Marshall MB4410 output only onheadphone jack

[nosaj]

I have a Marshall MB4410 output only on headphone jack. None on send or receive effects loop. all 3 fuses are good. Does anyone have a schematic for this amp or know Marshalls policy on providing one?

Thanks,
nosaj

I did find this by searching the number on the board MB450-61-00,
https://www.google.com/url?sa=t&rct=...v7xro9tvCqtgTg So I'll check the rails and go from there.

[nickb]

I'm assuming this is the same as an MB450 inside.

It's rather odd that you have nothing on the FX loop yet do on the headphone since the headphone output is located after the FX loop.

Try unplugging and re-plugging the ribbon cable that go to CON2 on on the rear PCB with the FX/send return on it. Same for the one that goes from CON4 on the front preamp board to the PSU/AMP board.

Try plugging into the FX return as see if you can hear anything. Same for CD in.

Can you hear anything from the speaker at all such as a faint hiss or hum?

What test gear do you have?

[Jazz P Bass]

Full Schematic set:

mb450__mb4210__mb4410_power_stage_cct.pdf
-mb450__mb4210__mb4410_front_pcb.pdf

[nosaj]

I'm assuming this is the same as an MB450 inside.

It's rather odd that you have nothing on the FX loop yet do on the headphone since the headphone output is located after the FX loop.

Try unplugging and re-plugging the ribbon cable that go to CON2 on on the rear PCB with the FX/send return on it. Same for the one that goes from CON4 on the front preamp board to the PSU/AMP board.

Try plugging into the FX return as see if you can hear anything. Same for CD in.

Can you hear anything from the speaker at all such as a faint hiss or hum?

What test gear do you have?

Ok let me clarify I can input on cdin, input, effects send recieve and only hear anything if I connect the speakers to the headphone jack.

Con 1
Pin1 -14.2
pin6 -14.2
pin7 14.5
pin 8 238vdc
pin10 13.65
When i can get to it I think i need to check for signal at C4 then move down the chain?
Got meters analog / DVM, scope and dummy load.

Thanks,
nosaj

[nickb]

Ok let me clarify I can input on cdin, input, effects send recieve and only hear anything if I connect the speakers to the headphone jack.

Con 1
Pin1 -14.2
pin6 -14.2
pin7 14.5
pin 8 238vdc
pin10 13.65
When i can get to it I think i need to check for signal at C4 then move down the chain?
Got meters analog / DVM, scope and dummy load.

Thanks,
nosaj

That would be a good plan. Don't forget to remove any load while probing.

[nosaj]

That would be a good plan. Don't forget to remove any load while probing.

Can you explain why please?
Thanks,
nosaj

[Jazz P Bass]

There is a few things that could 'kill' the output signal.

The Headphone Out is separate from the main output.

So start at pin 3/ Con 1.
If you don't have it there, well......

[nickb]

Can you explain why please?
Thanks,
nosaj

Once you get into the power amp proper you might have a probe slip. If you accidentally short something then you could get DC across the load which could cause damage to speaker & transistors. Aside from scaring the c^@p out of you.

I think starting at C4 is a good place. The concept is the "Wolf Fence Paradigm". You have a wolf but you can't see it so you erect a fence that divides your property in half and listen to see on which side you hear the howl. Then put up a new fence to divide that half and so on. It's really a binary search but I like that way of explaining it and it is the fastest method of converging on the trouble spot.

So C4 is not exactly in the middle but it's not at one end either. if you see no signal you know the problem is between that and the headphone driver. If it is then look after.

[nosaj]

Once you get into the power amp proper you might have a probe slip. If you accidentally short something then you could get DC across the load which could cause damage to speaker & transistors. Aside from scaring the c^@p out of you.

I think starting at C4 is a good place. The concept is the "Wolf Fence Paradigm". You have a wolf but you can't see it so you erect a fence that divides your property in half and listen to see on which side you hear the howl. Then put up a new fence to divide that half and so on. It's really a binary search but I like that way of explaining it and it is the fastest method of converging on the trouble spot.

So C4 is not exactly in the middle but it's not at one end either. if you see no signal you know the problem is between that and the headphone driver. If it is then look after.

Thanks for the explanation and the analogy i love analogies.

nosaj

[Jazz P Bass]

There is also the limiter ic that could be causing grief.

You will know more when you start signal tracing.

[nosaj]

Ok we have signal at pin3 and c4. Next step on the TL074 chip I'm looking for signal on pins 1,7,8,and 14 that should rule out a fair portion of the circuit or hone in on a section.
updates to follow,
nosaj

[The Dude]

I would next verify that signal is getting all the way to the base of TR11. Did you check and make sure your V+ and V- rails are there?

[nosaj]

I would next verify that signal is getting all the way to the base of TR11. Did you check and make sure your V+ and V- rails are there?

No I did not but I will. No signal on pins 1 and 7 , signal injected at input.

nosaj

[nickb]

What the Dude said +

IC1d is the amp for the full wave rectifier of the limiter. It should have a signal.

IC1c is the rectifier buffer for the limiter. It will have DC that follows the amplitude of the signal.

IC1b turns the fan on when it gets hot enough

IC1a turns the power amp off when it get too hot or also if the output of IC1c gets to be more than about 1.3V i.e input signal too big. Check this IC1a output- if it's low the amp is turned off.

[nosaj]

What the Dude said +

IC1d is the amp for the full wave rectifier of the limiter. It should have a signal.

IC1c is the rectifier buffer for the limiter. It will have DC that follows the amplitude of the signal.

IC1b turns the fan on when it gets hot enough

IC1a turns the power amp off when it get too hot or also if the output of IC1c gets to be more than about 1.3V i.e input signal too big. Check this IC1a output- if it's low the amp is turned off.

Yes there are 15 v +- rails. TR11 gets signal.
Here is what interests me that I found. Speaker plugged in no audio passing. With nothing plugged into the amp
If i use the signal tracer I get sound. I thought it might be the nuetric jack but I put a audio cable in the nuetric jack and use the signal tracer on the end of the audio cable and the pass audio. So when there's a load on it something collapse.
So I'm befuddled.
nosaj