Marshall Bass Control

Marshall Amp Discussion

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lpd
Posts: 204
Joined: Fri Nov 14, 2008 1:45 am

Marshall Bass Control

Post by lpd »

Hi guys have this circuit with pedal to switch between Plexi/800 and I recently lost bass control. Pot was working but now does nothing to increase decrease bass. How do I diagnose where the issue is? I reflowed all solder joints no improvemnet. Wondering if it’s the pot?? Ideas? Can post pics of the board as well if necessary.

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Littlewyan
Posts: 1911
Joined: Thu Sep 12, 2013 6:50 pm
Location: UK

Re: Marshall Bass Control

Post by Littlewyan »

Go through the entire tonestack to ensure it's wired up correctly. Check connections with an Ohmmeter.

Put a meter on that pot (wiper and one of the sides), turn it and see if the resistance changes. From memory you won't see the full 1M but you should see a couple of hundred k.

If the resistance doesn't change at all then unsolder the wires from the pot and then measure it.

Let us know how you get on :)
lpd
Posts: 204
Joined: Fri Nov 14, 2008 1:45 am

Re: Marshall Bass Control

Post by lpd »

Littlewyan wrote: Thu Oct 05, 2017 11:17 am Go through the entire tonestack to ensure it's wired up correctly. Check connections with an Ohmmeter.

Put a meter on that pot (wiper and one of the sides), turn it and see if the resistance changes. From memory you won't see the full 1M but you should see a couple of hundred k.

If the resistance doesn't change at all then unsolder the wires from the pot and then measure it.

Let us know how you get on :)
Will do tonight!! I done learned somethin 😊
lpd
Posts: 204
Joined: Fri Nov 14, 2008 1:45 am

Re: Marshall Bass Control

Post by lpd »

Littlewyan wrote: Thu Oct 05, 2017 11:17 am Go through the entire tonestack to ensure it's wired up correctly. Check connections with an Ohmmeter.

Put a meter on that pot (wiper and one of the sides), turn it and see if the resistance changes. From memory you won't see the full 1M but you should see a couple of hundred k.

If the resistance doesn't change at all then unsolder the wires from the pot and then measure it.

Let us know how you get on :)
2.98k-548k when I rotate the pot and measure off wiper and outer leg.
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Littlewyan
Posts: 1911
Joined: Thu Sep 12, 2013 6:50 pm
Location: UK

Re: Marshall Bass Control

Post by Littlewyan »

Sounds about right.

Have you checked the tonestack to ensure it's wired up correctly? Checked each connection with an Ohmmeter?

Were any mods done just before you lost the bass control?
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