newbie help with marshall amp please

[simon1974]

hi all well im looking into my marshall amp
it is a g50rcd model .
now im looking at the curcuits and notice its darkened around the under diode area.
now for some time i been having problems with it running the guitar,
threw clean and boost.the boost light no longer comes on either.
it does give output ocasionaly and well now i would llike to fix it.

so i notice the zd2 and zd3 diodes are dark on the cuircuit board underneath.
i was wondering if anyone would know or give me an idea as to the problem.
or possiblly a way around this to get the old amp up and running .any help appreiciated guys .im desperate to make some noise thankyou all who reply in advance

[booj]

I'd re-solder the board, especially around the darkened areas. Might be best to use a little solder braid and really clean the leads and pads first, then re-touch with solder

[simon1974]

thanks for the replie appreiciated .
now ive looked and tested diodes i beleive they have gone.
now the ones in it a 15w and i cant seem to see any of this type
on the net .would it be possible to bo up or down on the 15w at all.
sorry for the silly questions but well somthing i would like to do myself
if possible but id liek not to make worse lol ,thanks again

[Jazz P Bass]

ZD2 & ZD3

If I am not mistaken , ZD2&3 are 15 Volt, 3 watt zener diodes.
They regulate the +15 & -15 volt supplies.
The only schematic I have is for the MG100RCD.
Maybe it will help.
You need to test the zeners, use diode check on your DVM. They should read around 0.700.
See if the +15 & -15 volt supply is even working.

[simon1974]

If I am not mistaken , ZD2&3 are 15 Volt, 3 watt zener diodes.
They regulate the +15 & -15 volt supplies.
The only schematic I have is for the MG100RCD.
Maybe it will help.
You need to test the zeners, use diode check on your DVM. They should read around 0.700.
See if the +15 & -15 volt supply is even working.

thanks for the reply p bass.
yes thats correct i have tested the diodes and ,their both testing at under.
0.700 one way ,and both irratic readings the other ,ive read up and believe, they should only give a reading threw in one direction,i could be wrong.
other than that im a little confused

[Jazz P Bass]

Marshall MG50 RCD

If you tested the zener diodes in circuit, that may explain the erratic reading one way. You are charging C66 & C67. If you are not sure, test out of circuit.
How much under 0.700 did you read? A little variation is o/k.
Before you test the +15 & -15 Vdc rails, measure the resistance to ground of each test point. If it is above 1000 ohms, your good. If it is really low, then you have a shorted rail.

[simon1974]

well i took the diode out had a test pbase all fine as you well suggested.
now in the process of looking over the board,well i found a slight rock in the input jack.
well resoldered and like new.i feel a bit of a wally lol.but well you gave me some valuable
knowledge and really appreiciate your advice ad help ,thankyou very much