SHFA 1 hum in single channel when RSCU2 connected.

[Marcel Bogert]

Curious problem on a 222.

Single channel of the SHFA1 has a slight hum when in stand-by, no record playing.
When in the living room the hum is clearly present.

When I disconnect J506 the hum is gone.

swapped the SHFA1 hum remains.

TSU1 has all fresh capacitors including the RSCU2.

I checked for hum on a 220 that i have in, no hum.
So this hum is abnormal.

Seems related to the TSU1/RCSU2. 

No clue how this would relate to the amp anyone have a suggestion ?

[Ron Rich]

Hi Marcel,
Curious, indeed !
I am wondering if it's not a muting problem on the mechanism ? Does removing the mute and input plugs have any effect ?
I don't have a manual here--what connects to J 506 ? Ron Rich

[Marcel Bogert]

Hi Ron,

I can disconnect the input and mute plug no difference.
I can remove the output tubes and the 2 12ax7's next to it, no change.

J506 is the power-supply plug for the RCSU2.

[Ron Rich]

Hi Marcel,

Maybe (??) something about the transformer-- they did have a problem with the 25 volt wallbox supply transformer they first used on the RCSU-4's-- had to reverse the secondary output leads--can't recall the reason ? Other then that, only guess is cabinet cable "dressing" ? Ron Rich

P.S. -Unplug flour lamps ?

[Marcel Bogert]

I moved just the RSCU2 to another TSU1 in the 220.
Hum moves to the 220

I disconnected the wallbox transformer mains, hum is gone.

I connected the transformer on my testbench no abnormal behaviour (noise, current draw or outputvoltage), does have wax around the wiring coming from the internal wiring.

Will try a different transformer to check if this makes a difference, wax from the transformer could indicate a possible overheating of the transformer at some point.

The wallbox transformer is next to the OT of the channel that has the hum.
will post my results

Replaced the transformer hum is close to zero.

My best guess is the transformer was influencing the OT

[Ron Rich]

Hi Marcel,
Try swapping the output leads, of that transformer first--- ??

Ron Rich

What size is the fuse on the RCSU ?

[Marcel Bogert]

I will check the transformer later.
Want to see if it's the transformer or the connection of the output too.
Need to fix another RCSU2.
I did remove the GMQ fuse to disconnect the output of the transformer figuring it would no longer be a cause of the hum.

Need to get this machine out the door.

GMQ fuse 61/4 which is wrong should be 3.2amp according to the screenprint
Should not fit normally but it does.

[Ron Rich]

Hi Marcel,
Yep-- I suspected it has been "over-fused"-- Is it a code A or code B RCSU ?
Ron Rich