Welcome, Guest. Please login or register.

January 18, 2021, 08:36:13 AM

Login with username, password and session length

Recent Posts

 

Author Topic: marshall mb-450h signal to speaker but no sound  (Read 2100 times)

EDWARDEFFECT1

  • Elite
  • ****
  • Posts: 152
  • Chip Points: 3
    • View Profile
marshall mb-450h signal to speaker but no sound
« on: July 18, 2011, 10:58:45 AM »
does anyone know where i can get a schematic for a marshall mb-450h amp head.i put a signal in the input and get a signal at the speaker that is controllable by the volume controls on the amp.when i hook up a guitar and speaker i get nothing.

J M Fahey

  • SSGuitar Global Mod
  • Legendary
  • ****
  • Posts: 4142
  • Chip Points: 429
    • View Profile
Re: marshall mb-450h signal to speaker but no sound
« Reply #1 on: July 18, 2011, 11:35:02 AM »
What "input" do you refer to?
The front panel "guitar" input or the back panel "Power_amp/loop_in/return" one?.
Maybe you have a weak loop jack contact; try plugging a known good guitar cord drom send to receive or whatever it's labelled.

Enzo

  • Legendary
  • ******
  • Posts: 1989
  • Chip Points: 216
    • View Profile
Re: marshall mb-450h signal to speaker but no sound
« Reply #2 on: July 18, 2011, 06:16:53 PM »
If I read you correctly, you have the signal at the speaker jacks.   For anything to work, there must be a complete circuit, so ASSUMING you have tried other speakers and other speaker cords, then I have to suspect the ground return for the speaker is open. 

EDWARDEFFECT1

  • Elite
  • ****
  • Posts: 152
  • Chip Points: 3
    • View Profile
Re: marshall mb-450h signal to speaker but no sound
« Reply #3 on: July 19, 2011, 12:23:13 PM »
got it going.found another bad ic.i was injecting a signal into the input with my mjf signal tracer injector (love this thing for non digital solid state circuits)i had volume on the hot leg of the speaker jack when it was in my load box that was controlable from the front panel. you would swear it was working fine.when you plugged a guitar and speaker cabinet while playing a guitar i had no sound. after replacing a couple of suspect ic's with sockets (tl072,tl074 quad chip, & ne5532)bam it got a lot louder signal in the speaker connector of my load box. i pulgged it into a speaker cabinet and hooked up a chord and bass and working good as new....thanks for the help....ed

EDWARDEFFECT1

  • Elite
  • ****
  • Posts: 152
  • Chip Points: 3
    • View Profile
Re: marshall mb-450h signal to speaker but no sound
« Reply #4 on: July 19, 2011, 12:26:34 PM »
guessing it was the tl074 quad chip as i had no signal on one of the outside output legs.there was signal on the other 2 chips but it was very low.since i had the board out and time is of value i replaced all 3 ic's.....ed