Electronics > Beginners
NAD 218 THX amplifier Repair.
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Richard Crowley:

--- Quote from: SantaClaw on February 23, 2019, 12:06:41 pm ---Well, I have been using a cheap transistor tester with all the transistors I have de-soldered.
--- End quote ---
WHAT "cheap transistor tester". Specifically.


--- Quote ---I figured using the DMM was ok for testing for shorts
--- End quote ---
We are past that stage. We need better detail at this stage.
Maybe those transistors are not dead.  But how close are they to their twins over on the good side?
SantaClaw:
I have two identical kits, one in a nice plastic case, the other just as is.

https://www.banggood.com/Supporting-Shell-For-DIY-M12864-Graphics-Version-Transistor-Tester-Kit-p-989949.html

https://www.banggood.com/DIY-M12864-Graphics-Version-Transistor-Tester-Kit-LCR-ESR-PWM-p-986954.html

Basically, a kit. It seems to be accurate from what I can tell, with repeatable values that measure the same on both kits.
Richard Crowley:
OK. going forward, we are going to use the component testers to get more detailed intelligence of what is going on inside the transistor package.
1) To confirm that they are behaving properly as a bipolar NPN or PNP transistor (as appropriate for each device)
If they have developed some weird behavior, even those cheap transistor testers will produce results that appear bizarre. That is an indication that the device is no longer behaving the way we want it to do
2) To compare the details (particularly Beta = hFE = gain) for parallel array matching. Specifically those places where there are four power transistors working in parallel. But also to compare how alike the transistors are to their twins over on the good channel for troubleshooting purposes.  That is what we are trying to do now. Compare the failed channel vs. the good channel. Component by component, and starting with the transistors as they are the prime suspects in this mystery.
SantaClaw:

--- Quote from: Richard Crowley on February 23, 2019, 04:52:27 pm ---OK. going forward, we are going to use the component testers to get more detailed intelligence of what is going on inside the transistor package.
1) To confirm that they are behaving properly as a bipolar NPN or PNP transistor (as appropriate for each device)
If they have developed some weird behavior, even those cheap transistor testers will produce results that appear bizarre. That is an indication that the device is no longer behaving the way we want it to do
2) To compare the details (particularly Beta = hFE = gain) for parallel array matching. Specifically those places where there are four power transistors working in parallel. But also to compare how alike the transistors are to their twins over on the good channel for troubleshooting purposes.  That is what we are trying to do now. Compare the failed channel vs. the good channel. Component by component, and starting with the transistors as they are the prime suspects in this mystery.

--- End quote ---

Right, I'll start de-sodlering, labling, and posting the comparison numbers here.
Thanx for the help, I really appreciate it. As I said I'm a newbie at this.
Doctorandus_P:
https://octopart.com/search?q=2SC5200
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