Technics SA-206 stereo receiver

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#3
as posted above, I would first check the potentiometer and spray it with some kind of potentiometer/switch cleaner (spray). make sure after you spray potentiometer, start turning all the way up/down the potentiometer at least 20 times (amp off) and then Turn on amp and check if problem disappeared. repeat this until volume gets steady and scratch free. Good luck.
 
#8
It's baaaaack

so I still need a free-for-nothing schematic. I did get a schematic in Japanese for the large output IC, the STK4833 and this might be enough.

If nothing else works I can take digital photos of both sides of the PC board and eke out the wiring & component placement by marking up the photo. 🙂

There is an output shutdown circuit which is maybe falsely shutting down - I guess I'll chase after that first.
 
#13
That is a very good way to blow your amp ...Amplifiers is about accuracy and symmetry If you have soldering issues and you put pressure on them for trouble shooting you will probably disorder at some point the operation of the amplifier with catastrophic results .

It will be better to tap over the relay of the output with a plastic to see if this effects the problem this is to be done in low listening level

If so just replace the relay ...consider your self a full recaping also ...that will add 20 years on the life expectancy of your amp
 
#15
ClassAB said:
.....How do you figure out areas of a device schematic that are important to a troubleshooting effort, with test equipment or without?.....
Click to expand...
That's nearly as big a question as how to design the device.
The short answer is :-
1. History - how all amplifiers fail 90+% of the time there are problems and how, in particular, this brand/model fails. (if known to technicians). It's cheating and not always productive but service organizations invest big money in fault lists that occupy DVDs full of references and sell for serious money.
2. Current- anywhere high current flows, trouble follows and failures increase in some relationship to it.
3. Contacts- any switch, slider or removable connection is a suspect in fault-finding. Experience and logical deduction tells how more important or easier it is to pursue one line of investigation (say, relays) than another (say, volume pots.)
4. Components - some brands/models use devices or designs known to be ill-concieved, poor quality over stressed or have short service life. Zero in to check these if there are grounds for suspicion.

Much of this is down to study and experience as you would expect a pro. at anything to have. For Mr/Ms DIY though, searching (use the button) and reading the woe and fixit threads is the way to go. Over time, you can learn an awful lot and better still, get the understanding of how these gizmos work and how to solve unique problems all by yourself.

Actually, I'm still working on that one myself, but one day, maybe......😱;
 
#17
A late but useful inclusion (#5) to the above list is to trace out the principal signal path on the schematic. Some Japanese service manuals feature this as a heavy circuit trace through the schematic of the device and this is good for finding where the signal flows from input to output and highlights the parts directly involved in getting it there.

That's instructive and helpful for the electronically inexperienced or challenged, like most of us but doesn't necessarily lead to a solution, since the fault(s) sometimes are elsewhere. YMMV
 
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