Help needed with...
Marshall Lead 100 Mosfet 3210 ss amp, pcb: jm88
The quality control sticker inside is dated 06/06/86 & appears to be unmolested.
This is the schematic I'm using since the only other one I could find is too difficult to read...
http://drtube.com/schematics/marshall/3210-iss7.gif
This amp powers on, but I'm getting loud intermittent cracking & popping noises thru the speakers [2x12" 8Ω Celestion V30's wired into 16Ω].
When patched thru another amp [same speakers] it produces a nice clean sound so that should rule out the preamp correct?
I'm a novice to guitar amplifier repair but I have a grasp on electrical components & the tools/ability to solder,
so please don't become impatient if I don't completely understand everything right off.
At first glance after opening it up, I saw melted insulation on the wires connected to the K135 mosfet.
Although it was still producing sound the pin on K135 with the yellow wire was actually able to move [up & down] in the mosfet.
Obviously this part got really hot & needs replacing so I'll replace both mosfets to keep them closer together in spec.
I removed the board & inspected the solder joints which all looked ok.
However, there were a few dark spots on the circuit board.
I'm not very experienced at following voltage across a schematic but I'd like to make sure the components near these dark spots aren't damaged from overheating.
Perhaps with your help I can test these components & be sure to correct any problems the first time & not blow up new parts by rushing thru the repair.
I sourced some parts but have yet to dive into replacing anything yet,
until I can get some opinions & advice from those with the experience I am lacking.
I don't want to make any rookie mistakes, so if anybody would like to offer their expertise in which components should be tested & why, It would be very much appreciated.
Hopefully I didn't leave out any pertinent info.
Thank you guys for your time & any help you can offer...
Marshall Lead 100 Mosfet 3210 ss amp, pcb: jm88
The quality control sticker inside is dated 06/06/86 & appears to be unmolested.
This is the schematic I'm using since the only other one I could find is too difficult to read...
http://drtube.com/schematics/marshall/3210-iss7.gif
This amp powers on, but I'm getting loud intermittent cracking & popping noises thru the speakers [2x12" 8Ω Celestion V30's wired into 16Ω].
When patched thru another amp [same speakers] it produces a nice clean sound so that should rule out the preamp correct?
I'm a novice to guitar amplifier repair but I have a grasp on electrical components & the tools/ability to solder,
so please don't become impatient if I don't completely understand everything right off.
At first glance after opening it up, I saw melted insulation on the wires connected to the K135 mosfet.
Although it was still producing sound the pin on K135 with the yellow wire was actually able to move [up & down] in the mosfet.
Obviously this part got really hot & needs replacing so I'll replace both mosfets to keep them closer together in spec.
I removed the board & inspected the solder joints which all looked ok.
However, there were a few dark spots on the circuit board.
I'm not very experienced at following voltage across a schematic but I'd like to make sure the components near these dark spots aren't damaged from overheating.
Perhaps with your help I can test these components & be sure to correct any problems the first time & not blow up new parts by rushing thru the repair.
I sourced some parts but have yet to dive into replacing anything yet,
until I can get some opinions & advice from those with the experience I am lacking.
I don't want to make any rookie mistakes, so if anybody would like to offer their expertise in which components should be tested & why, It would be very much appreciated.
Hopefully I didn't leave out any pertinent info.
Thank you guys for your time & any help you can offer...
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