Sansui 9090 (DRV-BRD/F-2436) Resistor R42 smokes??

T

Topper74

New Member
I recently acquired a Sansui 9090 (NON-DB). When I received the unit it was stuck in protection mode. I replaced a resistor on the protection board.

Now, when I power up with the driver board installed it immediately begins to burn then smoke Resistor (R42). If I rotate the driver board 180 deg. and install it smokes Resistor (R41). I'm guessing, but it seems that there might be something on the power board (F-2546) or the protection board (F-2547) that may still be causing an issue.

When I power up without the driver board the unit comes out of protection mode, no issues but no sound (of course) I have a laundry list of items I replaced in search of a remedy. Is there anyone out there that may be able to assist me with troubleshooting? I have the ability to take and send pictures if required.

Thanks, Brian.
 
I just replaced the fuse resistors in my 9090 on that same F-2436 board after it went into protection and now it is working fine. I think there are 10 in total on that board so try and replace the rest and then reset the DC offset and see if the unit starts working. Here is a thread about it including a pic of the board with the resistors in need of replacement circled:

http://www.audiokarma.org/forums/showthread.php?t=522730
 
Topper74 said:
I recently acquired a Sansui 9090 (NON-DB). When I received the unit it was stuck in protection mode. I replaced a resistor on the protection board.

Now, when I power up with the driver board installed it immediately begins to burn then smoke Resistor (R42). If I rotate the driver board 180 deg. and install it smokes Resistor (R41). I'm guessing, but it seems that there might be something on the power board (F-2546) or the protection board (F-2547) that may still be causing an issue.

When I power up without the driver board the unit comes out of protection mode, no issues but no sound (of course) I have a laundry list of items I replaced in search of a remedy. Is there anyone out there that may be able to assist me with troubleshooting? I have the ability to take and send pictures if required.

Thanks, Brian.
Click to expand...

Start pulling and checking output transistors. Me thinks you have at least 1 shorted one.
 
So far I have replaced all 8 output transistors and replaced all fuse resistors on the driver board.
I think I've narrowed it to something between the output transistors and the power supply board (connector for the driver board) or to the protection board. I haven't been able to find a good "clear" picture of the solder connections on the back of the connector.
I am very confused as to which of the solder joints are supposed to connect together. Someone messed with it and attempted to separate the solder connections. It is clean but I think that pins 38 and 36 should be soldered together.
Also, if the output transistors are disconnected (not installed) the resistor still smokes. I attempted a power up without the transistors to eliminate the possibility of a short or a leakage.
You would think with an open circuit nothing would happen. Odd?
 
Anybody got any better ideas of where to look next.
-No bad output transistors.
-No bad fuse resistors.
-Looking for pictures (close up) of the back of the power board to check the wiring connections?
Thanks for your inputs!
 
Pg 10 of the Service Manual does not show the wiring that is connected to the pins on the back of the power supply board.
I have attached a pic of the board and what I'm attempting to check.
As you can see it is unclear as to what terminals are supposed to be joined by solder and what is supposed to be separated.
My thoughts are that there might be a short between 2 pins on this board but I can not tell.
Whomever the last owner was he made a mess of this part of the board.
I'm am also unsure if the correct wires are on the correct pins.
Also added F2436-1 driver board pics of the location of the resistor that burns on power up.
 

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Nothing Good??

Nobody has anything other than output transistors and fuse resistors. Been there changed that and still blowing R42 and R40. Hmm? I'm thinking trash but I have high hopes. Please help me??
 
Look deeper into F-2436 there are 2 transistors connected to the resistors you mention. you also mention that the system recovers when you pull the driver board so you are inserting and removing the short circuit when you do that and please don't reverse plug that board. The resistor that burns when the board is properly plugged is an indication where the short is. Make sure those outputs are still good.
 
As you can see it is unclear as to what terminals are supposed to be joined by solder and what is supposed to be separated.
Click to expand...
Looks pretty clear to me.None of those pins should be shorted together except the two grounding pins 29 and 30 each have two connections available.
 
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Thanks again Avionic.
I guess I was looking for someone that had a picture of how it is supposed to look, not the one I took of how messed up it looks now.
I will work with what I got. and attempt to find pictures elsewhere.
 
Board connections

Topper74, had to search through my pile to find a 9090 and I found one. It looks like there has been a lot of work done on that power supply board (F-2546) the caps in your picture are on the component side of my system and I see some other changes made along the way. I have a picture that will help you, The connections that cross over pin to pin are indicated and note that the ground wire from the brown cable in the center of the picture is only connected to one pin #30.
 

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Double T,
Thank you for the pic and the information. Very helpful but not the problem or the fix. I'm still finding that output transistors and resistors are still shorting out or burning when I power up. So far I've replaced all the transistors for the LH channel about 3 times and I have replaced the resistors for the LH channel on the Driver board about 4 times. I'm starting to think that I'm not able to locate this problem.
 
I don't know your tech level but you may try doing resistance checks on that board comparing the right channel to the bad left channel to locate a value that is very different using the same points on each channel. There is also a unit called a dim bulb tester you can build and use to stop blowing all those transistors when you power up, look it up there is info on the net. You might also try some of the guys on here they may take that board and repair it for you. I would still use the DBT when you get it back to plug it in with the latest pair of output transistors you install.

Those caps that were moved to the bottom of the board can you tell if they were soldered cleanly and polarity is correct?

The 9090 that I have will probably be my next project about a week away and has lots of issues created by a soldering iron.
 
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Do a serach for the 9090DB

I just read a ten page workup on this, and you might want to search the Sansui forum only for it. Fix was in the last few pages. Good luck.
 
R40 seems to be the collector resistor of tr12 - I had a similar issue where the equivalent resistor in my eight burnt when powered up - turned out to be a short in one of the driver transistors - (bad mica insulator) Once new mica was put in - it was back to normal. I did some further reading on the matter and it turns out that collector resistors was common practice in order to save the output against short, thus rather let a resistor burn than a more expensive output when trouble upstream.
 
Your driver board has problems, and you are using NTE parts from what I can tell. Not a good idea. What are the outputs you are using and where are you getting them?

Are you watching the pinout on the new parts you are putting in there? Looks like allot of random parts are being used...

At this point, if I were you, I'd be pulling and checking all the transistors, diodes, emitter resistors, and the bias trim pot. That transistor on top of the driver transistor as well.

You need to make a list of all the original parts that were in there and I can then edit to show the new parts you should use...
 
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Your correct on using the random parts. I have had to resort to NTE replacements cause all of the original replacements are not made anymore. I have ordered the majority of the parts from Allied elect., Mouser and Digi Key. I have gone through this forum and found replacement parts for all items. I have also paid close attention to the transistors and their pin out I.E. Emitter Base Collector placement. I will gather a list of the replacement parts so far.

I am having troubles following the wiring diagram cause of the lack of information that it provides, such as:
The Power board has the F03 and F04 fuses. Are they supposed to be installed and how much are they rated. (10 amp or 1 amp)
The pin out of the power board to the driver board to the output transistors has repeating numbers that are not labeled on the board itself. "So confused"
 

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cableguy2 said:
I just read a ten page workup on this, and you might want to search the Sansui forum only for it. Fix was in the last few pages. Good luck.
Click to expand...

You read a 10 page work up on this subject? Was this on Audio Karma? If not what is the link? I'm willing to read it if it is similar?
 
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