looks like the LED's for those stages are also a bit dimmer which could indicate somethings pulling the voltage down on those stages.

Looking at the schematic here's a few more things to check:

1. Check pins 3 and 7 of the CD4017 are soldered correctly.
2. Check all the connectors between the boards are soldered correctly - nothing shorting etc.
3. If you have another CD4017 handy try a different one.
OB1
Thanks! I retouched all the pins on the connectors this morning and had a look at the pins on the 4017 and it looks OK, but I’ll check again. I might have another 4017 in my components box, so will try that as well.
DMR
LEDs shouldn't matter much, they may just be more or less bright than the originals. The pots act as voltage dividers from the 4017, in addition to what mcop suggested I would use a multimeter to test the voltages on the CD4017 pins 3 and 7, and if they're ok (match pins 2, 4, & 10) work your way towards the CV output.
OB1
Thanks :-)
OB1
DMR wrote:
LEDs shouldn't matter much, they may just be more or less bright than the originals. The pots act as voltage dividers from the 4017, in addition to what mcop suggested I would use a multimeter to test the voltages on the CD4017 pins 3 and 7, and if they're ok (match pins 2, 4, & 10) work your way towards the CV output.


OK, so have double checked all soldering and it seems fine. All resistor values are correct.

However, with all the pots set at the same values, I'm getting very different voltages from pins 3 and 7 compared to 2, 4 and 10 on the CD4017. Would this indicate a defective IC or something else? I don't have a spare 4017, but can get hold of one quickly if changing it is likely to fix...
duff
Have you tested the pins with the front panel on and off? It sounds like you have a short between 1 and 4 (and 5 ?)

Perhaps try removing the 4017 and putting 5V to each output pin on the socket in turn to see if that makes any difference. If you get the same result the then the 4017 is fine.
OB1
Thanks, more things to try :-)
OB1
So last night, I went back over the board and retouched everything using plenty of flux.

This seems to have fixed some of the issues, but introduced a new one...

Step 1 now seems to be working correctly, in so far as it now seems to output a full range of CV values rather than the limited range it was outputting previously, however, the Penta will no longer cycle. It's stuck on step 1.

Any ideas where I should be checking next...?

Apologies for my ignorance, I'm still learning and I'm finding the Penta schematic a little confusing eek!
mcop
Can you post photo's?
My first guess would be a short to the reset of the CD4017.
This could well be on one of the board to board connectors. When looking at the back of the boards (back of switch on panel PCB/power header on PCB 2) check the top right pin. This is the connection which carries the RESET signal back to the CD4017. If there's a short to 0V here that would cause your problem.
OB1
mcop wrote:
Can you post photo's?
My first guess would be a short to the reset of the CD4017.
This could well be on one of the board to board connectors. When looking at the back of the boards (back of switch on panel PCB/power header on PCB 2) check the top right pin. This is the connection which carries the RESET signal back to the CD4017. If there's a short to 0V here that would cause your problem.


Thanks, I'll post a new pic later tonight. I think you could well be right - the board to board connectors have been a real PITA on this build! They seem just a bit too tight in the holes and I'm getting very little capillary action, so it really wouldn't surprise me if the problem was there...
OB1
Here it is in its current state. I've been over both boards again, checked for shorts, dry/cold joints, etc and retouched a few bits, including all the connectors and IC sockets. I've also tried a different CD4017.






It's still doing the same thing, i.e. step 1 seems to be working correctly, but its not cycling.



It's making me a bit sad now :-(
csaban
Have you tried shorting the reset and clock enable pins on the 4017 (13 & 15)? Mine has similar problems (only first step is cycled), and out of curiosity, I tried to invert the clock enable and it started to behave, sort of. The 4017 has +5V on the reset pin and 0V on the clock enable, which I think is wrong. I'm still trying to find what's going on. Hope that helps.
duff
Pin 13 is clock inhibit. You want this low for it to step with the clock.

The 5V on reset is why it is stuck on step 1.

See the timing diagrams on 4017 data sheet https://www.intersil.com/content/dam/Intersil/documents/cd40/cd4017bms -22bms.pdf
OB1
I also have 0V at pin 13 and 5V on pin 15, so that looks like my issue. Pin 14 is definitely getting the clock.

Guess I need to work out where that 5V on the reset is coming from!

Thanks :-)
duff
If you haven't already, check what the voltage is on the reset pin with the boards separated. If that doesn't help you narrow it down try again with the 40106 removed.
OB1
Thanks duff. With the boards separated, I'm still getting 5V at pin 15, so I guess that rules out an issue on PCB 1(?). With the 40106 removed, it's 0V at pin 15... so maybe something shorting around there? Or could the 40106 itself be at fault?

Trying to get my head around the schematic now and I'll scrutinise that area of the board more closely!

Still feeling pretty clueless, but I've definitely learned more from this build than the previous 20 or so successful ones!
OB1
With the 40106 installed, I'm getting 5V at its output pins 10 and 12. Not sure if that's right or not!
OB1




These are the best pics I can get of the offending board.
duff
I think 5V at pin 10 on the 40106 is to be expected but not at 12.

I am assuming this means that pin 13 is low (< 1V) so something is dragging it down. This is either the switch header pin or q1.

I’d start by checking for short between the header pin and the one next to it given that it is ground. I have no idea which header that is on the board but bleep testing from pin13 to the headers with your DMM will tell you.
csaban
I think I've found the issue with mine, Q1 (2n7000) seems to be broken. By using a multimeter in continuity tester mode, the source and drain legs seems to be connected. As far as I understand electronics (and bare in mind I'm not an expert in any sense) the diode between source and drain should not conduct or at least not both ways.
So: the +5V on pin 10 of the 40106 never gets to pin 13 as Q1 conducts towards ground. So pin 13 has 0V which gives +5V on pin 12. And that keeps reset constantly high.
OB1: try measuring the voltage between pin 10 and pin 13 on the 40106. They both should have +5V. If you only have +5 on pin 10, then there are three things that can go wrong:
A) the reset jack is shorted
B) R9 is broken
C) Q1 is broken
And of course I'm extremely sorry if I'm talking nonsense.
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