Help with Humming 4000

[Wickateer]

I picked up a Sansui 4000 this week from a local vet who was downsizing and getting rid of old stereo equipment. Purchased in the Philippines in 1970 or so, it, along the SP-2000's that came with it, had not been used in years. The 4000 was dirty but it, and the wood case, are in over all very good cosmetic condition. After a thorough cleaning with deoxit and replacing the incorrect fuses, I still have a decent hum when the unit turns on. It you turn up the music (which sounds great) it drowns it out. If you turn on the low pass filter it quiets it down. All bulbs work and the protection bulb appears to be fine.

Any suggestions on next troubleshooting steps? Inspecting it with the cover off, there are no obvious signs of leaking, burned out or disconnected components. I have run it for 15 min or so and there are no odd odors.

I love the sound of my 350A and want to get this 4000 dialed in. Thanks!

 

[noogies]

Have you tried teaching it the words?

Sorry, but you knew somebody was going to suggest that.

 

[1rebmem]

The humming is probably due to the old capacitors in the power supply section.

 

[Wickateer]

Thank you. Now I just need to find a tech in the Mid-Atlantic area. That is above my skill level.

 

[avionic]

Welcome to AK...

 

[KingJT]

I'm experiencing the same problem with a 4000 I picked up while on vacation.
It's from the original owner purchased new while deployed to the Caribbean in the early 70s.
Otherwise sounds pretty good.
Thanks for posting this!

Mike

 

[Wickateer]

I'm experiencing the same problem with a 4000 I picked up while on vacation.
It's from the original owner purchased new while deployed to the Caribbean in the early 70s.
Otherwise sounds pretty good.
Thanks for posting this!

Mike

I brought mine into a local audio repair shop to get it diagnosed. They confirmed it was the caps in the power supply section as 1rebmem suggested above. The repair cost they quoted was more than I wanted to spend, but I am still on the fence. If you have the skills to do it yourself or know someone who can help you, it is a no brainer.

 

[KingJT]

I brought mine into a local audio repair shop to get it diagnosed. They confirmed it was the caps in the power supply section as 1rebmem suggested above. The repair cost they quoted was more than I wanted to spend, but I am still on the fence. If you have the skills to do it yourself or know someone who can help you, it is a no brainer.

Someone has been doing some work for me so hopefully he'll be able to look at this one as well.
I have an AU-222 that has the same issue so i might try my hand at working on that one.

 

[chazix]

FWIW, the hum in KingJT's 4000 was caused not by tired capacitors, but by a shorted pass transistor in the 25V regulator. The shorted part was TR001 on the F-1187 board. There was no reason to suspect any capacitors, but the ones on this board are exposed to heat from the two regulators, so it seemed prudent to replace them.

Cheers,

chazix