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Problems With Sansui G9000 - Cooked?

S

SteveCap

New Member
Long story short, Unit was working fine after not being plugged in for quite some time, then it let some smoke out and shut off.. Took a look around inside to find burned resistors on both the F-2808 (power supply) and F-2806 (driver amp) boards. The Resistors on the 2806 are so badly burned that no clue as to there value is left. I found a manual but, conveniently, every part cooked on the boards are omitted from the parts lists in the manual. One other thing I've been trying to figure out, is this the root of the problem? or was it more likely something else in the system that failed first causing these resistors to catch a little more than they were rated for..

In summary, If there's any sansui gurus out there willing to contribute the .02 I would be greatfull. Any info as to the values of R3 on the 2808 and the values of R25, R26 and R27 on the 2806 board would be awesome. As well as any clue as to what may have caused this failure.

Thanks in advance,
Steve Cap
 
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Did it cook both the F-2806 boards ? They are identicle .
F-2808 according to the scat
R3--- 1kΩ 1/4 watt

F-2806
R25,26 ---- 390 Ω 1/4 watt
R27 -------- 560 Ω 1/4 watt
Check your output transistors for the channel this board was plugged into.( F-2806)
as well as the TO-220 transistors on this board.

http://www.audiokarma.org/forums/showpost.php?p=3252037&postcount=1
 
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every part cooked on the boards are omitted from the parts lists in the manual
Click to expand...
Chances are if omitted in the parts list they are labeled in the schematic diagram.
 
Thanks avionic, now that you say it... I didn't even check the schematic, total brain fart. I will check the other driver board when I'm near the unit again. as far as the TO-220's, I should check TR05-TR10 on the F-2806(s)?
 
SteveCap said:
Thanks avionic, now that you say it... I didn't even check the schematic, total brain fart. I will check the other driver board when I'm near the unit again. as far as the TO-220's, I should check TR05-TR10 on the F-2806(s)?
Click to expand...

Yep, all of them.
 
OK guys I'm back to this unit again, as far as the other 2806 board, it shows no visible signs of damage at all. As for checking the transistors, Would you recommend removing them to test them or do so in place?
 
SteveCap said:
OK guys I'm back to this unit again, as far as the other 2806 board, it shows no visible signs of damage at all. As for checking the transistors, Would you recommend removing them to test them or do so in place?
Click to expand...

I recommend removing them to test - but either take lots of pictures (best) or make copious notes about their orientation, and type number /TR number in the PCB.

There is a sticky around somewhere regarding basic transistor testing...
 
Before I plug the 2806 back in, Will powering up the unit without the 2806 plugged in trigger the protect indicator? I'd like to see if there is a problem upstream and avoid cooking the board again.
 
All resistors replaced and all TO-220's checked out ok, also have to replace the R28. but search as i may in the manual and schematics, cant find a value for it. Have not checked the output transistors for the channel, been looking for the best way to test them, not sure I can check them the same way I checked the TO-220's on the F-2806 board, any suggestions?
 
The output transistors have 3 connections, the case =collector and the 2 pins are the base and emitter. You will posssibly have to disconnect them (physically remove them?) from the rest of the circuitry, to avoid false readings, (due to measuring other connected components) but I am not sure how the output transistors are connected on this model so removal/disconnection might not be necessary. The readings you obtained from the T0-220's should be very similar to the readings you will get with the output transistors - post your results if you are not sure how to interpret them.

If you do remove them, make sure you note well where each one came from, this is very important.

Need a G-9000 expert here - I'm trying to help - but have very limited knowledge of this model. (this thread should be in 'Exclusively Sansui' not 'DIY' !)
 
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r28 and r27 on the 2806 board are 560 ohms according to the schematic i have here
check against other board to be sure
 
Yeah, In the service manual from sansui R27 is specified, but only on one of the 2806 board (i know there identical, but it's only noted in the one spot on the schem) and R28 seems completely unspecified, I put a 560 in there because of noting the other 2806 physical board.
 
SteveCap said:
Yeah, In the service manual from sansui R27 is specified, but only on one of the 2806 board (i know there identical, but it's only noted in the one spot on the schem) and R28 seems completely unspecified, I put a 560 in there because of noting the other 2806 physical board.
Click to expand...

looking at the circuit r27 r28 are doing a similar/same job . i said to look at other board as well to be certain .
 
petehall: I did what you said, by looking at the other board, my last post may not have been clear as to what led me to my decision, but it was your advice.

HOLY PITA! I knew there was a reason I was putting off checking the power transistors. Looks like a wicked pain in the ass to undersold everything being that it's heavy gauge and wrapped around eyelet terminals on the transistors. We are talking about the ones bolted to the HUGE heatsink on the back of the unit, correct?
 
These power transistors have more than the typical ECB leads, anyone know anything about the other leads. there all disconnected now and testing as we speak.
 

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negative, they are hard wired/soldered. I am now typing up the results from testing. you should see them in a few minutes.
 
The power transistors were tested with the diode function of a multimeter, The results are as follows:

Transistor 1:
B+ & C- = .000
B- & C+ = OL
B+ & E- = OL
B- & E+ = OL
E+ & C- = OL
E- & C+ = OL

Transistor 2:
B+ & C- = .015
B- & C+ = .015
B+ & E- = OL
B- & E+ = OL
E+ & C- = OL
E- & C+ = OL

Transistor 3:
B+ & C- = OL
B- & C+ = .449
B+ & E- = OL
B- & E+ = .486
E+ & C- = OL
E- & C+ = OL

Transistor 4:
B+ & C- = .012
B- & C+ = .012
B+ & E- = .012
B- & E+ = .012
E+ & C- = .000
E- & C+ = .000

So, Im guessing 4 is toast, 1&2 look not so good, the only one that acted like I expected was 3. What do you guys think?
 
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