How To Diagnose Faults In Transistor Circuits - A Practical Example Samson TXM16 1000W Powered Mixer

LER #328 So this started off as a repair video - and ended up as a kinda MASTERCLASS in Transistor Fault Finding and Diagnosis! Yeah it's 2 hours - BUT if you watch this through, maybe in a few sessions, you will learn a LOT about Transistor Circuits and HOW TO FIX THEM. Skip parts and you are gonna miss important stuff! Enjoy.

Mentioned in this vide0
All You Need To Know About Amplifiers To fix Stuff

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TEST METERS
ANENG AN8009 MULITIMETER
KAIWEETS HT118E MULTIMETER
VC480C+ MILLIOHM METER
MESR-100 ESR METER
XC6013L CAPACITOR METER

TM-902C TEMPERATURE METER
LCR-T4 COMPONENT ANALYZER
FNB58 USB ANALYZER
PCI POST ANALYZER
TL460S PLUS PCI_E ANALYZER
TOOLTOP ET120MC2 SCOPE
FNIRSI 1014D SCOPE
NPS3010W 30V 10A PSU
T12 STATION WITH M8 9501 HANDLE
M8 9501 HANDLE
YIHUA 982 Soldering Station C210/C245
FNIRSI HS-02 PORTABLE SOLDERING C210/C245
QUICK 861DW
PROS'KIT SS-331H

INFIRAY P2 PRO IR CAMERA + MACRO LENS
TOOLTOP ET13S THERMAL CAMERA METER
ET13S MACRO LENS
OPTICAL MICROSCOPE
TOMLOV TM4K AF FLEX
TL866 II+ PROGRAMMER
CH341 PROGRAMMER
NC-559-ASM FLUX

DESOLDER BRAID (I use size 8045)
HX-T100 SOLDER (0.6MM)
ESD-11 TWEEZERS

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Thank you
Richard

[fixitdaz]

Don't change a thing it's great that you are willing to go into the nitti gritty and explain your process and explain how the curcit works thanks for being part of the process Big thanks.

[keithglynn]

DONT SHORTEN THE VIDEOS ! I am just starting out with electronics repair and although a lot of your procedures are familliar, I still enjoy the explanations of circuit design and why certain components are "in circuit" to limit noise, feedback, to block d.c. and other situations. Your continuous speaking/thinking out loud while you work gets my brain engaged so I can block out distractions and follow you along. This helps me with my own work. Thanks for the videos and your plain sight honesty in your work.

[NeoThePren]

If there were more people like you, we would not have so much e-waste in the world. Your explanations are always great, keep on going. Thank you

[CarlDidur]

I am a repair tech and I watch these both to learn and to relax. So nice to see someone else saying "that just doesn't make SENSE...". Thanks for all your work.

[victorreppeto]

I love seeing you make mistakes because you are not really sure about what reading on the meter mean, because then your figure it out and things start to make sense. This such a remarkably valuable and stimulating video to watch from beginning to end. I have learned more in the last two hours in one video than I have in the last several months of watching other videos. This is just what I was looking for. Practical steps I can follow. Thank you so much.

[kriswillems]

In case you have a class AB amplifier all the output transistors need to be biased to a point in the linear working ares of the transistors. This class G amplifier is a kind of class AB amplifier. That's what the potentiometers are for. The transistor that you incorrectly replaced (Q220) is the transistor responsible for giving a bias voltage to the bases of out output transistors. The NPN and PNP output transistors must have an output current running through them even if the input voltage of the amplifier is zero volt, else they are not working in the linear area of the transistors.
In case the potentiometer breaks, the voltage on the BE of the bias regulating transistor will go up, causing CE voltage to go down, causing too little bias voltage and thus causing non-linear amplification, because the output transistor are not in their linear working area (like a class B amplifier, but this is class AB).
You can measure the idle current over the emitter resistor of the output stage. Normally the service manual says what is the best value.
If you can't find the service manual I would set the idle current to 10mA. Your emitter resistor is 0.47 ohm, so that's about 4.7mV.
The perfect way to set the idle current is to use a spectrum analyser, put a sine wave at the input and set the idle current just high enough to make the cross-over distortion disappear.

[chillidogkev]

It was a long video....but a long and utterly brilliant video that needs no editing! I've recently discovered this channel and am absolutely loving it. Your commentary, explanations, delivery and overall listenable appeal are the difference and genius of your output. Don't change, this is pure gold 👍

[ineedstuff]

Aside from obvious employment opps, I have finally embarked on my electronics-learning journey. Also due to my love of music equipment (especially vintage tho). I clicked on this without seeing whole title. Imagine the enhancement in my pelvic region… 😄💪 Thank you so much for the channel

[Megawatt]

What a great tutorial, Richard! Learnt more in 2 hrs than all the other tut vids on utube. Gives me motivation to go back to my amp repair I've been at for 6 mths.

[Mcfreddo]

Hey, awesome video. Don't change a thing. You're a great guy and a great teacher. When I found your channel about a year ago(?) I was very very pleased and happy.

[rishanranatunga]

This will be a different comment...Thanks to the World Wide Web, YouTube, all the search engines, browsers, Chinese technology to help share and fascilitate your magnificiant knowledge among all over the world community freely. Oneday you gonna be a legend. I hope you missed to explain why the higher power loss dissipated 45v using power transistors replaced instead of 90v supplied power FETs at once.

[metalmix]

You are giving out probably the best information I've seen on electronics. Cool stuff!

[Rvw]

You know your job sir. Keep up the good work.

[jameswaddington]

Watched it straight thru. So very helpful. Been working on a NAD2200. I am an auto/boat wrench, an old dawg learning new tricks. Thank you so much.

[TrevAutoTech]

Dont know how i stumbled on your channel but.... I LOVE IT.. something about you keeps me coming back "yeah" lol. Thank you from Ontario Canada !! Im a licensed auto tech who is learning how to repair modules and keys instead of always replacing!

[bonniebo]

Great!
I've bee'n fiddling around with electronics for ages, as a former musician, but never realized to presolder, before unsoldering ... And it nice to have these videos smoldering around, and occasionally you pick up something you've always thought about, but never cared to understand. And the schematics

[HnsxToP]

Always learning a lot from you sir, hope you're getting well by Monday, looking forward to seeing this thing working as intended and you healthy again.

[fredflickinger]

These types of faults always are always a great learning and teaching moment!

[edwinwaugh]

Great video. You are very knowledgeable in electronics field. I don't have a clue about any of this but great to watch and listen to.

[nicktucker]

These are such amazing videos. Thanks so much for taking the time - much appreciated!!!