Marshall Amp Forum - View Single Post - JCM2000 DSL100 hums when standby switched.

TheRuleOfThree · 10-20-2009, 06:34 AM

Hi,
I was wondering if anyone can point me in the right direction in respect to my JCM2000 DSL100. After bringing it home from a jam, it's suddenly developed a hum through the cab when standby switch is switched on (not on standby). Otherwise the only audible hum is from the transformers and no cab hum at all. The hum is loud enough to be annoying at very low levels, especially when using the clean channel but it's volume does not change at all no matter what volume I'm running at or what channel I'm using.

I always have a spare set of valves handy and thought that I'd try and change the output valves first (and Bias adjust) but the "hum remains the same" (pardon the pun) This also goes for the preamp valves. No good....

I've had a bit of a look across the internet, and because this hum remains the same regardless with what I do to the pre-amp section, I'm suspecting the main filter capacitors in the HT rectifier section, in my case C38, C39, C34 & C35. Easily enough done, but are there any other caps that could cause this problem while I've got it open and exposed?

Any help would be greatly appreciated!!

Danny.

10-20-2009, 06:34 AM	#1 (permalink)
TheRuleOfThree Junior Member Join Date: Oct 2009 Location: Melbourne, Australia Posts: 5	JCM2000 DSL100 hums when standby switched. Hi, I was wondering if anyone can point me in the right direction in respect to my JCM2000 DSL100. After bringing it home from a jam, it's suddenly developed a hum through the cab when standby switch is switched on (not on standby). Otherwise the only audible hum is from the transformers and no cab hum at all. The hum is loud enough to be annoying at very low levels, especially when using the clean channel but it's volume does not change at all no matter what volume I'm running at or what channel I'm using. I always have a spare set of valves handy and thought that I'd try and change the output valves first (and Bias adjust) but the "hum remains the same" (pardon the pun) This also goes for the preamp valves. No good.... I've had a bit of a look across the internet, and because this hum remains the same regardless with what I do to the pre-amp section, I'm suspecting the main filter capacitors in the HT rectifier section, in my case C38, C39, C34 & C35. Easily enough done, but are there any other caps that could cause this problem while I've got it open and exposed? Any help would be greatly appreciated!! Danny.