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Sansui 9090 Blowing fuses 250V 10A Instantly

F

FunkSquad

New Member
Well, sad to say my 9090 receiver is on the fritz. It worked fine for a month or two, and in the last week or so, started having channel drop out (left) issues. I would turn the receiver off, wait a sec, turn it on until it popped green in protection mode, and then both channels would be working again (sometimes took two or more tries). Today, while doing this, it blew two 10A 250 volt fuses. I went and hunted down some new fuses, and after replacing the two blown fuses, it continued to blow fuses at random in the dozen or so fuses on the board in the middle of the receiver. My family member who is versed in this area thinks it is a bad power transformer. What do you guys think the issue is? Is this worth trying to fix? Thanks so much for any help; this is a really cool forum that has already helped me a couple times on the 9090 (light mod etc). I'll be sad for sure if its a goner - greg
 
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first off its not good to keep replacing fuses if they are blowing as more damage is likely plus its just a waste of fuses and time anyway ..
first off is see what the fuses feed and find the short ..
what number on the board are the blown fuses ?
 
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Nope, won't be the transformer.......

You have probably got blown/shorted output transistors and or driver transistors.

You will need to know how to remove the transistors to test them and find out which ones have failed.
Then you'll need to replace the fusible resistors on the driver boards which have probably gone hiZ over time which may have been causing the initial problem....

Its totally worth repairing, you could have a go yourself with the help of the forum here, or you could get it to the right tech....
 
Typically NOT the transformer.. it's the load ( Short ) on the secondary that makes it act like that….Something this old needs to be serviced… lots of good info here IF you have the tools & skills ~

Mike
 
kevzep said:
Nope, won't be the transformer.......

You have probably got blown/shorted output transistors and or driver transistors.

You will need to know how to remove the transistors to test them and find out which ones have failed.
Then you'll need to replace the fusible resistors on the driver boards which have probably gone hiZ over time which may have been causing the initial problem....

Its totally worth repairing, you could have a go yourself with the help of the forum here, or you could get it to the right tech....
Click to expand...

Thanks guys. I guess my next question would be where could I acquire these output/driver transistors /fusible resistors and what are the specs for them? After pondering on the subject, I really want to save the receiver rather than sell it for parts as its a Sansui (I have a Sansui turntable and speakers to pair with it) and it has the look I want and isn't a Marantz (which everybody seems to be getting in this vintage craze etc). Again, thanks for your help, it is most appreciated. - greg
 
Funk, do you own a DVM that has a semi conductor/ diode test function , and know how to use it ??
 
Your next best step to to search here for a DBT ( dim bulb tester ) build one.. this will save you from letting additional smoke out of the unit and costs down on spare parts…
 
clean driver board receptical

My 9090 had a bunch of corrosion on the F-2436 driver board contacts. Its the verticle mounted board that plugs into power board F-2546 (shown on page 21 of service manual, available free here http://www.hifiengine.com/manual_library/sansui/9090.shtml . Remove the black cover and board pulls straight up like a PCI board on a PC. If corrosion is jumping across pins clean them using pipe cleaner and Dexoit or Iso alcohol then blow out with compressed air. Mine had bad green corrosion buildup. Hope its something that simple for you, my bet would be transistor though. Mine is still not working as it only powers up when on its side, I refuse to mess with it until I get more experience (using my cheaper units).

Lots of higher wattage bulbs can be found at Habitat Thrift stores, I also have had luck at garage sales. Still see them in Home Depots and other hardware stores. They can continue to sell them, but once inventories are gone there gone.
 
Well than the future will have a BIG power resistor and an Amp meter to replace the common light bulb…...
 
we can can light bulbs still at poundland ..i guess for america its the dollar store ..
writing on the box states "unsuitable for household room illumination " suppose that just gets around the law
 
petehall347 said:
first off its not good to keep replacing fuses if they are blowing as more damage is likely plus its just a waste of fuses and time anyway ..
first off is see what the fuses feed and find the short ..
what number on the board are the blown fuses ?
Click to expand...

So we've determined (we think) that its an issue with the output driver transistors and fusible resistors on the driver board. We took the board out and tested all the transistors and 3-4 came up bad (I have ordered replacements from China; same exact transistor). Also, 4 resistors came up bad (R33, R34, R35, and R36 on the driver board). Two resistors were not the value they were supposed to be (according to the list we found in a thread somewhere). These two are R43 and R44. They were supposed to be 150 ohm but read about 22.5 ohm. Also, there is a fuse right above each that didn't show up on the driver board diagram. It is pictured here:

https://imageshack.com/i/nmwbr1j
https://imageshack.com/i/npd8cnj

They didn't read open lead, so we think they're good and its a design change that didn't make it into the manual?? Any help on the issue is most appreciated. Other than that speed bump, we are going ahead with the plan to replace the bad transistors, resistors, and all the fuses for the board. Thanks again! Cheers- greg
 
couple of things .. be wary of transistors from china especially if they are obsolete ..
resistors don't go low in value they go high ..you must be measuring them in circuit or your meter is no good .
 
petehall347 said:
couple of things .. be wary of transistors from china especially if they are obsolete ..
resistors don't go low in value they go high ..you must be measuring them in circuit or your meter is no good .
Click to expand...

OK. Its probably the case that we weren't measuring them in circuit (meter is good). Anywhere you can recommend to get the transistors? Thanks for your response. - greg
 
think you misunderstood me ... resistors have to be measured out of circuit ...i have yet to see one fail low ohms ..
 
petehall347 said:
think you misunderstood me ... resistors have to be measured out of circuit ...i have yet to see one fail low ohms ..
Click to expand...

Ok. We will double check those two again. Any ideas on a source for the transistors. A guy out of china has Sanken 2SC1116A (600) transistors. Don't buy from him?
 
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