Marshall JCM900 SLX Tech Help

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japetus

japetus

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I've had this JCM900 SLX awhile, but hadn't really been playing it. Got it back home today, plugged it in and sound was cutting in and out and getting quiet. Checked the tubes, they are fine. Talked to an amp tech I know and he asked me to look at the Bridge Rectifer and see if it has been replaced (apparently these amps are known for them messing up). I am a total idiot when it comes to electronics, but I think I found it...and it looks like some work has been done. Can someone tell me which part is the bridge rectifier and confirm my suspicions work has been done..it looks like someone did a sloppy job, but I don't know. Don't worry I am not going to try to work on this myself...he just is asking questions before I drive 2 hours.
 

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I believe that's one of them. I think there's 3 on that board (that's the leftmost one - there's two more as you go right on that board, but I believe that one is the culprit) and it looks like someone added that "heat sink" to try to fix the problem they had with that bridge rectifier overheating.
 
Large blue electrolytic cap on the left in the first pic looks f'd.
Hard to tell from a pic, but that cap looks like the top is bulged out and it's leaking the brown goop.
 
Thanks guys. It's going to the tech, I don't trust myself with any of this, haha. I am thinking about going with 6L6 in it.
 
sutepaj":1jquwndj said:
Thanks guys. It's going to the tech, I don't trust myself with any of this, haha. I am thinking about going with 6L6 in it.
Click to expand...

Before you take it to your amp tech, you might want to clean the effects loop jacks with contact cleaner. It should stop your sound from cutting out as the effects loop jacks tend to get oxidized over time from smoke/grime/moisture.
 
Hamer95USA":1thdvsbw said:
sutepaj":1thdvsbw said:
Thanks guys. It's going to the tech, I don't trust myself with any of this, haha. I am thinking about going with 6L6 in it.
Click to expand...

Before you take it to your amp tech, you might want to clean the effects loop jacks with contact cleaner. It should stop your sound from cutting out as the effects loop jacks tend to get oxidized over time from

Ismoke/grime/moisture.
Click to expand...

Definitely. Personally every new to me amp I get, I use deoxit on all of the tube sockets and jacks, on occasion also the pots. Not that it will solve your whole issue but for me, it's a good practice.

Edit: obviously this will not fix your blown cap or a bridge rectifier, but just in general I consider it good practice. Especially on a 30+ year old amp.
 
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