au-519 project/protection

kfz01

New Member
Couple years ago i bought a defective (i didnt know at that time..) sansui au-519. When I first plugged it in, i saw the red blinking light.. that didnt seem too good. Of course..no sound came out of my speaker, i was very disapointed of my 35$ amp. Anyway.. i made a few research and turns out its a great amp! But it is not working.. Life was very busy so it just got stored into the basement for approx 8 years.. Now i am partially unemployed (free time!) so i decided to try to fix it!

After cracking it open, there was a blown fuse. Oh.. it might be just that! so i replaced the fuse .. and it blew again! Oh no. So i did more testing (my electronic skill arent very good, but i love to learn) So i searched how to test transistors.. diodes .. Grabbed my multi meter and focused on the board that was connected to the same side that the fuse was blown. I found a bad output transistor 2sc2580, So I ordered a pair of transistor to replace it, which i have not received. The said board is the f-2927. As i red on the forum, they usualy take other component down with them when they blow. So i used the other channel to compare reading (even they are not exactly the same) they sure look a like. I found that i get different voltage drop from the TR16 on the F-2627 than on the other one.

I am getting
c-b = 0.37v
c-e = 0.1v

and the other board i get
c-b = 0.47v
c-e = 0.51v

but when its pulled out of the board i get around 0.7 for both readings..
 
No, it was removed from the circuit. I did try to use another transistor of same type to see if it would affect reading and it did not.

when the collector is not screwed in the reading are
c-b: 0.64v
c-e: 0.54v

I really appreciate your help.
 
Last edited:
output looks shorted to me ..
only way to really check is pull the transistors for testing .. readings get pretty confusing with them in circuit
 
Is there other parts i should replace as a preventive mesure while I have the board in hands ?
 
Last edited:
Change ONLY the parts you need to change get the unit working correctly. There may be a few parts you can change later, but only after the unit is fully operational.

Just my 3 ha'pence worth ;)
 
Alright, thanks for your input guys!

I'll be patient and wait for those transistor to arrive from china! I also ordered that 25$ component tester .. might be a better tool to test the transistors than just a diode test..
 
The bad NPN power transistor was removed from the circuit, but you should also remove the PNP power transistor from the circuit. I have good reasons to think that the PNP (2SA1105) is shorted and you should test it outside of the board. By the same occasion test again TR16 in situ. If it looks good then try the amp with headphones alone, and with both power transistors on the defective channel removed. Compare the sound (with headphones only) of both channels, one with the power transistors and the other without power transistors.
 
OHHHHH China transistors are a WAY RISKY move at best.. Typically they are forgeries and are NOT up to the task. The transistor testers do work ( for a while ) I went thru 3 ( complain, wait, get, use, POOF.. repeat 2X more ) before I just tossed it out. Toni made a Sansui X ref transistor chart... lots O great subs from On Semi....That freaking WORK 1 st time, no issues.PERIOD!!
I ( personally ) would NEVER put a China transistor " replacement " in ANY of my gear.
http://sound.westhost.com/fake/counterfeit-p1.htm
http://www.cdkands.com/counterfeits.html
http://www.eham.net/articles/28672

MOST Chinese E bay sellers are NOT about helping YOU...
They are about taking your cash and tying it up giving you SHITE.

Procede with EXTREEEEEEEM caution
 
Hi guys! Sorry for taking so much time but i was out of town! however i did read your comments about chinese transistor and ordered some from a local supplier. Heading to the bench to get those replaced! I also built a dim light bulb.

I hope that's the only thing wrong with it!
 
Alright! i replaced the pair of transistor. Put it all back togheter, plugged it into the dim light.. crossed fingers, flip the switch..light glow bright for a sec or so then dims. no weird smell! woot! but it wont get out of protection. damn! I'm guessing i have to take a look at the power supply board??
 
start by taking the offset voltage readings .. basically speaker outputs before the relay ..
pins 13 driver boards f-2927 right channel f-2926 left channel .
both readings reference ground ..so black lead on chassis .red on pin 13 ..then the other pin 13 ..report back with voltages ..
these are ideally 0mv .. start with your meter on say 200v dc and work your down voltage settings until you get a sensible reading
 
Last edited:
i used vr01 to tune f-2927 to 0mv (i got +0.001v)

checked bias on f-2927, was 0.030, tuned to 0.021v, still blinking.
 
KFZ
Decimal point are critical here…
I assume your measuring DC VOLTS
-.13 should not be enough to keep the amp in protection.
Verify this prior to proceeding.
 
and still no relay click ?
see if you can get voltage at cathode end of d607 ..its next to the relay ..
also get voltage across it
 
ground to cathode = oscillating between 36.10v and 36.92v , between I am getting 0v
shouldn't i be getting something like 0.7v?
 
vigman, i am positive it was -0,130V, i did dial it down. I know decimals are important. I am a machinist. Did you mean UNITS were important? I did fail to say i was mesuring
DC volts. Thanks for your input! :)
 
Back
Top Bottom