Marshall JTM30 problems (?)

[APB_4]

It mostly works fine, which is nice. The normal channel is a bit odd though, while changing the preamp volume it can make the odd crackle but when cranked it tends to be really loud for about half a second then jump between loud and not so loud then settle into not so loud. It's a bit odd and seems to get substantially louder than the boost channel. I took the chassis out and had a poke around with my multi meter and a lot of the big caps won't read which is odd but as I say it still plays. The volume pot on the normal channel seems a bit dodgy, the outer lugs measure 1M when the pot is at minimum but half a meg at full. The vol pot on the boost channel always measures 1M between the outer lugs.
Any ideas?
Should I change anything?

[DesertRose]

Re: Marshall JTM30 problems (?)

It's a bit odd and seems to get substantially louder than the boost channel.

How did you know it gets louder than the boost channel?
You actually tried switching in between at equal volumes?

Which means the actual volume of channel 1 was always at a certain volume but now it could go higher than what it should be intermittently?

[stevie_bees]

Re: Marshall JTM30 problems (?)

You won't necessarily get the readings you expect from components when they're in a circuit.

[APB_4]

Re: Marshall JTM30 problems (?)

How did you know it gets louder than the boost channel?
You actually tried switching in between at equal volumes?

Which means the actual volume of channel 1 was always at a certain volume but now it could go higher than what it should be intermittently?

Yes switching between the two even with the gain on full on the boost channel and the pre set at the same number as the normal channel the volume is/used to be much higher.

It used to be louder most of the time now it likes to flick around and half deafen you. I think it's been like this pretty much since I got it but I generally didn't turn it up all that much. It's much worse near full volume.