Quick question, can transistors and resistors be tested in situ and with the amp powered off if I use a DMM in diode test mode?
Yes most of the time. Keep in mind that resistors in series or parallel with each other will alter their values, but generally speaking you can get an accurate resistance measurement in circuit.
Transistors are a yes and a no.
Yes, you can test in circuit and unless they tied to another transistor you can test them for voltage drop from the Base to Collector and Base to Emitter, as well as check for any open circuits or dead shorts, especially C-E.
The no comes in because the only sure way to test a transistor is out of circuit.
I generally start by testing in circuit and if something doesn’t look right, that is where I start pulling them out and testing and moving forward and/or backward if it tests good out of circuit.
Transistors are a yes and a no.
Yes, you can test in circuit and unless they tied to another transistor you can test them for voltage drop from the Base to Collector and Base to Emitter, as well as check for any open circuits or dead shorts, especially C-E.
The no comes in because the only sure way to test a transistor is out of circuit.
I generally start by testing in circuit and if something doesn’t look right, that is where I start pulling them out and testing and moving forward and/or backward if it tests good out of circuit.
Actually your “gold” and “red” are connected via the trim pot, as the “blue” are directly tied together.
Start with Red, then Gold then Blue in your testing since your main issue is bias fluctuating
Start with Red, then Gold then Blue in your testing since your main issue is bias fluctuating
Great, thank you.
Have just discharged the big caps on this unit and will test.
With red and gold being tied via the trimpot, might different settings on the trimpot affect the readings? Not too bothered by this question, just crossed my mind, will get on with the task.
Have just discharged the big caps on this unit and will test.
With red and gold being tied via the trimpot, might different settings on the trimpot affect the readings? Not too bothered by this question, just crossed my mind, will get on with the task.
Yes you can take readings whoever you can get access, look up the data sheet and determine which legs are BCE, so you can measure correctly with your DMM leads.
Don’t worry about them being connected, unless you get strange readings, it shouldn’t be an issue.
Don’t worry about them being connected, unless you get strange readings, it shouldn’t be an issue.
Hi Bullittstang, thanks again for your help so far. If it suits, please feel free to have a look on the readings that I've now posted on the other thread at
Yamaha A-1 idle current issue
Yamaha A-1 idle current issue