Hi all
I’m quite new to electronics so be gentle.
I know enough to reasonably diagnose a guitar amp problem but as this is my first time with actual soldering iron in hand trying to fix things I would like to run my theories past experts first.
The amp
It’s a G10 Marshal (no reverb, twin gain pots, high middle low equaliser pots and master volume)
The problem
The gain controls produce really bad hiss even at low settings.
My thoughts on fixes
Visual inspection of the board I find no visible problems (cap leaking, dry joints or burns on components)
So do I suspect coupling caps are leaking DC - it’s my go to pat idea for hiss
Tools available
I have basic multimeter + DSO TC3 meter
To attack the problem.
I’m very competent at soldering
I’ve got a schematic of the circuit (very grainy print) but useable.
So how to trace this problem so gratefully for any help.
TIA
BTW - it’s 20+ years old
I’m quite new to electronics so be gentle.
I know enough to reasonably diagnose a guitar amp problem but as this is my first time with actual soldering iron in hand trying to fix things I would like to run my theories past experts first.
The amp
It’s a G10 Marshal (no reverb, twin gain pots, high middle low equaliser pots and master volume)
The problem
The gain controls produce really bad hiss even at low settings.
My thoughts on fixes
Visual inspection of the board I find no visible problems (cap leaking, dry joints or burns on components)
So do I suspect coupling caps are leaking DC - it’s my go to pat idea for hiss
Tools available
I have basic multimeter + DSO TC3 meter
To attack the problem.
I’m very competent at soldering
I’ve got a schematic of the circuit (very grainy print) but useable.
So how to trace this problem so gratefully for any help.
TIA
BTW - it’s 20+ years old
this is the basic unit without reverb
Yes the main volume down decreases hiss
Both gains increase hiss independently
So ic1 handles both gains (dual transistor chip) - would a transistor change for new not be damaged as old one has suffered?
Or is this a first place to suspect problems like this
I can pull the chip and test if you could help how. I am so keen to learn electronics
Thank fo the speedy reply BTW 👍
Yes the main volume down decreases hiss
Both gains increase hiss independently
So ic1 handles both gains (dual transistor chip) - would a transistor change for new not be damaged as old one has suffered?
Or is this a first place to suspect problems like this
I can pull the chip and test if you could help how. I am so keen to learn electronics
Thank fo the speedy reply BTW 👍
Update
I now have a blown fuse (internal) after pulling and testing a coupling cap that proved ok according to the dso-tc3.
May have grounded the board and smoked it against the chassis- whoops my bad
I now need on a really basic level (that’s where I’m at) - what’s the fuse rate?
There’s a confusing narrative on the schematic next to the fuse that basically
says a max of 200mA for a 240v supply which it is too small imo🤷♀️
I can just read the spec on the fuse that reads 250v and maybe T1AL
Any help greatly appreciated
👍
I now have a blown fuse (internal) after pulling and testing a coupling cap that proved ok according to the dso-tc3.
May have grounded the board and smoked it against the chassis- whoops my bad
I now need on a really basic level (that’s where I’m at) - what’s the fuse rate?
There’s a confusing narrative on the schematic next to the fuse that basically
says a max of 200mA for a 240v supply which it is too small imo🤷♀️
I can just read the spec on the fuse that reads 250v and maybe T1AL
Any help greatly appreciated
👍