I just bought a Sansui 4000. The right channel plays great. The left channel blows speaker fuses. The output transistors plus two more transistors on the driver board appear to be shorted after doing a simply diode test with a multimeter. My question is how to physically replace the output transistors. They are surrounded by a heat sink. I took out six screws to try to remove the heat sink block, but that wasn't enough. I figured I would ask here for expert advice before I get in over my head, which maybe I already am. Thanks for any help you can provide.
Sansui 4000 output transistor replacement
- Thread starter Bart Eddy
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That is most likely correct. DO NOT PANIC.
Slow down.. How much experience do you have, in general, at taking things apart and putting them back together? Cars, bicycles, anything, not necessarily electronics.
First item of business is building a Dim Bulb Tester so you don't instantly, or are less likely to, blow any replacement parts. Instruction for building a Dim Bulb Tester (DBT) can be found on AK, U-tube, etc.
I'm an engineer, so I was born to take things apart. Getting them back together is a different issue. I have a year of experience is all, but am fairly handy. I built a dim bulb tester a year ago. There is no short in the unit. I then plugged it in and it plays fine on the right channel. The left channel blows fuses. The voltage to the right is 32 volts, as it should be. The left is less than 1 volt, meaning any wattage to the speaker will show up as amps, not volts, and blow the 4 amp fuse. I checked the output transistors on the left channel and compared them to the right. Significant differences. The emitter and collector on the left transistors are definitely shorted as are two transistors on the driver board. My issue is how to get at the power transistors. Any help with that task would be appreciated. This receiver deserves to be treated right. If I can't figure out how to do it right, I'll sell it for repair on Ebay. It has a wood case and is in good overall condition.
Thanks to some insomnia induced boredom I went through AK and ebay to find some pictures.
Are the six screws you took out from the top and back of the heat sinks?
If it the heat sinks are set up similar to the 5000 each section will also be attached from the bottom with machine screws accessed by removing the bottom cover.
Are the six screws you took out from the top and back of the heat sinks?
If it the heat sinks are set up similar to the 5000 each section will also be attached from the bottom with machine screws accessed by removing the bottom cover.
Four of the screws were on top of the heat sink outside the unit. The other two simply attached the speaker label and do nothing to remove the heat sink. I saw four screws on the bottom of the heat sink inside the unit. I wasn't prepared to go that far with it without asking for some help. I just need to muster up the courage to take them out and see what may be next. I appreciate your persistence with this. I'll try to get to it later today or tomorrow and let you know how it goes.
Those are the ones to go after. From what i've seen each output haS ITS OWN sub section of heat sink, recommend you start with one one the end. biggest pita i've found is getting the wires back neatly. be careful since at the age of these units it is possible someone has been in there before and possibly hacked something up, though that is less likely with the 4000 than some other models.
Each of the power transistors checked good out of circuit. I put them back in, but switched them (9 to 10, 10 to 11, 11 to 12, and 12 to 9) to put them on different channels. The right channel still played great and the left blows fuses, so it wasn't them. I swapped the driver cards and the problem moves with the card, so one of them is bad. That narrows it down dramatically. The two transistors on one of the boards look like they're shorted out when tested in circuit while the other board's transistors tested great, but that didn't work so well testing the power transistors in circuit. I'll pull them and test out of circuit. Hopefully it is that simple. Wish me luck.
Adam9501230p
New Member
I found a good f-1150 Driver amp board on ebay. I gave up on repairing the bad one. Would be cool to find new replacement transistors for it. Not sure how to substitute these particular units.
petes'picks
Super Member
What transistors you replaced and what part did you replace them with is always great information to have for someone who reads your thread with similar issues.
You're right. Still learning how to be a giver and not just a taker on the forum. I'm learning a lot. TR805 was a 2SC708. I replaced it with a KSC2690. TR807 was a 2SA537. I replaced it with a KSA1220. They have a different package, but they work. You can't attach the varistor to the top of the transistor with the new package, but I'm told that isn't a big issue.
Zip tie it to the side?
From where can I find out KSA1220 transistor as it's almost out of stock everywhere.? Please answer to my query.
