Help with Mark IV! Smoke!!

[Enc3f4L0]

Hello, my name is Thiago and I'm new to the forum...

I own a Mark IV, short combo, made in 1990. Bought it used a couple of years ago and I simply LOVE IT!

Today I experienced a problem and need some assistance, I'm hoping you guys can help.

First, some background on an olderr problem... A few months ago my FU-3 started having issues... It would light up all leds simutaneously, or none at all (except eq), unabling me to select a specific channel... It seemed like a bad contact or something, since when I moved around the connection a bit it would eventually solve it (almost). The only thing that wouldn't fix is that my amp would have NO CHANNELs selected (all leds off on the front panel) once the footswitch was disconected, or with the LEAD + EQ button pressed down while connected. The sound would be something like a clean channel but much LOUDER, I could only actually activate the lead channel if I pressed the Lead button on the footswitch (without "+ EQ").

Okay, today I was at a rehearsal and turned on the amp as usual (still in standby). The footswitch did the regular random blinking/fading of the leds unabling me to select ch. I then went to the back of the amp to check if the connector was properly stuck. While I was handling the contact, some white/greyish smoke started coming out of the front of the amp with a horrible smell.

I IMMEDIATLY turned the amp (which strangely enough had all the leds still on, just like normal) OFF to double check voltage and whatnot. Everything was fine considering current, voltage etc... I turned the amp back on again after triple-checking everything, this time with the footswitch unplugged.... The power/channel leds were still okay but once again smoke!

Now, I'm not sure if this has anything to do with the footswitch at all, or if it was just some strange coinscidence.... Right now I'm too scared to attempt turning the amp on again (at my home now, not at the rehearsal house) without looking for information on the matter, to avoid any more damages.

What should I do? Anyone experienced anything similar? I live in Brasília, Brazil and I know there aren't any Mesa Boogie dealers/repairs around. Should I just take it to any reputable tech?

Is it reason enough for me to send it to MESA for repairs (considering this problem, the footswitch problem, and another issue with the rhythm 1 volume pot malfunctioning I forgot to mention)?

On another note... Does MESA convert COMBOs into a HEAD + CAB? This combo has been too much of a hassle to carry around because of the weight, so I was interested in such a thing... Has anyone done this.

I prefer avoid sending it over to the US, considering the absurd price shipping will be, but if it's the only way to fix it then I'll consider it (the combo into head+cab will be a plus in my decision).

Thank you for your time.

Thiago

 

[screengrid]

Hi, sorry to hear about your problems with your Mk IV. According to your description I would recommend to have a phone call with Mesa Boogie directly. The guys there are very friendly and try to help as far as possible. IMO, it is surely necessary to have a look inside the amp and your FU3. Smoke out pof a tube amp always is a bad sign and you should keep your amp switched off, until a good amp tech has looked after the reason for the failure. If you have luck, the needed repair it is no big deal, perhaps only a resistor or a IC of the switching matrix is bad and caused a short inside !

Good luck

BTW, mine is also a model from 1990, never had a serious problem with the amp until today.

 

[Enc3f4L0]

I opened the chasis to try some troubleshooting... Here are some pics I took. The circle is the area where the smoke is coming from (I couldn't spot EXACTLY the origin just by looking). The red dot indicates where I THINK it came from because the tip of that specific thingy (sorry I don't know the name of each part, I'm a newb in all of this) was much hotter than the other 2 after I turned the amp off (it wasn't on for more than 15-20s).

Maybe this might help you help me out.

Here's another bit of info... My fan stopped working completely. It normally is always ON if the power cord is plugged in, independently of the amps On/Off switch. Now it is just OFF, despite the amp still being able to turn on.

Here's a pic of the FUSE that was in use when it all happened. I can't identify a blown fuse... I'm not sure how a good/bad fuse looks like. Is it supposed to look like it's full of sand inside? LoL. BTW, the amp still turns on with this fuse.

 

[Enc3f4L0]

I just noticed this loose power cord on the back of the amp now... I'm not sure if it was loose already before the incident, or if it got loose in transport. What is this for anyway? The fan? Cab?

I don't think it's supposed to be hanging loose, or else it shouldn't be connected to the amp's power out... (brown connector thing).

http://www.owlfour.com/back01.jpg
http://www.owlfour.com/back02.jpg
http://www.owlfour.com/back03.jpg
http://www.owlfour.com/back04.jpg

 

[lockbody]

Its for the fan.

 

[screengrid]

Hi,

the component with the red dot is a electrolyt condenser. such caps tend to dry out over many years of use, some do some not and seem to last ever. But your Mk IV is around 16 years old and so if you have luck, this cap was simply worn out and his last action was to say goodby with some smoke :lol:
But it could be, that also other components around this cap could be involved and so it is better that the repair work is done by a good amp tech of your trust.
I'm not sure, but according to a schematic I have, it should be one of the three filter caps of the low voltage supply. This supply exactly offers the needed voltage ( 15 V+ ) for the footswitch. At least this would make sence and could be the reason for the ftsw problems you descriped.
The main fuse ( 3A slow blow ) seems to be still ok, otherwise the amp would remain completely dead. The main fuse of my MK IV is a 1,5 A slow blow one, due to the fact, that the amp is a export model, wired for 220 V~ ! Don't worry so much, it's not a big deal, IMO it should be a quite quick and inexpensive repair, as far ias in the hands of a good amp tech.
Nice pictures btw


Regards

 

[Enc3f4L0]

That makes sense...

I guess the amp is in need of some looking at after 16 years.

Since this seems like a simple repair, I'd normally just take it to a good tech around here (when I do find one...), but.... I'll probably send it to MESA to do the other things I mentioned, if it's under my budget.

Can anyone give me an idea (from past experiences, roughly) how much they'd charge me to:

- Fix this issue
- Fix Rythm 1 Volume Pot (it's acting randomly, lowering volume after 5 and whatnot)
- Check other aspects of the amp to make sure they're ok (regular check-up I'm sure they do)
- Turn my chassis into a head.

If anyone knows how long they stay with the amp for these kind of services I'll also appreciate it....

Thanks, once again.