Rumbling popping Marshall 5210 Please help !!

[sebgreen]

Hello
I've got an old solid state Marshall 5210 which for a few months now has been crackling and popping after about 15 mins playing time. The noise is present on both the clean and boost channels and its volume is only modified by the master volume. I've tried changing 2 oxidised capacitors but to no avail. Please help if you can !!
Cheers !!
Seb.

[J M Fahey]

Hi sebgreen.
If it responds to the master volume, it can't be *that* bad.
Please search and post the schematic (or a link to it) so we are all talking the same here; so C24 is the same for all of us , not "the one close to the output jack but slightly to the left" which causes generalized head scratching.
Good luck.

[Enzo]

This is a simple amp.  If the master vol comtrol turns the noise down, then the noise is before it.  You say it is the only control affecting the volume.  So that means the noise is still there even with both channels having ALL controls at zero?

I would be surprised if it were not IC1.  A TL072, very common part.  In any case it sounds like a noisy semiconductor to me.  And before the MAster vol control there really are not many, other than the two ICs, there is the JFET TR1, and really less likely are the three bipolar muting transistors.

[sebgreen]

Hello

Thanx for taking the time to answer. I suppose it isn't that audible but it is quite bad.

Here is a link to a schematic    http://www.drtube.com/schematics/marshall/5210.gif

I don't really know much so it mustn't get too technical. I understand the basics but that's about it...

Cheers

[moegreen77]

I've had the rumbling issue too, and replacing C13 seems to have solved it. C13 got my attention because it was very microphonic. The thing is, it's STILL very microphonic. And just putting my finger near it causes an increase in hum, let alone tapping it.

Btw, my amp is the older version - the hand drawn schematic, op-amps are all 1458's and it does have C14.
So, I'm touching up any solder joints that seem remotely relevant, and maybe I'll try replacing the transistors at each end of C13, and maybe go ahead and replace C12 fwiw.
Anyway, any thoughts about the microphonics?

[Roly]

Broken link to the circuit on Dr Tube.

5210 ('86)


5210-II ('88)

I've had the rumbling issue too, and replacing C13 seems to have solved it. C13 got my attention because it was very microphonic. The thing is, it's STILL very microphonic. And just putting my finger near it causes an increase in hum, let alone tapping it.

C13 appears to be on the gate of the second FET, and is part of the channel switching, AC shorting that point to signal ground when the transistor (TR-blodge turns on from the pedal circuitry).  Otherwise this is pretty much a wide open input so it's not surprising that it's a pickup hot spot.


I'm of a mind that randomly replacing components trusting to luck doesn't work.

What works is diagnosing what is wrong, identifying the basic cause, and fixing that.


@sebgreen - Try a known good lead between Fx Send and Fx Return.  Any change?

Feed a programme in at Fx Return.  Quiet now?