[sdiy] Help trouble shooting mfos echo rockit

[Ian Fritz]

Oh, just noticed: the circuit calls for LM13700 and uses the output buffers. Hopefully “LM13600” in your post was a typo?

Ian

> On Nov 20, 2022, at 5:23 PM, JoeF <frey at radioles.com> wrote:
> 
> 
> Hello and tx again. So, I followed the schematic and there are indeed resistors before the labc inputs. They are 22K. I measured a voltage drop of 3.61V across them and calculate a current of 165micro amps. So, is that a reasonable value. I have also recorded the 13600 pin voltage values below.
> Starting at pin 1 and finishing at 16. 
> 1.25-1
> 0-2
> 3.73-3
> 3.68-4
> 8.4-5
> 0-6
> 0.31-7
> 1.28-8
> 0.32-9
> 0.31-10
> 9.14-11
> 0.61-12
> 3.76-13
> 3.74-14
> 0-15
> 1.25-16
> I am pretty much under water here. I don't know whether these are appropriate values for this circuit or not. I can hear an audio signal on pin 3. And, I hear it on pin 8.
> Tx for the help. JoeF.
> 
> 
> 
> 
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>> On Nov 20, 2022, at 3:24 PM, Roman <modular at go2.pl> wrote:
>> I don't have any schematics at hand so it's just basic guideline. There is something going into Iabc pin of LM13600. If it's a resistor, then simply measure voltage across that resistor and use Ohm law to calculate current. If it's supplied directly from PNP transistor's collector (most typical use) find a resistor that is going to emiter of that transistor, and do as previously described. In any scenario you may just desolder or cut the trace to Iabc pin and measure it with ampmeter. Or better yet, put a resistor there if there wasn't any, it can only help. 4k7 for starters. It will make future troubleshoting easier, not to mention it also prevents LM13600 from accidental smoking.
>> 
>> Roman
>> 
>> 
>> ---- Użytkownik JoeF napisał ---- 
>> 
>> Roman and Pete, TY. Roman, I want to move to the next level. Could you pont the way to how to determine current flow. I know how to check voltage and perform audio traces but I don't know how to determine current. If it's not too difficult, could you explain or point to a site that would explain. Tx again. JoeF. 
>> 
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>> On Nov 20, 2022, at 2:44 AM, Roman < modular at go2.pl> wrote:
>>> 
>>> Measure the Iabc current going to LM13600 to check if they are open at all. Measure voltages at OTAs and opamps outputs to see if they are not terribly close to one of supply rails.
>>> 
>>> Roman
>>> 
>>> 
>>> ---- Użytkownik JoeF napisał ---- 
>>> 
>>> Hello all, not sure if this is the right place to ask for guidance but, I'll try. I have put together an Echo Rockit I got as a kit. And, of course I need to troubleshoot. 
>>> This is an oscillator and external input into a VCF into a PT2399 delay. I am getting no sound at the output and I believe it is because the VCF is not functioning. I have audio traced a signal to the VCF from the input and the internal oscillator. And, I have jumped the signals around the VCF straight to the delay and then I get output and have verified the delay is operating as expected. I have correct power to all IC power pins. The transistors are getting power on their source pins.The IC in the VCF is an 13600D which I have spares of and have swapped to no avail. I have re-soldered the components in the VCF circuit. I don't have extras of the MPF102 transistors and am questioning whether I burned them up when I soldered them in? What do you think? 
>>> What's next? Thanks for any advice in advance. JoeF. 
>>> 
>>> Get TypeApp for Android
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