Sansui A-1100 Driver stage issue and distorted output

Okay need someone to look over and tell me if there is a way to have the fan run. this thing gets VERY hot after one song at around 50W output. i can only imagine if i was running it at full power. maybe i can stuff a 9V regulator somewhere :dunno:
 
Maybe i should have ran it for more than 20 minutes to say its working perfectly. now the channel getting very distorted and going back to clear is now intermittent :/ it almost seems like a bad connection because SOMETIMES if i bang on it it will work, then go back to distorted. but ive already resoldered the entire PCB. if i push down on the heatsink right, it will work. then go back to distorted. ive never seen anything like this before. im lost with this. Maybe its the circuit glue?
Man i wouldn't make a very good tech would i lol

EDIT: The distortion IS affected by the speaker load if the power lights are anything to do by. when i shut the speaker button off the meters both indicate the same. but once i turn it back on it goes back down and the distortion resumes

EDIT2: Headphones its working good, connect speakers i loose output and the distortion comes back. cant be the outputs as i swapped the left and right outputs and the right channel with the left outputs is working 100% no matter what.
 
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Okay i looked over the schematic again and see what appears to be discrete driver transistors after the STK pack and before the outputs. almost like its multistage
upload_2017-5-30_2-43-14.png
im going to swap those transistors with the other channel first thing tomorrow. 2:45AM for me right now
 
Although arranged a bit differently those transistors are the VI, voltage/current, limiters. When the voltage between the base and emitter is large enough they will turn on limiting the signal to the drivers. Most amplifiers will work fine without them for troubleshooting purposes.

NEVERMIND, I was looking at lQ2/3 NOT kQ2/3. lQ2/3 are the limiters and kQ2/3 are indeed the drivers.

Craig
 
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After looking at a photo i took it looks like on the drive board pad 4 had a cold joint. none of the other pads looks to be cold or shorted.
i wonder if it took out anything else in the circuit
upload_2017-6-14_21-49-37.png
 
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since i go no replies i went ahead and ordered all my parts. driver board recap and new transistors and made sure all the stupid pads were soldered. found out the main 7A fuse blew when the driver board blew...only had a 3A that i put in. went to power it up for the first time on a DBT with a 100W bulb and it lit full brightness and NO lights on the Sansui lit. could really use some help with this now. going to pull the outputs again. maybe they shorted and thats what took out the driver board.
 
removed all 4 output transistors and was able to get it to power on, and more parts on the driver board went up in smoke. 100W bulb was about a quarter lit.
EDIT: Tested all 4 outputs on my transistor tester and BOTH on the right channel are completely cooked. why me
 
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Been following along but not chiming in, would be VERY suspicious of the bias circuit, the power supply voltages (as shown by the missing negative portion of your scope trace) and then once that is checked the oscillation issue. Working with stk outputs is a real pita :(
 
Been following along but not chiming in, would be VERY suspicious of the bias circuit, the power supply voltages (as shown by the missing negative portion of your scope trace) and then once that is checked the oscillation issue. Working with stk outputs is a real pita :(
It uses discrete transistors on the outputs, but an STK pack as the driver. What should I do with to attempt to get it working again. Could it be the exposed bias adjustment pots?:dunno:
 
So after testing more parts the right channels outputs A1106/C2581 are shorted. replace with NJW1302G/NJW3281G
IMG_0798[1].JPG IMG_0799[1].JPG


Right channel drivers are also completely shorted A1111/C2591 replace with MJE15033G/MJE15032G

the 2 resistors that went into smoke were on the F-4762 driver board R12 47 Ohm and R13 47 Ohm.

In the pic you can see the bias pots are those crappy open style ones. ill figure out the value and replace those as well.
IMG_0789[1].JPG

I Think everything is on the right track now.
 
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Oh boy....found another fried transistor but thats not the bad part. its the thermal comp transistor mounted on the heatsink, bad thing is i have no idea how to get them out...so i cant see what they are and what to replace them with. but i found out the trimmer resistors are 1K
IMG_0834[1].JPG

Testing them gives me this
LEFT
IMG_0832[1].JPG

RIGHT
IMG_0833[1].JPG
 
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i got it completely torn down to access those temp comp transistors mounted to the heatsink. Glad to say they are bone standard C1845's which i have almost 100 of. so i just replaced then right there

Originals
IMG_0870[1].JPG
IMG_0872[1].JPG

NEW, a little crooked but i straightened them up before i reinstalled the main PCB
IMG_0873[1].JPG
 
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More parts came in today.
IMG_1024[1].JPG
Ill get these installed and hope all is good, there's more than those transistors of course, but those are the main goodies
 
Well since no one cares about this amp i decided to not post after every few steps and wait untill it was finished. its fully working as of now and i got the bias set exactly to 10mV per channel. have to run it for a while to see if the half wave distortion thing comes back. at first i do know the2 SA1962/2SC5200 run alot hotter at idle then the factory 2SA1106/2SC2581
IMG_1032[1].JPG

New Drivers, 33pF caps on the drivers, new 47 Ohm resistors to replace the ones that went into smoke, new emitter resistors and new trimmers
IMG_1038[1].JPG

Bias, Ignore the negitive, just had the clips backwards
IMG_1041[1].JPG
 
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After the new transistors were installed both sides were running quite warm just at idle, but once i got the bias adjusted its much more normal now. the bias was way off. one channel was sitting at 70mV and the other was over 200mV
 
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