Sansui 9090DB noisy/dirty sound before and after cleaning pots

[Juan9568]

Hi guys.
I'm going over the restoration of my amp and I'm still having this same issue. It sounds like dirty when listening and it makes a huge noise when I move the volume control knob, I have to do it very slowly so I don't blow off the speakers, needles go crazy. This same thing happens when I press any of the buttons of the push switch circuit board...

At first I thought that this was because of dirty pots but after a deep cleaning the same thing happens.
I thought also that maybe I had an issue with the equalizer board but after rebuilding, recapping and cleaning pots the issue remains.

Strange thing is that when I choose FM radio I don't get any strange noise or scratchy pots. It works great

I still have to recap the dolby board and the push switch circuit board, could the problem be in this section?

All the other boards have been recapped and pots cleaned.

I'll upload a video with the issue.

Thanks!

 

[AlTinkster92]

Sometimes you have to clean the pots and all switches more than once, especially the Dolby switch. My 8080DB had to be cleaned 4 times before things finally cleared up. Don't give up!

 

[Juan9568]

Sometimes you have to clean the pots and all switches more than once, especially the Dolby switch. My 8080DB had to be cleaned 4 times before things finally cleared up. Don't give up!

Yes but I don't get this issue when listening to FM radio...Maybe the dolby board or the push switch is not grounded to chasis??..

I realized that the dolby board doesn't work, I don't get the test tone..

 

[Juan9568]

Here a video:

 

[AlTinkster92]

Try cleaning ALL the switches again, Dolby and Selector switch as well....pain in the you know what but it fixed my issues. Hope it does yours as well.

 

[Tom B]

Hopefully you are using something like "Faderlube" (F5, or F100) for the volume and balance controls. It is the best for them. If you are using just a cleaner, they may stay noisy. Also check for DC volts on the volume control with is a sign of a leaky cap, or bridged connection when soldering in new caps.

 

[Juan9568]

Haven't gone through the dolby board and the push switch yet...The rest of them are clean and recapped...

It sounds to me that something in the dolby or push switch board is wrong + that I don't get the test tone, because when listening to FM works OK

 

[Trnsfmr_Jr]

You absolutely sure that FM doesn't scratch too? Doesn't make much sense because Phono inputs and FM all go into the dolby board on the same two wires on the bottom of the dolby board. Grey and Blue wire on the bottom of the dolby switch board. Besides the phono preamp those inputs see the same path the whole way through. When you recapped the tone board there were a couple black ground wires connected to a few caps on that board. Those all make it back on there? If not I'm thinking you still might need another clean, or you got a DC voltage on the pot as Tom B said.

 

[ManyMoonsAudio]

You might want to check the ribbon cables at the input jacks. They can cause problems. Make sure all the outer sleeves of the RCA inputs are grounded to chassis for one.

 

[Juan9568]

You absolutely sure that FM doesn't scratch too? Doesn't make much sense because Phono inputs and FM all go into the dolby board on the same two wires on the bottom of the dolby board. Grey and Blue wire on the bottom of the dolby switch board. Besides the phono preamp those inputs see the same path the whole way through. When you recapped the tone board there were a couple black ground wires connected to a few caps on that board. Those all make it back on there? If not I'm thinking you still might need another clean, or you got a DC voltage on the pot as Tom B said.

Absolutely, FM works fine without noise...

Black wires back in place..



How would I get DC voltage on the volume pot?? In that case I should have that scratch sound while listening to FM

 

[Juan9568]

You might want to check the ribbon cables at the input jacks. They can cause problems. Make sure all the outer sleeves of the RCA inputs are grounded to chassis for one.

Maybe there's something there?

Check out the back of the amp..is a mess





What about that capacitor on the back of the chasis? Is that one normal? should I replace it?

 

[ManyMoonsAudio]

No. Leave that cap be.