- This topic has 6 replies, 2 voices, and was last updated 3 years, 3 months ago by
.
-
Posts
-
I recently was building a circuit on a PCB and when finished, things did not add up. True bypass worked, but the Collector and other BJT voltages were not even close to what they should be. First I checked to make sure all components were the correct values, even though I confirm and test each component before soldering it to the appropriate site on the PCB. Next I performed continuity testing on the entire circuit. There was continuity between all components except those involving the Collector of Q1. I reflowed all the solder joints of all of the components involved in the non-continuity, but the non-continuity problems persisted, so it appears that the issue is not related to a dead solder connection. The non-continuity problem involves a Darlington pair configuration with non-continuity between the Collectors of Q1 and Q2. Continuity issues are as below (somewhat involved).
Area of interest in the circuit:
Non-Continuity involving Q1 Collector area:
Non-Continuity involving Q2 Collector:
Overall Non-Continuity:
Continuity (first involving Q1 Collector then Q2):
Overall Continuity involving Q2 side:
There is also a “Test” part of the circuit involving Q1 and Q2 as below:
Next results showing Continuity and overall Continuity and Non-continuity:
My conclusion is that there must be a break in the PCB connection between Q1 collector and Q2 collector as below. What do the experts on the board think?
Okay, my 8th attempt to fix this post. I get so far in a somewhat long post and the post is lost after I submit it. Maybe it is timing out on me.
As I stated previously, I recently was building a circuit on a PCB and when finished, things did not add up. True bypass worked, but the Collector and other BJT voltages were not even close to what they should be. First I checked to make sure all components were the correct values, even though I confirm and test each component before soldering it to the appropriate site on the PCB. Next I performed continuity testing on the entire circuit. There was continuity between all components except those involving the Collector of Q1. I reflowed all the solder joints of all of the components involved in the non-continuity, but the non-continuity problems persisted, so it appears that the issue is not related to a dead solder connection. The non-continuity problem involves a Darlington pair configuration with non-continuity between the Collectors of Q1 and Q2. Continuity issues are as below (somewhat involved).
Area of interest in the circuit:
Non-Continuity involving Q1 Collector area:
Non-Continuity involving C2 to other components:
Overall Non-Continuity:
Continuity (first involving Q1 Collector then Q2):
Overall Continuity involving Q2 collector:
I will continue with another post (Part 2) to complete the whole shebang.
There is also a “Test” part of the circuit involving Q1 and Q2 as below. This was confirmed by visual inspection and continuity testing.
Next are results showing Continuity involving the Test circuit.
Continuity of the Test circuit and Non-continuity relative to the Test circuit. Continuity = Green tracing and Non-continuity = Red Dotted Line.
My conclusion is that there must be a break in or absence of the PCB connection between the Q1 collector and Q2 collector as below (red dotted line). What do the experts on the board think from the test results? Continuity in Green, Broken/absent segment in Dotted Red.
As a final comment, I did place a temporary, non-soldered jumper (blue tracing on schematic below) between C2 and the Test eyelet. The voltages then tested more appropriately to what they should be in this part of the circuit. I believe I likely have a defective PCB. I would like to hear the experts’ opinions and input regarding my test findings because maybe I am barking up the wrong tree.
I agree. If there is no continuity between Q1 Col and Q2 Col, the board is defective.
(In my humble opinion!)
Thanks for the follow-up and input Wilkie!
Sorry for a somewhat tardy reply. Yesterday before seeing your post, I placed a jumper between R3 and the Q1 Collector, and of course the measured voltages behaved more like they should. Now I am trying to dial in the Fuzz. I may have to increase the size of the Q1/2 trimpot to 20K from 10K. Thought about that before soldering the 10K trimmer to the board and now regret it.
Below images show the jumper passing right to left beneath the tone pot from R3 to the Q1 Collector.
- You must be logged in to reply to this topic.