MM Kit - several issues: power sup., vco

[SysKill]

Hello together!

This is my first post, so please forgive me, if I ask something you can't hear anymore. I tried to find help with the search-function, but I wasn't successful. Also please forgive me my bad english. I'm not a native speaker.

This is my first x0xb0x-Kit. I knew nothing about "good" or "bad" kits. I bought my Mode Machines kit spontaneously in a shop in Germany. After fixing several problems (smashed ac-adaptor, faked sc2291, other IO-Board as used in manual) I finally started to work and now - finally - my questions:

1. power supply:

After the assembling of the power supply unit on the IO-board I got good measurement results on J4. 5.33 Volts and narrow 12 Volts. Everything seems to work fine, but IC20 and IC25 are getting really hot. So hot, that I can't touch them longer than 1 second, then it starts to hurt. Is this normal?

2. vco

2.1:
When I finished the soldering of the vco, everything worked fine. All measurement were fine (bias, pin7 of IC11 and so on) and i got this saw-wave, taken at R105, on my rookie-scope on the iPad:



After soldering the vcf, I can't measure a saw at R105 anymore. I always find this wave:



It's a kind of square. Is it a bug or a feature?

2.2:
The tuning is very unstable. Everytime I re-measure the tuning at the saw-square-switch, it changed up or down. The difference is about 2 or 3 Hz. I guess this is not normal.

Thank you for your time!
Joerg

[Altitude]

Nothing should be getting that hot especially the serial to USB chip, check for shorts on digital power rail, dont reconnect it till you figured it out. Take a magnifier to the surface mount part and look for shorts there, that part may very well be dead now.

The waveforms look fine, the "square" on the x0x is far from being an actual square. Yours looks almost too square. The osc will work fine if there is a problem with the digital side so make sure you sort that out

[guest]

im assuming that ic25 is the usb chip
also check that the usb chip
is put in the correct orientation
pictures can be found here
http://ladyada.net/make/x0xb0x/fab/ioboard/index.html

if you need to clean up solder shorts
get some good solder braid and maybe flux
it makes it a lot easier

what are the voltages
on all 3 pins of ic20

[MMM]

After soldering the vcf, I can't measure a saw at R105 anymore. I always find this wave:

The square looks nothing like the typical square to me.

Is this behaviour independent of the position of the waveform switch?

You may want to remove the waveform switch or R62 temporarily and see if something is coming from the filter circuit.

Edit: You may first want to check if the two waveforms at the waveform switch SOUND like saw and square. Because looking at the "square" waveform again I couldn't help but notice that the leading edge of the waveform slopes upward.
Long shot: I don't know how this oscilloscope works at all. Could it be that the range is completely off and what we're seeing is merely a badly clipped saw?

[antto]

After soldering the vcf, I can't measure a saw at R105 anymore. I always find this wave:



It's a kind of square. Is it a bug or a feature?

this looks like the sawtooth, but it's too loud, and your scope is clipping it
check your probes, put more resistance on em

[Altitude]

FYI, the square should look like this:

[SysKill]

Thank you, i really appreciate you taking the time to help me.

I guess the wave-issue is fixed. You were right, when you said the wave is clipping. The input gain of my alesis IO-Dock was switched on maximum input level. Stupid me!

Now I got this wave at pin 3 of the saw-sqaure switch:


It looks upside down, but i guess it's a scope issue.

And this one at r105:


Everything's fine. Thank you for helping me solving this, this... I don't dare to write "problem."

And now to the much more frightening psu heat issue:

I took a magnifier and didn't found any short. The voltages on the three pins of ic20 are 5.02, 0.00 and 11.72 Volts. Nothing unusual, i guess.

But I found, that I, as an absolute beginner, caused some scratches on the surface of the IO-Board using the wrong equipment as a stand:





I guess I should get used to the thought, that I have to buy a new IO-board...

[Luap]

That just looks like a few scratches, so it's unlikely you need a new IO board. You can always double check, by doing a continuity check on those traces with a multimeter.

[SysKill]

That just looks like a few scratches, so it's unlikely you need a new IO board. You can always double check, by doing a continuity check on those traces with a multimeter.

That sounds good. but I have to find the reason, why the ICs are getting so hot...

[Altitude]

Take your meter, put it in "beep" mode and probe a 5v trace and ground, it should open (no beep)

[guest]

turn off the power
and measure the resistance to ground
from the 5v rail

if the usb chip is still getting hot
and you cant find any shorts
and its properly orientated
then you should probably remove it
as the short is either underneath the chip
or the chip itself is bad

[SysKill]

Take your meter, put it in "beep" mode and probe a 5v trace and ground, it should open (no beep)

In "beep-mode" my meter does not beep probing 5v and ground and...

turn off the power
and measure the resistance to ground
from the 5v rail

...shows about 75 Ohm between 5V and ground but 0 Ohm between 12V and ground (measured directly on IC 20)...

[guest]

there is definitely a short of some sort on the 5v line
but measure the 12v line again
it cant be 0ohms to ground
if it still produces 12v

another thing you can do
is cut the 5v trace that runs to the usb chip
and see if the heat problems go away
that will narrow down the issue to the usb chip
and you can get on with the rest of the build

[SysKill]

Directly measured on ic20 to ground:
5V pin: 60-70 Ohm
12V pin: Starts at 1 kOhm and rises up to 20 MOhm, then falls again.

Measured on j4 o ground:
5V pin: I'm not able to measure any resistance.
12V pin: Exactly 3,57 kOhm.

I guess I bring it back to the shop and buy another one... Far too many problems with this Kit.

[SysKill]

I guess I bring it back to the shop and buy another one... Far too many problems with this Kit.

Meanwhile i localized IC25 definitely as the causer of the heat issue. I removed it and everything works fine. So I can go on with the rest of the build (thanks guest). Special thanks to SubStyler! He helped me a lot!

Meanwhile Mode Machines wrote, that it could be, that my skills are too low for a project like this. They might be right, but I will make this damn machine run.