My Mark III died!

[Bullen]

So, I let a friend borrow my Mark III over the weekend. He played it at a wedding, And it worked fine in the church, but then he wanted to play it some more at the party and it wouldn´t turn on. He called me and I thought the fuse might have blown for some reason.

So, today I changed the fuse when I went to pick the amp up, but the amp still won´t turn on. The tubes look fine and they are pretty new, perhaps 20h playing time on them.

I´m taking the amp to a tech, but I wanted to check here first.
Does anyone have any ideas what the problem might be?

Thanks!

 

[Bullen]

Just tried putting in some other tubes, but still no luck. I checked the wireing but it looks good. Nothing loose or burnt that I can see.

Any ideas?

 

[Boogiebabies]

It could be a bad preamp tube. If one of the triodes dies, it does not pass the signal to the next stage. If the path to the phase inverter is stopped, no sound.

Note to self: Never lend out tube amps....

 

[Boogiebabies]

Oh, don't forget to do the effects loop test. Just jump the send and return with a short cable.

 

[disassembled]

In a serial effects loop if a cable is plugged into the return jack it cuts off the signal coming from the preamp. Now imagine a bit of dust or dirt getting on the contacts of the return jack over time that can mess up the connection that passes the preamp signal to the rest of the amp(kind of like plugging a cable into the return jack). This becomes a bit of a problem on amps with multiple loops like the PV rockmaster preamp (has 5 or 6 loops) but it is easy to fix (either clean the jack or leave a cable plugged into the send and return).

It's a simple test that only requires a good cable.


Greg

 

[Boogiebabies]

Well done ole chap.

 

[Bullen]

The problem is that there is no power. The amp doesn´t turn on, which made me think it was just the fuse.

All the tubes are fine, tried them in another amp just to make sure.

Perhaps he didn´t have the speaker connected. He says he did though. He used the built in speaker of the combo.

If it is the OT, can I get a replacement from Mesa? The amp is simul-class.

Anyway the amp is at the tech now. Hopefully he will get back to me when he locates the problem.

Yeah, I will NEVER lend my amp to ANYONE AGAIN!

 

[Boogiebabies]

I bet $ 10 Kronar on the power cable and $ 5 on the switch....

I would be more concerned with the PT, but they are hard to blow up.

Mesa may have some leftover PT's. There close to the DR and MK IV, but the OT's are long gone.

 

[phyrexia]

I would imagine a Mark IV OT would work. Hopefully that's not the problem.

You did make sure it's not something silly like the surge protector it's plugged into, right?

 

[Shep]

does it keep blowing fuses? or the fuse doesn't even get power .if the fuse fuse is blown is it black inside or just ailttle melted.. does anything light up at all for half a second or something when you turn it....

 

[Bullen]

No, the amp has never blown a fuse before, and from what I could see the old fuse was fine, but I replaced it anyway, just to be sure.

The amp doesn´t light up at all. Completely dead.
The amp was plugged straight into the jack, no other devices were used. And I tried it at his house and at home and he tried it in several jacks at the wedding party.

Hopefully it´s just the switch or the power cable. Might have been broken when he moved it.

How much would a PT cost me, if that is the case?

Thanks guys!

 

[vcamargo99]

I had the same problem on my Mark III Blue, and it ended up being the power switch. I also happened to my old Hiwatt, but it was the opposite (which is easier to diagnose). The Power would never turn off. After changing out their power switches they both worked fine. Hopefully you'll have the same fortune.

 

[Bullen]

Yeah, I hope so to.

 

[pmb]

Mesa may have some leftover PT's. There close to the DR and MK IV, but the OT's are long gone.

So whenever your OT in an older markseries blows up, your amp is garbage
?? :shock: :shock:

 

[Boogiebabies]

I am sure in a pinch you can use the MK IV transformer or have the original rebuilt.

 

[Bullen]

Uptdate: I just got the Mark III back.

The problem was something with the export transformer, some wire that was loose or something. So now it´s back, better than ever. I noticed a lot more punch and bass than before, so I guess the amp didn´t get full power before. It probably hasn´t worked right since I bought it a year and a half ago. He didn´t change anything else, so it must have been the re-soldering he did.

Only cost me about 80$.

Very happy day!