My MT200 freaks out

[Kim]

Well, I have Microtube 200 problems now too and rather than hijack another thread I'll start my own....   ::)

I think I hurt it.    :'(   It only gets a fraction of loud as it used to, and it just "freaks out" if I try to get the kind of decent volume out of it that I think it should.  It does that Zap and Burp thing in between chords until eventually it'll go into some kind of a feedback shriek that won't stop until you hit Standby.  Swapping out the tubes made no difference.  You may remember a short time ago I thought I was having problems with "unintentionally overdriving the Loop on the MP-2" before with that Zap and Burp.  (Sounds like the name of a morning radio talk show...be the 9th caller to the Zap and Burp Show and win Metallica tickets!)  I'm pretty sure it was the MT200 acting out on me all along.  Is it possible that I was driving the Inputs too hard?  Or running the Volumes too high for too long?  Or both?  I don't play at "stupid loud" volume at band rehearsals, but the gradual decrease in its overall volume may have caused me to try to compensate by turning it up more.   

I was hoping to still use it for the Mel9 section of my rig after acquiring the Peavey poweramp, but it doesn't work out there either; plugging into the Mono Input only resulted in a very weak signal coming from one side and not both like it should.

So, hopefully I can get in there and make this sing again.  MJMP, what should I look at inside there first?

[rnolan]

Hey Kim, bummer. One thing you can try just to start (and see/hear what happens) is re-flow all the joins. Hey it can't hurt and it fixed my B200s  and zap and burp is one way I could  describe the B200s crackles I was getting.

[Harley Hexxe]

Hey Kim, bummer. One thing you can try just to start (and see/hear what happens) is re-flow all the joins. Hey it can't hurt and it fixed my B200s  and zap and burp is one way I could  describe the B200s crackles I was getting.

   Don't you think Trullmon would have done that before sending it on to Kim?

[rnolan]

Hey Harley, sorry, no idea  , I've no knowledge of where Kim got it from. Solder joints get old, tired and vibrated, hence my suggestion...

[MarshallJMP]

It happends on both channels?

[Kim]

It happends on both channels?

Yes about the Volume Decrease and the Zap n Burps.

[MarshallJMP]

Well the common factor could be the PSU so I would measure the voltages on the red connector  (the big one)

[Harley Hexxe]

Hey Harley, sorry, no idea  , I've no knowledge of where Kim got it from. Solder joints get old, tired and vibrated, hence my suggestion...

   That was one of my power amps that I donated to the cause when we were sending Kim the MP-2/MT200 rig back when he was having all the issues with the Classic. It was one of my best sounding ones at the time.

Harley 8)

[Kim]

Well the common factor could be the PSU so I would measure the voltages on the red connector  (the big one)

K2 and K102?    The voltages there at both plugs check out good....but with 78v where it should be 65v.

[MarshallJMP]

On the PSU schematics it says 75V, so should be okay.Maybe something in the input section.Maybe one of those 4053 ic's.

[Kim]

Maybe something in the input section.Maybe one of those 4053 ic's.

I think you may be right, but I don't know how to check those unless I'm just looking for a visible problem like a burn mark or crack. 

[MarshallJMP]

It could also be the bridge output jack or the mono input jack. There is a contact in it that drives those 4053's. It's a sense if the jack is used or not.

[Soloist]

My MT200 does the occasional "burp" as well. It only does it when I am not playing anything. Now that I think about it, it only does it with the MP2. Maybe it's my MP2? No issues when I use a different preamp.

[Kim]

I only see one 4053 (MJMP, you say there's more than one?) on the pot board schematic, and it's already socketed on my unit so it will be easy to change.

I don't normally use the Bridge jack or Mono Input jack, but I did try the Mono Input after all this stuff happened.  It resulted in still having a crappy faint signal but now only on one side.

[MarshallJMP]

Yes correct Kim, but one 4053 has 3 switches inside. Now if it's in a socket then replace it and try it out. It's a cheap ic.