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Sansui G-5700 no sound

kevzep said:
TR20 detects DC and activates the protection, you can pull this transistor out if you think its a problem, it does not need to be installed for the amplifier to run, but I have never seen one of these fail in all the G5700/6700/7700 I have repaired, which is quite a few..........
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with r70 pulled then the only way i can see the reason for r58 to measure 1.2 ohms in circuit is through tr20 . i would say its short base to emitter . what are your thoughts on this ?
 
unless your readings are wrong or r58 is the wrong value installed .it should be brown red red .then i suggest pulling out tr20 and testing it .
if r58 happens to be brown red gold then its the wrong one . 1.2 ohms not 1.2k ohms
 
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being 1.2 ohms certainly wont help things . when its out try and check tr20 anyway in case it took a hit . leave it in circuit to test it .tell me the results
also keep one leg up on r70 while testing it
 
i thought i had i posted the transistor testing thread already ? ok i will explain . looking at the front of it the flat side with writing on . the pins are ECB emitter collector base ..
so meter on diode test black lead on base red on emitter take reading . keep black on base red on collector . take reading . reverse leads and do them tests again take reading . then black on emitter red on collector take reading .reverse leads emitter collector .take reading .
transistors are like 2 diodes inside .
take a look here .http://www.electronicsarea.com/diode_transistor_test.asp
 
black on base and red on e- I got no reading
black to base and red on collector I got- .62
no reading on black on e and red on base
no reading on red to base and black to collector
no reading on black on e and red on collector
no reading on black on collector and red on e
 
2SA992 might be a better match .:Dhttp://www.ebay.com/itm/1X-2SA992-A992-TRANSISTOR-FAST-SHIPPING-IN-USA-/180881057187?pt=US_TV_Boards_Parts_Components&hash=item2a1d59e5a3
 
Dont worry about TR20, forget it for the moment until you have the amplifier running, as I said several posts back, all this transistor does is turn on when there is DC on the output and activate the protection circuit....
You can take it out if the amplifier for now, its not the problem....
But do NOT connect the amplifier to a speaker until it is running correctly.

The transistors which affect bias are TR06, 08, 10 and TR16, 18 which are the drivers. Tr601, 602 which are the output transistors.
Also the STV-3H diode which regulates the bias current by thermally tracking the heat of the output transistors.

The surrounding resistors are also contributors to lack of or no bias current....

These are R36, R40. R52,R54. R60, R66. And R38 which is a current limiter for the bias circuit, these can go open when the amplifier has been subject to excess bias current.

I recommend replacing the bias and DC offset trimmers with multi-turn bournes trimmers.
The Alps trimmers in there are prone to failure because of their age......
 
lambord said:
ok I got the right resistor but the shipping from MCM is insane, would this work even though the watts are different by .5
http://www.ebay.com/itm/QTY-1-2SB71...300?pt=LH_DefaultDomain_0&hash=item3ccecffa5c
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petehall347 said:
2SA992 might be a better match .:Dhttp://www.ebay.com/itm/1X-2SA992-A992-TRANSISTOR-FAST-SHIPPING-IN-USA-/180881057187?pt=US_TV_Boards_Parts_Components&hash=item2a1d59e5a3
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Guys, do not buy components from ebay, there is too many fakes and fraudulent activity, buy from mouser, digikey etc.....there are modern equivalents available, all you have to do is ask.....
 
kevzep said:
Guys, do not buy components from ebay, there is too many fakes and fraudulent activity, buy from mouser, digikey etc.....there are modern equivalents available, all you have to do is ask.....
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How many times do we have to say this !

You put your transistor in, it might go bang (or it might not) but if it does, you wonder if it was because it was from ebay - or because you haven't isolated the real problem ! - at least if you buy from a reputable source you KNOW it wasn't a duff transistor.
 
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