Looks like I need to return my Mark III Head (black dot) for a refund this Thursday to the guitar store. Hopefully I will be able to buy that one again after it is repaired. I will be starting my search again for a Mark III (or maybe Mark IV). I hope I have better luck this time.
Soon to be ex Mark III owner
- Thread starter Mjj
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Justice1988
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What was wrong with it?
Justice - The volume fade / drop out happens after about 1hr of playing. I replaced the preamp and power amp tubes just to make sure that wasn't the problem. I can prevent the problem by putting a patch cable in the effects loop. I think the effects loop has caused this same thing for others (corrosion??). I really want to understand the schematic for the effects loop so I can get a better understanding of why bypassing the effects loop "solves" the problem.
I am going to hold off on returning the amp.
I am going to hold off on returning the amp.
Justice1988
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hmm I'm no electronics expert, but at least you found a simple fix however temporary it may be. How do you like your black stripe?
The loop is series so if you plug into the send loop it disconnects anything after untill you plug back into the return.
The contacts on the jacks just need cleaning try that.
The contacts on the jacks just need cleaning try that.
Justice - I am liking the black dot/stripe - It fills in nicely between the my lonestar and mini rec. I am noticing that it can be a little bit fizzy. The guys at Mesa Boogie said that I should probably replace the two silver caps 50 mf 75 volts (w/ 50mf 100volts) based on the age and failure rate of the parts. I noticed that someone else on the board mentioned these caps and they might be related to biasing. One of the power tubes is red plating and it sounds like this is a sign of pending failure but might also be caused by a bias problem....
JD - Thinking about this as a series circuit makes sense to me now. I guess the patch cable doesn't do anyting different than when the cable is removed other than utilize different contact points. There must be corrosion between the contact points when the cable is not in place. I do find it interesting that this only happens after the amp heats up. Perhaps when the jacks are "cool" the points of contact aren't corroded but as it expands slightly from the heat, something shifts and the corroded portion breaks the circuit. Not sure how likely this is.
JD - Thinking about this as a series circuit makes sense to me now. I guess the patch cable doesn't do anyting different than when the cable is removed other than utilize different contact points. There must be corrosion between the contact points when the cable is not in place. I do find it interesting that this only happens after the amp heats up. Perhaps when the jacks are "cool" the points of contact aren't corroded but as it expands slightly from the heat, something shifts and the corroded portion breaks the circuit. Not sure how likely this is.
Marvel
Member
Mjj said:
Basically that's exactly how it works.
You have three options:
1. clean and bend the contacts
2. replace the jack sockets
3. always have the patch cable plugged in send/ return.
1. is not that easy if you have plastic switchcraft sockets, like I do on my MKIII. 2. you will not probably manage by yourself. 3. is the best option and it DOES NOT alter the sound in any way nor BYPASS anything, except for the bad contact in the socket.
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