I don't know if you can fix it yourself or not.  It will require soldering parts to the circuit board, I'll bet my lunch money.

Leaving it running is not going to hurt it.

Look closely at the cone of the speaker when you turn it on.  If the cone moves one direction and stays there, along with a loud hum, then your output stage is blown, and there is DC voltage on the speaker.   DOn;t leave that on.

If the speaker seems to stay at rest but hums loud, you may just need a filter cap resoldered.  or maybe replaced.

Byond that, it should not be complicated for e technician to repair.

Yes, Peavey has it, as they do schematics for any of their products.  COntact customer service at Peavey and ask for it.

I don't know what schematic you are looking at, but yes, as a rule when you see a + in a circle and a "wire" going to it, it represents the + power supply.

Schematics show the electrical relationship between parts.  Wiring diagrams and layouts show the physical relationship between parts.  The schematic has no relation to how you lay the parts out.  SO unless you have a VERY simple little circuit, the layout won;t look like the schematic.

Layout isn't random, you want most times to keep the input and output circuits away from each other for example.

And last night I sent an email to www.marshallparts.com and asked if they had them.  Today I had a replay in my email from them.  They have them in stock at $5 each.

I don't use B&D all that often, but I have had success ordering Sanken power transistors from them.  So far no counterfeit ones.  That is mainly what I buy from them.  SO if you are putting together an order, consider that.  www.bdent.com

B&D showed the M5201 in stock at a little over $2 each.

www.bdent.com

I am glad you fo0und them.

I am sorry I was unclear.  I meant that they would be a likely source, I didn't mean to infer they would list all their parts online.

I guess I am the Lab Series guy this week.

The L4 preamp is below.  The power amp is the same as the L5 etc, and I had to scan it gray scale to see everything.  The layout also had to be gray scale and the files are several times the limit of this board.  SO I will post those in the Enzo gallery at www.ampix.org

Please be careful.  Solid state amps run on lower voltages than tube amps but still can be dangerous, after all the mains voltages are inside it.

That having been said, most of these amps discharge themselves pretty quickly.  Always check with a meter until you understand how the circuit acts.

Yes we would discharge power supplies while still wired in.  REmoving a capacitor from the circuit board to discharge it would be a futile exercise.

If i want to check for shorted power transistors or the like I would work with the amp unplugged and discharged.  You can rarely take meaningful resistance measurements in a powered circuit.  (One exception might be measuring a JFET for on or off resistance)

In the other hand the ONLY way to take voltage readings is with the circuit powered up.

Most ICs are tested functionally, though if they start getting hot, that is often a sign of failure.

TP usually means test point, yes.  And Crate often has a chart of test point condition on their drawings.

Multitester?  Maybe.  Depends on what you are calling a multitester.  The tool of choice among technicians is usually  DMM - digital multi meter.  Though some (mainly old timers) still use VTVMs or the classic SImpson 260 type analog meter.

Ah, always good to have additional options.  Thanks for cleaning up the scan for me.  I didn;t want to gray-scale it and make the file huge.

If we can post files directly here, I don;t spot how, so I posted this schematic in the Enzo Gallery at www.ampix.org.  Right now they are in the "most recent" area as well, but look under member galleries for mine and they should be there.

Sorry it is in three pieces, it is a long foldout drawing.

The center segment has some resistor numbers in gray circles which obscures them on the scan.  From highest to lowest position, they are:

R4  3k  (above C4)
R3  15k  (below C4)
R7  470  (base of Q3)
R6  15k  (base of Q2)
R1  33k  (base of Q1)
R5  680  (series C3)
R2  1.8k  (collector Q1)

why would you assume EVERY part someone sells is on their web site.  COntact them directly and ASK for goodness sake.   Otherwise the web site gets filled up with page after page or plastic corner, plastic corner mounting rivet, plastic corner mounting rivet washer, etc etc.

A rule in our shop is never think up reasons not to check something.


I don;t buy the conspiracy theory.  Marshall wouldn;t bother.  Anyone wanting to steal the Marshall circuits could replace the 5201 with a couple JFETs and your op amp.  Doesn;t PV use the DG212 in their TL604 workaround?

As a Marshall service center, I just order them from Marshall when I need some.  (Korg in the USA)  You could order them through any Marshall dealer or someplace like www.marshallparts.com

OOr, if it doesn;t hum with nothing plugged in but does hum with a guitar.  The input jack may have lost its ground connection - specifically the sleeve connection to ground.  The tip shunt will still work and silence the empty jack, but plug any signal source in and no ground.  You'd only hear hum with a cord plugged in.

I hope this doesn;t duplicate.

I posted your schematics at www.ampix.org in the Enzo gallery.

This board would not let me post a pdf file.

Also, there is a reason most bass amps have no reverb.  Bottom end through a reverb makes not much but mud.  You will find a lot of reverb circuits limit the bottom end coming into the pan, so the send signal may be real tinny if you try this.