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Re: Ultimate DIY debugger award/No Go


 :
5/26/1999 4:26 PM
aron

 Re: Ultimate DIY debugger award/No Go
I handwired 3 protos and have tested continuity on all traces using my multi meter.  
 
In all 3 protos on perfboard, they all have the exact same results with 5 different transistors, 3 different pairs of zeners, 2 sets of caps.  
 
They all measure voltages around the same range.  
 
Aron
  
5/26/1999 6:37 PM
R.G.
...er... you haven't offended any minor deities, have you ??  
 
;-)
  
5/26/1999 12:26 PM
GFR
The "P" means a plastic DIP package. The "C" is the operating temperature  
range (0C to 70C). The "A" is the maximum input offset voltage at 25C (10mV  
for no letter, 6mV for "A" and 3mV for "B") - less is better.  
 
 
The symptoms you describe - 2.7 V on pin 3, 6V on pin 5 and 6V elsewhere - look like the transistor is ON while it should be OFF. The transistor may be shorted, may have the wrong pinout or may be of the wrong type.  
 
Please do the following tests:  
 
1) make sure that the circuit works without the transistor, as you have already done. Now insert the transistor but DON'T connect the collector to pin 5 (leave it unconnected). Measure all voltages if they're normal plug your guitar and play. If something is wrong the problem is the transistor. If everything is OK goto test number 2)  
 
2) Now connect just the base and collector and connect the emitter to ground INSTEAD of connecting it to the output of the opamp. Measure all voltages and play through it. If something is wrong the problem is the transistor. If everything is OK goto test number 3)  
 
3) Now connect just the emitter and collector and connect the base to +9V INSTEAD of connecting it to the zeners. Measure all voltages and play through it. If something is wrong the problem is the transistor.  
 
The tests above try to guarantee that the transistor will be OFF independently of what is happening to the opamp.
  
5/26/1999 4:27 PM
aron
We DO agree that the transistor should be PNP right?  
 
I will do the test tonight.  
 
Thank you,  
 
Aron
  
5/26/1999 10:49 PM
aron
OK,  
 
Hopefully it will work tonight.  
 
I have genuine TL081cp op amp. 3.3, 3.6, 3.9?? Zeners - .5amp.  
 
NEW, brand new 2N3906 transistors.  
 
I mean, it's gotta work already right.  
 
BTW: I removed the tone circuit and measured with my DMM from the inv input to the output and got close to 110K which is what I would think I should get with the IC removed.  
 
I will let you know.  
 
Aron
  

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