MARK III BLACK STRIPE SNAP CRACKLE POPPING

[gregfromhawaii]

Hi folks - I am a newbie to this forum. I have a problem with my Mesa Boogie Mark III Black Stripe Long Head, which just makes this horrible loud snap, crackle and popping. The amp stopped working and I found that one of the two 50uf 75v capacitor leaked out. I changed both of those capacitors and changed out the 220uF 300V Axial capacitors in the high voltage supply as they were leaking as well. Since I never had the capacitors changed since 1985, I proceeded to basically change all of the capacitors except one which would require me to take off the board.

Anyway, my amp turns on and both the pre-amp and power amp tubes glow red, but the amp just makes a crackling/static sound when I turn it from standby and no sound is heard from my guitar. The crackling/static gets worse when I tap the amp.

I changed out all the pre-amp and power amp tubes (twice) in order to make sure it wasn’t a tube issue, and it still makes the crackling/static sound with brand new tubes.

The weird thing is that If I flip the amp upside down, the crackling/static sound stops (even when I tap the amp), but still no sound comes through either the speaker or the output line.

Any ideas that you folks have would be appreciated.

 

[gregfromhawaii]

I uploaded videos of these issues:

https://www.youtube.com/watch?v=QdNiAvCiQFU

https://www.youtube.com/watch?v=QdNiAvCiQFU

 

[lovetoboogie]

You have something relatively easy to track down. It's an intermittent connection with a component or connection somewhere. Question, was it making that noise by tapping before you changed the caps, or after?

 

[gregfromhawaii]

It occurred after the cap change. Before that it stopped working and I assumed it was the ruptured capacitor.

 

[kc_ksom]

hey

I had similar noises from my Mark III

The screen grid resistors were one problem (well a few problems) they were replaced them - and then replaced again..

I also found that after the tech had done some work it always use to crackle & pop on start up for a while before it would come good - sometimes it would crackle on heavy palm muted cords or times where it was fairly loud it would randomly crackle - he found that there was a blob of solder that had formed under the pre amp tube from a previous repair or his repair - this blob shorted out every now and again - If you search my name there should be a thread - hopefully it will help you - I no tech sorry
Casey

 

[lovetoboogie]

It occurred after the cap change. Before that it stopped working and I assumed it was the ruptured capacitor.

You will need a chopstick and start looking around with it to find the loose component or connection. Since you replaced several caps you should start looking in those areas. You can clearly hear in your YouTube video that it is something intermittent. By tapping on it you are giving the chassis just enough vibration to make or break contact. With chopstick you can narrow down the location and then attack that area...

Since you did your own caps I trust you know how to work a DMM? Chop sticks test first...then start taking B+ voltage readings from after the rectifier diodes all the way downstream to the preamp. Also check all your replaced caps as they reference ground. Make sure you are seeing clean paths to ground at the necessary points...

 

[gregfromhawaii]

Thanks for the replies! I will try the chop stick method!

My amp repair skills (or lack thereof) consists of looking for blown capacitors, loose wires or burnt out resistors. Replacing the caps were not that difficult in terms of soldering loose the old caps and sucking out the old solder and soldering in the new caps. As far as multimeter use, frankly, all I know is set it ohms and see if they register reading or not; if I get no reading, I assume it's bad.

 

[gregfromhawaii]

And Casey - I did check out your old thread! I dread to take out the board, but I might have to if I can't locate the source of the issue using lovetoboogie's chopstick method.

Here's another video of the amp when I first turn it on from standby:

https://www.youtube.com/watch?v=DL4DVattF1o

I popping and clicking gets pretty bad as I turn it on and off standby.

I love this amp and am not willing to send it out to pasture just yet!

I'll keep you folks posted as to how things go. Seriously, thanks for all of your help. It is greatly appreciated!

 

[lovetoboogie]

When you get a chance can you post a clean pic of the chassis guts. A good overhead of the whole or maybe in three sections R-L... Often one of us will just see something amiss.

If you have a good pair of insulated(rubber handle)needle nose pliers you can do the following... With the amp powered up and off standby(in playing mode), WITH ONE HAND BEHIND YOUR BACK, very gently tug on those B+ leads coming off the standby switch and the AC leads on the power switch. Are you able to recreate that noise doing that?

 

[gregfromhawaii]

When you get a chance can you post a clean pic of the chassis guts. A good overhead of the whole or maybe in three sections R-L... Often one of us will just see something amiss.

If you have a good pair of insulated(rubber handle)needle nose pliers you can do the following... With the amp powered up and off standby(in playing mode), WITH ONE HAND BEHIND YOUR BACK, very gently tug on those B+ leads coming off the standby switch and the AC leads on the power switch. Are you able to recreate that noise doing that?

Thank you! And I did the chopstick method you suggested and found that one of the orange Sprague 715p .1uF @400DC capacitors had broken off a leg and was pushing against another part of the board -- hence the popping and clicking.



I assume it blew from the hole next to it, but I'll check the schematic to make sure.

 

[gregfromhawaii]

And given the burn mark under it, I ordered several new orange Sprague caps, which should come in a few days.

 

[lovetoboogie]

Congrats my friend!!! You just successfully narrowed down an intermittent component. Your video helped us do it.

That looks to be C511 on our Black Stripe Schematic. It's rotated completely opposite where it should sit.
Here is the board layout and schematic so you can position correctly:
https://drive.google.com/open?id=1fAjkr ... rhnay8ZXjJ
https://drive.google.com/open?id=1vurMa ... kTfTuyGAuH

Additionally here's a photo showing the layout in and around V5 so you can find the right solder pad for our runaway cap!



It's odd that came loose. Amp must have taken a hit at some point or someone had worked on it previously and lifted that cap end without soldering it back down correctly. Lemme know what you come up with and how the amp sounds...

-j

 

[gregfromhawaii]

Congrats my friend!!! You just successfully narrowed down an intermittent component. Your video helped us do it.

That looks to be C511 on our Black Stripe Schematic. It's rotated completely opposite where it should sit.
Here is the board layout and schematic so you can position correctly:
https://drive.google.com/open?id=1fAjkr ... rhnay8ZXjJ
https://drive.google.com/open?id=1vurMa ... kTfTuyGAuH

Additionally here's a photo showing the layout in and around V5 so you can find the right solder pad for our runaway cap!



It's odd that came loose. Amp must have taken a hit at some point or someone had worked on it previously and lifted that cap end without soldering it back down correctly. Lemme know what you come up with and how the amp sounds...

-j

You totally rock! The cap should come in tomorrow. Gonna try to fix this weekend!

I probably jarred it loose when I was recapping the amp.

Hopefully this takes care if it, but even if it doesn't, at least I'm one step closer! If it does work, I'll put of a youtube link of how it sounds.

Thanks again for your help!

 

[gregfromhawaii]

Capacitors not coming in until 4/15 - I guess they are shipping by boat. I’ll keep u folks posted.

 

[woodbutcher65]

I have a topic on this issue.

Guys, if your amp hasn't been recapped and it's 20 years old or more, it's due. Caps can fail at any time and at 20 years old they're past their designed expected lifespan.

https://forum.grailtone.com/viewtopic.php?f=3&t=84878


Red plating tubes indicates absent or insufficent bias supply voltage, too. Or a shorted tube, which drags down the bias voltage.