Marshall DSL 401 help!!!!

[bru10]

I have a marshall dsl 401 about 4 years now and I never had a problem with it until now, I was at rehersals last night and my amp just cut off, I use the amp threw a peavey 4 x 10 cab at 16ohms, and run it on clean level volume at 4, I have checked both exterior fuses, and I also checked the inside circuit board fuse, I think the valves might need replacing, but I dont think the power should short if a valve is blown, after I checked the fuses i tryed turning it back on and the power switch flickered and went off again.. I dont want to replace the valves until i know the real problem incase the new ones get damaged, both transformers have been replaced before I got it... Any help??

[Gibsonman63]

That could be a real can of worms. You said you checked the fuses, I am assuming that one of the exterior fuses was blown and you replaced it? If it has been working for a long time and suddenly quit, I would suspect the power tubes. Sometimes they short when they go bad. Try pulling the power tubes and see if it will power up without blowing the fuse.

[bru10]

Thanks for the reply, the exterior fuses didnt blow and neither did the internal one, the power light just flickered and switched off, so i checked the fuses they were fine i tryed turning it back on and the same happened i got the power ligh for a 2nd then it turned off.. do you think it would be ok to turn it on to test the power without the 4 power tubes in??

[Gibsonman63]

To be honest, I am a little confused that the power light is going off and it is not taking the fuse with it. Could it be a faulty switch? I have seen some of these switches that you have to giggle a little to make them work, but I have never seen one come one and then go off. It would be easy enough to check with a meter to see if the switch is passing voltage.

I had a DSL401 for a couple of years when I first got tired of dragging a half-stack around. I know that they had a lot of soldering problems with these during production and some of them ran pretty hot.

[bru10]

Iv heard of them running really hot, I used to leave a fan behind it, Ill check the switch tho.. have you ever heard of an amp powering off if the valves go? I think definitly one is gone.. is it ok to power it if i take the valves out just to test it?

[Gibsonman63]

Usually the power tubes will take the fuse with them when they go, so this still sounds odd to me. It won't hurt the amp at all to pull the power tubes and power the amp up.

[Gtr_tech]

Could be the switch, could be cracked solder somewhere around it, could be a bad crimped connector, could be......

[bru10]

Ok cool im going to check out all those things, would a picture help diagnose the problem??

[bru10]

I tryed to power on the amp without the valves no power or even a flash came out of it, if the swicth is broke would it prevent power going to the circuit?

[Gibsonman63]

A broken switch would. Are you comfortable working on this? It goes without saying that there are lethal voltages inside this amp, in fact much higher than wall voltage.

I would check the voltages without tubes from the supply voltage to the power transformer with a meter to start. As Gtr_tech pointed out, it could be quite a few things.