JCM TSL 100 Hum issue

[Markusv]

Folks

Hope you can help

I have a JCM2000 TSL 100 on the bench with steady hum

Pulled all the 12 ax 7 tubes so not there (pre-amp)
There is no improvement with the reverb disconnected

Voltages seem OK

Any suggestions?

I did my chopsticking for loose connections etc. Do anyone of you know of typical failures in these amps?
Do I strat to suspect filter caps?

Thank you in advance

Markus V

[Structo]

Can you tell if it is 60Hz or 120Hz?

[Markusv]

Thanks Tom

So a grounding issue with a bad guitar cable for instance is 60 cycle - right?
That is a buzzy type hum

This is more of a soft drone
Not sure but does that seem like 120 cycle?

Markus

[Firestorm]

Maybe check to see that everything that is supposed to be at ground really is. Ground gets "passed" from board to board so maybe a bad connector. Different amp, but I've seen a JCM900 where the ground trace burned itself open and it hummed like hell.

[Structo]

Well what I was getting at is that most of the time a 60Hz hum will be something in the power supply, like a bad cap or other component that is letting the AC through.

The 120Hz hum is generally from heater wiring.\


Here is a pretty good troubleshooting flow chart for tracking down sources of hum.

http://www.geofex.com/ampdbug/hum.htm

[Markusv]

Thanks to all who replied

I will be looking at this amp again today and let you know. I will see if I can narrrow it down with a scope

Markus

[Reeltarded]

You need a spatula scope.

I use a little art/painting spatula wrapped in electrical tape. The wooden handle is removed. You hold it in your hand, and hover over areas of the amp listening for similar noise or additional similar noise.. or just noise, or whatever.

That helps me find problems like that one sometimes.

Play a Bb on the low E string and pull it slightly sharp. Does the note match the hum?

[Markusv]

You need a spatula scope.

I use a little art/painting spatula wrapped in electrical tape. The wooden handle is removed. You hold it in your hand, and hover over areas of the amp listening for similar noise or additional similar noise.. or just noise, or whatever.

That helps me find problems like that one sometimes.

Play a Bb on the low E string and pull it slightly sharp. Does the note match the hum?

Thanks Reeltarded!!
So if it matches the sharp'ish B flat - then what does it indicate for you?
I'm not in front of the amp now but I think you're onto something

Markus

[Reeltarded]

60hz is Bb bent a little sharp.

[Markusv]

60hz is Bb bent a little sharp.

So in that case I could suspect power supply issues - right?

[Reeltarded]

Wiggling the connectors or cleaning them doesn't help?

Tubes pulled? Hrrrmm..